Design and Analysis of Bow-tie Antennas for GPR Applications

Abstract

Ground penetrating radar (GPR) is a non-destructive testing (NDT) technology, which uses electromagnetic (EM) techniques to map the buried structures in the shallow sub-surface. The efficiency of the GPR system significantly depends on the antenna performance as the signal has to propagate through lossy and inhomogeneous media. The GPR antennas should possess a low frequency of operation for more depth of penetration, ultra-wide band (UWB) performance for high resolution, high gain and efficiency for increasing the receiving power, minimal ringing, compact and lightweight for ease of GPR surveying. Bow-tie antennas are widely used as it can provide most of the above mentioned antenna performances. Though a number of researchers have carried out their research work for the design and development of the Bow-tie antennas for the GPR applications, still there is ample of scopes for the improvement of this antenna to achieve compactness and lightweight, reduced end-fire reflections, better gain and directivity, high radiation efficiency, etc. In this work, two improved Bow-tie antennas for the GPR applications have been proposed. A compact resistive loaded Bowtie antenna is designed and investigated which can provide an impedance bandwidth of 167% (0.4 - 4.5 GHz) with reduced end-fire reflections. The compactness is achieved by using a thin sheet of graphite for the resistive loading instead of using volumetric electromagnetic absorbing materials. The end-fire reflections are minimized by blending the sharp corners of the Bowtie antenna. However, the radiation efficiency and gain of the antenna are degraded significantly due to resistive loading which has been in the second proposed antenna by using an improved RC-loading scheme. The improved and compact RC-loaded Bowtie antenna with metamaterial based planar lens is designed and investigated which can operate over a UWB bandwidth of 3.71GHz (0.29 GHz - 4.5 GHz). This provides a maximum gain of 12.4 dB and maximum radiation efficiency of 94 % throughout the operating band. An improvement in the gain of 5 dB in the bore side direction is achieved by using a modified meta-material lens. The performance of both the designed antennas is investigated in the temperature varying environment and GPR scenario at the simulation level. A comparative analysis of the designed antennas with the other reported antennas indicates that the proposed antennas are advantageous for the GPR applications.