Development of low-profile wideband microstrip antennas for CubeSat phased-array applications

Abstract

CubeSat missions rely heavily on effective communication systems in order to transmit and receive large amounts of data quickly and efficiently. The total throughput is limited by the capacity of the channel - a quantity dependent upon the signal quality and bandwidth of the link. Volume and power constraints on a CubeSat impede overall capacity in a fixed bandwidth channel. Phased-array antennas provide a more power efficient solution to improving signal quality by optimizing the spatial properties of the link, rather than broadcasting higher signal power over a broader area through power amplification alone. In order to take advantage of a larger antenna gain without having to mechanically rotate, the array must be controlled properly such that the radiated power is focused in the desired direction. The appropriate steering vector can be determined autonomously through Retrodirective beamforming - a process where the characteristics of arriving signals are used to determine the direction of arrival, and the resulting array directivity is maximized in that direction. In order to accommodate enough bandwidth to transmit and receive at separate frequencies, a low-profile antenna element was developed in this work and arrayed for a 1U CubeSat. The individual circularly-polarized antenna element shows a wide measured impedance bandwidth of 21% (for a 2:1 VSWR) at a low profile of 0.34λ0 × 0.39λ0 × 0.025λ0. The resulting gain of the circularly polarized array averaged a realized gain of ~10-dBic between 2.0 and 2.3-GHz, yielding roughly twice the gain of traditional planar CubeSat antennas at these frequencies, with the added bonus of an array interface for potential beam-steerability.