Abstract: Based on the substrate integrated waveguide （SIW） technology and the standard single-layer printed circuit board （PCB） process, a multi-beam slot array antenna at W-band is designed, fabricated and measured. For the measurement purpose, the vertical transition between SIW and the standard metallic wavegnide is designed using full-wave simulations in the first step. Secondly, the SIW slot array antenna is designed using the theoretical method as well as the full-wave simulations for optimization. The feeding network of the multi-beam antenna is realized by using a 4 × 4 Butler matrix on the same layer of the antenna, in which the couplers and phase smilers are all designed with the SIW technology. Finally, the simulated and measured results of the whole W-band multi-beam antenna are presented. The measured and the simulation results, which are in good agreement, indicate that the multi-beam antenna can be realized in relatively high frequency band of millimeter waves using the SIW technology and tow-cost single-layer PCB process.