Retrodirective Antenna Arrays for Small-Satellite Applications


Small-satellite networks promise increased mission flexibility by distributing the tasks and subsystems typical of a single large satellite, while reducing the possibility of catastrophic single-point failures. One of the challenges in designing a distributed small-satellite network – especially a dynamically reconfigurable network consisting of satellites too small to contain an attitude control system – is in establishing and maintaining a reliable crosslink with other satellites in the network without a priori knowledge of their positions.

While omnidirectional antennas are the obvious choice for crosslinking satellites that are subject to constant repositioning, this method is inefficient and susceptible to third-party eavesdropping. Omnidirectional antennas are also inefficient, as power is radiated in all directions, not just in the direction of the receiver. In security-sensitive networks, direct crosslinks using dynamically beam-steered directional antennas can prevent signal interception, but these systems require phase shifters or digital signal processing algorithms – adding another layer of complexity to the system and negating the advantages of the simple, low-cost nature of small satellites.

An attractive alternative to dynamic beam steering is a self-steering retrodirective array that permits secure crosslink communications between satellites moving randomly in space. Retrodirective antennas are able to sense the direction of an interrogating radio transmission and send a reply in that same direction, without any a priori knowledge of the interrogator’s location. The automatic, self-steering function is performed autonomously, without user-controlled phase shifters, digital circuitry, or computational software. The directivity associated with retrodirective arrays not only improves network security, but also improves the communication link efficiency by minimizing power consumption.
This talk will review various retrodirective array architectures: phase-conjugating arrays; phase-detection/phase-shifting arrays; and phase-detection/frequency-scanning arrays.