Tri-Band Bandpass Filter Incorporating CMRC

Abstract

In this project, the compact microstrip resonant cell (CMRC) structure is investigated especially on the resonant modes. The structure shows three fundamental modes, and the corresponding three resonant frequencies can be tuned sequentially by modifying the relevant dimensions or the shapes of the upper T-shaped patches of CMRC. The three resonant modes of CMRC are used to constitute three passbands respectively and hence a tri-band bandpass filter can be achieved. A complete design methodology is developed for this particular case. As the three passbands can be tuned sequentially, the design procedures are efficient. As an example, a two-pole tri-band bandpass filter is fabricated on printed circuit board (PCB). Good agreement is obtained between the simulated and measured results. The filter shows low insertion loss, and for some roll-offs it exhibits good frequency selectivity characteristics.