125% Bandwidth Superconducting Chirp Filters

A previously-presented synthesis procedure is employed to design ultra-wide bandwidth linear chirp (quadratic phase) filters. The synthesis procedure eliminates the harmonic responses, theoretically permitting a bandwidth close to 200% (i.e. the frequency band zero to twice centre frequency) without aliasing problems. It can also be configured so that the chirp Fresnel ripples are relegated to the time domain. (This avoids a large frequency domain ripple which in a low-loss device would create the inadmissible requirement that gain at the peak of the ripple be greater than unity.) The design procedure is equally suitable for single and dual delay line implementations. Measurements to be presented will be on superconducting single-track coplanar and microstrip filters, patterned from epitaxial YBCO films sputtered onto 2-inch diameter LaAlO3 substrates. They have a centre frequency of 8 GHz, bandwidth of 10 GHz (125%), and a TB product of 80.