Research On Electrically Tunable Balanced Filters Based On Laminates And Multimode Resonators

With the rapid development of modern wireless communication technology,balanced filters have been widely used and studied,due to their high immunity to environmental noise and electromagnetic interference.At present,many kinds of communication standards coexist,and spectrum resources are becoming increasingly tight.In order to improve the utilization of spectrum resources,tunable filters have the advantage of being able to tune to the required frequency band according to actual operating conditions,and are becoming a hot spot in the field of filters.In order to realize high immunity to environmental noise and electromagnetic interference of wireless communication systems and the requirement of reconfigurable operating frequency band,it is necessary to research and design tunable balanced filters.This paper designs two types of tunable balanced filters.The first type is based on Stepped-Impedance Resonator,triangular patch resonators and stacked structure.A compact tunable balanced filter with the tunable first passband and the fixed second passband is designed.In order to achieve independent tunable of both passbands,a second type of tunable balanced filter based on a multi-mode resonator is designed.The second type is based on a multi-mode resonator and two tunable balanced filters are designed.Firstly,based on a multi-mode resonator,a balanced filter with dual-band tunability was designed.In view of the fact that the balanced filter could not be fully reconfigurable,In view of the fact that this balanced filter cannot be fully tunable,a balanced filter with tunable center frequency and bandwidth was designed.Because the achievements of reconfigurable balanced filters are few,especially the achievements of dual-band tunable filters,the three filters proposed in this paper have certain reference significance for the research of reconfigurable balanced filters.1)A miniaturized dual-band tunable filter with the tunable first passband and the fixed second passband is designed.Based on the stacked structure,stepped impedance resonators and isosceles right-angled triangular patch resonators are respectively placed on different dielectric substrates to achieve independently controllable two passbands,and because of the stacked structure,the balanced filter is made the size is greatly reduced.The center frequency of the first passband of the filter in the differential mode response can be adjusted in the range of 1.1GHz to 1.32 GHz.The center frequency of the second passband is 3.85 GHz.2)A dual-band independently tunable balanced filter and a fully reconfigurable balanced filter are designed.Firstly,based on a multi-mode loaded four-mode resonator,varactor diodes are embedded in the branches to achieve tunable functions.After analysis,the first two modes of the resonator can be used to form the first passband,and the second two mode constitutes the second passband,and the two passbands are independent of each other and can be controlled independently,and this tunable balanced filter based on a multi-mode resonator achieves miniaturization.Defective ground structure is combined to suppress common mode signals of balanced filters.Although this balanced filter can achieve the function of independently tunable dual-band,it has the disadvantage that it cannot achieve full reconfigurability.Then designed a tunable balanced filter with tunable center frequency and bandwidth.Using the three modes of the cross-type multimode resonator,the varactor diode is loaded at the appropriate position of the resonator to control the resonator mode.By adjusting the change in the capacitance of the varactor diode,the center of the balanced filter can be realized both frequency and bandwidth are tunable.Because the varactor-loaded multimode resonator works in different states under the excitation of differential and common mode signals,the differential and common mode responses of the balanced filter are separated.This can achieve good common-mode rejection in the differential mode passband without additional loading of varactor diodes or microstrip branches.The center frequency adjustment range of the balanced filter under differential mode response is 0.84 GHz ? 1.46 GHz,the bandwidth adjustment range is 100 ? 160 MHz,and the common mode rejection reaches 20 d B in the differential mode passband.