High-Order Resonating Cavity-Backed Slot Antenna Array Based on Contactless Air-Filled Substrate-Integrated Waveguide and Transition to Inverted Grounded Coplanar Gap Waveguide

A contactless planar slot antenna array is proposed in this article with high realized radiation efficiency. To simplify the feeding network, slot elements in the subarray are excited by the back cavity with a high-order resonating mode (the TE430 mode). To reduce the loss and increase the efficiency, the entire antenna array, including the resonating cavity and feeding network, is realized by low-loss contactless air-filled substrate-integrated waveguide (CLAF-SIW). In addition, an inverted grounded coplanar gap waveguide (IGCPGW) is first proposed for measurements using the contactless ridge substrate-integrated waveguide (CLRSIW) as the transition to connect the CLAF-SIW. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 6$ </tex-math></inline-formula> slot array with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> subarrays is fabricated and fastened only by metal screws. From 36.92 to 40 GHz, the measured reflection coefficient is better than −10 dB, and the realized radiation efficiency is greater than 78.6%. The measured peak realized radiation efficiency is 89.4% at 38 GHz.