Antenna Theory Slot - Antenna Theory

What is Antenna Theory Slot?

Slot Antenna is an instance of Aperture antenna. A rectangular slot is prepared on the conducting sheet. These slot antennas can be designed by merely creating a cut on the surface, where they are attached on.

Frequency Range

The frequency range used for the application of Slot antenna is 300 MHz to 30 GHz. It works in UHF and SHF frequency ranges.

Construction & Working of Slot Antennas

The usage of slot antennas is well assumed over its working principle. Let us have a look at the arrangement of a slot antenna.

When a countless directing sheet is prepared a rectangular cut and the fields are motivated in the aperture (which is called as a slot), it is termed as Slot antenna. This can be assumed by detecting the image of a slot antenna. The resulting image displays the model of a Slot antenna.

The functioning of Slot Antenna can be simply assumed through Babinet’s principle of optics. This idea gives an outline to the slot antennas.

Babinet’s Principle

Babinet’s principle states that- “When the field behind a screen with an opening is added to the field of a complementary structure, the sum is equal to the field when there is no screen”.

The beyond images obviously clarify the principle. In all the regions, which are non-collinear with the beam, the above two screens, in figures 1 & 2, produce the same diffraction pattern.

Case 1 − Think through a light source and a conducting plane (field) with an aperture before a screen. The light does not pass through the opaque area, but passes through the aperture.

Case 2 − Think through the light source and a conducting plane of the size of the aperture in the previous case, being held against the screen. The light does not pass through the plane but through the remaining portion.

Case 3 − Combine these two conducting planes of both the cases and put before the light source. The screen is not located to detect the resulting combination. The effect of screen gets nullified.

Working of Slot Antenna

This principle of optics is applied to electromagnetic waves for the wave to get radiated. It is correct that when a HF field happens across a narrow slot in a conducting plane, the energy is radiated.

The image displays a slot antenna, which clarifies well about its working.

Think through an infinite plane directing screen is taken and pierced with apertures of anticipated shape and size and this will be the screen of slot antenna. Another screen is measured swapping the places of aperture and screen area which is the complementary screen.
These two screens are said to be complementary as they result in complete infinite metal screen. Currently, this converts the slot antenna. The terminal impedance is quite desirable for the radiation.

Radiation Pattern

The radiation pattern of the Slot antenna is Omni-directional, just like a half-wave dipole antenna.Have a look at the resulting image. It displays the radiation pattern of Slot antenna drawn in Horizontal and Vertical planes correspondingly



The resulting are the advantages of Slot antenna −

  • It can be fabricated and concealed within metallic objects
  • It can provide covert communications with a small transmitter


The following are the disadvantages of Slot antenna −

  • Higher cross-polarization levels
  • Lower radiation efficiency


The following are the applications of Slot antenna −

  • Commonly for radar navigational purposes
  • Used as an array fed by a wave guide

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