UWB antennas with the general appearance of metal button structures will be discussed in this paper. The antennas can have wide-band characteristics when fed by a coaxial or microstrip line to create body-centric UWB monopole antennas. The authors of the present manuscript have reported the feasibility of producing button based monopole antennas capable to operate at the Bluetooth and WLAN bands [1]. The UWB button operation is achieved by transforming the upper part of the button shape antenna to a conical structure, while maintaining the base with the same cylindrical shape. The antenna improves its matched bandwidth to an extent that achieves sufficient coverage to be considered for UWB applications.

Figure 1 shows the main dimension of the wearable button antenna to be presented. The UWB antenna has a total height of 12.5mm and top disc diameter of 26mm. Other dimensions were: Db = 8mm, Dc = 12mm, Hc = 9.5mm. Similarly to [1], the UWB button antenna employs a 1.8mm Velcro substrate between the antenna and the ground plane. Another thin textile material can be placed at the top of the Velcro substrate with no significant mismatch in the antenna. The antenna was fed by a 50Ù coaxial line connected from the back of the ground plane to the centre of the monopole; however, other feeding connections could be possible for instance, side feeding as discussed in [1].

The antenna was simulated and a first prototype was measured. The simulated S11 for the UWB button antenna achieves a UWB band width from 3 GHz to over 12 GHz. The measured -10dB S11 for the first prototype achieves a UWB bandwidth from 3.2 GHz to 10.7 GHz and a -9dB bandwidth from 3GHz to over 12 GHz. Omni-directional radiation patterns in the H-plane are predicted which is desirable for mobile on body transmission.

In conclusion, a novel UWB wearable button antenna has been presented. The antenna uses the wideband characteristics of a standard metal button, to extend the bandwidth and achieve UWB. Although, the size of the antenna has increased with respect to the narrow band antenna reported in [1], it can still be camouflaged within the garment and resemble a metal button. Good omni-directional patterns are predicted in the H-plane. CST Microwave studio was used for the simulations. References:

[1] Benito Sanz-Izquierdo, F. Huang and J.C. Batchelor, "Dual Band Button Antennas for Wearable Applications", IWAT2006, White Plains, New York, March 6-8

Ultra-wideband applications have drawn very much attention from antenna designers, especially for those who are working on wireless consumer electronics products. Recently, WiMedia Alliance in the US has proposed the Multi-band OFDM for commercial wireless applications. The OFDM approach makes the application robust to multi-path interference with well-defined spectrum shape.

In this paper, a novel balanced small planar antenna fed with coplanar strips (CPS) for wireless PC card application is proposed and it works over 3.1-7.2GHz for VSWR<2. The antenna which can directly be connected with a differential amplifier covers most of the multi-band OFDM applications like wireless USB.

The proposed antenna is derived from semi-circular disc (SCD) dipole as shown in Fig.1. The antenna consists of a half-wavelength SCD dipole with extended portions and a 100Ω CPS feed network. This dipole antenna is printed on a FR4-substrate with a relative dielectric constant of 5.4 and a thickness of 1.6mm. The values of radius R and extended width W3 are 13mm and 5.4mm respectively. The CPS employed as feed line consists of two right-angle bends. The space G and line width S of the CPS is 1mm and 1.5mm respectively.

The return loss of the printed dipole is shown in Fig.2 and it clearly demonstrates that the antenna has an impedance bandwidth of 3.1-7.2GHz. While current distribution at 4GHz is shown in Fig.3, currents mainly concentrate on the edges of the two SCDs where most radiation takes place. The two principal pattern cuts of the antenna illustrate a dipole like pattern in E-plane and omni-directional pattern in H-plane as shown in Fig.4.

L1=26, L2=11.5, W1=41.8, W2=5, W3=5.4, G=1, R=13, D=0.5, S = 1.5 (mm)
Fig.1: Geometry of balanced CPS-fed dipole antenna.

Fig.2: Simulated return loss of balanced CPS-fed dipole antenna.

Fig.3: Current distribution of balanced CPS-fed dipole antenna at 4GHz.

Fig.4: Two principal radiation pattern cuts of balanced CPS-fed dipole antenna at 4GHz.

D'Errico, R.; Ghannoum, H.; Roblin, C.; Sibille, A.
Ecole Nationale Supérieure de Techniques Avancées, FRANCE

In this paper we improve a design of an UWB semi-directional antenna for low-cost applications in terms of size and performance. The design of the proposed antenna is derived from a previous work on a dual-fed microstrip monopole (DFMM), and it combines a quasi omni-directional radiator with a dielectric lens which redirects the radiation. The DFMM antenna already presents a slightly more directive behaviour in the direction normal to the monopole plane. The idea is then to enhance this radiation asymmetry by placing a lens on the substrate-ground plane side. The final prototype size is 33 mm x 20 mm x 11.5 mm, lens included.

Simulations have demonstrated that, using a half ellipsoid shape for the lens design, the most important dimension is its height, which sensitively affects the performance of the antenna. The optimized lens height is 10 mm. The ellipsoid horizontal section is chosen in order to have the diameter equal to the DFFM width (20 mm). The final adopted shape is then a half sphere of radius 10 mm, which is also easier to fabricate. The lens position over the ground plane has been optimized in order to achieve the best antenna gain performances.

The measured input bandwidth is 3.9-15 GHz with respect to S₁₁ < -10 dB.

The lowest frequency of the impedance matching band is determined by the single radiator without lens. However for UWB applications one of the most important features in antenna design is the realized gain (RG), which also includes the information about impedance matching. We show the Antenna Under Test (AUT) performances only in the ground plane-lens direction: angular behaviour will be presented in the full paper.

Measurements results show that the AUT presents a RG>0 dBi over the 3.4-15 GHz band in comparison to the 4-11.1 GHz band of the DFMM without lens. In Fig.1 we show the measured RG and front-to-back ratio (FTBR) of the AUT and DFMM in the FCC band (3.1-10.6 GHz). The use of the dielectric lens improves the antenna gain up to 4 dB, except for the frequencies around 10 GHz, where anyway FTBR is enhanced. The AUT provides a mean FTBR of 4.7 dB over the FCC band. Using an appropriate sub-band (e.g. 4.5-6 GHz) it is possible to improve the mean FTBR. More details about the influence of the excitation signal on antenna performances will be presented in the final paper.

In addition the frequency dependence of the antenna gain can be exploited in order to compensate that of free space attenuation, when two such antennas are used in the radio link. As depicted in Fig.2, the transmitted/received power ratio of the overall system, in the Line Of Sight (LOS) direction, is almost constant over the 3.4-9.5 GHz band (maximum variation of 2.5 dB). Such a feature is rarely obtained, and is very interesting in that all sub-bands within the FCC band will exhibit identical performance.

Finally Time Domain results intended to characterize precisely the distortion introduced by the antenna have been obtained. They will be shown in the full paper.

Fig. 1: Measured RG (black) and FTBR (grey) of the AUT (solid) and DFMM without lens (dash)

Fig 2: Transmitted/received power ratio (at 1 m) in a 2-AUT system

The Longitudinally tapered coplanar waveguide antenna has been found to offer ultra-wideband characteristics. Its construction does not require transition regions between different transmission line types, such as found in UWB Vivaldi antennas. As a tapered, relatively long antenna it generates an endfire beam rather than an omnidirectional pattern.

The tapered coplanar waveguide antenna is formed by tapering the dimensions of a coplanar waveguide. As such it can be easily connected to coplanar waveguide with little reflection. This is a clear advantage in comparison to Vivaldi antennas where transitions from microstrip to slotline or to double strip line are needed before the transition to the radiating element.

The radiation characteristics of the antenna are governed by the dimensions of the coplanar structure. A major factor governing the frequency where radiation is most apparent is the separation of the slots.

An example of a simple linear taper antenna is examined here using our Finite Difference Time Domain (FDTD) software. The taper is 10cm long and tapers from 5mm wide at the 50Ω feed to 2cm wide at the end. The dielectric material is 0.787mm thick and has a relative permittivity of ε_r=2.2. The return loss characteristics are shown in the diagram. The FDTD analysis allows us to decompose the reflection in time, showing that there is a small reflection from the input junction between the feed line and the antenna taper, typically less than -20dB. Most of the reflection occurs at the abrupt end of the taper where the antenna circuit is terminated in air. The return loss from the complete antenna structure shows the 'ringing' characteristic that results from the two distinct reflection sources.

The return loss characteristic shows bands where the loss is more than 10dB from about 6GHz to over 12GHz and 15GHz to 19GHz. The return loss exceeds 6dB from under 5GHz to above 28GHz, the upper limit of the reliable data in this analysis. Clearly the antenna shows UWB characteristics, and these characteristics can be governed by the design of the taper.

In the analysis the dielectrics are all lossless and the total radiated power is easily established as P= 1 - |S₁₁|². This characteristic is also shown, and the antenna circuit is seen to radiate more than half the incident power between 3GHz and 30GHz.

There are some radiation peaks at lower frequencies but once the taper is longer than one or two wavelengths the antenna tends to radiate all frequencies equally. Being a relatively long structure the radiation is mainly endfire, and the beamwidth is governed by the taper length.

In conclusion we have demonstrated the use of the longitudinally tapered coplanar structure as a UWB antenna. It has shown excellent wideband performance and has a natural advantage over other UWB Vivaldi structures in having a very simple and naturally well matched feed.

The Ultra-Wideband (UWB) wireless communication technology has been attracting enormous interests from both academia and industries worldwide. It features high-speed transmission data rate for short-range, indoor communications [1]. For antennas to fulfil UWB technology requirements, various monopole-like UWB antennas have been developed. The circular disc monopole can achieve a -10 dB ultra-wide impedance bandwidth from 2.4 GHz to 18.5 GHz, but it suffers radiation pattern distortion at higher frequencies [2]. P.V.Anob and K.P.Ray constructed an orthogonal square monopole antenna with semi-circular base, which not only exhibits a wide impedance bandwidth but also shows an omnidirectional pattern across the entire frequency band. However, this type of antenna has a relative large dimension [3].

In this paper, an orthogonal half disc UWB antenna fed by a 50 coaxial cable is firstly studied. It can yield a -10 dB impedance bandwidth from 4.6 GHz to 11 GHz in both the simulation and measurement. In order to cover the entire UWB band defined by FCC, i.e. 3.1 GHz to 10.6 GHz, an inductive loading is then introduced to enlarge the bandwidth on the lower band. The loading effects on the antenna performance and characteristics are investigated both numerically and experimentally. It has been shown that the improvement on the antenna performance can be achieved by using this inductive loading. In addition, it is also found that the size of ground plane can be largely reduced. The proposed antenna has an impedance bandwidth from 2.6 GHz to 10.8 GHz while its radiation patterns are omnidirectional across the entire band. Therefore, this improved orthogonal half disc antenna demonstrates its suitability for UWB applications.

References:

[1] Liuqing Yang, Giannakis, G.B: "Ultra-wideband communications: an idea whose time has come", IEEE Signal Processing Magazine, vol.21, no.6, pp26-54, 2004.
[2] J.Liang, C.C.Chiau, X.Chen and C.G.Parini, "Analysis and design of UWB disc monopole antennas", The IEE Seminar on Ultra Wideband Communications Technologies and System Design, pp.103-106, 8 July 2004, at Queen Mary, University of London.
[3] Anob,P.V, K.P.Ray, Girish Kumar, "Wideband orthogonal square monopole antennas with semi-circular base", 2001 IEEE Antenna and Propagation Society International Symposium. Boston, Massachusetts. July 8-13, 2001, vol.3, pp.294-297.

Abstract This paper presents a new type of ultra wide band (3.67Ghz~10.8Ghz) coplanar waveguide-fed LI-shaped monopole antenna for WLAN 802.11a, b & g in ISM band. The coplanar waveguide-fed monopole antenna consists of an L-shaped monopole and an I-shaped monopole, which are simply connected at the end of a coplanar waveguide feed line. The two adjacent resonance frequencies of the proposed antenna are associated with two monopoles of different lengths and parasitic elements between monopoles and grounds. The longer monopole(p2) works for the lower resonance frequency of 5.8Ghz while the shorter one(p1) works for the higher resonance frequency of 9.49Ghz. The impedance matching for the proposed antenna has been conducted by adjusting the length and shape of the monopoles, the length of additive feed line ground and the space between L-shaped monopole and ground. Especially the propagation and radiation condition could be improved (VSWR=2.0) by adjustment of the space between L-shaped monopole and ground and the unsymmetrical grounds. From the simulated results, the resonance frequencies operate at 5.8Ghz and 9.49Ghz, their impedance bandwidth of 7.04Ghz(3.76Ghz~10.8Ghz, 97%) and this antenna exhibits omni-directional radiation patterns in H-plane. Key words : Coplanar waveguide(CPW), monopole antenna, ultra wide band, unsymmetrical ground Fig. 1. Geometry of the proposed LI shaped wide band antenna fed by a CPW transmission line Fig. 2. Simulated return loss for the proposed wide band monopole antenna REFERENCES [1] H. D. Chen and H. T. Chen, "A CPW-fed dual-frequency monopole antenna," IEEE Trans. Antennas and Propagat., vol. 46, pp. 788-793, June 1998.

I. Introduction

The Impulse Radio Ultra Wideband (IR-UWB) technology has been disclosing fascinating perspectives for fusing digital communications and localization capabilities with low-cost and low-consumption. Based on time of flight estimation of impulses transmitted between several terminals, UWB signals benefit from fine resolution and good penetrating properties thanks to the extreme shortness of transmitted signals. However, due to wave propagation properties through obstacles such as wall, vegetation, snow, etc..., lower part of the spectrum (i.e. below 1GHz) is highly recommended in order to preserve reasonable link budgets. So, taking into account to the well known fundamental limits of antenna miniaturization, the design of efficient small hand-held terminal UWB antennas operating at frequencies lower than 1 GHz becomes a great challenge. This paper describes a compact antenna intended for an impulse radio localization device operating below 1 GHz. A combination of miniaturization techniques has been used to obtain antennas dimensions compatible with hand-held demonstration terminal size.Time domain descriptors have been used to estimate the antenna ability to transmit short electromagnetic pulses.
II. Antenna Presentation

Due to reduced dimensions of the terminal compared to the lowest wavelength (Lo/5.5) and the difficulty to use efficient ground plane, a balanced radiating structure has been studied for optimal performances. The developed antenna geometry results from miniaturization works carried out from notch antenna structures. Reducing the ground plane dimensions where the slot is etched leads to a balanced planar dipole structure with wide band properties. Loading techniques using shorting strip and folding wide dipole arms have been used to reduce the antenna dimensions. The volume loading principle has been applied by using the maximum allowed volume inside the terminal to optimize antenna performances. To improve wideband matching, the slot between the dipole arms has an elliptical shape. The overall dimensions of the developed antenna printed on a low cost FR4 substrate are 120 mm (Lo/5.5) x 73 mm (Lo/9.1) x 7mm (Lo/95) (Lo being the lowest operational frequency wavelength) with an operational frequency band extending from 450 MHz to 1.2 GHz.

Experimental characterization has been carried out using frequency and time domain antenna measurement set-up. An example of antenna input impedance is proposed in figure 2 showing a correct impedance matching from 450 MHz to 1.2 GHz (figure 2). The antenna efficiency (without taking into account the mismatch losses) remains greater than 80% within the frequency band of interest. The antenna has a radiation pattern of a dipole.

III. Time Domain Characterization

Time domain antenna behaviour has been studied using specific descriptors such as time domain gain and transmitting/receiving fidelity factors (presented in the final paper). Thanks to an home made simulation tool, the incident field on the receiving antenna and the pulse at the load port have been computed for a given pulse supplying the emitting antenna. An illustation of pulse evolution is proposed in the figure 3 where signals have been normalized for an easier comparison. The slight distortion of the pulse shape can be partially explained by the variations of the antenna time group delay within the frequency band (presented in the final paper).

UWB technologies will play an important role in the future, for a wide variety of short-range high data-rate applications. This includes traditional wireless LAN and PAN applications as well as consumer electronic devices (such as in photo and video cameras, set-top boxes, modem-router, etc) that increasingly have the need to communicate. A further application of UWB is long-range asset tracking, where the positioning information that can be obtained very accurately in UWB systems is privileged over data-rate. The concept presented here is capable of being used in all of these contexts, with limitations on its use only for the most stringent size constraints.

We present a new approach for UWB antennas taking advantages from the classical and the fractal techniques by applying a log spiral transformation to a fractal design. In this manner, the self similarity properties are given to the initial fractal. Stricto senso, this antenna looses its mathematical fractal properties but keeps the physical advantages of the real fractal pattern. A concrete realisation of this concept on a twisted Sierpinsky Carpet is presented. To avoid multi-band resonance effects typical of fractal antennas, that cause phase stability problem for pulsed UWB systems, we also propose to use different iterations of the pattern or different fractal generator functions for each arm of this antenna. Based upon the simulation of a dipole twisted Sierpinski carpet, several advantages related to this concept have been emphasized and are detailed here.

Definition of the log transformation using the polar coordinates: r' = r O' = O + 1/a log(r)

Electrical Characteristics

Monitoring the impedance is a good way to characterise an ultra wideband antenna. Looking at the impedance of fractal antenna, we observed that the real part rippling over a large bandwidth and its mean value remains high. On the other hand, the imaginary part remains constant, close to zero. Concerning the spiral antenna, the simulations show a real part of the impedance roughly stable and close to 50Ohm but with an imaginary part very high in absolute value penalizing the corresponding S11 parameter of such antenna. Our design takes advantages of both characteristics and presents a real part of the impedance more stable and lower than the one from the initial fractal design (stability coming from the spiral shape), and an imaginary part of the impedance as low as the one from the fractal pattern. Moreover, this antenna presents an S11 parameter (see figure 1a) and a radiation pattern comparable to classical UWB antenna designs.

Size

Comparing the size of the initial fractal shape and the one of the twisted shape, we observed a great reduction for the same bandwidth of the electrical response: 12x6cm for the initial dipolar fractal shape and 4.5x5cm for the twisted fractal with similar electrical performance. The simulated radiation efficiency for such a configuration remained acceptable. Fabrication. We keep the advantage of a planar antenna. All the complexity is confined in the initial definition of the twisted fractal. The pattern is then printed on a substrate as usual for a patch antenna.

Simulated S11 parameter (module and phase)	Simulated radiation efficiency of our design compared to bow tie antenna

Recently wireless Unversal Serial Bus (USB) system using Ultra Wide Band (UWB) technique is discussed and many kinds of antenna for UWB application are proposed. This paper shows the small and wide band antenna made of the printed circuit board and its performance.

The small UWB antenna which we proposed consists of four triangular elements on the front and the back sides of the printed circuit board. Its size is 10mm by 20mm and the VSWR performance is less than 2.5 in the band from 3.1GHz to 4.9GHz. But it was too small to achieve better VSWR performance. So we tried to improve the VSWR performance by increasing the ground area of the printed circuit board. In general, the antenna for UWB application is located on the printed circuit board which the UWB circuit, for example, LSI and other circuit, are located.

Therefore it is possible for the antenna to use the ground area of the UWB circuit as the ground area of the antenna. We assumed that the size of the printed circuit board of the antenna and the UWB circuit is 10mm by 45mm at worst, whose size is as almost same as the USB stick memory. This time, we tried to improve the antenna performance by using the ground area of the UWB circuit.

The outline of the printed circuit board of the UWB unit which includes the antenna area and the area of the UWB circuit is shown in Fig.1. The antenna size is 10mm by 20mm and the area of the UWB circuit is 10mm and 25mm. So the total size is 10mm by 45mm. This antenna is constructed by two pairs of the trianglar elements on the front and the back sides. Especially, it is characteristic that the left side elements on the front and the back sides are connected at the upper and the lower edges by the through holes in order to adjust the impedance. The stub sectin on the back side is also for matching for impedance. These elements are located symmetrically and fed at the front side by the microstripline.

This antenna is optimized by experiment and simulation. First the antenna is adjusted roughly by experiment. After that, it optimized by simulation using Moment Method. As an example, the current distributions are shown in Fig.2. The current is distributed on the ground area of the UWB circuit. This means that this antenna works better by using the wider ground area. And the measured return loss is shown in FIg.3. The return loss is less than -11dB from 3.1GHz to 4.9GHz and is improved greatly comparing with that of the 10mm by 20mm size antenna.

On addition, this paper will shows the measured radiation patterns, which include the Co-polarization patterns and Cross polarizaion patterns, and the radiation efficiencies. And it is shown the 10mm by 20mm small antenna on the printed circuit board of 10mm by 45mm achieved better performance.

This paper presents a planar UWB triangular monopole antenna (PTMA) printed on a FR-4 substrate with a rigid ground plane to increase the antenna bandwidth. Compared with other configurations of planar monopole antennas, such as square or circular, the bandwidth of the PTMA is relative narrow. In order to improve the bandwidth of the printed PTMA, the means of ridging the conventional rectangular ground plane is employed. The function of the ridged ground plane keeps the input impedance maintaining constant and more than 3:1 bandwidth can be achieved. The HFSS 3-D EM solver is employed for design simulation. The parametric study on the ridged ground plane is also investigated. A printed PTMA is fabricated on the FR-4 PCB substrate, and the measured VSWR is less than 2 from 3 to 10 GHz. The proposed antenna also maintains the monopole-type omni-directional radiation patterns.