| The micro-strip low pass filter plays an important role in modern communication technology,and its performance has a great influence on the stability of the entire communication transmission system.In this paper,we focus on the miniaturization and wide stopband design of microstrip low-pass filters,two different types of microstrip low-pass filters are designed in different ways,the simulation performance is better and meets the expected design specifications.First of all,the paper expounded the basic theory of microstrip filter design and HFSS-MATLAB-API library function technology,which provided theoretical support for the subsequent microstrip low-pass filter design.Secondly,according to the preset index,the elliptic function low-pass prototype filter was designed by the ADS simulation software.Due to the large area of the microstrip circuit,the microstrip lowpass filter that met the design index and the area was reduced by 47.7% is obtained through circuit improvement.Then,an wide stopband microstrip low-pass filter based on parallel branch resonant unit was designed by the HFSS simulation software.The resonant unit was connected in parallel through the main transmission line to introduce the transmission zero point to improve the stopband attenuation rate.In order to reduce the return loss in the passband and suppress the parasitic passband,an improved method of port-loaded single-segment matching network is adopted to realize the microstrip low-pass filter sharp cutoff,small volume,small return loss and wide stop band.At the same time,by using the cross coupling between the resonant units,the position of the first transmission zero is adjusted to optimize the overall performance of the low pass filter.The HFSS simulation results show that the low-pass filter has a cutoff frequency of 2 GHz,the transition band is very steep,the maximum return loss of the passband is lower than-20 d B,and the stopband range of insertion loss below-20 d B is 2.36 GHz to 11.6058 GHz.In addition,using HFSS-MATLAB-API script interface,the program was written in low-pass filter in Matlab,the VBS file was compiled and generated,and run that file in HFSS to automatically generate 3D model,which greatly improves the design efficiency.The final size of the filter is 50mm×21.21 mm,and the physical test results are in good agreement with the simulation results.Finally,in order to obtain a microstrip low-pass filter with more miniaturization and wide stop band,a defective ground structure(DGS)and a defective microstrip structure(DMS)are introduced.The relationship between the single T-type DMS and the size of the defective groove is analyzed in depth,and the transmission characteristics of the single T-type DMS loaded dumbbell DGS are further discussed.A microstrip low-pass filter with a cutoff frequency of 2GHz T-type DMS loaded dumbbell DGS is designed in HFSS by using the improved method of microstrip line etching T-type DMS and dumbbell-type DGS.The optimized simulation results show that the maximum return loss in the passband is less than-15 d B,the stopband range of the stopband rejection is less than-20 d B from 2.91 GHz to 14.86 GHz,and the suppression can be up to-60 d B.The filter size is only 20 mm ×18.75 mm,which is reduced by nearly 65%,and the stop band is widened. |
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