Design and Fabrication of Adjustable Reflectionless Microstrip Diplexer for L-Band

In this study, an adjustable reflectionless diplexer is designed and fabricated for the Lband based on microstrip transmission lines. The proposed diplexer can separate and combine different frequencies within the L-band frequency range. The equations and theoretical process of the structure can be proved from coupling matrix and even/odd mode circuit analysis. In this design, our aim is that the proposed diplexer not only has low insertion loss and proper return loss in the channels’ stopband but also can change the channels’ frequency. The physical specifications are calculated proportionally to the central frequency based on the coupling coefficients and diagram. Also, frequency adjustability is achieved by connecting the varactor diode to the structure’s resonator. The proposed structure can be used in the frequency range of 1.6–2.2 GHz. Furthermore, the measured return losses in the stopband and passband are 8 dB and 13 dB, respectively. In this paper, all simulations are performed by ADS software. © 2022, Electromagnetics Academy. All rights reserved.