Isolation improvement in dual port cross-slot coupled patch

A compensation of the mutual coupling of the ports of dual port cross-slot coupled patch is described in this paper. The cross-slot is formed of two identical slots orthogonally crossed in their centers. The excitation is coupled asymmetrically aside the slot center. The inductive mutual impedance of the slots, shorter than its resonant length, is compensated with capacitive coupling between the ends of the microstrip feeding lines. In this way the port isolation and cross-polarization properties of the patch are improved. The principal considerations for a successful design are explained in the paper. Comparison between the properties of a conventionally fed patch and such with compensated mutual coupling of the slots show that the cross polarization ratio of the compensated design is about 25 dB, while uncompensated one has approximately 15 dB.