A single-layer corporate-fed substrate integrated waveguide slot array antenna is newly proposed and verified. It is characterized by low profile, easy fabrication, low cost, low sidelobes, wideband operation, and high efficiency. A V-band <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16\times 16$ </tex-math></inline-formula> -element array with uniform excitation is designed for demonstration. The radiating elements and feeding waveguides are arranged within a single-layer substrate, whose dielectric constant and loss tangent are appropriately selected. By adopting the full-corporate feed, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16\times 16$ </tex-math></inline-formula> radiating slots are excited by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16\times 16$ </tex-math></inline-formula> output ports of the feeding circuit, which is composed of cascaded H-plane T-junctions. For further bandwidth improvement, a metal grid plate is introduced on the top of the radiating slots. The test antenna is fabricated by the conventional PCB process. The measured bandwidth for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11}\vert < -10$ </tex-math></inline-formula> dB is 16.2%, fully covering the 57–67 GHz frequency range. Meanwhile, the measured antenna gain higher than 30 dBi associated with the antenna efficiency higher than 45% is achieved over the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$58-65$ </tex-math></inline-formula> GHz frequency range.