A planar millimeter-wave high gain multi-beam antenna with 5 beams in azimuth based on substrate integrated waveguide (SIW) fed antipodal linear tapered slot antennas (ALTSAs) and a coplanar cylindrical dielectric lens is proposed and implemented at 28 GHz. Both the antennas and the lens are fabricated on a single planar substrate covered by high permittivity substrate with a radius of 0.5λ0 . A prototype with 5 beams has been designed, fabricated and measured. The measured gain of each beam is around 20 dB which is about 6.5 dB higher than that of the ALTSA element. The gain enhanced multi-beam lens antenna is with the advantages of high gain, good beam uniformity, higher isolation between ports, low cost, and easily be integrated with other coplanar circuits etc.