A Quad-Polarization and Beam Agile Array Antenna Using Rat-Race Coupler and Switched-Line Phase Shifter

This paper proposes a quad-polarized microstrip array antenna with beam steering capability. The proposed antenna consists of two patch elements, one rat-race coupler, and two 90° switchable phase shifters. With the aid of just four PIN diodes, the two 90° phase shifters can provide four different diode arrangements for each port of the rat-race coupler. The array elements are excited by using orthogonal feed lines. Due to the combination of the rat-race coupler and phase shifters, different phase conditions are generated between the patch elements or orthogonal modes of the patches. As a result, the proposed antenna can achieve two beams for each of four polarizations, i.e., two circular polarizations (CP) and two linear polarizations (LP). In the case of CP, the antenna can switch the beams between sum and difference radiation patterns. On the other hand, the beam can be tilted to ±15° and ±12° for horizontal and vertical LP states, respectively. A prototype of the antenna is manufactured and measured demonstrating results in accordance with simulation expectations. Measured results indicate that the 10-dB impedance covers from 5.6 to 5.9 GHz and the measured gains range from 7 to 8.5 dBic.