Miniaturized wideband bandpass filter in IPD technology with passive equalizer to improve the flatness of insertion loss response

In this paper, a wideband bandpass filter (BPF) with very compact circuit size is proposed. Specifically, the circuit size of a 5th-order multi-mode resonator BPF is largely reduced by replacing all transmission line sections with bridged-T coils. The resulted lumped-element BPF can then be implemented using the integrated passive device technology to achieve very compact chip size. To improve also the flatness of inband insertion loss, a passive equalizer is then introduced. The measured in-band insertion loss of proposed BPF is within 2.10±0.2 dB from 4.5 to 12.5 GHz while the measured in-band group delay is within 0.152±0.017 ns. Notably, it features a compact chip size of 1.83 mm × 1.69 mm, which is only 0.052λ₀ × 0.048λ₀ at the center frequency f_o = 8.5 GHz.