Applications of high frequency radiation, in the ranges of 30-300 GHz (millimeter-wave) and 300-1000 GHz (terahertz), require the development of specialized components, specifically low-loss waveguides and antennas. Conventional waveguide antennas must be flared in both lateral dimensions requiring a large space and are challenging to fabricate. Previous work has shown the promise of tapered dielectric rod antennas for their high transmission and ease of integration into waveguide systems. However, practical repeatable machining techniques are neglected. This work develops the design, manufacturing, and analysis of step-tapered waveguide inserts and antennas, fabricated via controlled acid etching of high resistivity silicon, optimized for good transmission in the range of 75-110 GHz.