Research On Highly Selective Hybrid Coupled Filter Based On LTCC

Microwave filters play an important role in the modern communication systems. Due to the rapid development of wireless systems and limited frequency spectrum, filters with compact sizes and good selectivity are highly demanded. This study is aimed at realization of miniaturization and high frequency selectivity of microwave filters. The main contributions of this dissertation are summarized as follows:Firstly, a multilayer planar helical resonator is proposed, the equivalent circuit model and field distributions are used to explain the resonating mechanism. Different types of coupled resonator pairs are proposed, the designed filters may realize responses with different characteristics.Secondly, three types of mixed coupling filters constructed by helical resonator pairs are proposed. The response of Type-S1 filter is asymmetric, the response of Type-S2 filter is symmetric, both filters have one transmission zero (TZ) located on each side of the passband, respectively; the response of Type-S3 filter is asymmetric, with two TZs located on one side of the passband. Generation principle of TZs is verified. Even/odd-mode method is used to study the equivalent circuit model and then calculate the frequency of TZ for further circuit design.The proposed filters are all fabricated using low-temperature co-fired ceramic (LTCC) technology. The size of each filter is only about 0.05λg × 0.03λg, indicating very compact features. Good agreements are observed between the simulated and measured responses of the filters, verifying the validity of the design strategies.Thirdly, a fourth-order filter and a duplexer constructed by resonator pairs are proposed successively. The simulation results further indicate the validity of the proposed design strategies.The proposed helical resonator pairs own both advantages of miniaturization and high selectivity. With these features, they are also suitable for other compact microwave circuits.