Via-hole coupled oversized microstrip line and its band-pass filter application

A simple via-hole coupled oversized microstrip line filter is proposed and demonstrated in this article. The via-hole in this case works as an inductor coupling structure whereas the oversized microstrip line resonator has a higher Q-factor than its conventional counterpart. Full-wave-based circuit models of a series of via-holes embedded in the oversized microstrip line are extracted by using our proposed numerical calibration technique combined with a commercial method-of-moments simulator. A simple 3-pole via-hole coupled oversized microstrip line filter is designed and fabricated on the basis of the extracted circuit models of via-holes. Measured results show that the demonstrated filter has a center frequency of 1.853 GHz, a bandwidth of 6.98% and an insertion loss of 1.36 dB. Measured results of the fabricated filter sample are in agreement with its simulated results, showing a good performance of the proposed scheme. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.