Compact and low-loss IPD bandpass filter using 3D glass-based redistribution layer technology

A low-loss miniaturized bandpass filter is presented using 3D glass-based RDL packaging technology. A new topology consisting of one modified Pi-section and one modified T-section is introduced to generate three transmission zeros which can achieve the high out-of-band rejection. A combination of 2D planar inductors and high-Q 3D inductors is used to achieve low insertion loss and minimize the filter size. In addition, one grounded resonator at input terminal is introduced to generate an extra transmission zero in the low end. The proposed bandpass filter covering 3.3-4.2 GHz is fabricated with a compact size of 1.6 mm x 0.8 mm x 0.25 mm. It exhibits an insertion loss of less than 1.0 dB at a center frequency of 3.75GHz and a return loss of better than 14 dB. The proposed design has a 3 dB fractional bandwidth of 37.6%. Its out-of-band rejection is better than 20 dB at the low frequency band from DC to 2.0 GHz and better than 19 dB at the high frequency band from 5.0 to 9.0 GHz. The simulated and measured results of the proposed BPF are in reasonably good agreement.