The Theoty And Optimization Desing Of Asymmetric Half-Wavelength Resonators Coupling Filter

With the rapid development of wireless communication technology, especially the systems, such as GSM, WIMAX, WCDMA, WLAN and UWB, are widely used, which have spurred a tremendous development in communication system. Microwave filter is one of the most important part in the wireless communication system and the filters with smaller size, multi-band and harmonic suppression are required by the system. The research cycle and costs of the microwave filter can be reduced by Computer-aided design (CAD). Neural network technology often is used to process information and it has been used in computer aided design (CAD), because the mathematical model can be established and the filter performance can be optimized, expediently, by it. Based on the asymmetric half-wavelength resonators coupling filter, firstly, the equivalent circuit and neural network modeling are analyzed, then the filter design method of smaller size, multi-band, and harmonic suppression is presented. The filters with smaller size, multi-band, and harmonic suppression are designed. The author’s works mainly consist of:1. In order to analysis asymmetric half-wavelength resonators coupling filter more comprehensive, the equivalent circuit model is established, then, according to the transmission zeros, resonance and coupling, the equivalent circuit parameters are extracted. Based on the neural network theory, the smart model of asymmetric half-wavelength resonators coupling filter is established. In the smart model, the input variables are frequency and three key structure dimensions of the filter, the output variables are insertion loss and return loss of the filter. 2. According to two miniaturized asymmetric half-wavelength resonators coupling filters with stepped impedance resonators, the method of slotting is present to miniature them. Two new filters are designed by slotting and the sizes of the two new filters are reduced by20%and37%, respectively.3. The method of shunt open stubs is presented to miniature asymmetric half-wavelength resonators coupling filter and the method is analyzed by the method of ABCD matrix and equivalent circuit. Three filters are designed by the method and the sizes of them are reduced by70%,67%and76%, respectively.4. The method to design miniaturized multi-band filter is presented by shunt open stubs and two filters with the center frequency of2.4/5.7GHz are designed, the sizes of them are12.5×10.5mm2and9.3×9.6mm2and the sizes of them are reduced by72%and81%, respectively. For the multi-band filter designed by the method, in order to prove there are two transmission zeros on both sides of each passband, the tri-band and quad-band filters are designed.5. In order to improve the rejection band of the miniaturized filter, the method of connecting the shunt open stubs is presented; the resonance frequency of the parasitic pass band, caused by the shunt open stubs, can be reduced by half by the method. Based on the method, three filters with well rejection band is designed, the insertion loss of the one filter is less than-20dB between1.25f0and3f0.6. Based on the asymmetric half-wavelength resonators coupling filter, the methods to design tunable filter, constant bandwidth tunable filter and dual-band tunable filter are presented and the methods are analyzed and demonstrated.