Abstract-In this paper we propose a circularly polarized (CP) microstrip antenna on a suspended substrate with a coplanar capacitive feed and a slot within the rectangular patch. The antenna has an axial ratio bandwidth (< 3 dB) of 7.1%. The proposed antenna exhibits a much higher impedance bandwidth of about 49% (S 11 < −10 dB) and also yields return loss better than −15 dB in the useful range of circular polarization. Measured characteristics of the antenna are in good agreement with the simulated results. The radiation patterns indicate good cross polarization rejection and low back lobe radiations. The design proposed here can be scaled to any frequency of interest.

The design of an ultra-wideband microstrip patch antenna with a small coplanar capacitive feed strip is presented. The proposed rectangular patch antenna provides an impedance bandwidth of nearly 50%, and has stable radiation patterns for almost all frequencies in the operational band. Results presented here show that such wide bandwidths are also possible for triangular and semiellipse geometries with a similar feed arrangement. The proposed feed is a very small strip placed very close to the radiator on a substrate above the ground plane. Shape of the feed strip can also be different, so long as the area is not changed. Experimental results agree with the simulated results. Effects of key design parameters such as the air gap between the substrate and the ground plane, the distance between radiator patch and feed strip, and the dimensions of the feed strip on the input characteristics of the antenna have been investigated and discussed. As demonstrated here, the proposed antenna can be redesigned for any frequency in the L-, S-, C-, or X-band. A design criterion for the air gap has been empirically obtained to enable maximum antenna bandwidth for all these operational frequencies.

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A wideband microstrip antenna using a coplanar capacitive feed with nearly 50% impedance bandwidth has been realized on a stacked air‐dielectric substrate with only one metal layer above the ground plane. In this article an approach of modifying the patch shape is proposed to obtain symmetric radiation patterns in the entire frequency band of this antenna. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1991–1995, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23575