A TECHNIQUE FOR MEASURING ANTENNA DRIVE PORT IMPEDANCE USING BACKSCATTER DATA

This paper describes a technique for measuring the drive port impedanc e, denoted Z(D), of an antenna using radar backscatter data. It requir es only that one has access to the antenna terminal ports, and the abi lity to attach a known load to the terminals. In the technique describ ed here, three sets of backscatter data (amplitude and phase) are requ ired: one with the terminals short-circuited, denoted E(s), one with t he terminals open-circuited, denoted E(o), and the third with the term inals 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 (8). An analysis of the effects of the various error sourc es 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 t he quality of the backscatter measurement over the frequency range und er consideration.