Integrated Microstrip-to-Waveguide Transition With Microstrip Directional Coupler

In this letter, a novel design of microstrip-to-waveguide transition integrated with a microstrip directional coupler (MDC) is presented. This integration was designed, so that the MDC not only does not add extra loss to the main signal but also provides high directivity. The measurement results of the proposed structures, designed at 5.8 GHz, demonstrate less than 0.25-dB insertion loss, about 38-dB coupling factor, and greater than 20-dB return loss as well as 15-dB directivity for 20% fractional bandwidth. This structure can be therefore seen as a suitable candidate for high-power transmitter modules for which insertion loss at the output stage is a critical issue and a high coupling factor is required.