What is a slot antenna?
A slot antenna is a narrow aperture cut in a conducting sheet. By Babinet’s principle, a slot is the complement of a strip dipole: its fields are those of the dipole with E and H interchanged, and its impedance is Zslot = η0²/(4Zdipole). A half-wave slot in an infinite sheet therefore has an impedance of about 363 − j211 Ω.[1][2]
What pattern does a slot have?
A slot in an infinite plane radiates bidirectionally with the dipole’s pattern but with polarization rotated 90°: a horizontal slot radiates vertical polarization. A cavity behind the slot makes it unidirectional and is used for flush-mounted aircraft antennas.[2]
How are slots fed?
By a coaxial line across the slot offset from the center (impedance falls toward the ends), by a microstrip line crossing the slot (as in aperture-coupled patches), or by a waveguide in which the slot interrupts wall currents.[1]
What are waveguide slot arrays?
Longitudinal slots in the broad wall of a rectangular waveguide, offset from the centerline, radiate with an amplitude set by the offset. Arrays of them form efficient, low-loss planar antennas used in radar and point-to-point links.[3][4]
Frequently asked questions
Is a slot magnetic or electric?
It behaves as a magnetic dipole, the dual of the strip dipole.
Can a slot be printed?
Yes; printed slots in PCB ground planes are common, including tapered slot (Vivaldi) antennas.
Why are slot arrays used in radar?
They are low-loss, rugged and allow precise amplitude tapers for low sidelobes.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.
- “Antennas for All Applications, 3rd ed.”. J. D. Kraus and R. J. Marhefka, McGraw-Hill. 2002.
- “Introduction to Radar Systems, 3rd ed.”. M. I. Skolnik, McGraw-Hill. 2001.
- “Antenna Engineering Handbook, 4th ed.”. J. L. Volakis (ed.), McGraw-Hill. 2007.