Development of a UHF transponder for geological monitoring of boreholes drilled through ice sheets using phase-sensitive FMCW radar

Abstract

This paper presents an active UHF transponder designed for geological monitoring of boreholes drilled through ice sheets. It forms part of a phase-sensitive frequency modulated continuous wave (FMCW) radar system to measure the horizontal position of a borehole with depth. To distinguish the transponder response from stationary clutter, the transponder modulates the received signal before re-transmission to the surface radars. The transponder operates from 292 to 492 MHz with a gain around 18 dB. The transponder employs two novel antennas optimized for deployment within a 15 cm diameter borehole. The simulation and indoor laboratory measurement results of the transponder design are presented.