A travelling-wave long sinusoidal slot in the broad face of a millimeter-wave (Ka-Band) rectangular waveguide is investigated. Similarities and differences with a same-shaped slot, but in the narrow face of the waveguide, which was investigated in a former study , are also discussed. It is observed that the most important difference between two antenna structures is the applied analytical model. It is found in measurements that the antenna with a broad face can only be described by an electric current model unlike the antenna with a narrow face where the magnetic current model agrees with measurements. In experimental study, some antenna parameters of the structure are demonstrated. The sinusoidal slot antenna investigated in this study has also a cross-polarized beam like the one in the narrow face of rectangular waveguide and a similar metallic grid polarizer is used like in the previous study to suppress this cross polarized beam. A suppression level up to 12 dB is reached. Antenna efficiency is calculated using S-parameters measurement and a remarkable increment is obtained after the polarizer is applied. (C) 2011 Elsevier GmbH. All rights reserved.