Short backfire antenna

A short backfire antenna (or short back-fire, SBA, SBF or SBFA) is a type of a directional antenna, characterized by high gain, relatively small size, and narrow band.

It has a shape of a disc with a straight edge, with a vertical pillar with a dipole acting as the driven element in roughly the middle and a conductive disc at the top acting as a sub-reflector.

[1] This structure behaves like a resonant cavity, resulting in a substantial gain in small space.

The SBF antenna was invented by Dr. Hermann W. Ehrenspeck[2] of Air Force Cambridge Research Labs based at Hanscom Air Force Base in Bedford, MA and was used for, among other purposes, to provide Tactical Satellite Communications for U.S. Army ground forces due to the SBF's portability and gain.

[1] Short backfire antennas are able to achieve high aperture efficiencies, at right cavity size even beyond 100%.