Optimized bow-tie antenna for pulsed low-frequency ground-penetrating radar

Abstract

The bowtie antenna provides a solution to the requirements of a broadband non-dispersive antenna for low frequency pulsed ground penetration radar (GPR) applications. This paper reports on a bowtie antenna numerically optimized with respect to bandwidth and radiation performance into the ground over the 10-100 MHz band. Rounding the edges of the bowtie was found to stabilize the antenna performance by reducing the internal angle dependence of the 1St resonant frequency. Half hemisphere radiation was achieved using a nonabsorptive cylindrical cavity placed over the rounded geometry bowtie. Late time ringing due to reflections was minimized by the use of edge termination resistors connected between the cavity wall and the bowtie. The antenna match to the ground was improved using an optimized low permittivity polypropylene slab. This restored the radiation pattern distortion due to the presence of the ground and stabilized the input impedance for fluctuations in ground parameters. This also permitted the antenna to be wheel mounted at various heights above the ground with minimal influence on the antenna performance.