Slotted waveguide

The slot antenna was submitted by Dr. Heinrich Bosse in 1951 for the first time as a patent DE894573 C in Germany and is a special type of antenna that follows an unusual principle: Usually antennas are designed so that a metallic structure in the space of air ( as a non-conductor is surrounded ) and so radiates the waves. Of the slot radiators, however, is an interruption of a metallic structure (for example, a metal plate of a waveguide, etc.), which provides for the emission of waves. This break often follows the principle of the dipole, but may theoretically have any other geometry.

A dipole consisting of a conductor in a dielectric (typically air). In the reverse case, you can cut this conductor as a negative into a surface conductor. Physics is based on the Babinet's principle here that describes a duality of field propagation in metals and dielectrics, if they disrupt their structures are mutually exclusive. The Babinet's principle is originally from the optics, but can be transmitted to the antenna technology, as it makes no restriction on the frequency range and it is in light like antennas to processes associated with electromagnetic waves.

One uses slot antennas especially for high frequencies at which dipoles are difficult to manufacture or in special applications. Such slot antennas in the aircraft industry are particularly suitable, because they do not protrude beyond the outer skin of an aircraft. In a tin can so whole groups of parallel dipoles contribute. The entry points and conditions similar to those of normal dipoles.

Another construction is based on a waveguide, are milled in the slots at a distance of half the wavelength. On the right is shown an antenna for 2.4 GHz. At a wavelength of about 12 cm with an antenna 16 elements reaches nearly a length of 2 m. The antenna gain of an array with 16 emitters is 12-14 dBd. The slots must be fitted so that they interfere as much as possible in the waveguide propagating field. With this disorder the field from the waveguide emerges, breaks away from this and spreads out into the room.

The radar antennas in the shipping industry are mostly also waveguide slot antennas, recognizable by the straight design. The antenna gain is indeed lower than that of a satellite dish, but the production is cheaper.