A coplanar waveguide (CPW)-fed wideband beam-changed slot antenna is presented in this paper. The basis for achieving such a broadband operation is to create a multi-resonator in a slot cavity. By using a modified fork-like feeding structure, several different equivalent magnetic current paths are alternatively excited when the operated frequency is changed. Due to different radiation regions, the radiation pattern, including in the end-fire or bore-sight direction, can be changed frequency-dependently. A 220% impedance bandwidth (S11 < -10 dB) is demonstrated. Simulated and measured results of the antenna are presented.

The current trend in mobile terminals is that the number of systems is increasing all the time. Because of that, the volume reserved for the antennas of radio systems is decreasing. As known, at the lower RF frequencies the EMC shielding and the printed circuit board, briefly called chassis, operate as the main radiator. Normally currents to the chassis are induced with an antenna element, e.g. a PIFA or a coupling element. A further reduction in the size of a mobile terminal antenna can be achieved by replacing an antenna element by a direct feed, i.e. galvanically inducing currents on the surface of the chassis. The best way would be to cut the chassis in half and place the feed between the parts. In that case the chassis would operate as a thick dipole antenna. Because of the EMC issues, it is not always allowed to cut the chassis in parts and the chassis has to be a solid piece of metal. The feed can then be placed over an impedance discontinuity, e.g. formed by a slot, see Figure 1.

The achievable bandwidth of the antenna is very clearly affected by the resonant frequencies of the chassis. The largest bandwidth is achieved when the chassis is in resonance at the operation frequency of a system. The first order resonant frequency of a solid chassis, whose length is 130 mm, is about 900 MHz. Because a slot lengthens the current path compared to the solid case, the first order resonant frequency of the chassis decreases. This is especially important in the digital television application (DVB-H) that operates at the frequency band 470 – 702 MHz. By designing other impedance discontinuities it is possible to integrate several systems to the same antenna structure.

By using the presented idea, an antenna for DVB-H has been studied, designed and manufactured. The prototype fulfills the DVB-H system realized gain specification over the DVB-H band 470 – 702 MHz with a 4 dB margin.

With the development of mobile communication systems and miniaturization of hand sets, requirements for compact antennas are rapidly growing. In this regard, Planar Inverted F Antenna (PIFA) has found internal utilization within mobile units due to its small size for both single and dual band applications [1-2]. The PIFA has many known advantages, e.g. ease of fabrication, low manufacturing cost, ground plane compatibility and conformity with complex geometries. Perhaps most importantly, it can without difficulty be matched to any impedance (by simply choosing the location of the short circuit) without matching network, and the design concept is easily extended to dual band functionality [2]. On the other hand, it typically suffers from a narrow impedance bandwidth, which excludes the PIFA from a variety of applications. For example, modern transceiver front-ends are available with quad band support (GSM850/900/1800/1900) for global roaming. Unfortunately, this bandwidth is extremely difficult to achieve with a PIFA within the volume typically allocated for the antenna element. However, it should be kept in mind that without designing a matching network, one would never know what the real achievable bandwidth of the antenna is. Therefore, in this paper, an attempt is made to design a dual band PIFA antenna together with its matching network to asses the antenna performance. In deed, it has been experienced that careful design of the matching network results, as expected, in a substantial bandwidth improvement.

This paper presents the design and evaluation of a dual band PIFA antenna for the cellular bands GSM900/1800 (890-960 MHz). By applying a complex matching network, synthesized using the Simplified Real Frequency Technique (SRFT) [3], the bandwidth of the antenna has been extended for GSM850/900/1800/1900 coverage (824-960 & 1710-1990 MHz). To the authors knowledge, this is the first PIFA reported in the literature that simultaneously cover all these bands. Since the resulting network is of low-pass ladder structure type, additional improvements are achieved in terms of harmonic filtering (for Tx) and natural absorption of parasitic reactances into the component values. As the optimum component values given by the SRFT are all fairly small, the network is highly suitable for monolithic on-chip integration, thus enabling small-sized low-cost matching modules. We believe that this kind of module could find widespread application in wide/multi-band terminal antenna designs. In particular, as the input impedance of most PIFA elements are typically very similar (reasonably independent of the exact geometry), the matching modules (perhaps from a small library of different variations) could conveniently be used as an ad-hoc solution to already designed antenna elements.

References

[1] Kathleen L. Virga and Yahya Rahmat-Samii, "Low-Profile Enhanced-Bandwidth PIFA Antennas for Wireless Communications Packaging", IEEE Transaction on Microwave Theory and Techniques, vol.45, no.10, pp.1879-1888, October 1997.
[2] Z. Liu, P. Hall and D. Wake, "Dual-Frequency Planar Inverted-F Antenna", IEEE Transactions on Antennas and Propagation, vol. 45, no. 10, pp. 1451-1458, Oct. 1997.
[3] B. S. Yarman, H. J. Carlin "A Simplified ‘Real Frequency Technique Applied to Broad-Band Multistage Microwave Amplifiers", IEEE Tr. MTT., v.30, pp.2216-2222, 1982.

Modern automotive applications like RKE (Remote Keyless Entry) and TPMS (Tyre Pressure Monitoring System) increase the requirements for the overall performance of the in-vehicle integrated antennas. New solutions are needed to substitute traditionally used both printed and wire monopoles. The requirements include enhanced performance in term of range of the RKE System and received power from the wheel unit sensors for the TPMS system. These aspects are directly related to the gain, bandwidth and radiation characteristics as well as robustness and compact size of the antenna. The compact size is constrained by the avaliable space in the car.

Low profile (with the biggest dimension of 0.13 of the wavelength) planar inverted F-Antenna (PIFA) can be used to fulfil the requirements. This paper is presenting the design of a single band PIFA antenna and its extension to a dual-band antenna in order to cover the RKE and the TPMS application. Furthermore, calculations of the radiation pattern, link budget and range of the RKE system will be presented. Measurements of the stand alone antenna as well as measurements of the antenna together with the car will be presented and compared with the simulations.

First the antenna has been designed to operate at the frequency of 434MHz (Fig. 1a) and then extended to a dual-band version. The antenna consists of the ground plane, a top radiating element (upper face) and a feeding wire. Instead of a shortening pin, a shortening wall has been introduced as it presents a reactive load with the reducing effect on the resonance frequency. To assure the stability other strips (inductive supporters) without any electrical connection to the ground have been used. For tuning to the desired frequencies the antenna has been inductively loaded by using a slot pair in the upper face. Considering the current distribution the slots were placed strategically near the feeding strip. Thereby the effective length of the current flow becomes longer. Appropriate matching network for the antenna has been developed. The antenna design includes also the housing PPT (εr= 2.7, tanδ=0.003) and the FR4 (εr= 4.2, tanδ=0.02) PCB. The housing hasn't been depicted in Fig. 1.



Fig. 1 Geometry of the designed antennas: a) mono-band antenna for 434MHz b) dual-band antenna for 434MHz and 868MHz

For the right estimation of the antenna performance in the vehicle, already during the development of the first prototype the placement of the module has been taken into consideration. In this case the antenna was placed in the proximity of the roof. Therefore all measurements and simulations have been made on a metal plate.

This paper presents the design of mono- and dualband PIFA for automotive applications. The geometry of the antenna and the module design together with the placement in the car is concerned. The simulation results obtained with FEKO are compared with the measured results. The performance of the antenna in the vehicle is predicted. Further results will be presented in the full version of the paper.

The growing demand of electronic products employing several wireless standards for data exchange, working in different frequency bands, requires the adoption of multi-band components and devices. In this framework one of the most critical issue is the design of the radiating device since the development of a single antenna working in two or more frequency bands and belonging to a limited geometry is, in general, a hard task.

Wire antennas (basically dipoles and monopoles) can work in several frequency bands corresponding to the resonances of the structure, but multiple working frequencies are strictly linked by harmonic relationships and, in addition, their electrical performances (VSWR and gain) vary with the considered resonant frequency. Classical techniques for the development of multiband wire antennas are based on the insertion of reactive loads in the antenna structure in order to obtain and allocate multiple resonant frequencies.

In recent years the problem has been faced also exploiting the properties of fractal geometries combined with an optimization algorithm in order to optimize both antenna geometry and loads values and positions [1]. As a matter of fact, the use of fractal geometries for antenna synthesis has been proven to be very useful in order to achieve enhanced bandwidth and miniaturization [2]. However the insertion of additional circuital elements in the antenna structure requires longer manufacturing times and some uncertainty on antenna performances may be introduced by the tolerances of lumped components values.

In order to overcome the insertion of lumped load in the antenna geometry some degrees of freedom can be added by perturbing the characteristic fractal parameters. The synthesis of multi-band fractal antenna in the paper is faced as an optimization problem by minimizing specific cost functions written for the particular fractal structure considered. The optimization is carried out through a numerical procedure based on a Particle Swarm Optimizer (PSO) [3] [4], by optimizing only the parameters of the fractal geometry, without the insertion of any lumped load. In the paper, in order to assess the effectiveness of the synthesis procedure, numerical and experimental results obtained with some pre-fractal structures are presented and discussed.

References

[1] D. H. Werner, P. L. Werner, and K. H. Church, "Genetically engineered multiband fractal antennas," Electron. Lett., vol. 37, pp. 1150-1151, Sep. 2001.
[2] J. Gianvittorio and Y. Rahmat-Samii, "Fractals antennas: A novel antenna miniaturization technique, and applications," IEEE Antennas Propagat. Mag., vol. 44, pp. 20-36, Feb. 2002.
[3] M. Donelli and A. Massa, "A computational approach based on a particle swarm optimizer for microwave imaging of two-dimensional dielectric scatterers," IEEE Trans. Microwave Theory Tech., vol. 53, pp. 1761-1776, May 2005.
[4] R. Azaro, F. De Natale, M. Donelli, A. Massa, and E. Zeni, "Optimized design of a multi-function/multi-band antenna for automotive rescue systems," IEEE Trans. Antennas Propagat. - Special Issue on "Multifunction Antennas and Antenna Systems", vol. 54, pp. 394-400, Feb. 2006.

In this work a new integrated diplexed antenna is presented. It uses the CRLH transmission lines concept described in [1]. These transmission lines allow controlling the phase response at two arbitrary frequencies. Using this property, a diplexer based on the rat-race hybrid can be designed [2]. This diplexer can be integrated with a radiator to achieve a low loss, compact diplexed antenna. In this paper, a diplexed antenna operating in the UMTS bands is designed and measured.

First, the CRLH transmission lines are designed for the operating frequencies. Due to the narrow separation between both frequencies, a high number of cells are needed. This fact makes the use of lumped elements impractical. Besides, the tolerance of the components must be very tight. Because of this, the diplexer has been implemented using a dual layer printed technology.

As presented in [2], the diplexer is a four port network which splits the signal from the transmitter into two equal-amplitude, 180º out-of-phase signals in one direction at one frequency, and combines two incoming signals at the other frequency into the remaining output. So, the diplexer can also be seen as a balanced-unbalanced transition (balun) at both frequencies. Therefore, a balanced radiator is needed to be integrated with the diplexer.

The second step is designing the radiator. In this case, a dual-feed printed patch antenna will be used. The radiator must be either broadband or dual band, so it can cover both frequency bands.

Finally both elements have been built and measured on its own, and then integrated. High isolation between transmitting and receiving ports and low overall losses have been achieved. The figures show the parameters for a 1900-2200 self-diplexed antenna.

Microstrip (patch) antennas usually strongly radiate in directions along the ground plane. This effect causes unwanted radiation patterns and increased coupling among antennas. In [1], dielectric polarization currents are identified as the physical source of this radiation.

The first aim of the present paper is to analytically evaluate the influence of the polarization currents on a simplified model of a patch antenna. Data are given to estimate the deterioration of the radiation pattern. The results are compared with numerical simulations using the program of Ref. [2].

The second aim is to prove that various existing techniques for improving the radiation pattern merely reduce or compensate the radiation due to the polarization currents, rather than deal with surface waves (whose effect is negligible in most practical cases). For example, micromachining the dielectric under a metallic patch [3] removes the polarization currents. A superstrate [4] introduces polarization currents that are counter-directed with respect to those in the substrate. The metallic annular ring [5] supports counter-directed conduction currents. The technique proposed in [1] also introduces counter-directed conduction currents in an array of pins that acts like a metamaterial embedded into the substrate.

The third aim of the present paper is to propose some novel technical solutions for compensating the polarization currents, like adding metallic ailerons to a patch.

All these techniques for improving the radiation pattern are compared with respect to their efficacy, bandwidth, and ease of manufacturing.

REFERENCES

[1] M.M. Nikolic, A.R. Djordjevic, and A. Nehorai, "Microstrip antennas with suppressed radiation in horizontal directions and reduced coupling", IEEE Trans. on Antennas and Propagation, vol. AP-53, no. 11, November 2005, pp. 3469-3476.

[2] B. Kolundzija, J. Ognjanoviæ, T. Sarkar, M. Tasic, D. Olcan, B. Janic, D. Sumic, WIPL-D Pro. v5.1, WIPL-D, 2004.

[3] J.-G. Yook and L. Katehi, "Micromachined microstrip patch antenna with controlled mutual coupling and surface waves", IEEE Trans. Antennas Propagat., vol. 49, pp. 1282-1289, Sept. 2001.

[4] N.G. Alexopoulos and D.R. Jackson, "Fundamental superstrate (cover) effects on printed circuit antennas," IEEE Trans. Antennas Propagat., vol. AP-32, pp. 807-816, Aug. 1984.

[5] M.A. Khayat, J.T. Williams, D.R. Jackson, and S.A. Long, "Mutual coupling between reduced surface-wave microstrip antennas", IEEE Trans. Antennas Propagat., vol. 48, pp. 1581-1593, Oct. 2000.

Recently, it is strongly required for the mobile station to cover multi-band with a single internal
type antenna. It has a close relation with an activation of BCN (Broadband Convergence Network)
service which provides communication, broadcasting, wire, radio data services with a single terminal.
In this paper, therefore, we propose a multi-band internal monopole type antenna for a mobile station. We
design and implement the multi-band internal monopole type antenna for cellular (824~894MHz), GPS
(Global Positioning System: 1,575MHz), K-PCS (Korea - Personal Communication Service: 1,750
~1,870MHz) and S-DMB (Satellite - Digital Multimedia Broadcasting: 2,630~2,655MHz) with three
branch lines.

Figure 1. Geometry of the proposed antenna. Figure 2. Return loss of the proposed antenna.
Table1. Results of the antenna gain measurement.

Plane	Polarization	Gain(dBi)	Cellular(859MHz)	GPS(1,575MHz)	PCS(1,810MHz)	S-DMB(2.642MHz)
x-y	co	Peak	-2.88	1.66	3.15	5.57
		Ave.	-7.60	-2.49	-1.53	-0.05
	cross	Peak	-6.18	-2.74	-1.36	-3.14
		Ave.	-11.46	-6.50	-6.21	-7.14
y-z	co	Peak	-1.63	1.35	0.82	-0.39
		Ave.	-4.71	-1.65	-3.13	-4.14
	cross	Peak	-6.00	-4.34	0.23	5.45
		Ave.	-13.63	-8.49	-5.48	-0.93
z-x	co	Peak	-2.25	1.76	3.89	1.33
		Ave.	-7.18	-1.84	-1.19	-3.13
	cross	Peak	-5.17	-4.83	-5.25	2.40
		Ave.	-11.28	-8.96	-8.70	-0.30