A 3.5-/28-GHz Dual-Band IPD Bandpass Filter Using GaAs Process for 5G Application

In this letter, a dual-band bandpass filter (BPF) is proposed with a large frequency ratio, utilizing gallium arsenide (GaAs)-based integrated passive device (IPD) technology. To address the challenge of integrating microwave (MW) and millimeter-wave (mm-Wave) bands with a large frequency ratio, a parallel topology is introduced. This topology combines an MW BPF with a wide upper stopband and a mm-Wave BPF with a wide lower stopband. The enhanced stopband suppression will naturally realize an open circuit to the adjacent filtering channel, and the conventional T-junction is removed for size reduction. To realize a wide upper stopband, a quasi-lumped BPF and two low-pass stubs are co-designed. To enhance the suppression of lower and inter stopband, lumped metal–insulator–metal (MIM) capacitors are added to the feeding line of mm-Wave BPF. For demonstration, a 3.5-/28-GHz dual-band BPF is designed, fabricated, and measured. All simulation and measurement results are in good agreement, validating the proposed structures.