Development of superconduct-ive microwave filters for mobile communications and filter banks

The development of superconductive microwave filters connected to the use o f cooled electronics is now in the critical phase of system integration. Al l the different steps of filter development, design and fabrication must be controlled, reproducible and technically realisable by conventional microe lectronics tools. We developed filters for mobile communications and filter banks with the goal of optimising these aspects. Lanthanum aluminate subst rates were chosen instead of magnesium oxide or sapphire substrates. The fa brication 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 mere modelled by ERI software. Exact agreement has been obtained between mo delling and measurements. Results on a 10-pole 1.75 GBz bandpass filter wit h 5% bandwidth and on a 5-pole 9.1 GBz passband filter with 0.5 % bandwidth are presented.