ON THE BASIC PRINCIPLES OF RADAR POLARIMETRY - THE TARGET CHARACTERISTIC POLARIZATION STATE THEORY OF KENNAUGH, HUYNENS POLARIZATION FORK CONCEPT, AND ITS EXTENSION TO THE PARTIALLY POLARIZED CASE

Basic principles of radar polarimetry are introduced. The target characteristic polarization state theory is developed first for the coherent case using the three stage, the basis transformation, and the power (Mueller) matrix optimization procedures. Kennaugh's and Huynen's theories of radar target polarimetry are verified for the monostatic reciprocal case. It is shown that there exist, in total, five unique pairs of characteristic polarization states for the symmetric scattering matrix of which the two pairs, the cross-polarization null and copolarization max pairs are identical; whereas, the cross-pol max and the cross-pol saddlepoint pairs are distinct. These three distinct pairs of orthogonal characteristic states are also at right angles on the polarization sphere. The fifth pair, the co-pol null pair lies in the plane spanned by the co-pol max/cross-pol null and the cross-pol max pairs, which determines the target characteristic circle on the polarization sphere reestablishing Huynen's "polarization fork" concept. The theory is verified by an example for which next to the polarization fork the copolarized and cross-polarized power density plots are also presented. In a next step, the partially polarized case for completely polarized wave incidence is presented and compared with the results for the coherent and the partially coherent cases, the latter still being unresolved.