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, open-circuited 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.