19.4 A Small-Satellite-Mounted 256-Element Ka-Band CMOS Phased-Array Transmitter Achieving 63.8dBm EIRP Under 26.6W Power Consumption Using Single/Dual Circular Polarization Active Coupler

Environmental monitoring, the earth-observation, and non-terrestrial networks using small satellite constellations have become promising space applications for nextgeneration society. There are three key design considerations in small satellite systems. First is the limitation of power consumption due to not only the limited energy from solar panels but also severe thermal management in space. Second is the requirement of beam steerability with large equivalent isotropically radiated power (EIRP) to communicate from 500km to 2000km in low earth orbit (LEO). Active phased-array technology is a prominent satellite transmitter (TX) solution. When the element number increases by N times, single-power-amplifier (PA) output power and total power consumption can be reduced by N ² times and N times, respectively, under the constant EIRP condition. Thus, reducing PA output power and increasing the number of elements are the most efficient design strategies for lowering power consumption. This is illustrated in the upper left graphs in Fig. 19.4.1. The third consideration is that the satellite TX needs to generate accurate single and dual circular polarization (CP) signals for several situations: single polarization for polarization-multiplexing under a multi-satellite environment; dual circular polarization for high data throughput downlink. Especially in both cases, the crosspolarization discrimination (XPD), which represents the accuracy of CP, is the essentially required performance to avoid conflict between two satellite communication systems and/or interference between two signals in a single satellite communication system as the scenario is demonstrated in the upper right figure in Fig. 19.4.1.