In this work, a concept for designing two dimensional scan circularly polarized antenna array is introduced for advanced millimeter-wave imaging and sensing systems. Three-dimensional (3-D) integrated architecture of circularly polarized (CP) antenna system is studied, realized and demonstrated in substrate integrated waveguide (SIW) technology. Axial ratio bandwidth of a well-known slot antenna is increased by replacing each slot with antipodal linearly tapered slot antenna (ALTSA). Travelling-wave topology is chosen to implement a two-port CP antenna. Measured axial ratio (AR) bandwidth is less than 3 dB from 33.5 GHz to 37 GHz. Measured beam direction ranges from −16° to +16° with frequency scanning from 33.7 GHz to 37.3 GHz.