Design of Forward Looking Economical Monopole Antenna for Borehole RADAR Applications

In this paper, the design of a forward-looking economical monopole antenna with an outer assembly diameter of 48 mm to be used for borehole radar applications is presented. Two comparable antenna designs, one with an air core and other with dielectric-loaded core is presented and their performance is compared for different scenarios. The laboratory experiment results reveal that both antennas have major radiation lobes along the axis of the antenna center conductor. The experimental testing reveals that the air-core antenna outperforms the dielectric-loaded core antenna when in air but it falls behind once it is tested in the borehole. The experimental work was performed in a shallow borehole that intersects sediments. A reflector, located at the transition between fluvial sands and lacrustine sand and clays was detected at a distance of 1.5 m. The air-cored antenna was unable to propagate energy forward and had strongest coupling to a surficial shallow casing.