High Selectivity Differential Bandpass Filter Using Dual-Behavior Resonators

Abstract

Abstract-A high selectivity differential bandpass filter (BPF) using two pairs of dual-behavior resonators (DBRs) is proposed in this letter. A high selectivity passband for the differential mode with second harmonic suppression is achieved, by utilizing shorted coupled lines with two short stubs. For the commonmode (CM) circuit, the CM responses can be suppressed over a wide frequency band by the loaded open/shorted stubs. To validate the feasibility of the proposed filter, a planar differential BPF (3-dB fractional bandwidth 4.9%) with good CM suppression is designed and fabricated. The theoretical and measured results agree well and show good in-band filtering performances and out-ofband harmonic suppression performances.

Balanced Microwave Transmission Lines, Circuits, and Sensors

“…Concerning the implementation of balanced filters with narrow differential-mode pass bands, most implementations are based on coupled resonator topologies (see [135], [136], [137], [138], [139], [140], [141], [142], [143], [144], [145], [146], [147], [148], [149], [150], [151], [152], [153], [154], and [10, chapter 12]) It is sometimes difficult to differentiate between narrowband and wideband filters (either balanced or single-ended), since the frontier is rather diffuse (depending on the sources, the narrowband designation requires fractional bandwidths below 10 %, whereas in others, filters with fractional bandwidths as high as 20 % are considered to belong to the narrowband category). For this reason, some balanced filters reported in [10, chapter 12] (and references therein), dedicated to narrowband balanced filters, are considered to be wideband filters in this review paper.…”