PERFORMANCE CHARACTERIZATION OF POLARIMETRIC ACTIVE RADAR CALIBRATORS AND A NEW SINGLE ANTENNA DESIGN

A polarimetric active radar calibrator (PARC) is a high radar-cross-section transponder with a known scattering matrix. This paper deals with three PARC-related topics. The first involves experimental measurements of the magnitudes and phases of the scattering-matrix elements of a pair of PARC's that operate at 1.25 GHz and 5.3 GHz. The measurements, which were obtained by a polarimetric scatterometer calibrated using a recently developed single-target-calibration technique (STCT), were conducted over a wide range of incidence angles (relative to the boresight direction) in the azimuth, elevation, 45-degrees, and 135-degrees planes. The 5.3 GHz PARC, which consisted of two antennas placed several wavelengths apart, exhibited symmetrical patterns with no ripples and excellent isolation between orthogonal polarization channels. In contrast, the 1.25 GHz PARC, whose antennas were in very close proximity of one another, exhibited unsymmetrical patterns as well as ripples in the phase patterns, thereby introducing errors in the elements of the scattering matrix. To avoid this problem, the antennas should be placed several wavelengths apart. Alternatively, a single-antenna PARC can be designed using an orthomode transducer. The design, construction, and performance evaluation of such a PARC is the second topic discussed in this paper, and the third topic pertains to extending STCT so it may be applied equally well using a PARC rather than being limited to using reciprocal passive calibration devices such as spheres and trihedral corner reflectors.