Compact Balanced Dual-Band Bandpass Filter With High Common-Mode Suppression Using Planar Via-Free CRLH Resonator

A novel planar via-free composite right-/left-handed resonator with an interdigital capacitor and meander microstrip line is proposed in this letter. Under differential-mode (DM) excitation, the quasi-lumped resonator is virtually connected to ground, and it exhibits dual-mode characteristics. Moreover, two DMs can be tuned independently in an appropriate way. Under common-mode (CM) excitation, CM resonant modes are away from DM resonant modes, which contributes to the excellent CM suppression without additional circuits. Based on this resonator with compact size, CM suppression ability, and dual-mode DM characters, a balanced dual-band bandpass filter is analyzed and fabricated. Finally, simulated and measured results verify this design method.