A Balanced Symmetrical Branch-Line Microstrip Coupler for 5G Applications

Symmetry in designing a microstrip coupler is crucial because it ensures balanced power division and minimizes unwanted coupling between the coupled lines. In this paper, a filtering branch-line coupler (BLC) with a simple symmetrical microstrip structure was designed, analyzed and fabricated. Based on a mathematical design procedure, the operating frequency was set at 5.2 GHz for WLAN and 5G applications. Moreover, an optimization method was used to improve the performance of the proposed design. It occupied an area of 83.2 mm(2). Its harmonics were suppressed up to 15.5 GHz with a maximum level of -15 dB. Meanwhile, the isolation was better than -28 dB. Another advantage of this design was its high phase balance, where the phase difference between its output ports was 270(circle) +/- 0.1(circle). To verify the design method and simulation results, the proposed coupler was fabricated and measured. The results show that all the simulation, design methods, and experimental results are in good agreement. Therefore, the proposed design can be easily used in designing high-performance microstrip-based communication systems.