Differential Dual-Band Filter Using Ground Bar-Loaded Dielectric Strip Resonators

In this letter, a new differential dielectric strip resonator (DSR) filter with dual passbands is proposed. By loading a pair of ground bars underneath the traditional halfwavelength (λ/2) DSR with high permittivity (supported by a low-permittivity substrate with the bottom ground plane), the TM10 and TM30 modes can be controlled to be in a close spacing. Meanwhile, both of them can be differentially excited for the design of the differential dual-band bandpass filter (BPF). The external quality factors and coupling coefficients for both bands can be independently controlled through proper layout; meanwhile, the common-mode (CM) suppression in the two differential-mode (DM) passbands is more than 25 dB. Finally, a differential DSR BPF with dual-band response operating at 8.13 and 11.13 GHz is given to verify the proposed idea.