DUAL‐BAND BALANCED FILTERS BASED ON LOADED AND COUPLED RESONATORS

This chapter addresses the analysis and design of dual‐band balanced filters using loaded and coupled resonators. Two objectives must be carefully addressed in the design of such filters: the construction of two differential‐mode passbands and the suppression of the common‐mode signal inside and outside of the two differential‐mode passbands. Two types of resonators, that is, uniform impedance resonators and stepped‐impedance resonators, are primarily used for the implementation of dual‐band balanced filters. The even‐mode resonant frequency can be controlled through the uniform impedance resonator with a center‐loaded stub. The loaded capacitor, inductor, and open/short stub are primarily used to control the even‐mode resonant frequency, and the loaded resistor is used in even‐mode absorption. The chapter shows a typical center‐loaded uniform impedance resonator in which the center‐loaded element can be lumped element or stub.