Retrodirective arrays for RFID and microwave tracking beacon applications

Abstract

Retrodirective array (RDA) is a kind of self-phasing array sub-system which has many applications in both military and commercial communication systems. In recent years, it has gained a particular interest from many microwave or millimeter-wave researchers due to its cost effectiveness and compactness. A retrodirective array can transmit a signal along the direction between the interrogator and the RDA without any prior knowledge of the incoming direction. In addition, it does not rely on any complex digital signal processing algorithms or phase shifters, which appear in smart antennas. RDA is novel, much simpler and potentially faster because digital calculation is never processed. In this project, two single elements for RDA based on phase-conjugation are realized. In the first design, the incoming signal, RF, shares the same path with the re-transmitted signal, IF, of operating frequency 5.8 GHz and 5.81 GHz respectively; while the second design is implemented to have different paths for these two signals, RF and IF, and operates at 9.8 GHz and 9.81 GHz respectively. A local oscillating signal, LO, is pumped into the element such that the mixer generates IF signal. A novel and compact retrodirective array based on a phase-conjugating mixer, the second design, with conversion gain of 5.46 dB has been designed and fabricated. A 4-element array prototype demonstrates excellent performance in terms of retrodirectivity and sensitivity.