Broadband Resistive Microstrip Directional Coupler

This paper presents a novel broadband directional resistive coupler. A simple, low-cost coupler is designed for a project to measure moisture content with a fast network analyzer. A novel approach to directional coupler design is presented, which eliminates the need for ferrites and enables a nearly frequency-independent coupling of -16 dB. The innovative design, which works on the Wheatstone Bridge principle, uses crossed ohmic resistors on a Roger 4003C substrate and has a high bandwidth from 1 to 12.6 GHz with a directivity over 20 dB. The study combines simulations and practical implementations to validate the performance of the proposed directional coupler. A circuit board has been developed that uses two high bandwidth directional couplers to demonstrate its potential for microwave applications.