Study On Bandpass Filters With High Selectivity And Wide Stopband

Band-pass filter is one of the important parts of modern wireless communication system.Its selectivity and stopband characteristics both determine the comprehensive performance of the system.In all kinds of ultra-wideband,super stopband,RF module microminiaturization demand under the traction of the industry,more and more RF product to filter the stopband,pass band broadening put forward higher request,this prompted the ultra wide stopband,the rapid development of ultra-wideband(UWB)technology,and is widely used all kinds of wide stop-band RF filter products.Aiming at the technical requirements of ultra-wide stopband and ultra-wide passband,this paper studies the new wide-stopband design technology and ultra-wide wideband design technology based on cross-coupling bandpass filter.The main work contents and innovation points are as follows:1.To improve the stopband suppression performance of band-pass filter,this paper designed a center frequency for more than 2 GHz fourth-order zero broad stopband bandpass filter,the filter based on fourth-order cross coupling band-pass filter circuit model,the load non-resonant component technology,the harmonic components of load introduced an extra transmission zeros,effectively improve the stopband suppression.At the same time,based on the circuit model of the fourth-order cross-coupling bandpass filter,a wide stopband bandpass filter with a center frequency of 2 GHz is designed using the source/load coupling technology.The source/load coupling technology can also introduce an additional transmission zero,which can effectively improve stopband suppression.2.In order to solve the problem of the influence of the second harmonic of the fourth-order cross-coupled bandpass filter on the high-end stopband in 1,a wide stopband bandpass filter is designed and its equivalent circuit is analyzed by using the same impedance ratio ladder impedance resonator technology.Because the second harmonic can be far away from the passband,the upper stopband can be extended to about 4 octaves,and the stopband of the filter is wider and the out-of-band suppression is better.3.In order to further broaden the stopband,this article also studies the technique of different impedance ratio stepped impedance resonator,adopted each resonator is composed of different impedance ratio of the transmission line,resulting in a number of different location of the harmonic restrain each other,thus designed a super wide stopband bandpass filter,the filter on the stopband until around 11 times frequency,successfully implement ultra wide stopband characteristics.4.In order to achieve wide stopband characteristics at the same time can realize UWB characteristics of the ultra-wideband filter design techniques are studied,and the distribution/lumped hybrid technology,will be designed based on multi-mode resonator bandpass filter and wide stopband filters based on capacitive load,designed a new type of super wide stopband characteristics of ultra-wideband filter,physical model test results and the simulation result was consistent,verified the feasibility and correctness of design,test results show that the relative bandwidth is 120% of the ultra wideband characteristics and stopband on extended to 6.7 times the frequency of ultra wide stopband characteristics.