Circularly Polarized Microstrip Patch Array Antenna at Ku-Band for CubeSat Applications

Ku-band CubeSat downlinks need compact antennas with high gain and circular polarization. We present a single-feed, single-layer circularly polarized patch array for a 1.5 U CubeSat. Asymmetric microstrip extensions provide circular polarization, and a 1×4 power divider feeds four 3×1 series-fed sub-arrays on RT/Duroid 5880. We simulated the 54.12 mm × 106.53 mm antenna alone and on a skeletonized 1.5 U CubeSat frame and measured it in an anechoic chamber. Simulations predict a right-hand circularly polarized (RHCP) gain of about 15 dBi and an axial ratio of about 1 dB at 12.5 GHz. The prototype is matched over 12.3–13.0 GHz, and its axial ratio reaches about 1 dB at 12.6 GHz with a 3 dB bandwidth of about 0.1 GHz; the measured RHCP gain is about 10 dBi. In simulation, the modeled frame hardly affects matching and gain but raises the axial ratio to about 2.3 dB. Approximate estimates attribute most of the ∼5 dB gain difference to pattern degradation, polarization mismatch, and unmodeled feed losses; substrate tolerances account for only about a quarter of the frequency shift. Thus, the simple planar antenna provides circular polarization and about 10 dBi gain, but its narrow axial-ratio bandwidth constrains on-orbit use.