A directional monostatic borehole radar system

A directional, monostatic borehole radar system was developed to overcome some disadvantages of the existing bistatic system. The challenges of combining transmitter and receiver in a single module are apparent, since one wants both high transmitting power and high receiver sensitivity. A dead time in the receiver response is unavoidable and thus prevents radar measurements at small distances. With sophisticated electronics consisting of e.g., variable gain control, advanced antenna switching and pulse generation, we are able to keep the dead time below 200 ns for a transmitted pulse with a center frequency of about 50 MHz. Other improvements allow for autonomous measurement mode. With our monostatic system, the probe length is reduced to 2.5 m as compared to a bistatic system of typical 13 m. In this paper, we present the improvements of the receiver electronics as well as the realization of the antenna switching and pulse generation. After a brief discussion of the disadvantages of a bistatic system and the basic theory, the implementations in hardware are discussed. Finally, some results of measurements are presented.