Research Of Microwave Lossy Filter And Microwave Duplexer

The performance requirements of various devices in communication systems are increasing because of the rapid development of wireless communication systems in the 21 st century.The filter and duplexer,which are two important frequency selective devices in the communication system,are naturally required to have better frequency selection characteristics in the increasingly strained spectrum resources,the flatness and group delay characteristics of the passband must also be as good as possible in order to avoid signal distortion,the filters and duplexers are also required to have a small size in order to meet the increasingly miniaturized,lightweight,and low cost conditions of modern circuits,at the same time,insertion loss,return loss,and isolation of the duplexer cannot be ignored.The lossy filter and the microwave duplexer are designed in the form of separate electrical and magnetic coupling(SEMC)resonators,which greatly reduces these two devices' physical size and improves their frequency selection characteristics by introducing effective transmission zeros.The specific work is arranged as follows:Firstly,a parallel lossy filter are proposed based on the SEMC resonators.Through the method of artificially introducing loss to improve the flatness in the passband,the introduced loss can be passed through the low noise amplifier compensate.First,a parallel structured lossless filter is designed according to the SEMC resonators.The lossless filter and the lossy filter synthesis method are used to synthesize the lossy filter's coupling matrix,and then the value of the no-load quality factor of some resonators is reduced by adding resistors,so a lossy filter is designed by using the inconsistent Qu value method.Finally this lossy filter is converted to a lumped parameter element for analysis.This lossy filter achieves the purpose of improving in-band flatness,and the resulting two transmission zeroes also improve its frequency selection characteristics.After that,a duplexer based on the 0-degree feed and the SEMC structure is implemented.Firstly,the fact that the zero-degree feed can produce two transmission zeros is analyzed.Then,a short-circuit transmission line is introduced between the original two resonators to introduce a SEMC structure.The SEMC produces a transmission zero,and both types of transmission zeros can be individually controlled.Finally,connecting two well-designed filters through a T-junction forms a duplexer with multiple transmission zeros.This duplexer has improved frequency selectivity due to transmission zeros,but isolation and physical dimensions without significant improvement.Finally,a multi-resonator duplexer is proposed based on the SEMC resonator and the new duplexer design method.First,two SEMC resonators with different frequency bands are designed,and then the two resonant frequencies of a dual mode resonator are adjusted to fall on the center frequencies of the two different frequency bands respectively.Finally,a multi-resonator duplexer is formed by coupling the three resonators.The dual-mode resonator is used to replace the T type joint as a common resonator,which greatly reducing the physical size of the device,and because the resonators of each channel of the duplexer are not directly connected,the isolation is also higher than the T-connector duplexer.