Design of a circular polarization switchable microstrip array antenna using magic-T bias circuit

In this paper, a 4-element circular polarization switchable patch array antenna is proposed. The array antenna is realized by the successful employment of the both-sided MIC technology, where the odd and even mode of the slot line and microstrip lines are used for the realization of the orthogonal feed and magic-T switching circuit respectively. The advantage of the magic-T circuit is the excellent isolation between the RF signal and the switching signal. In order to realize the polarization switching, two switching diodes are integrated with each patch elements. Unequal feed line is introduced to realize 90° phase difference between the patch elements and this way, circular polarization switchable array antenna can be realized. The array antenna unit is realized in very simple and compact structure as all the antenna elements, feeding circuit and switching circuit are arranged on both sides of a Teflon glass fiber substrate. The structure and the basic behavior of the circular polarization switchable array antenna are demonstrated in this paper. In addition, the simulated S-parameters and the phase difference of the feed circuit are explained.