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.
This work has been supported by the Deep Exploration Technology Cooperative Research Centre whose activities are funded by the Australian Government's Cooperative Research Centre Programme, DET/CRC Document 2016/808.
Additionally, authors would like to thank the University of New Brunswick, Fredericton for providing laboratory space and equipment needed to carry out this research.
We would also like to thank Dr. Karl E. Butler for continuous guidance and feedback throughout experimental validations of the antennas.
Finally, thanks to the City of Fredericton for providing access to the boreholes at the bank of Saint John River to carry out experimental testing of the antennas.