A mutual coupling study of circular polarized microstrip antennas with applications to diversity combining mobile communications

The reliability of communication in mobile wireless systems can be improved by transmitting and/or receiving the signal on multiple independent channels and combining the received signals in some optimum manner. Diversity combining, as this technique is called, can be realized by using independent antenna elements as the channels. The correlation between the signals at each antenna element can be reduced by decreasing the mutual coupling between the antenna elements. The antenna geometry is an aperture coupled microstrip antenna. The center frequency, f/sub 0/=5.22 GHz, lies within the Personal Communications Service (PCS) band 5.1-5.3 GHz. For two antennas on a rigid foam plastic substrate, /spl epsi//sub ra/=1.07, and at the same interelement distance D, the mutual coupling can be reduced an additional 5-10 dB when both antennas have the same sense of polarization as compared to when both antennas have the opposite sense of polarizations. Conversely, using polytetrafluoroethylene (PTFE) composite and ceramic polymer composite substrates, /spl epsi//sub ra/=2.2, 4.5, respectively, the mutual coupling can be reduced an additional 5-10 dB when the antennas have the opposite sense of polarization as compared to the same sense of polarization. The mutual coupling is independent of the feed substrate parameters.