Design Studies of Ultra-Wideband Microstrip Antennas with a Small Capacitive Feed

Abstract

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.

Design of Small Dual Band Microstrip Antenna for Broadband Applications

“…Many microstrip antennas which operate for dual and tri-band operation are being reported [6][7][8][9][10][11]. For example bandwidth enhancement of printed slot antenna [6] having wideband of 2.80 to 11.81 GHz is reported.…”

“…Antennas reported in [7] have a circular polarization with frequency ratio of 1.11. On the other hand, the antenna in [8] offers for ultra wideband frequency band from 840MHz to 960MHz and [9] offers for maximum antenna bandwidth.…”

Dual Band Coplanar Capacitive Coupled Microstrip Antennas With and Without Air Gap for Wireless Applications

“…Using this technique a single layer suspended microstrip antenna which offers 50% (S 11 < −10 dB) impedance bandwidth has been reported in [9].…”

“…It is well known that considerable bandwidth enhancement can be achieved by increasing the overall height of the composite airdielectric medium [9][10][11][12][13][14]. However, the use of air gap increases the height/volume of the antenna which is undesired in several (compact) applications [15].…”

“…The design starts with the selection of center frequency and it may be noted that the design approach can be easily scaled to any frequency of interest [9]. The antenna without air gap is presented in Section 3.…”