Short Backfire Antenna

[Admin 2425]

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. The bottom disc has the diameter of two wavelengths, and its collar (edge) is quarter the wavelength tall. 

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

Short backfire antennas are used in some satellites, and in high-frequency (short-wavelength) communication equipment (often for communication with satellites) on ships and other applications where rugged construction is an advantage. They are also used for wireless LANs. The SBF antenna was invented by Dr. Hermann W. Ehrenspeck 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.

The bandwidth of the antenna can be increased by using a conical main reflector instead of a flat one.

The antenna proposed by me, presents an active element consisting of a patch antenna and a perpendicular butterfly antenna, both made of PCB.