A low-profile, broadband, dual-linearly polarized offset dual-reflector antenna is presented for high-gain operation at W-band (75-110 GHz). The dual-linear polarization is achieved by exciting two orthogonal modes in an overmoded parallel plate waveguide (PPW), namely the quasi-TEM mode and the quasi-TE1 mode. The offset dual-reflector system is illuminated by a dual-mode corrugated feed horn in the PPW. Since the reflector system only collimates the beam in one plane, an exponentially flared section is integrated at the end of its radiating aperture to collimate the beam in the orthogonal plane. The antenna is built in Aluminum and fabricated as a split block using computer numerical control (CNC) milling. Experimental results show an input reflection coefficient better than -10 dB over a fractional bandwidth exceeding 38% for the two modes of operation. A good agreement is observed between simulated and measured far-field patterns for both operating modes, thus validating the antenna concept. The measured gain remains stable over the entire W-band with a maximum value of 28.8 dBi and 28.5 dBi for the quasi-TEM mode and the quasi-TE1 mode, respectively.