A Balanced Bandpass Filter with Common-Mode Suppression for GPS Receiver

A balanced bandpass filter (BPF) with superior common-mode (CM) suppression is proposed in this paper. The proposed BPF is composed of a pair of dual-mode stepped-impedance resonators (SIRs) and the balanced stepped-impedance microstrip-to-slotline transition structure. Good differential-mode (DM) transmission and CM suppression can be achieved. In order to verify the feasibility of the design method, a balanced BPF with center frequency at 1.57 GHz has been fabricated and measured. Measured results indicate that the designed filter has insertion loss (IL) inside the passband less than 1.8 dB, together with return loss (RL) better than 14dB. Good agreement between the simulation and measurement results demonstrates the validity of the design.