Radiation properties of ring-microstrip antenna with slit as polarization controller

The radiation properties of the ring microstrip antenna (R-MSA) have previously been studied extensively; this is because of the advantage of the R-MSA that it can reduce its antenna size compared with the usual MSA element. On the other hand, since the R-MSA element excited by a dominant mode has high impedance characteristics at its feeding point, then impedance matching is not easy for this antenna system. For this reason, the authors investigated the slot-coupled R-MSA element which easily permits impedance matching. First, the radiation properties of the slot coupled standard R-MSA element are described. Second, various types of R-MSA elements are also discussed, and finally the authors investigate the performance of the R-MSA element with the slit as a polarization controller.