  The design, fabrication, and measurement of a coax to double-ridged waveguide
launcher and horn antenna is presented. The novel launcher design employs two
symmetric field probes across the ridge gap to minimize spreading inductance in
the transition, and achieves better than 15 dB return loss over a 10:1
bandwidth. The aperture-matched horn uses a half-cosine transition into a
linear taper for the outer waveguide dimensions and ridge width, and a
power-law scaled gap in order to realize monotonically-varying cutoff
frequencies, thus avoiding the appearance of trapped mode resonances. It
achieves a nearly constant beamwidth in both E- and H-planes for an overall
directivity of about 16.5 dB from 10-100 GHz.
