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 (PLL) PC solutions, the proposed DLL PC has a number of unique features which 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 re-transmission even when the incoming pilots are not available due to deep channel fading or time division duplex (TDD) operation; 3) the DLL PC can be flexibly configured as voltage controlled phase shifters for use in traditional phased beam-steering arrays; 4) the DLL PC can indicate direction of arrival (DOA) of incoming signals without recourse to any baseband algorithms; 5) the DLL PC is unconditionally stable. The operation of the DLL PC is articulated in this paper, prototypes are built and their performance and functions are tested. In addition, a K/Ka band RDA demonstrator for satellite communications (SATCOM), based on the proposed DLL PC architecture, is implemented and measured, validating the ‘retro-direct’ functionality over a wide view angle. To our best 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.