2003 International Student Seminar on Microwave Applications of Novel Physical Phenomena 26 – 27 May 2003 Helsinki University of Technology, Espoo, Finland COMPACT PLANAR MICROWAVE FILTER WITH SYMMETRICAL FREQUENCY RESPONSE Yaroslav Kolmakov St.-Petersburg Electrotechnical University St.-Petersburg, Russia 1

Modern band-pass filter must have: 1. FORMULATION OF PROBLEM high filter order, reduction of parasitic coupling high selectivity (high slope parameter) compact filter area (standard wafer size is 2 or 3 inches) small insertion loss additional transmission zeros near band edges high out of band rejection level Realisation: increasing quality of resonator, reduction of filter order using compact resonators, reduction of filter order Position of additional transmission zeros can not be strongly controllable in general case 2

2. ADDITIONAL TRANSMISSION ZEROS REALISATION simulated performance inputoutput inputoutput - single resonator 2.1. Start point: filter without cross-coupling 6.2 dB/MHz 3.2 dB/MHz Filter with high level of parasitic coupling 3

2.2. Filter with cross-coupling (quadruplet) inputoutput inputoutput main coupling simulated performance cross-coupling 4

2.3. Filter based on original cross-coupling structure (quadruplet+triplets) inputoutput simulated performance inputoutput main coupling cross-coupling 9.6 dB/MHz 8.2 dB/MHz 5

3. 8-POLE QUASI-ELLIPTIC FILTER input output 24.8 mm 15.5 mm 3.1. Filter layout input output 7 8 6

3.2. Simulated performance dB/MHz 15.1 dB/MHz

8 4. CONCLUSION The filter structure using combination of tri-section and quadruplet cross-coupling, which provides a symmetrical frequency response of filter is demonstrated. Position of two transmission zeros can be strongly controllable. The investigated coupling structure can be used for a design of high order quasi-elliptic filters based on HTS film.