slot antenna
Slot antennas belong to the omnidirectional antennas or omnidirectional radiators. Unlike other antennas, the electromagnetic waves are not radiated from conductive metal rods, but from slots of a waveguide.
The radiation is omnidirectional with horizontally polarized waves, although the radiation pattern differs by a few decibels from an ideal omnidirectional antenna. This radiation is achieved with a vertically arranged waveguide, which is provided with vertical slots from which the waves emerge. The arrangement of the slots, their number, length and spacing are decisive for the radiated wavelength, the radiation pattern and the efficiency of the slot antenna.
A slot antenna is a short-circuited waveguide at the end of which the wave is totally reflected and propagates as a standing wave in the waveguide. It can exit through the slots, which are arranged in vertical direction at a certain distance from the center axis of the waveguide at its broadside. The slots must be cut in the waveguide where the electromagnetic wave is particularly strong, and that is outside the center axis. The further the slots are arranged towards the edge, the more energy can be coupled out. The number of slots stands for the antenna gain, the distance for the wavelength. This results in a slot spacing of 12 cm at a frequency of 2.5 GHz. The antenna gain with 12 slots is about 10 dB.
Slot antennas are mainly used in microwave technology at frequencies between 1 GHz and 10 GHz.