Dual Circularly-Polarized Septum Antenna Array Based on an Air-Filled Dual-Mode Feeding Network

This communication proposes a dual circularly polarized (CP) antenna array based on a septum polarizer using an air-filled dual-mode feeding network. A simple layer of 1-to-4 circular cavities is covered with septum polarizers to combat the grating lobes. The full-corporate feeding network is achieved by using a dual-mode transmission line, thereby combining the transmission of both TEM-mode [excited by HW suspension line (HWSL)] and TE10-mode [excited by hollow waveguide (HW)] in one group of feeding network. This helps to decrease the feeding network complexity. New miniaturized dual-mode separators are inserted between the radiating structure and the dual-mode feeding network to connect them in a limited space so that the low complexity dual CPs can be achieved. An 8 x 8 array prototype is fabricated and measured to demonstrate this design. Experimental results present that an overlap bandwidth of 17.4% (18-21.4 GHz) (considering |S11| < -10 dB, |S22| < -10 dB, and AR < 3 dB) is obtained with no grating lobes. Moreover, the peak gain in the same frequency range is up to 26.6 dBic, while the aperture efficiency including antenna efficiency is higher than 69%.