EVALUATION OF SEVERAL SHAPED DIHEDRALS USEFUL FOR POLARIMETRIC CALIBRATION

Calculation, measurement and improvement of two-bounce passive reflect ors designed for the external cross-calibration of Iinearly polarized polarimetric: radars are addressed in this paper, Derived from the sta ndard right angled dihedral, the reflectors under consideration are de signed so that they have broad Co- and X-pol backscattering diagrams, These broad beamwidths are highly required for in situ SAR calibration , where uncertainties on the direction of flight and incidence angle m ay exist. Several examples are discussed, The first part is concerned with the standard dihedral which is made of two orthogonal conducting plates, Due to the narrow X-pol backscattering beamwidth of this type of dihedral, X-pol channels calibration is harder to achieve, especial ly outside laboratory. Therefore, dihedrals with elliptical vertex, in cluding the circular case, are studied The results are compared with t he standard dihedral, Subsequently, simulations conducted on this type of target have determined the vertex ellipticity influence on the Co- and X-pol backscattering diagrams. Finally we set up a synthesis proc ess to design an optimal shaped dihedral as long as the X-pol backscat tering diagram is required to be as at and as wide as possible, The op timization leads to an helicoidal vertex, Advantages and drawbacks for each kind of structures are also discussed.