Novel designs of high-temperature superconductingbandpass filters for future digital communication services

Abstract

The design and experimental results of a 5-, 10- and 23-pole lumped-element HTS bandpass filters for the applications in digital terrestrial television and other digital communication services is reported here. These filters are designed around 800 MHz centre frequency, 7.6 MHz bandwidth using end-coupled lumped element resonators on yttrium-barium-copper-oxide (YBCO) or thallium-barium-calcium-copper-oxide (TBCCO) thin films in a 2 inches lanthanum aluminate (LaAlO3) substrate. A new layout profile of a complex 23-pole filter for 70 dB outof- band rejection 0.4 MHz away from the passband edges is designed, fabricated and tested in an integrated RFcryocooler measurement system. The design of 23-pole filter was very compact and a significant amount of computer time was elapsed to electromagnetically simulate the structure-which was finally done by parts. These lumped element filters were tuned in liquid nitrogen using small pieces of lanthanum aluminate substrates and PTFE rods. The measured frequency responses of 5- and 10-pole filter are quite encouraging. In this investigation, a very useful conclusion is drawn that a compact lumped element design in twinned substrates like lanthanum aluminate is highly susceptible to the local variations in the film parameters and this effect becomes more and more severe as we increase the order of the lumped element filters.