A Review of HTS Thick-Film Microwave Filter Technology

For 10 years, thick-film YBCO has been used to make radio frequency filters out of three-dimensional superconductor coated structures. These filters are presented in a detail never before revealed. The chronology of solving technical problems such as coating and construction will be recounted from a historical perspective. The most recent design, which results in a 16-pole, 1.9 GHz filter in a housing measuring 145 mm×60 mm×35 mm, will be shown in detail. We will discuss the challenges in resonator design, substrate fabrication, coating technology, filter design, and filter realization associated with this filter. This overview demonstrates the progression of size over the past decade, resulting in an order of magnitude reduction in filter size and lessening size as a concern for system application of thick-film HTS filters. The impact of this size reduction on performance metrics such as Q and realizable filter order, as well as device characteristics such as intermodulation distortion, will be shown.