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Slot Antenna

Aperture Antennas

A narrow slot cut in a conducting sheet that radiates like a complementary dipole.

Band: VHF to SHF
Gain: ~2-5 dBi (single slot)
Polarization: Linear (perpendicular to the slot)

Photos

Real-world photo of a Slot Antenna in use — Real-world example. Source: Wikimedia Commons (Public domain; Ciacho5).

Radiation / wave patterns

Idealized radiation pattern of the Slot Antenna — Idealized azimuth radiation pattern (illustrative, generated). Radial scale in dB.

How & why it works

Cutting a half-wavelength slot in a large conducting surface produces an antenna that is the electromagnetic 'complement' of a dipole: by Babinet's principle the slot radiates much like a dipole would, but with the electric and magnetic field roles swapped. Because the radiator is just an opening, it can be flush-mounted into an aircraft skin, a vehicle panel, or a waveguide wall without protruding, and arrays of slots cut into waveguide make compact, rugged beam-forming antennas.

Real-world uses

Aircraft and missile flush antennas, radar slot arrays, and conformal installations.