Microwave Miniaturized Filters Based On Open-Loop Resonators

A lot of filters are used in modern communication systems. The lumped filters are suited for low frequency applications but the power loss is high and performance is unstable in high frequency. The coaxial filter is generally used below the frequency of 10 GHz, but the size is large. Performance improvements in traditional resonator filters depend on the increase of the resonators, but this will lead to high power loss, large size and high cost. In RF circuits, the size and performance are the major research subjects despite the large scale integrated circuit.This thesis is focus on the coupled resonators and their applicatons on microwave filters. Three type of filters based on the proposed coupled open-loop resonators are realized and satisfy the desired performace and size demands. The background, significance and applications of microwave filters based on coupled resonators are introduced at first. Then, the theories and methods of designing microwave filters are provided. At last, three type of microwave filters based on open-loop resonators are given and analyzed.Firstly, two square open-loop resonator bandpass filters are designed based on LTCC. Two resonators are placed on two adjacent dielectric layers by the LTCC multilayer technology. The edge coupling of planar structure is transferred to the stereoscopic structure. Two 5-pole points filters are designed and simulated. The results show that the filters can be obtained through the adjustment of space between resonators. The filters show good performance in their operating frequency range. The frequency response of the filter without via holes possesses a attenuation pole located at the side of high-frequency. The frequency response of the filter with via holes is similar to that of the ideal Chebyshev response.Secondly, microstrip bandpass filters using radial stub-loaded(RS-loaded) square open-loop resonator(SOLR) are presented. With theoretical and simulated analysis, the proposed microstrip resonator shows some novel features and is very flexible to be used on bandpass filters. The parameters of the proposed resonator are discussed. The simulatons and measurements are given. The filters based on the resonators have inherent finite-frequency transmission zeros and desired sizes. With the presence of the attenuation poles, the sharp transitional band is formed. The measurements correspond to the simulated results well.Finally, two coupled resonator filters based on microstrip are designed and fabricated. The unit structure, the equivalent circuit and the effects of that on the filters are given and discussed. The photos of the proposed filters are provided. The simulation and measurement are compared and analyzed. The single resonator filter has two attenuation poles at the side of high frequency. The double-resonator filter has three or more attenuation poles. Also, the double resonator filter has sharper transitional band, wider stop-band and more stop-band attenuation.The design, simulation and measurements all prove that the microwave filters based on the open-loop resonators proposed in this thesis can well satisfy the desired performance and size demands.