A resistive linear antenna for ground-penetrating radars

Abstract

The resistive vee dipole (RVD) loaded with the Wu-King profile has many advantages for use in groundpenetrating radar (GPR) applications. It can be designed to transmit a temporally-short pulse to a small spot on the ground. The shape of the transmitted pulse is simply related to the input signal, e.g., a derivative. The RVD also has a low radar cross section. In addition, it can be easily manufactured using a circuit board and discretely loading it with chip resistors. One drawback of the RVD is that the input impedance of the RVD increases significantly with decreasing frequency and, therefore, has a high voltage standing wave ratio (VSWR) at low frequencies, which limits the low-frequency response of the antenna. To improve the low-frequency response, a discretely-loaded resistive linear antenna (RLA) has been developed, whose basic principle of operation is the same as that of the RVD. The RLA has curved arms loaded with a modified Wu-King profile instead of straight arms loaded with the Wu-King profile. With an appropriate selection of the curve and the loading profile, the low-frequency response is significantly better for the RLA than for the RVD. The RLA has been developed using a method of moments code. The performance of the RLA is validated both numerically and experimentally.

Measured patterns of a resistive V‐dipole fed with a double‐Y balun

“…Measured far-field patterns for the V-dipole fed without a balun exhibited additional nulls and sidelobes. In contrast, the measured far-field patterns for the V-dipole fed with the double-Y balun did not exhibit the additional nulls and sidelobes, and approximated the numerical patterns computed in [7] for a resistive V-dipole with a balanced feed.…”

“…A double-Y balun was designed for feeding the resistively loaded V-dipole described in [7]. The balun was designed to transition from a 50⍀ coaxial line to a 200⍀ resistive V-dipole [8].…”

“…The measurement system was automated using a PC running LabVIEW [8]. Figure 4(a) illustrates the resistively loaded V-dipole in [7] fed directly with a coaxial line (models an unbalanced feed). Figure 4(b) illustrates the resistive V-dipole fed with the double-Y balun.…”

“…The measured patterns for the resistive V-dipole are compared with numerical patterns computed using the method of moments (MoM) as in [7]. The numerical model corresponds to a balanced feed and does not include the LR unit used in the measurements.…”

“…In section 4, the measured field patterns of a resistive V-dipole fed with and without the double-Y balun, are presented. The measured patterns are compared with the patterns computed numerically in [7].…”