Application of the Reflective Spiral Photonic Crystal-Delay Line in Beamforming for Phased Array Antennas

Beam-squint is the primary disadvantage when using conventional phase shifters in the beamforming network of phased array antennas. True time delay lines (TTD) enable squint-free beamforming, since the produced delay is independent of the microwave carrier frequency. Amongst all TTDs, optical delay lines (ODL) possess the highest bandwidth and have strong potential for use in the ultra-wideband systems. Recently, many works have been reported on design and fabrication of photonic crystal delay lines. All of these works, however, have based their delay lines on one dimensional photonic crystal (PC) structures. Therefore achieving longer time delays requires increasing the device size. The objective of this paper is to design a miniaturized TTD which can be used in beamforming network for wideband phased array systems. We propose a novel structure for TTD using total reflection of light in the blocked photonic crystal waveguides (PCW). This novel structure will be referred to here as reflective spiral. It is demonstrated that replacing PCW channels with coupled defects increases the time delay significantly. Using full-wave analysis, it is demonstrated that time delays longer than 8.75 ps can be achieved in a device size less than 20 mum which is 130 times shorter than the required straight distance in free space. The bandwidth of the proposed delay line is more than 2.3 THz