Design of Broadband Directional Coupler Based on Wiggly Line Structures

In this paper, the design of a broadband 5G (the fifth-generation) microstrip directional coupler is presented. This design adopts parallel coupling line structure based on regular wiggly line structure. The advantage of the wiggly line structure is the ability of increasing the coupling capacitance of parallel coupling line structure, achieve good impedance matching and greatly increase the working bandwidth of the directional coupler. Meanwhile, equivalent circuit is presented for the first time to describe its working principle. Adjusting the bending angle of the wiggly line can change the coupling capacitance and increase the degree of freedom, so as to obtain the best coupling capacitance to make a microstrip directional coupler with ultra-wideband, low insertion loss and miniaturization. Measured results show that return loss is more than 22 dB, port isolation is more than 25 dB, Insertion loss is less than 0.6 dB, therefore, the proposed design could provide a promising solution for 5G wireless communication systems. In order to verify the design, a broadband directional coupler in the frequency band of 2.3 – 5 GHz is simulated and designed by using the wiggly line structure, and the electromagnetic simulation software HFSS.