The Design Of RF Microstrip Linear Phase Bandpass Filter

With the rapid development of mobile communication and the highly integration ofmicrowave circuits, microwave circuits become a focus gradually, microwave filters areimportant in the filter elements, and the microstrip line becomes the main signal carrier inmonolithic microwave circuits, especially the band-pass filter develops most rapidly, it plays adecisive role in many systems, so the theoretical analysis, the structural studies and so on ofmicrostrip band-pass filters have become the top topic. Now, the phase-frequencycharacteristic for filter has been as important as the amplitude-frequency characteristic becauseof the reliability of the signal transmission in passive network, so the design and optimizationof the linear phase band-pass filter will be a significant project in the microwave circuits.This paper calculates the parameters of the linear phase filter by analyzing the normalizedlow-pass filter and analyses the principles of microstrip band-pass filter.Then it finishes thedesign process and the parameters calculation for the parallel coupled microstrip filter. Finallyit designs a linear phase band-pass filter whose center frequency is2GHz with parallel coupledmicrostrip. This object optimizes the phase-frequency and amplitude-frequency characteristicsimultaneously.It improves the pass-band flatness and stop-band attenuation in the largestextent. The simulation results can prove correctness, simplicity and efficiency of this method.This paper proposes a new algorithm to optimize the parameters, the algorithm establishes anideal transfer function as the target function based on the ideal microstrip size. A search rangis defined around the ideal parameters, the parameters in the range are limited within a certainmagnitude. Then the algorithm searches the parameters to establish transfer functions, all ofthem are compared with the target function, the one closest to the target function is the optimalfunction, and the parameters of the optimal function are the optimal parameters. For theverification of results, this paper uses moment method for filter simulation.The method is themost similar to the actual test. Although the filter is still processing because of the time, thesimulation based on the moment method is closed to the actual result, it can proves that theoptimized algorithm based target function is effective and feasible.