Research On High Performance Planar Microwave Filter And Diplexer

Filters and diplexers are important components for channel selection and signal separation in modern microwave and millimeter-wave systems. And the electrical performances are crucial for communication systems. The proposed filters and diplexers need to meet the basic requirements, including compact size, high performance and low cost. It is still a challenge for the filter and diplexer design due to the applications of the emerging wireless communication systems. Based on the multiple-mode resonator and the design theory of the cross-coupled resonator filter, the narrow band multiple-mode microstrip filters, multiband multiple-mode microstrip filters and ultra-wideband multiple-mode microstrip filters are designed in this dissertation. Meanwhile, the slotline filter and some conventional microstrip filters(including the combline filter, interdigital filter and hairpin-line filter) are analyzed. On the basis of these research, the novel balanced planar microwave filters are proposed by investigating the method which balances the single-ended filter. Finally, the mutual loading effect of two filters can be further investigated in detail. The novel planar microwave diplexers and balanced-to-balanced microstrip diplexer are designed through the combination of two filters and balanced filters without extra junction matching network, respectively. It is believed that the proposed planar microwave filters and diplexers with compact size and high performance have important theoretical value and a good prospect of engineering application.The main contributions of the dissertation can be summarized as follows:1. Based on the uniform transmission line theory, the miniaturized dual- and triple-mode microstrip resonators are designed by utilizing odd-even-mode method. Further, two new compact narrow band microstrip filters are designed by using the proposed resonators. Very wide upper-stopband can be achieved for the harmonics formed by the high mode are well suppressed by the transmission zero generated by the stub or source-loaded coupling.2. Based on the investigation of the microstrip stub loaded resonator and stepped-impedance resonator, novel quadruple- and quintuple-mode resonator structures are proposed with the flexibly controlled modes. With the constant improvement of the resonator structures, the quadruple- and quintuple-mode ultra-wideband microstrip filters are designed by using the proposed resonators. In some filter designs, the cross coupling and source-loaded coupling is introduced to improve the selectivity.3. Firstly, the dual-band dual-mode microstrip filter, whose central frequency ratio of the two passbands and bandwidth are flexibly controlled in a certain range, is proposed by using the single stub loaded resonator. The source-loaded coupling is introduced to improve the selectivity. Further, four compact and high selectivity dual-band microstrip filters(including dual-band wideband filter and the dual-band filter with one ultra-wideband passband) and two compact and high selectivity tri-band microstrip filters are designed by using the assembled resonator which are assembled by two or three resonators. The central frequency and bandwidth are flexibly controlled in a very wide range.4. The second-order balanced microstrip combline filter, SIR balanced microstrip combline filter, broadband balanced microstrip filter based on the dual-mode short stub centrally loaded short-ended resonator and broadband balanced filter with hybrid hairpin-interdigital structure are proposed with high CM suppression within the passband. For the SIR balanced microstrip combline filter, high CM suppression can be obtained for misaligning the fundamental resonant frequencies of two kinds of open bi-section SIRs and undesired external quality factor. For the other three balanced filters, high CM suppression can be achieved by introducing a CM transmission zero within the passband.5. Based on the analysis of the mode coupling of the slotline resonator with the different I/O coupling structure, novel high selectivity broadband balanced slotline filter is proposed. The spurious band is well suppressed, for the second mode coupling between two slotline resonators is approximately equal to null and the second mode of the slotline resonator coupled to the QWR cannot be effectively excited. Meanwhile, the slotline resonator is entirely destroyed under the CM excitation, so high CM suppression can be obtained in a very wide frequency range.6. Based on the second-order SIR mixed coupled filter, a new high selectivity and wide upper-stopband microstrip diplexer with the small central frequency ratio of the two channels is designed by adopting the T-junction method. High isolation can be realized, due to the intrinsic transmission zero of the filter and the transmission zero generated by the stub of the T-junction.7. High isolation planar microwave diplexer with one wideband channel and high isolation and suppression balanced-to-balanced microstrip diplexer are proposed without the extra junction matching network. More compact size and lower insertion loss can be obtained for the absence of the junction matching network. Moreover, the mutual loading effect of the two filters or balanced filters can generate new transmission zeros to improve the selectivity and isolation.