Improving cubesat downlink capacity with active phased array antennas

Power budgets on small satellites are restricted by the limited surface area for solar panels. This limits the power available for radio communications, which constrains the downlink budget. The limited transmit power translates to low downlink data rates on small satellites. Antenna gain from directive antennas may be a power efficient way of improving the downlink budget, thereby increasing the downlink rate of small satellites. We have developed a prototype low-power, electrically-steered S-band phased array RF front-end suitable for a CubeSat that could efficiently increase the EIRP, permitting higher data rates. A prototype of the array has been constructed and tested in an anechoic chamber. The four element array provides a minimum gain of 2.5 dB and average gain of 5 dB compared to a single patch antenna element with a 5 W power envelope across a range of up to 60 degrees from broadside of the array. Given the 100 mW overhead of each phased array element, the design is expected to scale to a 16 element array, which could fit on two 20 cm by 10 cm deployable panels on a 2U CubeSat. With a 10 watt average power budget for the transmitter, such an array would provide an estimated gain of 11 dB compared to a single omnidirectional antenna.