Photonic Approaches to Millimeter-Wave True Time-Delay Line

Two methods are presented for establishing variable microwave or millimeter-wave true-time delay utilizing photonic approaches. In many applications, there is a need for a significant time delay, which cannot be established by microwave methods. The optical fiber or other optical waveguides can offer a substantial time delay, which can be utilized by converting the microwave signal into the optical domain and after the proper delay, converting back to the microwave. The main challenge is the variation of the delay. One way to achieve this is the application of dispersive fibers and tunable lasers. It is advantageous for beam steering of phased array antennas because a single, standard delay line can control multiple radiating elements. In this way, the structure with more overall attributes is obtained.