AN4190

Antenna theory

Doc ID 023812 Rev 1

5/29

radiation pattern can sometimes obfuscate details. In practice, a three-dimensional plot of a

radiation pattern is of limited value in presenting quantitative information. Therefore, two-

dimensional “cuts” of the radiation pattern are often presented. In particular, cuts in the so-

called E and H planes are often presented.

1.1.1

Isotropic, directional and omnidirectional patterns

An isotropic radiator is defined as a “hypothetical” lossless antenna having equal radiation in

all directions. Although it is ideal and not physically realizable, it is taken as a reference for

expressing the directive properties of actual antennas.

A directional antenna is one having the property of radiating or receiving electromagnetic

waves more effectively in some directions than in others.

An omnidirectional antenna is defined as one having an essentially non-directional pattern

in a given plane and a directional pattern in any orthogonal plane. An omnidirectional

pattern is a special type of directional pattern. An example of an antenna with an

omnidirectional radiation pattern in the x - y plane is shown in Figure 2.

Figure 2.

x - y plane omnidirectional antenna pattern

1.1.2

Principal patterns

For a linearly polarized antenna, performance is often described in terms of its principal E

and H plane patterns.

The E plane is defined as the plane containing the electric field vector and the direction of

maximum radiation.

The H plane is the plane containing the magnetic field vector and the direction of a

maximum radiation.

The principal E and H planes are orthogonal planes. It is often sufficient to examine only E

and H plane cuts of the three-dimensional radiation pattern. An example of E and H plane

radiation patterns is shown in Figure 3.

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