LTCC Balun Bandpass Filters Using Dual-Response Resonators

The design of compact balanced-to-unbalanced (balun) bandpass filters (BPFs) in the low temperature co-fired ceramic (LTCC) technology is presented. By incorporating the proposed dual-response resonators, an LTCC balun filter with desired bandpass response in differential mode and bandstop response in common mode is obtained. To further improve the out-band suppression response of the filter, another LTCC balun BPF with two controllable transmission zeros is described. Both balun BPFs are practically implemented showing the desired filtering performance with good amplitude and phase imbalances, which are less than 0.05 dB/0.26 dB and 1.9°/2.3° in the passbands, respectively.