Design Of Multi-band And Wideband Balanced Passband Filters

With the opening of the intelligent era,various devices provide more convenience for our lives through different frequency bands.When the speed of wireless data transmission is increased greatly,serious crosstalk and electromagnetic interference problems may occur between different communication modules,which will affect the performance of different modules in the device,making electronic products unable to provide a good user experience.In order to minimize crosstalk and interference between systems,differential structures are widely used in low frequency analog circuits and RF equipment to resist the effects of environmental noise.However,the upgrading of wireless communication technology and the improvement of wireless data transmission rate put forward new requirements for the design of differential structure microwave devices.How to realize the multi-band and wideband differential filters have become one of the forefront topics in the current wireless and radio frequency industries.Based on the electromagnetic characteristics of slotlines and the coupling between slotlines and microstrip lines,a stepped impedance transfer structure is designed to balance the slotlines and microstrip lines in this thesis.Because of the characteristic of its own structure,the full band suppression of common mode signal can be realized.Using this structure as the input and output ports of the differential filters,the design of the resonators will no longer be restricted by the suppression of the common mode signal,which greatly improves the freedom of the design process and reduces the difficulty of the difference filters' design.In the design part of the resonators,the slotline resonators,stepped impedance resonators and uniform impedance resonators are used respectively to design two dual-band difference filters and one wideband difference filter in the thesis.By introducing a variety of coupling methods,namely electrical coupling,magnetic coupling and mixed coupling,and multiple transmission paths,the transmission zeros are generated on both sides of the differential mode's passband,which enhances the steepness of the passband.In addition,the bandwidths of each difference filters can be adjusted by controlling the coupling strength between the resonators.The dual-band balanced filters with passbands located at 1.54 / 2.48 GHz and 2.4 / 3.54 GHz respectively,wideband balanced BPF with passbands located at 1.54 GHz,frequency ranging from 2.79 to 3.58 GHz are fabricated and measured.Good agreement between the simulation and measurement results demonstrates the validity of the designs.