Design a novel bandpass filter with microstrip resonator loaded capacitors using CFO-HC algorithm

Abstract

This paper introduces a new way to reduce the length of a microstrip end-coupled resonator by loading its ends by a lumped capacitors. A new way of controlling the frequency of the 2nd harmonic even mode by loading the center of the resonator by a lumped capacitor directly or through less than 0.125 λ go part of a microstrip transmission line. Compact dual and triple modes bandpass filters with good selectivity are obtained. The length of transmission line section controls the phase and transforms the impedance of the capacitor which controls the bandwidth and generates transmission zeros. The transmission zeros can be located at upper or lower side of the passband by adjusting the loading capacitor values or the length of the transmission line. A second order bandpass filter with center frequency of 4 GHz is designed, fabricated and measured. The filter has a passband from 3.6 GHz to 4.4 GHz with a transmission zero at 4.8 GHz. The filter has good stopband performance with a rejection higher than 20 dB up to more than 10 GHz. Insertion loss of less than 0.75 is achieved within the passband. The measured results exhibit good agreement with the simulation one. An efficient global hybrid optimization method is proposed combining the Central Force Optimization (CFO) as a global optimizer and Hillclimbing (HC) algorithm as a local optimizer. After the final global iteration, a local optimization can be followed to further improve the solution obtained from the CFO. The hybrid Central Force Optimization and Hillclimbing (CFO-HC) algorithm is used to optimize the dimensions and values of the capacitance which contact them the filter, the (CFO-HC) algorithm was implemented using MATLAB-software and linked to the CST simulator to simulate the filter, In addition the optimized filter is simulated by the Finite Difference Time Domain (FDTD) program written with matlab to validate the results.