The Research And Design Of Radio-Frequency Filters

With the rapid development of wireless communications technology, Frequency resources of the Radio Frequency and Microwave are relatively tight, which results in an increasingly demanding for the performance of the microwave circuits. The filters play a significant role in the RF system such as the filtering interference, noise attenuation, frequency-doubling, amplifier circuit and so on. Furthermore, in order to suppress the external signal and the harmonic distortion caused by nonlinear devices, and to improve the overall performance of the circuit, a good shape factor and excellent band suppression are required for filter. Therefore, as a key component of the frequency microwave system, the quality of the filter is critical. Under the background, in order to meet the development needs of the RF system, the thesis elaborates two different filters, one is helical structures filter, the other is dual-mode filter.The main work and research results of the thesis can be summarized in the following areas:1. The basic principles of the Microwave and Radio frequency filters and frequency transformation rules are analyzed, and the new technology and application of Microwave filter are presented.2. With the research and analysis of the spiral filter's basic theory, a novel structure of spiral cavity bandtop filter is designed in the thesis, which works in the VHF/UHF. Based on the traditional stripline band-stop filter, with the use of the capacitive coupling stub harmonic structure and spiral resonator structure used to replace the coaxial, the size of the filter can be effectively reduced.3. Using dual-mode resonator structure, a novel structure of microstrip planar filter is presented in the thesis. To bring down the resonance frequency of the patch, the cross-slots are cut on the radiation patch. With the use of two end-open L-shaped microstrip lines for the input and output of the filter. the second harmonic frequency is pushed to 3 times of the fundamental, and the rejection level of harmonic suppression is very good, which is kept below -35 dB.The core idea of the thesis is to combine theory and computer-aided design. The Spiral cavity bandstop filte and dual-mode microstrip bandpass filter are processed. The measured results and simulation results are matched.