Planar circularly polarized X-band array antenna with low sidelobe and high aperture efficiency for small satellites

A planar broadband circularly polarized (CP) X-band array antenna with low sidelobe and high aperture efficiency is presented for small satellite applications. The array design is composed of 4 x 4 broadband CP stacked patch elements, which are fed by a feeding network consisted of unequal series-parallel power dividers to achieve the low sidelobe and high aperture efficiency. The final prototype with overall size of 100 mm x 100 mm x 3 mm (2.73 lambda(0) x 2.73 lambda(0) x 0.082 lambda(0) at 8.2 GHz) was fabricated and measured. The antenna has a broadband characteristic with |S-11| < -10 dB bandwidth of 15.9% (7.52-8.82 GHz) and 3-dB axial ratio bandwidth of 11.95% (7.63-8.60 GHz). Also, it achieves an excellent broadside CP radiation with a gain of 17.2-20.03 dBic, a sidelobe level of <-20 dB, and aperture efficiency of 65% to 97.5%. With these features, the proposed antenna is a good candidate for high-speed data downlink onboard small satellites (MiniSat, MicroSat, NanoSat, and CubeSat).