Narrow-band HTS microstrip combiner technology

Contiguous 7-pole filters centred at 7.97 and 8.00 GHz have been made by co-evaporation of YBa/sub 2/Cu/sub 3/O/sub x/ thin films on MgO substrates. The 0.3% bandwidth filters make stringent demands on the design and fabrication processes. Good control of the centre frequency and bandwidth, sharp cut-offs and high linearity have been achieved. A pair of filters has been assembled as a layer of a combiner circuit, and its characteristics studied. Although the individual filters have been successfully made to high accuracy, the extreme precision required by a combiner circuit would require some tuning for high performance, at least at the present state of the technology.