A compact WiMAX diplexer module with LTCC and FBAR technologies

This paper presents a compact diplexer module for WiMAX dual-band application using multilayer low temperature co-fired ceramic (LTCC) and film bulk acoustic wave resonator (FBAR) technologies. The proposed diplexer module consists of a 2.5-GHz LTCC balanced filter, a 5.8-GHz FBAR filter, a 5.8-GHz LTCC balun, and a LTCC matching circuit. The fabricated monolithic 1-chip RF FBAR filter with vertical air gap cavity provides an insertion loss of less than 2.6 dB in the WiMAX frequency range of 5.725 ~ 5.825 GHz. The 2.5-GHz balanced filter provides a relatively low insertion loss and good return loss from 2.5 GHz to 2.7 GHz. The amplitude and phase imbalance is 0.8 dB and 5 degree, respectively. The 5.8-GHz balanced filter, which is composed of the FBAR filter and the LTCC balun, provides a maximum insertion loss of 3 dB with 0.6-dB amplitude imbalance and 8-degree phase imbalance. The overall performance of the diplexer module based on two balanced filters shows a quite low insertion loss with good amplitude and phase balances for both WiMAX bands. The size of the proposed diplexer module is only 3.5 mm × 2.5 mm with a thickness of about 720 μm.