Theoretical analysis of coupling and cross polarization of perpendicular slot antennas on a dielectric half-space

In this paper, design curves are given for minimizing the coupling between two perpendicular slot antennas on a dielectric half space. Such antennas may be utilized in polarimetric receivers in which coupling must be minimized to ensure polarization purity and in polarization diplexed quasi-optical receivers in which the local oscillator (LO) is received in a polarization perpendicular to that of the RF signal. For this analysis, Galerkin´s method in the spectral domain is applied along the length of the slots and point matching across their widths. At the second resonance, for equal length slots and for constant width/length (w/L) of the slots, there is a decrease of about 2-dB coupling for a factor of three increase in dielectric constant (ε₁=1.0→3.8 and ε₁=3.8→12.8). For fixed dielectric constant there is a 1-2-dB increase in coupling for a factor of two increase in w/L. For slots of unequal length (L₂=L₁/2), the changes are even smaller. Design curves are shown for various relative positions of the slots in two dimensions. A strong correlation between coupling levels and peak cross-polarization levels is found