Surface Mounted Parallel Coupled Microstrip Bandpass Filter With Vertical Transition for 5G Millimeter Wave Applications

A parallel-coupled microstrip bandpass filter (BPF) for the fifth-generation (5G) millimeter-wave (mm-wave) base station is presented with a novel vertical transition for surface mounting. The vertical transition of side layer connection is applied to surface mounting technology (SMT). A simplified equivalent circuit model is introduced by theoretical analysis to prove the feasibility of the side layer connection structure. The proposed BPF is fabricated by 99.9% Al2O3 substrate with a compact dimension of 9 mm × 6 mm × 0.25 mm. The frequency response of proposed BPF is centered at 28 GHz with a fractional bandwidth (FBW) of more than 14%, a low insertion loss less than 1.5 dB and two transmission zeros near the passband edges. Both measured and simulated results suggest that the proposed BPF is a possible candidate for the application of base station at 5G mm-wave frequencies.