Characterization of a 2 GHz holographic radar antenna for detection of subsurface targets

The design of the holographic radar enables the search of landmines and other plastic objects while avoiding contact with soil. The holographic radar records the interference pattern between the transmitted and the reflected signal in the antenna. This interference occurs physically on the receiving feed mainly through direct coupling with the transmitting feed. However, the direct coupling signal is of a much higher level than the received signal, consequently limiting the usable dynamics of the conditioning electronics. An antenna was designed to increase the level of the received signal, optimizing the geometric size and the feeds position of a circular waveguide antenna for this purpose, in the (1.6, 1.9) GHz range, and modifying the reciprocal position of the feeds in order to reduce the signal level due to direct coupling. The setup was simulated and then the real antenna was characterized measuring radiation diagram and S parameters. The obtained experimental results confirm the simulation with a reduction of the direct coupling between -5dB and -13dB in the operating range of the antenna if compared to the former antenna configuration. In order to determine the depth of anti-personnel mines in the ground, a mathematical model was developed, then translated into an electronic circuit based on the use of an In phase/in Quadrature demodulator, which, starting from the signals exiting the radar antenna, allowed to obtain the distance of the reflective object from the antenna aperture. The model has been validated with an experimental test.