A Compact Umbrella-Shaped UWB Antenna with Gain Augmentation Using Frequency Selective Surface

Abstract

A compact (35 mm × 30 mm × 0.8 mm) co-planar waveguide fed ultra-wideband antenna with bended ground plane suitable for GPR applications is proposed in this article. The umbrella shaped radiating element is constructed using the intersection of two ellipses. The proposed antenna provides a wide impedance bandwidth of 10.35 GHz (3.05–13.4 GHz) covering the unlicensed UWB band. The simply structured antenna is easy to fabricate and to integrate in PCB board. A frequency selective surface (FSS) with two layers, each of 4×4 array, cascaded via air gap, is incorporated in the antenna as a substrate to enhance the gain by 2 to 4 dBi over the entire frequency band. Metamaterial inspired unit cells are chosen for the FSS layers, with unit cell dimension on the order of λ/10 with respect to 3 GHz, much less than λ/4. The spacing between the antenna and FSS is kept so as to enhance the gain value without hampering nearly flat gain response over the band. The gain is maintained between 5.5–8.5 dBi over the band. The antenna was investigated by comparing the simulated and measured fundamental antenna parameters. High radiation efficiency of more than 90% with non-varying group delay and nearly omnidirectional H-plane radiation pattern were achieved. Measurement results validated the antenna performance and gain enhancement due to the addition of FSS layers.