A technique for measuring antenna drive port impedance using backscatter data

This paper describes a technique for measuring the drive port impedance, denoted Z_D, of an antenna using radar backscatter data. It requires only that one has access to the antenna terminal ports, and the ability to attach a known load to the terminals. In the technique described here, three sets of backscatter data (amplitude and phase) are required: one with the terminals short-circuited, denoted E _s, one with the terminals open-circuited, denoted E_o , and the third with the terminals loaded with a known resistance R_o, denoted E₁. These data are readily processed to obtain Z_D, according to the simple relationship defined in equation (8). An analysis of the effects of the various error sources affecting the value of Z_D determined using this technique is also presented. The utility of the technique is illustrated by measuring Z_D for a “canonical” body using measured results at L band and UHF taken on three differing RCS ranges, selected so that they differ in the quality of the backscatter measurement over the frequency range under consideration