WIDE-BAND MULTIPORT ANTENNA CHARACTERIZATION BY POLARIMETRIC RCS MEASUREMENTS

A theoretical description of the scattering of multiport antennas is d erived in accordance with the polarimetric radar target characterizati on. For two-port antennas with dual linear orthogonal polarization, a procedure for the determination of the antenna mode scattering paramet ers and the structural scattering parameters of the complete polarimet ric antenna scattering matrix [S] is given. A measurement setup and ex perimental results of wide-band polarimetric radar cross section (RCS) antenna measurements are presented. For two-port antennas, in total, 24 unknowns have to be determined. The load variation method is used. The polarimetric RCS antenna measurement is especially advantageous ov er a wide bandwidth; for example 2-40 GHz with only one single calibra tion. From the antenna scattering matrix [S], the antenna parameters l ike polarimetric gain, optimum gain, gain bandwidth, wave admittance, structural scattering, etc., are derived. Results are shown for an X-b and horn antenna and a 2-18-GHz dual linearly polarized horn. The meas urement technique and evaluation gives the most complete and very accu rate information about antenna radiation, antenna characteristics, and scattering obtainable with one single measurement setup. Some quantit ies determined here, like the maximum available gain and the polarizat ion characteristics, are difficult to access with standard transmissio n measurements. No cable from the antenna to the receiver is necessary . This helps avoid some difficulties usually experienced at low signal levels.