A plastic, waveguide-fed, horn antenna is manufactured using a three-dimensional (3D), polymeric micro hot embossing process. Two cavity resonators may be designed to reduce the impedance mismatch between the pyramidal horn antenna and the feeding waveguide. The waveguide-fed antenna may be fabricated using a self-aligned 3D plastic hot embossing process followed by a selective electroplating and sealing process to coat an approximately 8 μm-thick gold layer around the internal surfaces of the system. As such, this plastic, low-cost manufacturing process may be used to replace the expensive metallic components for millimeter-wave systems and provides a scalable and integrated process for manufacturing an array of antenna.