Reseach On Syntheisis Diagnosis And Miniaturazation Of Microwave Filter

In modern microwave communication systems, bandpass filter is an essential component, which is usually used in both receivers and transmitters. With the rapid development of modern wireless communication systems, bandpass filters play more important roles in a variety of microwave circuits and gain increasing interesting in compact size and high performance. In this dissertation, the main work is realizing the synthesis of some special filters, for example, synthesis of ultra-wideband(UWB) filter and multi-band filter. In addition, some research works about the miniaturization of filters has done. The main contents of this dissertation are listed as follows:Firstly, a detailed research is given on the genetic algorithm and particle swarm algorithm. A novel hybrid algorithm based on the two algorithms and a new error function that can accelerate optimization process are proposed in this dissertation, which can get proper coupled matrix of filter rapidly. In some special situations, we cannot get the coupled matrix by using the synthesis technology, so the optimization algorithm can be used to get coupled matrix which satisfies the design specifications, it can accelerate the speed of design and save more time.Secondly, for synthesis of UWB filter, a new method of synthesis of UWB filter based on novel tubular filter is proposed. This method breaks through the limitation of 40% of fractional bandwidth in conventional tubular, realizing more than 110% of fractional bandwidth. In addition, there are two ways to generate transmission zero in the novel UWB filter according to where the transmission zero will be placed. For the upper stopband, the transmission zero can be generated by adding a cross-coupling capacitor to filter. When the value of the capacitor is increasing, the transmission zero will move to the passband. For the lower stopband and passband, the transmission zero is introduced by adding a resonant network. So, the transmission zero can be placed any place in order to enhance the selectivity of the filter or the suppression of interfere signal in passband, increasing dramatically the design freedom.Thirdly, for synthesis of multi-band filter, a novel method which combines the approach of synthesis of polynomial and least squares extreme point iterative method can realize the synthesis of multi-band filter by two steps. At first, the coefficients of the characteristic polynomial of the filter can be got by using the least squares extreme point iterative method. Second, the corresponding coupled matrix of filter can be calculated according to the characteristic polynomial. Finally, the synthesis of multi-band filter is finished. In addition, combing this novel method and the technology of synthesis of multiplexers, we can realize synthesis of multi-band multiplexers.Fourthly, two types of hybrid transmission line stepped impedance resonator consist of suspended stripline and microstrip line are proposed in this dissertation. The good performance of miniaturization is not achieved by increasing the capacitive loading, but modifying the characteristic impedance of the transmission line. The resonant condition, the parameter controlling the resonant frequency have been analyzed clearly. Compared to the conventional suspended stripline resonator, it has very good performance on miniaturization, which can be used in a variety of circuits.Fifthly, the technology of nonresonating node is studied deeply, the mechanism of this technique and the procedure of extracting elements is described clearly. Two novel coupling structure based on the technique are presented. The first one can generate a controllable transmission zero with the size of the filter unchanged. The second one is a dual-mode nonresonating node which can produce an adjustable transmission zero on both sides of the passband in order to enhance the skirt selectivity. A very compact filter with good performance can be designed by using the novel coupling structure and the hybrid transmission line stepped impedance resonator.Finally, a summary of the whole dissertation is given, and future research topics are suggested.