A Modified Bow-Tie Antenna for Improved Pulse Radiation

Abstract

The analysis, design, and realization of a modified bow-tie antenna optimized for impulse ground penetrating radar (GPR) applications is described. The proposed antenna shows improved properties important for GPR, which include its compact size (in comparison with a conventional bow-tie antenna) and ability to radiate UWB pulses with increased amplitude and very small late-time ringing. A substantial increase in the amplitude of the transmitted pulse is achieved by utilizing radiation from discontinuities introduced by the resistive loading employed in the antenna to suppress late-time ringing. By choosing an optimal distance between the antenna's feed point and the location of the resistive loading, radiations that occur from the antenna's feed point and the mentioned discontinuities at the resistive loading will combine constructively in the boreside direction of the antenna. As a result, one will observe a substantial increase of the amplitude of the transmitted pulse in the boreside direction. Furthermore, an analytical expression describing approximate time-harmonic current distribution is derived to indicate an optimal resistive loading profile for the proposed antenna. Additionally, the traveling-wave current distribution of the antenna is theoretically analyzed to examine the applicability of the obtained time-harmonic expression for pulse excitation. It has been found that when the antenna is resistively loaded both the time-harmonic and traveling-wave currents decay to approach nearly the same value at the end section of the antenna. As the amount of current at the antenna ends corresponds to the level of reflection which occurs there, the derived expression is found to be useful to indicate an optimal loading profile for the proposed antenna. A theoretical model of the proposed antenna has been developed to perform numerical analysis using a modified NEC-2 code. In addition, an experimental verification has been carried out and both the simulation and experiment confirmed the improved properties of the proposed antenna.

New Techniques for Increasing Antenna Bandwidth With Impedance Loading

“…Corresponding values for the least heavily loaded profile, ν = 0.05, are 0.27 Ω and 461.4 Ω Interestingly, the loading resistance increases with increasing profile exponent at all segments except the last where the three highest resistances in increasing order correspond to ν values of 1, 0.8, and 0.4. But for all values of ν the data reflect the typical characteristic of progressively increasing resistance with distance from the RF source as seen in [1,[3][4][5][6][7][8]. As will be seen below, however, monotonically increasing profiles are not necessarily the best.…”

“…Besides fractional profiles, other loading profiles have been proposed that combine resistance and inductance to improve bandwidth and efficiency [7]. Recently, Lestari et al revisited the WK analysis in order to develop an optimal linear loading profile for a ground penetrating radar bow-tie antenna [8]. Additional analyses of dipole structures generally appear in [9][10][11][12].…”

Improving the GPR Detectability Using a Novel Loop Bowtie Antenna

“…Another approach is to provide a continuous loading profile that increases towards the antenna end, which is found to be very good for pulse radiation. Many designs of resistive loaded bowtie antennas are available in the literature [7]- [9]. In this paper, we examine the detection capabilities of RC loaded bowtie and a novel loop loaded bowtie in an experimental GPR setup.…”

Using end reflections to improve the pulse radiation efficiency of bow-tie antenna

“…However, a more promising method should be exploiting the considerable energy in end reflections, which is rarely reported in literatures. Lestari's design [4,6] can be considered to belong to this category. But the radiation is optimized according to the central frequency of the exciting pulse, which is always of ultra wide band (UWB).…”