Two linearly polarized millimeter wave planar leaky wave antennas designed for broadside radiation at 61 GHz with high gain and low sidelobes of radiation patterns are presented. Both antennas have a center-fed single-layer structure composed of two one-dimensional periodic symmetric arrays of metal strips of variable width on a grounded dielectric waveguide, but with different excitation devices for the dielectric waveguide, represented by a microstrip combline and a waveguide-fed linear substrate integrated slotted waveguide array. The antennas exhibit low return loss, antenna gain 26-27 dBi and radiation pattern sidelobe level in both E- and H-planes, not exceeding −20 dB. The antennas may be used, for example, in security sensors.