Pattern distortion for patch antennas on finite and faceted ground planes

High performance microstrip patch antennas for aeronautical applications (altimetric radar) possess stringent requirements of side lobe and cross-polarisation levels, which are often affected by the effects of ground plane truncations. This paper presents an efficient and accurate computational model based on a high-frequency technique for the treatment of these effects, with reference to patch antennas printed on a faceted ground plane. The patch elements are printed on squared substrates slightly larger than the patch itself. The far field radiated by a patch antenna on a rectangular metallic plate is treated by reciprocity, i.e., by considering a receiving patch antenna under plane wave illumination. The radiation pattern is calculated by reaction between the electric current induced by the incident plane wave on the finite ground plane and the magnetic currents associated to the patch radiating edges. The electric currents induced by the incident plane wave are computed by means of the incremental theory of diffraction (ITD) including an accurate description of single, double and vertex diffraction mechanisms occurring at the edges and vertices of the finite ground plane.