A photonic bandgap microstrip filter based on YBCO superconducting film

Photonic bandgap (PBG) structures can stop propagation of electromagnetic waves of certain frequencies and hence can be applied to construction of microstrip filters. In this paper, a novel PBG microstrip filter based on YBa₂Cu₃O₇ high-temperature superconductor films is presented. The PBG patterns forming the filters were etched on a 0.3- and a 0.7-μm-thick film. Experimental results showed that the transmission coefficient S₂₁ of the filter is dependent on the thickness of the YBa₂Cu₃O_7-x film. The thinner PBG filter exhibits an effective stopband of a center frequency of 20 GHz, a bandwidth of 4.7 GHz (at -40 dB), an attenuation of -55 dB, and a rolloff rate of 38 dB/GHz, while the thicker structure exhibits narrow notches only in the S₂₁ characteristics.