Radiation is a term that describes the intensity of the electromagnetic waves transmitted or received by an antenna. In any antenna illustration, the diagram depicting the antenna's radiation characteristics is known as its radiation pattern. By observing the radiation pattern, one can intuitively understand the antenna's functionality and directivity. The power radiated by the antenna affects both the near-field and far-field regions.
Graphically, radiation can be expressed as a function of the antenna's angular position and radial distance. This mathematical function describes the radiation characteristics of the antenna, typically represented by the electric field E(θ,ϕ) and the magnetic field H(θ,ϕ) in spherical coordinates.
Radiation Pattern
The energy radiated by an antenna is characterized by its radiation pattern. A radiation pattern is a graphical representation of how the radiated energy is distributed in space as a function of direction.Let’s now take a look at the typical patterns of energy radiation.
The figure above shows the radiation pattern of a dipole antenna. The radiated energy is represented by the pattern plotted along specific directions, with arrows indicating the direction of radiation. Radiation patterns can be classified as field patterns or power patterns.
•The field pattern is a function of the electric and magnetic fields and is typically plotted on a logarithmic scale.
•The power pattern is a function of the square of the electric and magnetic field magnitudes and is typically plotted on a logarithmic scale, i.e., in dB.
3D Radiation Pattern
A 3D radiation pattern is a three-dimensional graph plotted in spherical coordinates (r,θ,ϕ), with its origin at the center of the coordinate system. It appears as shown in the figure below —
The figure shows a 3D radiation pattern of an omnidirectional antenna, clearly illustrating the three coordinate axes (x, y, z).
2D Radiation Pattern
A 2D radiation pattern can be obtained by splitting the 3D pattern into horizontal and vertical planes. The resulting two patterns are referred to as the horizontal plane pattern and the vertical plane pattern, respectively.
As mentioned above, the figure shows the radiation pattern of an omnidirectional antenna in the H‑plane and V‑plane. The H‑plane represents the horizontal pattern, while the V‑plane represents the vertical pattern.
Lobe Formation
In the representation of radiation patterns, various shapes are often encountered, which indicate the major and minor radiation regions. These regions help evaluate the antenna's radiation efficiency.For a better understanding, refer to the figure below, which illustrates the radiation pattern of a dipole antenna.
In a radiation pattern, there are typically a main lobe, side lobes, and a back lobe.
•The main part of the radiated field, which covers a large area, is called the main lobe or main beam. This is where the maximum radiated energy is concentrated, and its direction indicates the directivity of the antenna.
•The other parts of the radiation pattern that are distributed laterally are called side lobes or minor lobes. These are regions where power is wasted.
•Additionally, there is a lobe oriented exactly opposite to the main lobe, known as the back lobe, which is also a type of side lobe. A significant amount of energy is wasted here as well.
Example
If an antenna used in a radar system generates side lobes, target tracking becomes extremely difficult. This is because these side lobes introduce false targets. Distinguishing real targets from spurious ones is very troublesome. Therefore, to improve performance and conserve energy, these side lobes must be suppressed or eliminated.
Remedial Measure
The radiated energy wasted in this way needs to be utilized. If these minor lobes can be eliminated and that energy redirected into one direction—namely, toward the main lobe—the directivity of the antenna increases, thereby enhancing its performance.
Types of Radiation Patterns
Common types of radiation patterns include:
•Omnidirectional Pattern (also called nondirectional pattern): This pattern typically appears as a donut shape in a 3D view, while in a 2D view it forms a figure‑eight pattern.
•Pencil‑Beam Pattern: The beam exhibits a sharp, directional pencil‑like shape.
•Fan‑Beam Pattern: The beam takes on a fan‑shaped pattern.
•Shaped‑Beam Pattern: A non‑uniform beam with no regular pattern is called a shaped‑beam pattern.
The reference point for all these types of radiation is isotropic radiation. Even though isotropic radiation is not physically realizable, it remains an important reference.
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Post time: Apr-10-2026
