Design and Optimization of Broadband Directional Couplers and Power Dividers Using SIW Technology

This paper introduces a streamlined design that includes a broadband directional coupler, a set of three-port union-T power dividers, and several microstrip transitions. These components leverage substrate-integrated waveguide (SIW) technology, operating across multiple frequency bands and offering equal power distribution in all output ports. The directional coupler, dividers, and transitions underwent a comprehensive design, simulation, and optimization process using CST Microwave Studio. A crucial aspect of the SIW design was the meticulous consideration of transitions necessary to achieve optimal matching between the SIW devices and the connected structure (such as microstrip or SMA connectors). This approach ensured a consistent focus on seamless integration. For validation purposes, the devices were manufactured physically using the RF-5880 substrate, which works with frequencies up to 40 GHz. The experimental results were then compared with simulations conducted in CST Microwave Studio, validating the prototypes. The findings confirmed that the design performs as intended, exhibiting expected behavior and showcasing a notable agreement between the simulation and experimental results. Furthermore, the designs were treated as standard rectangular waveguides, functioning within microwave and millimeter wave frequencies ranging from 8 to 40 GHz. The paper not only outlines these designs but also proposes practical dimensions for SIW technology, offering a tangible guide for the realization of these devices.