—This　paper　proposes　an　improved　design　of　a　W-band　slot　array　antenna,　based　on　a　ridge　waveguide　and　a　rectangular　micro-coaxial　line.　To　achieve　a　high　gain　and　wideband　antenna　with　element　spacing　smaller　than　half　a　wavelength,　a　broadband　transition　of　rectangular　coaxial　line　to　ridge　waveguide　was　designed.　The　improved　design　has　bandwidth　around　15.4　GHz　(94.8　GHz–　110.2　GHz),　and　the　simulated　realized　gain　is　about　14.6　dB.　Measured　results　of　the　fabricated　antenna　demonstrate　that　the　gain　at　theta　=　0◦,　and　VSWR　is　better　than　13　dB　and　2.7,　respectively.　The　antenna’s　size　is　about　12　mm　×　5.5　mm　×　0.46　mm.　©　2023,　Electromagnetics　Academy.　All　rights　reserved.