A compact balanced UWB bandpass filter (BPF) is proposed in this paper, which is based on the half-mode substrate integrated waveguide (HMSIW) and the differential defected ground structure (D-DGS). Using the HMSIW, the filter can achieve compact size, wide passband and good compatibility. Two D-DGS cells are employed to provide good suppression for the common-mode (CM) noise, while they have small effect on the performance of differential-mode (DM) signals. To validate the design theory, a microstrip balanced UWB BPF is designed, fabricated and measured to meet compact size, low insertion loss, good return loss as well as proper bandwidth. The predicted results are compared with measured data and show reasonable agreement.
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