Design and implementation of capacitive coupled-line structure bandstop filters.

In this article, we propose and design bandstop filters with capacitive coupled-line structure. The coupled-line structure has small area, wide bandwidth, and steep insertion loss response. In simulation, we used Serenade and Sonnet EM simulation tools to analyze the characteristics of filters. In circuit implementation, we selected FR-4 substrates. We used coupled-lines on capacitive coupling bandstop filters to reduce the size about 58% and to create two attenuated poles for increasing bandwidth. First we derived the relation between the odd-mode and even-mode impedance theoretically. Then, we applied EM software tools to choose a proper coupling distance to implement circuit layout. Finally, the measured results were compared with the simulated results, and we found that coupled-lines can effectively improve the reduction size of the filters. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1363–1368, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23374 [ABSTRACT FROM AUTHOR]