A novel wide-band slot antenna for ground penetrating radar

Abstract

In this paper, a novel slot antenna is designed for ground penetrating radars (GPRs). The novel antenna consists of an array of cavity backed slot elements. Compared to microstrip patches, slot antennas have a few attractive advantages, such as ease in achieving relatively larger fractional bandwidth, minimal mutual coupling between array elements, less sensitivity to substrate truncation, and higher power tolerance (Hirokawa et al., 1989; Zheng et al., 2005). When applied to GPRs, the cavity backed slot array is placed conformal to, and in contact with the ground surface. The antenna elements are designed impedance matched to the ground. As a result, direct reflection from the ground surface, which constitutes the major source of clutter in GPRs (Rappaport et al., 2003), is avoided. Moreover, the slot array in this paper operates over a wide frequency band; hence it can be used for ultra-wide-band GPRs. The antenna elements are analyzed using full wave solvers. A two-element array is fabricated and tested over sand. Simulated and measured data agree closely with one another. Input impedance bandwidth of 35% is observed from measurements. Bistatic, step-frequency measurements are carried out to detect copper pipes buried in sand. Locations of the buried pipes are identified from bi-static scattering results, with signal-to-clutter ratio greater than 10 dB after subtraction of direct coupling between antenna elements, which demonstrates the viability of the proposed antenna to GPRs.