Microwave fracturing has a great potential in assisting excavators in breaking hard and abrasive rocks. The key to utilizing this technology is to design an antenna that is capable of fracturing low loss rocks at relatively low power levels in a short duration. This article presents the design of a dielectric-loaded converging waveguide antenna (DLCWA) composed of a pyramid-shaped alumina infilling and a converging waveguide. The design of the DLCWA is optimized based on the maximum temperature, the high-temperature volume, and the effective working distance. To validate the design, a prototype antenna is manufactured and used for microwave heating and fracturing tests. The numerical simulations and experimental tests demonstrate that the designed DLCWA has unparalleled advantages at the radiation distance of 0–30 mm over the WR430 waveguide and a 30 mm unloaded converging waveguide antenna. With improved performance in power focusing and directivity, the proposed DLCWA is by far the most suitable antenna for microwave fracturing of low loss hard rocks.