Superconducting microstrip line band-pass filter for mobile applications

Two types of 2 GHz band superconducting microstrip line band-pass filters were developed: a 5-pole filter with good spurious and sharp skirt characteristics, and an electrically tunable filter. The 5-pole filter with center frequency of 1.95 GHz, insertion loss of 0.1 dB or less, 3 dB bandwidth of 25 MHz, transmission zeros on both sides of desirable band, and good spurious characteristic between 1 and 9 GHz was obtained. Also the tunable filter with a measured unloaded Q factor of 2100 and a frequency shift of approximately 15 MHz was obtained.