The co-design of IPD high-selectivity diplexer and dual-band filter chips based on lumped element single-band filter

Abstract

In this paper, a dual-band bandpass filter (D-BPF) and a diplexer are proposed. Their core structures are both a lumped element single-band bandpass filter (S-BPF) with dual transmission poles (TPs) and dual transmission zeros (TZs). For the D-BPF, based on this S-BPF, single-band impedance matching networks (S-IMNs) are used to form the second/third passbands. Two S-BPFs with different first reactance elements are used for the diplexer to achieve good isolation without T-junction. Finally, the D-BPF and the diplexer with center frequencies of 2.26/4.75 GHz and 2.3/5.75 GHz are fabricated by thin-film integrated passive device (IPD) technology. The physical size of the D-BPF chip is only 1.5 × 1.1 mm2, and the diplexer chip is 2.3 × 1.5 mm2. Measured results show they both have the advantages of good insertion loss, excellent impedance matching, high roll-off, and broad stopband rejection. The isolation of the diplexer is greater than 23 dB from 0 to 10 GHz.