Design of Microstrip Multifunction Integrated Diplexers With Frequency Division, Frequency Selection, and Power Division Functions

In this study, a novel circuit model was proposed for the design of multifunction integrated diplexers with frequency division, frequency selection, and power division functions. The proposed highly integrated multifunctional diplexer mainly comprises only two different-frequency multimode resonators and two isolation resistors, which results in a compact circuit size. The distributed coupling technique was adopted to integrate the two multimode resonators. One resonator was used to form a channel passband, and the other resonator was used to form another channel passband. Moreover, each channel passband can be independently designed and flexibly allocated. The two resistors loaded between the output feeding lines were introduced to improve the impedance matching of the output ports and the isolation between the output ports for each channel. The coupling structures, theoretical analysis, and design procedure for the proposed multifunction integrated diplexers are described. For demonstration, multifunction integrated diplexers with second-order and third-order filtering responses were designed and fabricated using microstrip technology. The experiment and simulation results were consistent and indicated satisfactory in-band and out-of-band performance.