Low SWaP-C SATCOM User Terminals

The Air Force Research Lab (AFRL), through the Defense Experimentation Using Commercial Space Internet (DEUCSI) program, is developing path-agnostic satellite-based communication systems for the military using the commercial satellite internet. The program, which started in 2018, has awarded over $250 million to develop and test multi-constellation satellite communication (SATCOM) systems that can easily integrate onto aircraft platforms. There are three types of commercial space internet constellations: geosynchronous (GEO), medium (MEO), and low (LEO) earth orbit. Each type of constellation offers its own unique advantages but also places requirements on the type of user terminal required. Path-agnostic satellite communication refers to the ability of a given user terminal to operate across all orbits, meaning that the same user terminal is capable of establishing a link with GEO, MEO, and LEO satellites. LEO and MEO constellations require user terminals with the ability to scan since both types of satellites are moving with respect to the user terminal, even if the terminal is stationary. GEO satellites do not necessarily require user terminals with scanning capabilities since the satellite appears stationary with respect to a stationary user. Typically LEO constellations offer the shortest latency and require the smallest antennas, whereas GEO constellations require the larger antennas and result in the largest latency. Thus, a user terminal capable of operating in LEO, MEO, and GEO constellations needs to track fast-moving satellites and offer enough gain to close the communications link with GEO satellites in addition to the usual requirements of low size, weight, power, and cost (SWaP-C). Actively Electronically Scanned Antennas (AESA) are capable of tracking a satellite beam without requiring any moving parts. AESAs are smaller and have lower weight compared to passive mechanically steered antennas, making AESAs an ideal choice for user terminals operating in LEO constellations. A typical AESA consists of separate Transmit (Tx) and Receive (Rx) apertures. The isolation between Tx and Rx can be achieved by physically separating the apertures or by switching between Tx and Rx at a specified time interval. Physical separation results in a larger and heavier antenna that has the ability to transmit and receive at the same time (full-duplex). Implementing a time switch effectively reduces the receive throughput since the user terminal can only operate in transmit or receive mode at any given time (half-duplex). AESAs operating in GEO constellations require larger apertures than LEO applications, and hence the size and weight of a full-duplex AESA terminal becomes even more critical.