Search

Borehole radar (BHR) is one of the most important types of ground-penetrating radar and has very strict requirements for antenna. Considering the detection resolution and the limited borehole size, the BHR antenna should be both wideband and compact. In this article, a compact nonsymmetric wideband dipole (NSWD) antenna is proposed. One arm of the NSWD antenna consists of several patches with different lengths, and the other one is a hollow metal tube. The combination of patches which are resistively loaded at the ends is used for increasing antenna bandwidth and frequency reconstruction. In addition, a three-section binomial matching transformer is designed for impedances match between antenna ( $120~\Omega$ ) and coaxial cable ( $50~\Omega$ ). Matching transformer and other radar system devices are housed in the hollow metal tube, which makes the BHR system much compact. The central frequency of the antenna is set to 86 MHz for long-range detection. The proposed antenna is fabricated and measured. The measurement results show that the proposed antenna has the advantages of wide bandwidth (~41.8% from 68 to 104 MHz) and high radiation efficiency (~65%). Finally, the antenna (including electronics) is assembled into a polyvinyl chloride pipe to form a BHR prototype, and we used it to conduct a field test in a water-filled borehole. The experimental results show that the NSWD antenna can work well with the BHR system inside borehole.

An ultrawide band (UWB) antipodal Vivaldi antenna is designed for airborne ground penetrating radar (GPR) system. With exponential tapered slots and slot edges, the presented antenna demonstrates a wide operating band from 300 MHz to more than 2 GHz. The fabricated prototype of this antenna with a compact size of 450 mm $\times \,\, 600$ mm $\times \,\, 1.5$ mm has been measured in anechoic chamber. Both simulation and experimental results show that good radiation patterns with gain 4.4–11.5 dBi in the endfire direction could be achieved in the whole working band, which indicates that the proposed antenna is suitable for airborne GPR application.

In this study, a ground-based radar system with two multiple input multiple output (MIMO) arrays is developed for 2D displacement estimation applications. To reduce the influences of antenna position error, channel delay, and phase/gain difference on the imaging quality, calibration methods and phase coherence factor (PCF) based filtering methods are applied. For each MIMO array, target displacement can be measured along its line of sight direction. Co-registration is conducted to help to derive the 2D displacement vector estimations of the targets.

An Ultrawideband Antipodal Vivaldi Antenna with compact structure for borehole radar application is reported in this paper. The antenna is embedded in a cylindrical fiber-reinforced plastic (FRP) structure, operating in the frequency range from 600 MHz to more than 4 GHz. A metal reflector is attached to the cylindrical FRP to improve the direction of the antenna especially in low frequency. The simulation results show that good radiation patterns with direction of 4.6–8.7 dBi in end-fire direction is achieved in the whole working band, which indicates that the proposed antenna is suitable for directional borehole radar system.