Design Of Multi-band Filter And Balanced Filter Based On Microstrip Line

With the development of the modern communication industry,especially the mass adoption of multimedia smartphones,new requirements are put forward for each component of the wireless communication system.As an important component of the RF front-end circuit,the practical needs of multi-band,miniaturization and low insertion loss have become the research hotspots in recent years.Compared with other multi-passband filter technologies,the use of multimode resonators for filter design has the advantages of low insertion loss and small size.At the same time,in the face of the severe challenges of electromagnetic compatibility of wireless communication devices in complex electromagnetic environments,balanced microwave filters with good electromagnetic anti-interference characteristics,capable of suppressing common mode noise,and improving system sensitivity have received extensive attention and balanced.The band filter also has a multi-band frequency selection function.Based on the subject work undertaken during my master's degree,this paper systematically studies the design of multi-passband filters and balanced filters.The main research contents are as follows:(1)The asymmetric-line stepped-impedance resonator(SLSIR)is studied and analyzed.Based on the resonator,a high-temperature superconducting tri-band bandpass filter with miniaturization characteristics is designed.Firstly,the resonance characteristics of the SLSIR of the asymmetric parallel line step impedance resonator are analyzed,and the numerical relationship between the resonant frequency and the physical parameters is established.Then,by selecting the appropriate impedance ratio and electrical length ratio,multimode resonators for GPS,Wi Fi and Wi Max are obtained.Finally,the 0° feed is used to generate two transmission zeros on both sides of the passband to improve the selectivity of the filter.(2)Using an asymmetric parallel line step impedance resonator SLSIR designed a balanced double-band filter.Firstly,the differential common mode resonance characteristics of the resonator are analyzed,and the relationship between the differential common mode resonant frequency and the impedance ratio and the electrical length ratio is established.Then,based on the asymmetric parallel line step impedance resonator SLSIR,a balanced double is proposed.The band filter achieves better in-band common mode rejection characteristics.Finally,in order to improve the out-of-band common-mode rejection of differential mode response,a balanced dual-band filter with high common-mode rejection in a wide frequency band is designed by loading common lengths on the center plane and shifting the common mode frequency.(3)The stub-loaded stepped-impedance resonator is analyzed.The three differential-mode resonant frequencies of the resonator can be adjusted by changing the step-impedance resonator or changing the electrical length of the loading stub.The third differential-mode resonant frequency can be adjusted alone by changing the length of the loading stub.Finally,a tri-band balanced filter for GPS,5G and WLAN is proposed,and good common mode rejection is achieved in the differential mode passband.