Two-port circularly polarized microstrip antennas

A circularly polarized (CP) two-port microstrip antenna simultaneously operated at two CP states is investigated. The CP bandwidth of the antenna is increased from 0.35% to about 5%, almost 14 times wider than that of single port patch. The antenna directivity due to the loss in the load is reduced by about 3 dB. It is believed that such an advantageous trade-off for both will make this type of antenna much more useful, for example, in transmitting or receiving two CP waves of opposite senses simultaneously. The crosstalk between the two ports depends on the impurity of CP. It is about -19 dB for axial ratio (AR) equal to 2 dB, or -14 dB for AR equal to 3 dB. The method improving the isolation between two ports of an antenna is also discussed