Design And Implementation Of A Combination Switched Filter Bank

With the rapid development of wireless communication in the field of civilian communications and military radar, the requirements for microwave technology are increasing fast. Superheterodyne receivers become more widely used in communication systems, because of its brand dynamic range and wide channel bandwidth, also with high adjacent channel selectivity and sensitivity. Switched filter bank plays an important role in the superheterodyne receiver; in several cases the filter bank limits the system performance such as noise figure and purity of spectrum.In this thesis, a new type of switched filter bank is presented for the design of real-time signal spectrum analyzer, adopting combination with cavity and microstrip structure. Benefited from the tapped input-output structure and interdigital structure, the insertion loss of filters is low, and there is high-band rejection, compact size for every filter. The channel selection is achieved by two SP5 T microwave switches with fast switching speed, wide frequency bandwidth, and low insertion loss. The main work of this thesis is as follows:First of all, the research status of preselection filters is summarized, which is based on consulting a large number of domestic and foreign literatures. The combination type of switched filter bank is chosed by the comparation of the advantages and disadvantages between switched filter banks, YIG(Yttrium-Iron-Garnet) tuned filters and other frequency-selective programs.Secondly, the theory of microwave filter is introduced: filter types and achieved functions are explained, then the design equations of stripline and microstrip which will be used in this paper and the relationship between microwave filter design parameters and structural dimensions in order to derive the initial filter design will be discussed, and then the structural equivalent of tapped input and output as well as the initial extraction circuit is presented, and then the application of reflective delay filter design method in the debugging process is showed. Finally a kind of relatively rapid method for design and debugging cavity filter is summarized.Then, the filter is modeling in three-dimensional electromagnetic simulation software, and a method named reflective delay is applied in cavity filters design, which can greatly reduce time and cost in microwave filters design. Then microstrip filter model is built, the frequency offset caused by inductance from grounding is analyzed emphatically. One kind of model which is suitable for moderate bandwidth filter design is established. Microstrip length, width, interdigital gap to the affect of filter performance is discussed, these conclusions are very instructive to how to design microstrip interdigital filter quickly with good performance.Finally, taking mutual interference between channels and external electromagnetic interference into consideration, switched filter bank is designed with compact size, and then microstrip circuit assembled with cavity filter. After analyzing current problems appeared in the measurement of joint debugging of system, solutions to problems are proposed.