3D corner antenna was designed in the 1970s, and is very often used, even for military radars. The design given here is a modification by Dragoslav Dobricic. The modifications from the original design are smaller antenna and lowering the impedance with one director (the same principle is used with Yagi’s) which has as a consequence improved gain.
The antenna is practical for many bands, with slight modifications. For higher frequencies, 3D corner is one of the best feeds for offset parabolic satellite dishes.
Its mechanism of work can be split into two parts: reflector and monopole with director.
Reflector is known as Corner Reflector – three perpendicular flat conducting surfaces that reflect waves. For the maximum gain, antenna should be tilted by 45°.
Corner Reflector surface showing how it reflects different waves from all three surfaces
Yagi-like part consists from a monopole and a director.
Reflector can be of any size, keeping in mind that its size directly affects gain. Its optimum size is at 2.8 wavelengths for one side, for which the gain is 18dBi. Larger reflectors do not give significant increase in gain. Very good 16dBi can be obtained with 1.8 wavelengths.
|Reflector side [λ]
Horizontal and Vertical radiation pattern
Reflector should be made from 1mm thick aluminum plate for higher frequencies, or with net wire with density 0.1 wavelengths for 23cm band or lower frequencies. In some cases, because of the high wind resistance of the antenna, a metal frame is required.
Legend (all dimensions are in mm):
- m – monopole length,
- d – director length,
- w – net wire density,
- r – minimum reflector thickness,
- h – director and monopole thickness,
- x – monopole distance from reflector surfaces,
- y – director distance from reflector surfaces,
- R – length of a side of the reflector.
It seems that antenna is not usable at lower frequencies, for example for 2m band, but that might not be true if we can make use of some existing construction. However, the reflector that gives over 12dBi is not likely to be used.