Differential dual-band filter with flexible frequency ratio using H-shaped composite resonator for SCDMA and LTE applications

A differential dual-band bandpass filter (BPF) based on H-shaped composite resonator (HSCR) is proposed in this paper. The proposed BPF have two independent controllable passbands performance with two steerable resonant modes and two pairs of dual feedline structure. To obtain the differential mode (DM) transmission with common mode (CM) suppression, the coupling coefficients (k) and external qualities (Qe) are designed for two DM passbands, respectively. Moreover, a pair of unequal length E-shaped elements are introduced in the symmetrical of the HSCR to improve the CM suppression. To verify the method, a Chebyshev dual-band BPF with center frequency f
_l
= 1.95 GHz and f
_H
= 2.35 GHz, fractional bandwidth (FBW) Δl = 5.4%, and Δη = 3.5% has been designed and simulated for SCDMA and LTE applications.