Dual mode BP filters_ MTT-T031906 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 51, NO. 8, AUGUST 2003 A Dual-Mode Bandpass Filter With Enhanced Capacitive Perturbation Boon Tiong Tan, Siou Teck Chew, Member, IEEE, Mook Seng Leong, Senior Member, IEEE, and Ban Leong Ooi, Member, IEEE Abstract―A dual-mode ring bandpass filter with two pairs of capacitors has been designed. The capacitors are used to control the location of the even- and odd-mode frequencies independently, allowing weak coupling for narrow-band filter design with realizable capacitance values. Theoretical expressions have been derived for these frequencies. A 4% bandwidth bandpass filter centered at 1.9 GHz was designed and tested with good agreement between theoretical and measured results. Index Terms―Bandpass, dual mode, filter, ring.……