Development of superconductive microwave filters for mobile communications and filter banks

The development of superconductive microwave filters connected to the use of cooled electronics is now in the critical phase of system integration. All the different steps of filter development, design and fabrication must be controlled, reproducible and technically realisable by conventional microelectronics tools. We developed filters for mobile communications and filter banks with the goal of optimising these aspects. Lanthanum aluminate substrates were chosen instead of magnesium oxide or sapphire substrates. The fabrication of double-side sputtered film on 2" diameter wafer was optimised and stabilised resulting in very low insertion loss. To eliminate the time-consuming operation of tuning the filter with screws, the complete designs were modelled by EM software. Exact agreement has been obtained between modelling and measurements. Results on a 10-pole 1.75 GHz bandpass filter with 5% bandwidth and on a 5-pole 9.1 GHz passband filter with 0.5% bandwidth are presented.