Radar Bistatic Technique for Accurate Characterization of Small Antenna Radiation Patterns

An original method based on the radar bistatic technique (RBTech) is proposed to characterize key antenna parameters, with emphasis on radiation patterns. The bistatic configuration comprises two standard transmit/receive antennas, and the antenna under test. While the transmitting Tx antenna remains fixed, in front of the target (at normal incidence), the receiving Rx antenna rotates around with a bistatic angle. Rx measures the diffracted wave (i.e. backscattered field) as a function of the frequency, the wave polarization and the bistatic angle, for different terminal impedance; namely short-circuit, open circuit, and matched load. First, the antenna mode corresponding to the reradiated wave is recovered in the time domain by removing the structural mode. The structural mode is obtained by measuring the backscattered wave when the antenna is well matched, i.e., with a near-zero reflection coefficient. Second, time-gating and Fast Fourier Transform (FFT) processing are applied to extract the frequency spectrum of the recovered reradiated waves from the time-domain antenna-mode signal. By compiling these results as a function of the bistatic angle, the radiation pattern can be reconstructed in any cut-plane for both co-and cross-polarizations. Experimental measurements conducted in an anechoic chamber, based on an accurate wideband calibration procedure, along with full-wave simulations using the radar bistatic technique, were performed on a triband omnidirectional antenna and patch arrays. Very good agreement was observed between the reconstructed patterns and those obtained via conventional simulation and measurement methods. The developed radar bistatic technique demonstrates accuracy, potential for non-invasive operation, and remote applicability.