Study On The Synthesis Method For Multi-passband Microwave Filters Based On Frequency Transformation

To meet the requirement of the development of wireless communication towards multi-band and multi-mode, simplify the structure of the multi-band communication system, reduce its volume and mass, and decrease the manufacture cost, it is significant to investigate the synthesis method for multi-band microwave filters.This dissertation focuses on the analytical synthesis method based on frequency transformation for multi-band microwave filters. The following works are presented.1. The frequency transformation for in-line dual-band filters is employed to the synthesis of dual-band filters with cross-coupling, and the synthesis method for cross-coupled dual-band filters is developed, the analytical expressions of the coupling coefficients and the external quality factors are given.2. The dual-mode square waveguide resonator is applied to the design of dual-band microwave filter, and this disposal simplifies the structure of the filter.3. A frequency transformation expression from triple-band filter to low-pass prototype filter is presented, and the synthesis theory for in-line and cross-coupled triple-band filter is developed. In this theory, the circuit topology structure is constructed and the analytical equations for the calculating of coupling coefficients and external quality factors are derived.Based on the proposed synthesis theory, several synthesis examples of theoretical filter circuit and design examples of practical microwave filter are also presented in this dissertation, these examples have validated the synthesis theory and proved that the theory is applicable for the design of practical microwave filters.