|Session:||Session 4PP3A - Measurement (14a3)|
|Date:||Thursday, November 09, 2006|
|Time:||15:30 - 18:30|
Probe Distortion Correction in Near Field - Far Field Transformations Based on Equivalent Sources Characterization
Alvarez, Y.; Las-Heras, F.; R. Pino, M.
Universidad de Oviedo, SPAIN
This paper introduces a method for the determination and correction of the distortion introduced by the radiation pattern of directive probe antennas. The purpose is to correct the near field distortion when measuring antennas at near field ranges. The proposed probe correction method is thought to be used jointly with an integral equation description relating sources and fields. From near field measurements, NF-FF transformations are implemented by means of the characterization of the antenna through its equivalent sources, which are reconstructed using inverse Integral Equation techniques combined with the proposed probe correction method.
Size limitations when building anechoic chambers make it difficult to measure far field pattern. Consequently, well-known methods to retrieve far field pattern from near field measurements have been developed. With the purpose of mitigate probe distortion in near field acquisition, probe pattern should be as omnidirectional as possible. However, in microwave frequency bands, horn antennas are commonly used as probes, having their patterns certain directivity, and introducing some distortion in antenna under test (AUT) near field pattern.
Traditional systems of NF-FF transformation based on modal expansion (for example, spherical modes when measuring at spherical range) implement well-known algorithms for probe correction. However, new measurement techniques based on sources reconstruction through integral equation methods, involve more complexity in order to consider probe correction. The proposed method for probe correction has been integrated into an algorithm for equivalent sources reconstruction. Thus, equivalent sources are retrieved from near field acquisition as if an isotropic probe were used to measure near field.
To proceed with probe distortion correction, the probe pattern is required, as well as the geometric characterization of the acquisition system. From this point, the angle, under which the probe sees the AUT, is calculated by means of dot products and vector expressions. Then, the algorithm determines the correction parameters inserted into the integral equation relating sources and fields. Solutions to the inverse integral equations are the equivalent sources, from which the non-distorted far field is calculated, completing the NF-FF transformation.
The proposed technique does not depend on the acquisition system, and it can correct near field data measured over any canonical range (planar, cylindrical, spherical) as well as over an arbitrary acquisition system.
In order to check the algorithm, several examples have been analyzed. With the aim of remark the probe distortion introduced in the near field pattern, very directive AUT and probes have been considered. The results obtained from these simulations show that the proposed algorithm removes the probe distortion successfully, both in the calculation of the equivalent sources and in the transformation to far field pattern, without any additional computational cost.
 P. Petre, T. K. Sarkar, "Planar NF-FF transformation using an equivalent magnetic current approach", IEEE Trans. on Antenna and Propagation, Vol. 40, No. 11, Nov. 1992, pp. 1348-1356
Return Loss Reduction Techniques for an Ultra Wide Bandwidth Phased Array Antenna in V/UHF Band
Berisset, Ph.; De Kat, J.; Morvan, S.; Chevalier, Y.
V/UHF indoor Radar Cross Section (RCS) measurements can still be performed when the anechoic chamber dimensions are not large enough compared to the wavelength and the wall absorbing material performances are relatively low. In order to drastically reduce unwanted signals from the chamber, a dual polarization ultra wide bandwidth (120 MHz-1875 MHz) phased array antenna has been designed and developed in 2004. The optimization consisted in lowering the phased array side-lobes in the angular direction of the chamber walls. Clutter signals from these walls were reduced by 40 dB. Among the received signals from the chamber, the return loss of the phased array antenna is now the most significant.
The phased array antenna is built from 9 elementary dual polarization patch antenna (figure 1). In order to make RCS measurements from 120 to 1875 MHz the total bandwidth is split into three consecutive sub-bands : [120 - 300 MHz], [300 - 750 MHz], [750 - 1875 MHz]. So the phased array antenna is composed of three separated phased arrays, one for each sub-band of the overall bandwidth. Each phased array contains nine elementary antennas. The assembly (20 ft x 20 ft) is mounted on a vertical mast located on a rotating positioner. Therefore, each one of the three phased array antennas can be electrically oriented towards the target.
The return loss reduction experimental study is limited to the lowest sub band (120-300MHz) of the phased array antenna. The phased array antenna return loss is composed of the vector sum of :
Two main solutions were investigated to reduce the return loss. The first one is based on the following principle: make the received RF signal go through passive RF components in order to generate a signal cancellation with the return loss of the phased array antenna. The block diagram to cancel a single return loss contributor is presented in figure 2. A 27 dB return loss reduction is obtained on a 1 MHz bandwidth (see figure 3). Since the delay lines and the attenuators are programmable devices, a 30 dB to 50 dB CW return loss reduction can be achieved for any CW frequency of the phased array antenna bandwidth. These results show that after a "calibration" phase consisting in fine tuning the compensation device for each and every frequency of the spectrum of interest it is possible to avoid using range gating in the RCS measurements performed with this phased array antenna.
The second solution to reduce the return loss of the phased array antenna is to optimize an impedance matching circuit which could bring up a wide bandwidth return loss reduction solution avoiding the tedious "calibration phase". The final paper will present the design of the impedance matching circuit and the experimental return loss reductions results.
The Oblate Spheroid as Near-Field Scanning Surface for Far-Fied Reconstruction
Riccio, G.1; Ferrara, F.1; Gennarelli, C.1; Savarese, C.2
1University of Salerno, ITALY;
2Parthenope University at Naples, ITALY
When deciding on what measurement configuration in near-field (NF) region is the best for a particular application, the fundamental limitations of each approach and the corresponding advantages should be considered. In any case, it must be taken into account that NF measurements may be performed in a controlled environment, as an indoor shielded anechoic chamber, thus eliminating problems due to weather conditions (rain, snow, etc.), electromagnetic interferences, and other. Among the classical near-field to far-field (NF-FF) transformation techniques, that employing the spherical scanning is the most attractive of the three options since it gives the full pattern coverage, even though the data processing is considerably more complicated than that needed by planar and cylindrical NF facilities . A NF-FF transformation technique using a scanning surface that is spheroidal in shape has been recently developed by Ricciardi and Stutzman in . It is based on an eigenfunction expansion of spheroidal wave-harmonics and requires the knowledge of the full electric near-field (not just its tangential components) at the points fixed by an integration process that must be performed on the spheroidal surface. The benefit of using this particular geometry in the NF region is that it has the ability to closely conform to both linear and planar radiating systems while still permitting evaluation of the full radiation pattern of the antenna under test (AUT). A nonredundant sampling representation of the field is here proposed for reconstructing it at any point on a spheroidal surface that is oblate in shape and, in particular, at the points fixed by the NF-FF transformation process reported in . The surface used for modeling the AUT is an oblate spheroid having the same rotational axis of the sampling surface, but different focal points and dimensions. In order to obtain a nonredundant sampling representation , the optimal phase function to be extracted from the field expression is evaluated, and the optimal parameters to be used for describing meridian ellipses and azimuthal circumferences are determined. A fast, accurate and stable interpolation algorithm of central type is developed for reconstructing the field from a nonredundant number of samples. It minimizes the truncation error for a given number of (nearest) retained samples and, as compared with the Cardinal Series expansion, is more stable with respect to errors affecting the data. The effectiveness of the reconstruction process is proved by means of numerical tests.  C.Gennarelli, G.Riccio, F.D'Agostino, F.Ferrara, Near-Field - Far-Field Transformation Techniques, Salerno, CUES, 2004.  G.F.Ricciardi, W.L.Stutzman, "A near-field to far-field transformation for spheroidal geometry utilizing an eigenfunction expansion," IEEE Trans. Antennas Prop., vol. 52, pp. 3337-3349, 2004.  O.M.Bucci, C.Gennarelli, C.Savarese, "Representation of electromagnetic fields over arbitrary surfaces by a finite and non redundant number of samples," IEEE Trans. Antennas Prop., vol. 46, pp. 351-359, 1998.
Matrix Pseudo-Inversion Technique for the Diagnostics of Planar Arrays
Bregains, J.; Ares, F.
University of Santiago de Compostela, SPAIN
It is shown here, by numerical simulation, that the Moore-Penrose matrix pseudo–inversion technique can be applied to retrieve the excitation distribution of a planar array of parallel dipoles with faulty elements, by measuring its near zone complex radiated field. Failures on voltages and currents of several elements, as well as systematic amplitude or random (in amplitude or phase) measurement errors, are considered in the simulation. In all cases, mutual coupling between dipoles is taken into account. The scanning surfaces selected to obtain the field values are those customarily used in practical measurement systems: a plane (parallel to the array), a hemicylinder and a hemisphere. The technique can be used as a very reliable alternative for diagnostics of planar arrays in general, and of planar arrays of dipoles in particular. Several examples are worked out, and their results would be presented throughout the paper. Differences between excitations of failed and healthy arrays are studied. Table 1 and Figure 1 show an excerpt of the results obtained through the abovementioned examples.
Investigation of Low Cost Compact Base for W-band
Multari, M.1; Migliaccio, C.1; Dauvignac, J.Y.1; Pichot, Ch.1; Menzel, W.2; Desvilles, J.L.3
3France Telecom R&D, FRANCE
Millimeter-wave radars have been recently of increasing interest, especially for automotive or helicopter applications. Antennas requirements are various but still a high gain is needed leading to antenna diameters of several tens of wavelength. Most anechoic chambers are too small to provide accurate gain and radiation pattern measurements. A solution consists in using a compact base. It can be obtained either by placing a transmitting lens between the antenna under test and the emitting source , or by having a two mirror-arrangement made by metallic reflectors . Metallic reflectors are quite expensive especially at high frequency since their surface error has to be very low. The alternative solution  has some advantages considering cost and alignment problems because only one lens is needed. The purpose of this paper is to present a compact base using a dielectric lens of 500mm diameter for large antennas measurements.
The near filed of a 500 mm diameter Teflon lens was measured at 94 GHz providing maximum ripple of 2 dB (fig.1). A 42l diameter Fresnel reflector antenna has been placed and measured (fig.2) in anechoic chamber in order to validate the compact base concept. The level difference might come from the focusing of the lens but the compact base introduces unwanted effects: noise off axis (maximum of 20 dB around 180°) and oscillations on the main beam due to the diffraction occurring at the edge of the lens that is combined on the axis as described in . Similar results are obtained with a PVC lens of same diameter measuring a standard horn as shown on figure 5 (blue curve). The compact base has been simulated using a electromagnetic solver based on the electric and magnetic field integral equations, designed by France Télécom R&D. Diffraction effects can obviously observed in the near-field distribution along the axis for the PVC lens illuminated at -1 dB on the edge (fig.3). This problem can be overcome by adding a small dielectric lens to the former source providing -40 dB at the edge (fig. 4). Standard horn measurements confirm the suppression of on axis diffraction (fig. 5) but also reduce the spot of quiet zone to 15 cm (fig. 4). Furthermore, a compact misalignment tilts the spot of the quiet zone that creates an asymmetry in the radiation pattern measurement (fig. 5). Alternative solutions are under study for enhancing the quiet zone either by achieving a particular illumination law or by enlarging the lens.
 G. Beddeleem, C. Nardini, G. Forma, C. Bouvin, H. Garcia, B. Buralli, "Quiet Zone Characterisation for a Compensated Compact Range: Measurement and Prediction up to the Millimeter Band", JINA, Nice 8-10 Nov. 2004, pp. 312-313.
 R.C. Rudduck, Chin Long J. Chen, "New Plane Spectrum Formulations For The Near-Fields Of Circular And Strip Apertures", IEEE Trans. Antennas Propagat., AP -24, No 4, July 1976, pp. 438-449.
New Test-Bed for Evaluation of Antenna and System Performance for MIMO Systems
Garcia-Garcia, L.; Gomez-Calero, C.; de Haro-Ariet, L.
Universidad Politecnica de Madrid, SPAIN
The increasing interest in MIMO (Multiple-Input Multiple-Output) systems has given rise to a prolific research activity in this topic in recent years. Several aspects have been studied, including both theoretical and practical issues. So far much effort has been put in the study and design of schemes and algorithms for MIMO systems, taking into account different considerations such as some knowledge (full, partial or none) of channel information at the transmitter or the type of scenario. In order to evaluate the algorithm performance in realistic scenarios, the use of a real platform is of great interest, since it enables to include several aspects that are not usually addressed in theoretical studies or simulations. The work presented in this paper has been carried out by using a MIMO test-bed that has been specifically designed for evaluating the performance of MIMO algorithms and schemes.
Moreover, most of the previous work on the design of MIMO schemes and algorithms has been done from a system point of view and considers the antenna element as ideal, thus neglecting their effect on the system performance. On the other hand, when designing antenna arrays for MIMO systems, simplified channel characteristics such as Rayleigh distribution are usually assumed, and the algorithms and schemes are not included in the design. What is more, there is not a widely accepted method for evaluating the performance of antenna arrays for MIMO systems; generally, conventional antenna parameters such as radiation patterns or S parameters are used, or more recently measurements in a so-called reverberation chamber have been proposed. Also channel measurements obtained by using channel sounders with different antenna configurations have been used. Nevertheless, all these methods lack the possibility of including a certain algorithm. From a complete MIMO system perspective, it would be very interesting to jointly design the antenna module and the signal processing module, as well as being able to evaluate them simultaneously.
We have used a new test-bed to evaluate different MIMO algorithms. The test-bed has been designed to simplify the evaluation of the system performance, so the possibility of off-line signal pre- and post-processing is included, thus avoiding real-time constrains in the algorithm implementation. Moreover, to include different antenna configurations in the used test-bed is straightforward, so their effect in the MIMO algorithm can be studied. As preliminary results, the MIMO channel matrix was measured and the obtained capacity for a line of sight (LOS) environment with different element spacing is shown in Figure 1. In the full paper we will present the performance evaluation of different algorithms, including the effect of some antenna aspects such as coupling and polarization. A picocell environment and a WLAN frequency band are considered, including both indoor and indoor-to-outdoor scenarios.
Scalar Beam Pattern Measurements for Characterization of Sub-Millimeter Receivers
Pantaleev, M.1; Fredrixon, M.1; Svensson, M.1; Risacher, C.2; Vasilev, V.1; Belitsky, V.1
1Chalmers Technical University, SWEDEN;
The measurement concept presented in this article is based on scanning the receiver's beam with an isotropic radiating source at three to four parallel cross planes along the presumable optical axis. The receiver is operated in heterodyne mode and the output IF power is recorded for each coordinate point of the radiating source. The collected data provides information for the Gaussian beam profile at the particular distance from the receiver. According to the properties of the fundamental Gaussian beam, the maximum power value is located on the axis of the beam. Therefore, obtaining the coordinates of the beam center (of the maximum intensity) for each measured beam profile allows for the determination of the beam axis orientation. The location of the beam waist and its size can be calculated by solving a system of equations derived from the Gaussian beam theory, where the measured power values along the optical axis are used.
We report measurement results for two radio astronomical projects: Heterodyne Instrument for Far Infrared (HIFI) of Herschel Space Observatory and Athacama Path Finder Experiment (APEX). This article demonstrates that using this method a good accuracy can be achieved when budget limitation will not allow investment in expensive equipment, which is required for phase-amplitude measurements.
The HIFI has a frequency coverage of 480 to 1250 GHz in five receiver bands and 1410 to 1910 GHz in two additional bands. It is built on modular principle: the superconducting mixers together with three active mirrors are integrated into Mixer Sub-Assemblies (MSA). The measurement setup discussed in this article was build in purpose to characterize the beam parameters of the MSA Band 1 to 4. It houses entirely in vacuum a continuous wave probe source placed on a precise scanner and the device under test, which is at 4 K ambient temperature. An unique triangulation system was developed to allow measurements in absolute coordinates related to a mechanical reference on the MSA, after the entire system is evacuated and the cooling is finished. The scalar measurement technique together with the developed fitting routines allow characterization of the beam with an accuracy of 0,14mm in waist coordinates retrieval and 0,1degree in beam axis tilt. We present measurement results for MSA Band 1 at 480GHz and Band 2 at 640GHz. The measurement concept is compared to alternative measurement techniques in terms of accuracy based on the reference phase-amplitude measurements.
Using the experience from the HIFI project we built a simpler measurement setup which was used to characterize the APEX first light 345GHz receiver, prior to installation on the telescope. As a test source we used a Harmonic mixer, placed on x, y, z scanner. The triangulation between the scanner and the cryostat window was made with two sets of lasers and quadrant type position sensitive detectors. We obtain a dynamic range of about 23dB, which allowed to use the same measurement procedure as above. As a result significant beam offset from the cryostat window was measured and in couple of iterative measurements the mirrors inside the cryostat were shimmed and the tilt of the beam axis was compensated.
Analysis of Different Sampling Methods in a Reverberation Chamber
Andersson, J.; Ying, Z.
Sony Ericsson Mob Com AB, SWEDEN
This presentation deals with the analysis of four different measurement techniques. A Reverberation Chamber (or also called Scattered Field Chamber) has been used - with both the hardware and software designed within the department. When we design small, multi band terminal antennas, it is important that we have correct and fast tools in the R&D work. We need good measurement accuracy with good repeatability. An important parameter in the Scattered Field Chamber is then the number of independent samples, Nind, as well as the measurement time, T. The larger number of independent samples in a measurement, the better the measurement accuracy will be. A number of factors in the chamber will influence the measurement quality e.g. the chamber volume, the design of the stirrers, the number of stirrers and the sampling technique etc.
In order to get a better understanding we have investigated four fundamental sampling methods in the time domain and compared them:
1. Single sampling ( Single probe, single channel)
The four methods will be explained and compared, and a number of merit, ñ, will be defined in order to make a fair judgement of the methods
Antennas Link Synthesis Using Near Field Chamber Measurements
Tchoffo Talom, Friedman; Aubert, L.-M.; Uguen, B.
IETR - INSA, FRANCE
UWB technology offers great potential in term of high data rates wireless communications. The implementation of this technology requires accurate knowledge of elements involved in transmitters and receivers design. Particularly, one has to evaluate the impact of UWB propagation channel and antennas on systems performances. According to power limitations and the transmitted UWB waveforms, antennas are a key point to achieve link budget ensuring the expected high data rate for this technology. So, challenges in the design of UWB antennas are obtaining good characteristics in term of radiation efficiency and patterns, return loss on the whole covered band (3.1 GHz - 10.6 GHz) and phase linearity with the frequency. To measure these characteristics, various principle are proposed in literature [1-2]. Time domain characterization methods for UWB antennas require specific tools such as pulse generator and digital sampling oscilloscope. So most of the time, frequency domain characterizations are performed as they are well known for narrow band antennas and can be easily extended to UWB. From these frequency domain measurements, one needs to introduce appropriated signal processing to obtain antennas time domain characteristics.
This paper describes an approach for synthesizing antennas time domain S21 parameter using frequency domain measurements performed in a near field SATIMO chamber. This chamber gives access to the field radiated by the antenna in all directions. Thus, the proposed approach allows one to compute antennas direct link whatever their orientations. This approach has been implemented in a site specific tool for channel modeling .
Theoretical bases of the proposed S21 link synthesis are detailed. Then we consider two couples of antennas used to perform UWB propagation measurements: omnidirectional monopole antennas (Fig. 1 (a)) and directional horn antennas (Fig. 1 (b)). Results obtained using direct measurements of S21 and synthetic links are presented for the two couples of antennas. The measurements are made in an anechoic chamber to isolate the direct path between the transmitting and the receiving antennas. Figures 2(a) and 2(b) show the measurement configuration for the omnidirectional monopole couple of antennas and the comparison between measurement and proposed synthetic approach results respectively.
 W. Sörgel, C. Waldschmidt and Werner Wiesbeck, « Antenna Characterization for Ultra Wideband Communications», in IWUWBS 2003, Oulu (Finland).
 A. Shlivinski, E. Heyman and R. Kastner, « Antenna Characterization in the Time Domain», IEEE Trans. on Antennas and propagation, Vol. 45, No. 7, July 1997.
 F. Tchoffo Talom, B. Uguen, E. Plouhinec and G. Chassay, «Site-specific tool for UWB channel Modeling», in Joint UWBST & IWUWBS 2004, Kyoto (Japan).
Fig. 1: Couples of omnidirectional monopole (a) and directional horn (b) antennas.
Fig. 2: Measurement configuration (a) and Comparison with proposed synthesis (b) for omnidirectional antennas.
Design of a Cylindrical Near Field System for RADAR Antennas
Martín Jiménez, F.; Burgos Martínez, S.; Sierra Castañer, M.; Besada Sanmartín, J. L.
Universidad Politécnica de Madrid, SPAIN
A cylindrical near field measurement system for huge L-band RADAR antennas has been designed, and is under construction. The cylindrical near field system consists on a 17 meters tower (15.5 meters linear scanning), placed at a distance between 4 and 7 meters from the centre of the RADAR antenna. The RADAR antenna is placed on its azimuth positioner, and the system must allow the measurement of the antenna without stopping the rotation movement, measuring two linear polarizations (horizontal and vertical). The system can work in both transmission and reception. The system must work in an open and windy area. To assure the rectitude of the z-axis, a servo controlled by an optical detector has been implemented. This paper presents the main specifications of the measurement system (mechanical and electrical) and its design process. The paper will explain the acquisition routines (optimised for reducing measurement time without stopping the rotational movement of the Radar), the control of the motors and RF equipment, the near field to far field transformation software, the algorithms used to compensate some errors (as temperature variations) and, finally, the user friendly environment.
Checking of Large Deployable Reflector Geometry
Petrov, V.1; Chernyavsky, A.2; Krikalev, S.2; Mikryukov, P.1; Vorobey , I.3
1BumTechno, RUSSIAN FEDERATION;
2Rocket & Space Corporation (RSC) ENERGIA, RUSSIAN FEDERATION;
3NPO EGS, RUSSIAN FEDERATION
As the interest of various users in large deployable radio antennas has been constantly growing within last years, antenna manufacturers have to choose an efficient method to determine geometrical characteristics of structures (deviation from the shape of reflective surface, orientation of focal axis, focal point position) in the course of antennas manufacturing and operation.
The accuracy of reflective surface shape for soft antennas is lower then that of rigid reflectors and usually does not exceed 1-2 mm. This is due to the fact that it is difficult to follow the exact shape beyond the adjustment points, to ensure the same exact shape after folding/unfolding cycle etc. Since most of soft deployable reflectors use gilded mesh as reflective surface, which is very sensitive to mechanical effects, non-contact methods are to be used to determine deviations from the theoretical shape.
Fotogrammetrical methods (VSTARS et al.), used nowadays tend to significantly reduce the accuracy of coordinate determination with the increasing of the antenna size. Moreover, such methods imply placing targets on the reflector surface, which can obstruct normal unfolding of antenna during shape repeatability tests. In our view, the most perspective method is to use MV 200 Laser Radar and multiteodolite system, AXYZ MTM.
The report is about the analysis of results of adjustment of LDR reflective surface (12 meters aperture) using this method.
Measurement of a Biomimetic Antenna
Farmer, G.; Flint, J.A.; Leonard, G.
Loughborough University, UNITED KINGDOM
The ears or pinnae of bats are structures which have attracted recent research interest in the acoustic community. The vast diversity observed in bats ears and an increasing body of research evidence suggests that they are highly evolved wave-receiving structures. It is interesting to consider, therefore, the possibility to make an electromagnetic antenna with a similar geometry that could be similarly optimised. In this paper a simple 3D shape is presented that physically resembles the ear of a bat (see (a) to (c) below).
By means of an example a device with b/a=0.25 is considered. The return loss of a physical device with this ratio is shown below.
A radiation pattern of this device plotted on a linear scale at 5.7 GHz is given below. The dotted line shows the response of a monopole with the same length above a circular ground.
The device presented therefore possesses a directional radiation pattern and has a similar input characteristic to the monopole above ground, providing a sufficient number of modes exist in the triangular plate at the frequency of interest.
Optimized Feedhorn Designs for Compact Antenna Test Range at Limoges University
Teniente-Vallinas, J.1; Arnaud, E.2; Gonzalo-Garcia, R.1; del-Rio-Bocio, C.1
1Public University of Navarra, SPAIN;
2University Of Limoges, FRANCE
In this paper, high technology optimized corrugated horn antenna designs to be used as feedhorns for Compact Antenna Test Range (CATR) are being presented. These high technology feedhorns have been specifically designed to improve the quiet zone size and behaviour at the CATR of the antenna research team (OSA) from Limoges University XLIM laboratory. The feedhorns make use of the recently patented technology that uses the combination of horizontal and vertical corrugations in the horn profile to reduce size and increase performance.
Any compact range is defined by a volume where the far field condition is satisfied called quiet zone. Quiet zone must meet strict criteria and it is important to maximize its size because it will allow measuring bigger antennas. Such quiet zone volume is limited by the size and configuration of the reflectors, but its main limitation usually comes from the feedhorns used to feed the mirrors. Usually the radiation pattern of conventional feedhorns changes with frequency changing the quiet zone volume as well.
In this paper we present the design of five feedhorns covering from 8 to 50 GHz (each horn presents around 40% bandwidth) with a very stable radiation pattern over all the frequency range. The horn design and optimization has been made by means of Mician µWave Wizard electromagnetic CAD software package.
These corrugated horn antennas combining horizontal and vertical ridges reduce the size of the design and they are easy to manufacture because they avoid the conventional corrugated horn lambda/2 depth corrugations in the throat region. This lambda/2 depth corrugations are difficult to manufacture because usually are as deep as the throat radius. On the other hand, the use of horizontal corrugations (usually known as chokes) in this part doesn’t affect the nice radiation properties and wide bandwidth of corrugated horns.
Simulation results of the final prototypes perform very nice maintaining the quiet zone at the maximum size of the reflector configuration over the whole frequency range with low crosspolar levels and high phase centre stability. The designs are very simple and small, resulting in a low manufacturing cost. The horns are being manufactured and will be tested in a near future.
Manufactured 33 to 50 GHz feedhorn and a cross section picture of the design. The picture shows the combination of horizontal and vertical corrugations, (1 euro coin is photographed as well to compare the size)
Towards a Generalized Methodology for Smart Antenna Measurements
Alexandridis, A.1; Lazarakis, F.1; Zervos, T.1; Dangakis, K.1; Sierra Castaner, M.2
1Institute of Informatics & Telecommunications, NCSR “Demokritos”, Athens, GREECE;
2Signal, Systems and Radiocommunications Department, Technical University of Madrid (UPM), SPAIN
The huge expansion of mobile communications and the need for high data rate services require more efficient use of the spectrum to increase the capacity of networks and enhance the quality of services. Within that frame, the adoption of Smart Antenna techniques in future wireless systems is expected to have a significant impact on the aforementioned needs. Following the proliferation of the use of Smart Antennas systems there is a growing need for characterization of such systems which is still an open issue. In this work, a generalized methodology for Smart Antenna characterization measurements is introduced. Aiming to define such a generalized methodology for the evaluation and characterization of a Smart Antenna, we can consider the Smart Antenna as a system, which includes two individual subsystems as depicted in Fig. 1a:
It is obvious that the performance and the characteristics of a Smart Antenna are a combination of the performance and the characteristics of these individual subsystems.
Basically, there are two methods to approach the problem of characterizing the Smart Antenna through measurements:
In the first case the Smart Antenna measurements refer to the operation of the whole system. Therefore the engineer that designs a telecommunication system which uses Smart Antennas does not have the possibility to choose from a variety of Smart Antennas based on their characterization, because such characterization refers to the whole telecommunication system.
In order to tackle the above restrictions we suggest the second methodology based on the characterization of the individual Smart Antenna subsystems. Following this approach, it is necessary to define, develop and incorporate some test or reference subsystems into the measuring procedure, which will replace the corresponding (actual) subsystems.
Two test subsystems should be developed:
For the characterization measurements of the Antenna/RF subsystem, the DSP/algorithm subsystem of the antenna under test is replaced by the DSP/algorithm test subsystem and the measurements are taken under its control (Fig. 1b). In a similar way, for the characterization measurements of the DSP/algorithm subsystem, the antenna subsystem is replaced by the corresponding test subsystem and the performance of the algorithm is measured when it is (the algorithm) applied to the specific reference antenna subsystem (Fig. 1c).
In this paper a number of solutions are proposed for defining a possible set of reference antenna subsystems and DSP/algorithm test subsystems. Then combinations of the above sets are proposed in order to shape measurement scenarios for the individual characterization of the subsystems. The scope of this work is to serve as a guideline for establishing some common test cases for the complex problem of Smart Antennas characterization.
Applicability Investigation of Holographic Back-Projection of Spherical Near Field Measured Data
Mioc, F.1; Foged, L. J.1; Rosa, A.2
2A. Rosa, ITALY
Holographic back-projections of spherical near-field measurements to a plane have been available for some time. Due to finite resolution and truncation effects, the classical implementation of this technique has mainly been applied to high directivity antennas like phased arrays to investigate anomalies in the feeding network of the array and local faulting after the final integration. This paper discusses the applicability of the method for low and medium gain antenna mounted on a structure by comparison with equivalent source planar back-propagation technique. The field on the plane is evaluated as the summation of field contributions radiated by equivalent sources located on sampling points of the near field sphere. This paper discusses also the applicability of the method due to finite resolution, truncation effects, and finite measurement accuracy when applied to low and medium gain antennas. The holographic back propagation formulation has been implemented and validated by comprehensive measurement campaigns of vehicle mounted antennas, handsets and base station antennas and compared to numerical examples with Method of Moments technique.
Research of Geometric Characteristics of Steerable Reflector Antenna Dish
at Operating Elevation Angle Using Industrial Geodetic Systems
Petrov, V.1; Polyak, V.2; Kazarinov, A.1; Mikryukov , P.1
1BumTechno, RUSSIAN FEDERATION;
2R&D Institute of Industrial Stell Structures, RUSSIAN FEDERATION
The article is about creation of system of shape monitoring and relative position of components of mirror systems of large-scale (with aperture up to 70 meters) steerable antennas using state-of-the-art industrial geodetic systems based on Leica LTD800 laser tracker or Metric Vision MV260 laser radar, or local positioning system Indoor GPS.
Normal operation of antenna radio complex can be ensured only if the necessary shape as well as position of feeding system are followed with high accuracy in all operating elevation angle.
To compensate the distortions resulting from different kinds of antenna structure deformation (due to gravity and/or temperature), combinations of passive (form stabilization) active methods (adaptive surface, corrective movements of subreflector).
To check the efficiency of these methods, it is necessary to create a monitoring system that will make it possible to determine the shape and position of the mirror system components both in statics and dynamics. When compensation is found to be insufficient, it is possible to take additional measures on antenna geometry correction. Such geodetic measurements are difficult due to big size of reflective system of large-scale steerable antennas, required high accuracy of measurements and necessity to take dynamic measurements of reflector operating elevation angles.
Test and Measurement Requirements
on Wireless Devices
ETS-Lindgren, UNITED KINGDOM
In the Telecoms market Type Approval measurements are well established in terms of EMC standardization and EMC test facilities. Other requirements such as Operator radiation hazard safety (Specific Absorbing Rate), audio accessibility, hands-free capability, compatibility to hearing-aid devices (ANSI C63.19) have been introduced in the Telecoms market in the United States and are being adopted in both Europe and the Far-East. Major interest is now currently directed to the new requirements developed in the USA by the C.T.I.A. (Cellular Telecommunication and Internet Association) which describe new test methods and performance criteria for the Over-The-Air (OTA) testing of hand held devices. These OTA performance tests are fundamentally 3-D antenna pattern measurements of active antennas. Their purpose is to measure the entire signal connectivity of the mobile handset transceiver devices, detect and reject manufacturing defects of the mobile handset with the integrated product, determine operator impact on the mobile handset Over-The-Air connectivity performance, provide data to network providers to demonstrate meeting required performance criteria and reduce the need to perform drive test for connectivity. This allows network providers quicker evaluations of new phones to be introduced to market and will also provide the consumer a better product. The test methods and criteria will be discussed together with the current status on the standard and accredited test sites.
High Power, Dual Polarized Antenna Feed Technology for Mobile Applications
Dupessey, V.; Markland, P.; McDougall, J.; Richard, S.
With rising congestion in the L-Band spectrum, Mobile Satellite Antenna systems are now required to increase frequency re-use by upgrading from single to dual-polarization. Additionally, the operating bandwidths and power levels continue to increase to satisfy the demand for enhanced capacity at both L-Band and S-Band frequencies.
Over the years, MDA has developed a unique expertise in the design, manufacture and test of Feed Arrays for Mobile Satellites. MDA's heritage includes programs such as Inmarsat-2, MSAT, ACeS-1 & -2 and Inmarsat-4. Because all these mobile antenna systems were single-polarization a development effort was necessary to enhance the existing technology to operate in dual-polarization.
Compared to single-polarization systems, dual-polarization feed arrays for mobile antennas are more challenging in many areas. For instance, the packaging density is significantly higher since two diplexers, instead of one, are to be accommodated behind each radiating element while the inter-element spacing remains virtually unchanged. In addition, the PIM requirements are more stringent given the increased power levels and lower PIM orders resulting from the increased bandwidth.
This paper describes the new mobile antenna feed design developed at MDA. The innovative technology, although developed at L-band, is specifically designed to be easily scaled to S-band. The feed consists of a novel high-power dual-circular-polarization radiating-element, combined with a compact PIM-free dual-diplexer system. The diplexer uses a unique thermally compensated resonator technology that offers exceptional thermal stability (<1 ppm/°C), while substantially reducing fabrication costs. Finally, an original support panel and packaging arrangement facilitates a multi-element array configuration.
The mechanical design concept, including overall dimensions and mass, is presented in this paper together with the RF analyses and test measurements for a septet feed array and dual-diplexer assembly.
High-Power Rectifying Antennas
Alden, A.; Bouliane, P.; Zhang, M.
Communications Research Centre, CANADA
A high-power rectifying antenna has recently been proposed, in large, and small, area versions. These designs avoid the power limitations of previous 'rectennas', enabling power densities up to 4 orders of magnitude above conventional systems. Antenna design considerations are disclosed in this paper.
The rectenna uses a contiguous dipole array structure to reduce antenna length from that of earlier rectennas, while avoiding the large increase in antenna reactance found with separated antennas. This reduction in length allows for a decrease in the power required from each rectenna element. Unit cell height is thus considerably smaller than the wavelength of the powering beam. This enables a single-mode transmission line representation for both the powering frequency and significant harmonics. DC load circuits are included. Using this model, the maximum output power density is shown to be a function of only the diode breakdown voltage and the lower bound on dipole length. Once this dimension is chosen, unit cell width determines the output power. An upper bound is given for both dipole length and column spacing. This criterion prevents the contiguous array acting as an EM grating, diffracting beam energy into new reflected, transmitted, or surface waves. Because of the small area now allotted to each element, the circuit filters of conventional designs are relinquished. The antenna with its diode load must now match the characteristic impedance of the unit cell line. Resonance of the diode capacitance is now accomplished by the antenna inductance and the section of unit cell between the antenna plane and reflector. A combination of dielectrics is present behind the antennas, for both versions. For example, microchannel cooling has been proposed for a large-area extremely high power rectenna. These channels pass over the diode active area, at right angles to the dipoles, to minimize the effect of high-dielectric water on antenna performance.
These and other design relationships are presented in quantitative form. Previously unpublished simulation results are given for a large-area design using GaAs. These data show that, for a 50 mm unit cell size, a potential exists for output power densities of 2 kW/cm2 and efficiencies of 64 %.
Recent improvements in micro-air vehicle technologies provide immediate requirements for a low cost, 'off the shelf', small-area array with power densities up to 5 W/cm2. This capability is needed at 35 GHz, where beam transmit antennas are not prohibitively large, and high-power gyrotrons are available.
In the small-area version, flip-chip diode metallization, and end-to-end connections between chips, constitute the contiguous dipoles. At 35 GHz, commercially available GaAs Schottky flip-chips have diode parameters well-matched to the desired frequency, and physical dimensions considerably smaller than the upper bound described above. With breakdown voltages up to 10V and packing densities of 300 /cm2, a maximum output power density of 5 W/cm2 is possible, two orders of magnitude above conventional rectennas. A prototype, using a diode with 4 V breakdown, has given a conversion efficiency of 44% at 30 GHz, at an output power density of 1.2 W/cm2.
Review of Broadband Antenna Measurements
Huang, Y.; Chan, K.; Cheeseman, B.
University of Liverpool, UNITED KINGDOM
There has been an increasing demand for broadband wireless communications, which has been resulted from a number of reasons, including the increased communication data rate and the increased number of services. As a result, more and more broadband antennas are being developed.
Once an antenna is designed and made, the next task is to measure its performance. The subject of how to conduct a broadband antenna measurement is not well studied. The conventional frequency domain measurement is very effective for narrowband antenna characterisation. How to make efficient and accurate broadband antenna measurements is a subject yet to be fully investigated. The current and common view is that the time-domain technique should be a good option for such a broadband measurement.
This review paper is aimed at comparing various antenna measurement techniques developed so far, with an emphasis on making broadband measurements. Both the frequency and time domain techniques, and the near field and far field measurements will be considered over a frequency range up to 40 GHz. Some newly proposed techniques are also to be reviewed.
Calculating Q of Complex Small Antennas Using FDTD Method
Guezgouz, D.; Collardey, S.; Sharaiha, A.; Mahdjoubi, K.
University of Rennes 1 - IETR, FRANCE
The antenna radiation Q factor is a quantity of practical interest for small antennas which provides an indication of the antenna's bandwidth and can be defined and determined independently of the feed line characteristic impedance. The fundamental definition of Q is given by: Q=wW/Prad, where w is the radian frequency, W is the sum of the electric and magnetic average stored energies and Prad is the radiated power. The study of the lower bound of lossless antenna Q which fits inside the smallest circumscribing sphere (as defined by Wheeler 1947) can be traced back to Chu (1948). A lot of related studies have been done since then (Collin and Rothschild 1964, Fante 1969, Hansen 1981, McLean 1996). This lower bound has been found to be elusive to achieve in practice since it doesn't take into account the energy stored in the near field of the antenna (inside the sphere).
From the point of view of antenna design, it would be interesting to be able to predict an exact value of antenna radiation Q. Therefore, Thiele and al. have recently used the far field approach (2003) to obtain a more realistic value of Q as well as Mclean using an ellipsoidal volume (1999). Geyi (IEEE TAP, 51, 8, 2003) also proposed analytical formulas for small simple antennas deduced from the combination of the Poynting Theorem in time and frequency domain, taking into account the energy stored in all the space and this permitted to obtain a higher value of Q approaching the real one.
More recently, Yaghjian and Best introduced another method based on the derivative of antenna input impedance (A.D. Yaghjian and S.R. Best, IEEE TAP, 53, 4, 2005) to obtain a more precise value of Q. The approximate expression of Q obtained by them is the following: Q=w[(dZ/dw)/2R], where Z is the input impedance of the antenna and R its real part.
In earlier work, we proposed a simple method for numerically determining the radiation Q of an antenna using the FDTD method (Finite Difference in Time Domain) (IEE Electronics Letters, 41, 12, 2005). We used the same fundamental definition of Q where we first computed the total energy in a specified cubic volume in the near field and the far field of the antenna and then we deduced the non-propagated energy by subtracting the radiation energy from the total energy. The main advantage of using FDTD is that we can obtain an accurate value of the Q factor and that it can be used to characterize antennas of any shape or complexity.
The quality factor of small linear and elliptical polarized antennas like Pifa, helix... is calculated and compared to the other methods. Some details of the FDTD method and results will be shown during the conference.
Zero-Thickness Wideband Antennas for Small Radio Transceivers
Kabacik, P.1; Byndas, A.1; Hossa, R.1; Bialkowski, M.2
1Wroclaw University of Technology, POLAND;
2University of Queensland, AUSTRALIA
Recent years have observed intensified efforts in the direction of bandwidth broadening and reduction of volume occupied by antennas in small radio transceivers. The reasons for these activities are new services and applications of small radio systems. As more and more RF and signal processing chips are packed in a small volume of the transceivers, very little space is offered for radiating elements. At the same time, as new applications use newly allocated frequency bands, the radiating elements are forced to operate over increased bandwidths and in many bands.
In the last few years, milestone achievements in terms of bandwidth have become feasible due to explorations of mutual coupling between a primary radiating element and its supporting ground plane. These types of investigations have been carried out by some research groups, which have discovered the importance of ground plane in enhancing the operational bandwidth and multi-band frequency performance of small antennas. The work of these research groups has led to the concept of small zero-thickness antennas, which is the subject of the present contribution. These antennas are formed entirely in the ground plane of a small size mobile radio transceiver.
The paper reports on the most recent work, which has been accomplished in this area at the Wroclaw University of Technology. A generic sketch of the small zero-thickness antenna is depicted in Fig. 1. The focus of the investigations is on the proper meandering of metal strips within narrower or broader slits in a larger conductive surface, which operates as the ground plane. By exploiting the strong coupling between the radiating element and the ground plane optimal configurations are searched to obtain largest operational bandwidth of this new antenna structure.
Having determined the optimal configuration, the next step concerns the investigations of the changes of the electrical characteristics due to packaging effect, when the ground plane including its primary radiating structure is housed in a package. The presence of package affects the performance of this zero-thickness antenna. As a result, new iterations for the optimal antenna configuration, which now operates in the presence of the package, are required.
Fig. 1. A generic configuration of a zero-thickness antenna, as investigated at The Wroclaw University of Technology.
Equivalent Circuit Modelling of a Point to Point Wireless Power Transmission System
Douyere, A.; Lan Sun Luk, J.D.; Celeste, A.; Alicalapa, F.
University of La REUNION, REUNION
Fig. 1: Equivalent circuit of a complete energy transmission system at 2.45GHz.
This article presents an equivalent circuit approach used for the modeling of a complete system of energy transmission at 2.45GHz in a single non linear circuit simulator environment. The measurements and simulations steps used for parameter extraction and model validation are presented. It is shown that using this approach, no electromagnetic simulation tool is required for the simulation and optimization of the overall circuit. Furthermore, this method allows the physical origin of the energy losses to be studied. The results obtained using this simple example show a relatively good agreement with the experiment and can form the basis for further developments of more complex systems.
The antennas and the transmission channel of the energy transmission system are modelled by an equivalent circuit. The first two parts of this article present the equivalent circuit used to model the antennas, the transmission channel and the process of parameter extraction. In the modelled system, a patch antenna array is used as the transmitting antenna. At the receiving section we used a dipole antenna connected to a RF/DC rectifying circuit (rectenna). Subsequent parts show the simulations of the derived rectenna model and comparison with experiments. Figure 1 shows the equivalent circuit used to model the electrical behaviour of the antennas and the transmission channel in response to an incoming RF beam. A ‘Gradient’ method is used in the APLAC software for minimizing the error between the simulated S11 parameter of the antennas and the one measured using a network analyzer in the chosen frequency band. The optimization of the antennas is performed at each resonant frequency using the Qn, Kn, Rrn and Rcn parameters. Figure 2 shows that the behaviour of the overall transmission system is correctly described by our modelling approach.
The major interest of this approach lies in its ability to fully optimize the circuit in a single simulator environment. This equivalent circuit model may be used to optimize the complete system of energy transmission for low spurious emissions and high rectenna efficiency.
A Model for the Impedance of a Bent Planar Monopole Antenna
Aberbour, L.1; Craeye, C.2
1UCL (Universite catholique de Louvain), BELGIUM;
2Universite catholique de Louvain, BELGIUM
In our previous works , dedicated to antenna miniaturization, we proposed an efficient electrically small monopole antenna of lambda/17 by lambda/12 size (L1 by L2 in Fig. 1). The miniaturization is based among others on an intrinsic capacitive load, which avoids size enlargement due to the addition of extra components. A low profile antenna is achieved thanks to the use of planar technology.
Fig. 1 illustrates the E field distribution in the dielectric material, one can observe the highly concentrated fields in the area between the inner monopole arm and the ground plane. This is effectively the intrinsic capacitor yielded by the antenna shape itself. The horizontal arms have a low radiation level (resulting from the interaction with the ground plane) this property allows to bend the upper strip inward without drastically affecting the antenna performances. The radiation resistance is mostly dependent on the lengths of the vertical arms.
In order to complete our study, based previously on the surface currents and field distributions, we derive a model for the antenna impedance. We also compare it to the results for an horizontal rather then vertical ground plane. The design of Fig. 1 is a wedge-like structure. C.-T. Tai  and M. Felsen  have derived the Green's functions for such kinds of configurations, like an electrical dipole in the presence of a half-sheet and an infinite line source near a conducting wedge.
The 2D Green's function for an horizontal line source located at ka and in the same plane as the perfectly conducting wedge (at Phi=pi/2) is given by  as :
The E field pattern function, derived from the use of the asymptotic approximation of G, with respect to both the observation angle Phi and the location a of the line source from the conducting wedge is represented in Fig. 2.
The closer is the horizontal line source to the half-sheet the lower will be the radiation resistance of the bent part of the monopole. Its reactive part will be found from the wire length and the capacitance referred to above. The global radiation resistance will be essentially proportional to the square length of the vertical segment.
This will provide a global model for the antenna impedance, which should help the later optimization procedure.
 L. Aberbour, C. Craeye and D. Vanhoenacker,"Miniature Bent Folded Planar Monopole Antenna'', LAPC Conference Proceedings (expected for April 12th, 2006.
Miniature Microstrip Fractal Patch Antenna Working with Crossed-Diagonal Mode
Hazdra, P.1; Mazanek, M.2
1Czech Technical University in Prague, Faculty of Electrical Engineering, CZECH REPUBLIC;
2Czech Technical University in Prague, FEE, Dept. of Electromagnetic Field, CZECH REPUBLIC
Paper describes a novel type of miniature microstrip patch antenna based on fractal geometry. Antenna's geometry was created using the L-System algorithm  (with outer dimensions 31.3 x 31.3 mm) and the following recipe : F -> FGG+FG-G-FG+FGG, G->G, α=90°, LF=0.9, LG=0.1.
Miniature properties are achieved by the presence of unusual fundamental resonant mode which we call "crossed-diagonal" modal current (CDM). The whole antenna we call Fractal-Crossed-Diagonal-Mode (FCDM) antenna.
To study the modal properties of the antenna, we first employed the quasi-static cavity model and analyzed the modes, the fundamental one is shown at Fig.1 (left) with predicted resonant frequency 1.9GHz. Both current paths are in-phase, producing linear polarisation. Slotted structure also helps to extend the current paths and thus decrease the resonant frequency. The FCDM patch antenna was then simulated using the full-wave EM simulator IE3D with L-probe feeding technique used (Fig.1 right).
Best matching (Fig.2 left) was obtained with the following L-probe parameters Lv=12mm, Lh=15mm and H=15mm with resonant frequency f=1.876GHz. Although the antenna is considerable small (0.196 lambda x 0.196 lambda x 0.094 lambda), simulated radiation efficiency is satisfactory with gain G=7.2dBi. Radiation pattern is depicted at Fig.2 (right) showing cross-polarisation level being -10dB below the main co-polar component.
Full paper will focus more on the modal analysis, specially on the distribution and properties of higher order modes. L-System algorithm allows to freely modify the geometry parameters; effect on the antenna behavior will be shown as well.
 Hazdra, P.: Widely Configurable L-System Fractal Antenna Generator. In POSTER 2004 [CD-ROM]. Praha: CVUT FEL Praha, 2004
Acknowledgement: This work has been done under the ACE-2 framework
A Survey of Small Antenna Designs at the LEAT
Luxey, C.; Staraj, R.; Kossiavas, G.; Papiernik, A.
LEAT-CNRS University of Nice, FRANCE
Numerous small antennas have been designed at the Electronics, Antennas and Telecommunication Laboratory (LEAT) of the University of Nice Sophia-Antipolis. In this paper, we perform a detailed analysis of the evolution of the different techniques employed to miniaturize the size of these structures.
The C-patch is the first miniature antenna designed at the LEAT (Fig. 1). In 1988, two different C-elements were fabricated to operate in the UHF and the L frequency bands . The main miniaturization trick was to etch a slot in a square patch to increase the path length of the surface currents and then make the element resonating at a lower frequency. The next achieved step was to vertically fold two C-patch antennas (Fig. 2) in a stacked manner while still keeping them linked via a small vertical strip. This structure was further miniaturized by adding a short circuit to the lower C-patch and then patented with France Telecom R&D La Turbie (formerly France Telecom Le CNET) . All these different techniques were then applied to quarter wavelength resonators for dual and broad-band purposes (Fig. 3).
In the following years, a new challenge raised with the advent of the 2G mobile communications and especially the growing demand of using small internal antennas in cellular handsets: design miniature multiband PIFAs on small ground planes. A first GSM/UMTS antenna was co-patented with both Mobile Phone and Space Divisions of Alcatel . The used miniaturization techniques were to simultaneously stack slotted resonators and insert shorting posts on both lower and upper plates (Fig. 4). The benefit of using a small ground plane (the Printed Circuit Board of the mobile phone) as a counterpole of the small antenna was understood and controlled with the next designs, especially a GSM/DCS/PCS/UMTS/WLAN antenna (Fig. 5). In this structure, all the miniaturization techniques previously described were concurrently used with electromagnetically coupled parasitic resonators, distributed capacitive loads while positioning the antenna at the top edge of the PCB.
Today, with the upcoming implementation of diversity and MIMO techniques in cellular communications, the miniature antenna team of the LEAT works on the integration of several elements on a small ground plane while keeping a high isolation between them. Several multi-antenna systems have been successfully fabricated and measured while using a neutralization effect between the radiators (Fig. 6). Other exciting fields of interest are also to use the PCB as the main radiating element when excited by a non-resonant structure and to further miniaturize the antenna while accepting the degradation of its return loss and total efficiency.
 G. Kossiavas, A. Papiernik, J.P. Boisset, M. Sauvan, "The C-Patch - a small microstrip element", Electronics Letters, Vol. 25, no.4, p.253-254, 1989.
Analysing Radiation from a Cylindrical-Rectangular Microstrip Patch Antenna Loaded with a Superstrate and an Air Gap, Using the Electric Surface Current Model
Cooray, F. R.; Kot, J. S.
CSIRO ICT Centre, AUSTRALIA
Microstrip patch antennas are widely used as conformal antennas in many practical applications. When a microstrip patch antenna is employed as an outdoor antenna, a superstrate layer is generally added on top of the patch to act as a radome to provide protection from environmental hazards such as rain and snow. One such antenna that is of interest to us is a low profile antenna housed in a flexible collar for animal husbandry applications, and the effects of water, dirt, etc. on the radiation from this antenna. As the addition of a superstrate layer can change the characteristics of the microstrip structure, being able to analyse a microstrip antenna loaded with a superstrate is of importance, to understand how the radiation from it would change with the type of superstrate being used. Even though antennas of this kind have been analysed in the past, the emphasis had mainly been on calculating the resonance frequency, and the superstrates considered had been made of lossless dielectric. In this paper, we analyse a cylindrical-rectangular microstrip patch antenna loaded with a superstrate as well as an air gap between the substrate and the superstrate, using a full-wave approach and an electric surface current model. The addition of an air gap allows the directivity of the antenna to be enhanced. Also, we have used lossy dielectric material for the superstrate to find out how the loss in the material will affect the radiation from the antenna.
The antenna that we analyse is an infinitely long concentric circular cylindrical microstrip structure consisting of a perfectly conducting ground cylinder and coaxial cylindrical substrate, air gap, and superstrate layers. The patch is assumed to be a perfect conductor of zero thickness printed on the dielectric substrate. In order to perform the analysis, the patch is replaced by an assumed surface current distribution, which can be obtained in many cases using a cavity model approximation that is valid as long as the radiation is small compared to the stored energy.
In each region, the electromagnetic fields in the spatial and spectral domains are expressed in terms of a two-dimensional cylindrical Fourier transform pair with unknown expansion coefficients. Next, by imposing appropriate boundary conditions at each interface, a set of simultaneous equations for the unknown expansion coefficients is obtained. These equations are then solved to obtain the expansion coefficients associated with the fields exterior to the coaxial cylinder in terms of tangential components of the known surface current distribution. The radiation pattern of the antenna is finally calculated using these expansion coefficients and the saddle point method.
The radiation properties of the antenna depend on the orientation of the surface current relative to the cylinder axis. We have analysed both axial and azimuthal current elements, assuming that the current distribution is that of an open microstrip line half wavelengths long. Numerical results will be presented in the form of normalised radiation patterns for various thicknesses of the air gap and also for superstrates made of different lossy materials to show the effects of these on the radiation from the antenna.
Electromagnetic Cavity Sensor for Detecting Water in Oil Pipelines
Al-Shamma'a, A.; Wylie, S.R.; Shaw, A.; Lewis, G.
Liverpool John Moores University, UNITED KINGDOM
The ability to detect the amount of water in oil pipelines is very useful in production management. Water is routinely injected from sites around the production well to maintain the reservoir pressure and force the oil towards the producing wellbore. If this water leaks into the wellbore, a condition known as breakthrough, it will be produced along with the oil. If there are no facilities to separate water at the site, then pipeline capacity will be wasted in transporting it to a facility that can. Even if the water is removed on site, further cost is incurred ensuring that the water is sufficiently free of oil to meet the increasingly stringent environmental limits, before it can be disposed of.
This paper describes a sensor that can detect water as it flows through the pipeline. The sensor forms an electromagnetic cavity, and by monitoring the shift in the resonant frequencies, it is possible to determine the permittivity of the pipeline contents. Water is a polar liquid, so its permittivity is significantly higher than that of either oil or gas. As a result, even a small amount of water causes a significant frequency shift and so is readily detected.
An industrial prototype sensor has been tested under realistic conditions and results will be presented.
Patch Antenna with Reduced Size for 400 MHz Transmission in Confined Surroundings
EADS Space Transportation, FRANCE
This paper relates to the reduction of the size of a patch antenna to achieve a transmission by coupling with another antenna at a frequency close to 400 MHz (radio-control frequency), in a closed environment and with dimensionnal constraints . This study was carried out in order to reply to a need for radioelectric link in a closed space to allow the test of a radio-control system. The radio-control system , composed of a receiver connected to an antenna, operating with a frequency close to 400 MHz is located inside the confined space (closed caisson), opaque with the microwaves. Moreover space between the reception antenna and the wall of the box is about 100mm, and volume available for the transmission antenna (patch antenna) is of 100 mm*100 mm *10 mm. The objective was to obtain a coupling close to 20 dB between the two antennas. To produce the transmission antenna our choice went on antenna patch technology while trying to reduce at best the dimensions of the patch antenna. We applied techniques of reduction of dimensions by achieving slots to the non radiating edges and by introducing short-circuit points between the patch and the mass. By this way we could reduce the dimensions of the patch antenna of a factor 3 and integrate the transmission antenna in volume available. We at first carried out a study by simulation, using the software "ENSEMBLE - ANSOFT" in order to determine the influence of the width, length of the slots on the SWR, the frequency and the bandwidth. In a second step we produced a prototype, and compared the experimental results with the theoretical results. We noticed gaps between the experimental and theoretical results (5 % on the resonant frequency) , and identified several possible causes: tolerances on the dimensions obtained after engraving, tolerances on the permittivity, effect of the ambient temperature, gaps of calculation according to the parameters such as for example the frequency of mesh. After having achieved complementary calculations, we concluded that the only item responsible for the noticed gaps was the parameter setting of the frequency of mesh, and that for our patch antenna, it was necessary to increase the frequency of mesh to obtain a theoretical result in conformity with the experimental result taking into account the complexity of the patch antenna and the low frequency. Finally we carried out a last calculation in order to check the level of coupling between the reception antenna and the studied prototype. This study enabled us to answer the requirement concerning the radioelectric link with 400MHz in a closed and confined space, and this means will be soon operational.
RFID Transponder Antenna Design, Construction and Analysis
Javangwe, P. T. B.1; Huang, Y2; Beckman, C3
1UNIVERSITY OF LIVERPOOL, UNITED KINGDOM;
2University of Liverpool, UNITED KINGDOM;
3University of Gavle, SWEDEN
A technology known as Radio Frequency Identification (RFID) system has rapidly been developed and proven effective. It is becoming extensively used in industries. RFID uses radio frequency communication for applications such as:
•Car key identification.
• Computer Aided Manufacturing (CAM).
• Baggage check in airports.
• Entrance control in buildings and sporting arenas.
• Animal identification.
• Trash can / container identification/sewerage.
This technology overcomes the weaknesses exposed by the barcode system (commonly used in supermarkets presently). Barcode systems use a reader and coded labels on targets whilst the RFID system uses a reader and RFID tag/transponder attached to the target. Barcode uses optical signals to transfer information from the label to the reader; RFID uses RF signals to transfer information from the RFID device to the reader.
RFID systems can be divided into near-field systems and far-field systems. Near-field systems rely on magnetic coupling and work at lower frequencies for a distance up to a few metres whilst the far-field systems use radio waves and work at higher frequencies for longer distances. RFID can also be divided into passive (effectively operating at shorter distances) and active systems (effective even at longer distances). The vast majority of RFID systems operate in accordance with the principle of inductive coupling, i.e. passive near field systems. This paper is therefore focused on the design, construction and analysis of a transponder be focused on near-field system for frequencies up to 433 MHz.
A comprehensive literature survey has been conducted and this paper is going to compare the antennas used for RFID applications. Computer simulation is been conducted to assess various designs. Antenna design curves and guidelines for various RFID frequencies are produced to aid the design. Many previous designs have focused mainly on a single low resonant frequency, but this paper will address the transponder antenna design for frequencies up to 433 MHz and some key parameters of the system design will also be discussed, such as different antenna resonant frequency adjustments, detuning effects, communication distance ranges, impedance matching, transponder antenna design cost vs. performance. Computer software for such a purpose is under development.
Bi-Band Fractal Antenna for RFID Application at UHF
Ibrahiem, A.1; Giotto, A.2; Vuong, T.P.3; Tedjini, S.3
3LCIS INPGrenoble, FRANCE
In this paper the Koch fractal antenna at UHF frequency will be analyzed. In particular, a new technique proposed to adapt the input impedance of the Koch model for the impedance of RFID puce. Fractal antennas can obtain both input impedance and radiation pattern similar to a longer antenna, yet take less special area due to the many contours of shape. Fractal antennas are a fairly new research area and are likely to have a promising future in many applications of RFID.
The research is intended to propose small fractal antenna structures for applications such as Radio Frequency Identification (RFID). Since a passive tag does not have its own power supply it is important that tag-antenna can absorb as much of the energy, radiated from the reader, as possible. A factor that affects the size of the tags is the frequency that is used. As a solution to minimizing the antenna size while keeping high radiation efficiency, fractal antennas can be implemented. The fractal antenna not only has a large effective length, but the contours of its shape can generate a capacitance or inductance that can help to match the antenna to the circuit or the RFID chip.
The geometry of the fractal is important because the effective length of the fractal antenna can be increased while keeping the total special area relatively the same. The fractal bi-band antennas are analyzed as resonant dipole antennas using "CST Microwave Studio", a 3D electromagnetic solver based on Finite Difference Time Domain method. The 2nd, 3rd and 4th iterations shown in "Fig. 1" are studied and simulated.
Fig.1: First iterative steps for generating a Koch curve
We propose a simple technique to adapt the fractal dipole antenna to the complex impedance of the RFID chip by adding a strip line in the other side of the fractal model, as shown in fig. 2. We considered that the impedance of the RFID chip is equal to (10 - j 30 Ohms).
Fig.2: Calculated and measured return loss of the antenna
Simulation and Experimental Results The distance between this line and the Koch dipole antenna, the length and the width of this line are the different parameters which helped us to adapt the Koch dipole antenna at the UHF frequency. It is important to note that, the fractal model still has its bi-band resonance frequency at 868MHz and 2.45GHz. Fig. 3 compares between the return loss parameters for all the three models (2nd, 3rd and 4th iterations) of fractal antennas simulated to be matched to the impedance of the RFID chip. The calculations shows that the proposed fractal design is will adapted to the RFID chip.
Fig. 3: The return loss parameters simulated for all the three models (2nd, 3rd and 4th iterations) of fractal tags
A new technique is proposed to adapt the input impedance of the Koch model to match with the impedance of the RFID chip. This proposed technique conserves the same special form of the bi-band Koch dipole model. The calculations shows that the proposed fractal design is will adapted to the RFID chip.
Spherical Near-Field Antenna Test Range
for Automotive Testing from 70MHz to 6GHz
Dooghe, S.1; Duchesne, L.1; Gandois, A.1; Garreau, Ph.1; Iversen, P.O.2; Barone, G.3; Foged, L.J.3
2SATIMO, UNITED STATES;
A wide range of wireless services are being installed in modern vehicles. Applications include radio reception (FM), navigation systems (GPS), satellite radio, keyless entry, future data services (IEEE 802.11) and mobile telephone are increasingly installed in modern vehicles. Integration of these technologies in cars and trucks have generated a need to accurately validate the performances of the antenna devices when mounted on the vehicle.
This paper presents a general purpose spherical near-field automotive antenna testing facility, taking full advantage of the fast probe array technology. The new system operates in the full band from 70MHz to 6GHz using two arrays of probes, 32 operating from 70Mhz to 400MHz and 103 operating from 400MHz to 6GHz. The RF system is combined with an advanced and fully automated mechanical positioning system which is capable of transporting the vehicle under test from the integration room just outside the chamber to the test position in the center of the spherical range. The whole system is contained in a dedicated anechoic chamber with 1.5m pyramidal absorbers which provide excellent reflectivity performances over the full frequency range. The general design consideration and a summary of the results of extensive verification tests will be presented.