A dual-band, dielectric-loaded horn antenna is analyzed with XFdtd to demonstrate performance at 94 and 340 GHz. The antenna consists of a dual port rectangular waveguide section at the feed end that transitions to a circular waveguide and then a conical horn at the output side. The horn structure radiates the 94 GHz signal while a tapered dielectric block in the center of the structure guides the 340 GHz fields. The antenna has a strong single beam with a peak gain around 18 dBi that is symmetrical in the E and H planes.