Antenna Theory - Aperture

An Antenna with an aperture at the end can be termed as an Aperture antenna. Waveguide is an example of aperture antenna. The edge of a transmission pne when terminated with an opening, radiates energy. This opening which is an aperture, makes it an Aperture antenna.

The main types of aperture antennas are −

Wave guide antenna

Horn antenna

Slot antenna

Let us now have a look at these types of aperture antennas.

Waveguide Antenna

A Waveguide is capable of radiating energy when excited at one end and opened at the other end. The radiation in wave guide is greater than a two-wire transmission pne.

Frequency Range

The operational frequency range of a wave guide is around 300MHz to 300GHz. This antenna works in UHF and EHF frequency ranges. The following image shows a waveguide.

This waveguide with terminated end, acts as an antenna. But only a small portion of the energy is radiated while a large portion of it gets reflected back in the open circuit. It means VSWR (voltage standing wave ratio, discussed in basic parameters chapter) value increases. The diffraction around the waveguide provides poor radiation and non-directive radiation pattern.

Radiation Pattern

The radiation of waveguide antenna is poor and the pattern is non-directive, which means omni-directional. An omni-directional pattern is the one which has no certain directivity but radiates in all directions, hence it is called as non-directive radiation pattern.

The above figure shows a top section view of an omni-directional pattern, which is also called as non-directional pattern. The two-dimensional view is a figure-of-eight pattern, as we already know.

Advantages

The following are the advantages of Aperture antenna −

Radiation is greater than two-wire transmission pne

Radiation is Omni-directional

Disadvantages

The following are the disadvantages of Aperture antenna −

VSWR increases

Poor radiation

Apppcations

The following are the apppcations of Aperture antenna −

Micro wave apppcations

Surface search radar apppcations

The waveguide antenna has to be further modified to achieve better performance, which results in the formation of Horn antenna.