HTSC microstrip UHF filter at 2 GHz

HTSC planar high Q resonators can be used to realize microstrip filters. These filters have a low insertion loss and a sharp slope. The size of the substrates of 10 mm*10 mm leads to a low frequency limit of about 2 GHz for a two-pole filter. At 77 K the measured on-chip insertion loss of a two-pole Butterworth bandpass filter with 3% relative bandwidth is less than 0.2 dB. The complete filter including housing and coaxial connectors has an insertion loss of 0.4 dB. Improving the structuring process and reoptimizing the filter design will improve the filter characteristic. Particular low-loss bonded contacts instead of silver paint between the coaxial microstrip transition will decrease the insertion loss of the filter. Outer dimensions of the filter housing with coaxial connectors are 34 mm*30 mm* 20 mm. Waveguide filters with comparable filter characteristics will be approximately 100 times larger in volume than planar HTSC filters and they are useless for a planar system with active and passive components on a single board.