BALANCED SINGLE- AND DUAL-BAND BPFS USING RING RESONATORS

This paper presents new balanced single- and dual-band bandpass filters (BPFs), both of which are constructed using two ring resonators. For each BPF, opencircuited stubs are added to one of the two resonators so that the transmitted common-mode (CM) signals can be attenuated, and source-load coupling is established so that two transmission zeros are generated near the edges of each desired differential-mode (DM) passband to sharpen the passband selectivity. The measurement agrees well with the simulation. For the single-band BPF, the measured minimum DM insertion loss is 1.4 dB in the DM passband, in which the CM suppression is larger than 41.6 dB. For the dual-band BPF, the minimum DM insertion losses are 1 and 1.35 dB in the first and second passbands, respectively, in which the CM rejections are larger than 29 and 22 dB.