Microstrip Chirped Delay Lines based on Photonic Band-Gap Structures

In this paper, we report on the design and compaction through a coiling technique of microstrip Chirped Delay Lines (CDLs) based on optical-fiber Photonic Band-Gap (PBG) structures with chirped resonant Bragg coupling in reflection by means of a chirped sinusoidal-like modulation of the microstrip impedance. The coiled CDLs have almost the same frequency response as the straight devices but a small ripple appears in the ideally flat magnitude and linear group-delay of the S11-parameter due to mutual coupling between near strip segments. Designs with different coiling radii show that a trade-off has to be met between low-rippled response and miniaturization. Practical circuits for the chirped delaying of wide-band pulses can be performed using these compact microstrip CDLs, and some interesting potential applications like real-time spectral analysis or time-domain frequency-filtering in the joint of two CDLs are envisaged.