AFSIW-to-Microstrip Directional Coupler for High-Performance Systems on Substrate

Very recently, the relatively high power handling capability of the high performance air-filled substrate integrated waveguide (AFSIW) technology has been experimentally demonstrated and reported in literature. This important milestone confirms the interest of this novel technology for the design of low cost, high performance, self-packaged millimetre wave transmitters. In the purpose of designing such AFSIW systems with a required integrated power monitoring capability, an AFSIW to microstrip directional coupler is presented in this paper. The proposed coupler topology is inspired from the Moreno directional coupler structure to couple some of the high power signal of an inner layer AFSIW to a top layer microstrip line. For demonstration purposes, a wideband 25 dB coupler operating from 26 to 35 GHz has been fabricated and measured. It achieves a measured insertion loss, coupling and isolation of 0.6 ±0.2 dB, 18.7 ±1.3 dB and 44.7 ±13.7 dB, respectively.