Calibration procedures of a stepped frequency continuous wave radar for landmines detection

This paper deals with the calibration procedures for stepped frequency continuous wave radar, which operates from 400 MHz to 4845 MHz and transmits 128 frequencies in steps of 35 MHz. Because it is a continuous wave radar the information about distance is included in the phase variation of the received signal, so the behavior of the antenna is a very important issue. Two Archimedean spiral antennas have been employed for this radar. As it is known, spiral antennas show a dispersive behavior, thus, in the time domain, a "chirp" pulse will be displayed at the output. The calibration of the system has to correct the phase dispersion produced within the system. In order to identify the phase dispersion given by the antenna, a reference metallic plate is placed at a certain distance. The received signal is passed in the time domain by applying an IFFT, the multiple reflections are removed and the phase variation due to the time propagation is subtracted. After phase correction, the time domain response, as well as the side lobes level, are decreased.