Design of filtering coupled-line trans-directional coupler with broadband bandpass response

—In the paper, a filtering coupled-line trans-directional (CL-TRD) coupler with broadband bandpass response is presented for the first time. It is composed of three sections of coupled lines, four transmission lines, and four shunt stubs. Design equations of the proposed filtering CL-TRD coupler are derived using the even-and odd-mode analysis. For demonstration, a prototype operating at 2.4 GHz is designed, fabricated, and measured. Under the criterion of |S11| < −10 dB, the measured bandpass bandwidth is 41.7%. In this bandwidth, the output port phase difference is within 90◦ ± 5◦. Besides, two stopbands (0.91 GHz ∼ 1.89 GHz and 3.36 GHz ∼ 4.3 GHz) are obtained on both sides of the passband with sharp rejection. The measurements and comparisons results show that smaller size, wider bandwidth, and easier fabrication than the reported filtering couplers are exhibited by the proposed filtering CL-TRD coupler. It indicates that a good candidate for filtering-coupling applications can be served by the proposed coupler. © 2021, Electromagnetics Academy. All rights reserved.