Research And Design Of Non-Equiripple Microwave Filters For Reducing Manufacturing Sensitivity

Microwave filters play an important role in communication systems.The desired signal can pass through and the undesired signal can be suppressed,so the performance of microwave filters directly determines the quality of communication.In decades,many papers have been published about the filters,and the research on the one hand,is about the synthesis theory of microwave filters,on the other hand is about the design of the filters,which focuses more on sharper skirt selectivity,higher suppression outside the passband,lower loss,higher quality factor,dualband or multiband properties and so on.However,after decades of research,although the synthesis theory guiding the design of filters has been very mature,due to the inevitable manufacturing errors,the deviation in the properties of the material actually used,soldering quality,temperature effects and other complex situations in practice,there is always a certain gap between the measured results and the simulated and synthesis results,which may reflect the deterioration of the filters' in-band matching performance,the increase of return loss and insertion loss,etc.In order to reduce the adverse impact of errors in actual production on the filters,the traditional equiripple filters are modified in this thesis to make the passbands of the filters have the non-equiripple characteristics,so as to reduce the return loss which may increase in the actual processing compared with equiripple ones,so that the actual manufactured non-equiripple filters have lower sensitivity and more ideal in-band responses when dealing with manufacturing errors.This thesis first reviews the classic methods of the extraction of coupling matrix and on this basis,the possible influence of the errors in actual production on the responses of the filters is simulated by some numerical changes.Based on these preliminary conclusions,the filtering functions which can realize the non-equiripple characteristics are used to reduce the adverse effect of manufacturing errors in this thesis.This thesis resynthesizes the traditional all-pole ladder lumped circuit and obtains a series of lowpass prototype element values which can realize the non-equiripple filtering responses.In addition,a type of classic transmission line filters is resynthesized in this thesis,using certain mathematical conditions,the normalized characteristic impedance values of non-equiripple bandpass and lowpass filters are obtained,then the structures composite coplanar waveguide and slotlines are used for simulation,manufacturing and measuring.Comparing responses of equiripple and non-equiripple filters,the measured results show preliminarily that the return loss of the filters increases more near the passband edge and the deterioration of matching performance near the passband edge is more apparent,and the non-equiripple filters have lower return loss in dealing with manufacturing errors compared with equiripple ones.The experimental results show the superiority of non-equiripple filters in reducing manufacturing sensitivity.