Analog/Digital Hybrid Delay-Locked-Loop for K/Ka Band Satellite Retrodirective Arrays

An analog/digital hybrid delay-locked-loop (DLL) phase conjugator (PC) for use in retrodirective array (RDA) applications is proposed, implemented, and measured. Compared with previous phase-locked-loop PC solutions, the proposed DLL PC has a number of unique features that make it superior to previous solutions in many applications. These features include: 1) the ability to hold the phases of conjugated outputs even when input pilots disappear; 2) the ability to track the changing rate of phases of input pilots even when the pilot signals with dynamic phases disappear for a short period of time, i.e., the implemented RDAs can constantly track a moving target for retransmission even when the incoming pilots are not available due to deep channel fading or time division duplex operation; 3) the DLL PC can be flexibly configured as the voltage-controlled phase shifters for the use in traditional phased beam-steering arrays; 4) the DLL PC can indicate direction of arrival of the incoming signals without recourse to any baseband algorithms; and 5) the DLL PC is unconditionally stable. The operation of the DLL PC is articulated in this paper, and prototypes are built and their performance and functions are tested. In addition, a K-/Ka-band RDA demonstrator for satellite communications, based on the proposed DLL PC architecture, is implemented and measured, validating the “retro-direct” functionality over a wide view angle. To the best of our knowledge, this is the first time that a DLL has been used for PC, and it is the first time that a K-/Ka-band RDA based on this technology has been experimentally demonstrated.