The radiation pattern (RP) of a transmitting antenna characterizes the intensity of radiation (reception) of the antenna in various directions. For a transmitting antenna, the RP is determined by the field strength in the electric component of the electromagnetic field or by its power level. The radiation pattern describes how the antenna radiates or receives electromagnetic waves in different directions. It shows the distribution of radiation strength or reception sensitivity of the antenna depending on the angle or direction relative to the antenna axis.
The RP can be represented as a graph or a polar plot, where the vector radius indicates the power or signal level in a given direction. Its shape may vary depending on the antenna design. Some antennas may have a narrow radiation pattern, meaning they transmit or receive signals only within a narrow range of directions, while others may have a wide RP or be omnidirectional.
Typically, the antenna radiation pattern is plotted in a polar coordinate system. The direction of maximum radiation is called the main lobe of the antenna. The remaining lobes of the antenna RP are side lobes. The lobe radiating in the opposite direction to the main direction is called the back lobe of the antenna RP. Radiation patterns are plotted in both vertical and horizontal planes.
Normalized radiation patterns are often used to show the antenna's ability to transmit (receive) in a given direction regardless of the input power. In a normalized radiation pattern, the magnitude of the main lobe is taken as unity, and side lobes are plotted to scale relative to the main one.
The antenna radiation pattern is an important parameter in the design of radio systems, as it affects communication range, radiation directivity, and signal reception. Knowing the antenna RP makes it possible to determine how the antenna will behave in different directions and how it will interact with other antennas and the surrounding environment.
Amplitude Radiation Pattern
The amplitude RP by field is the dependence of field amplitude on angular coordinates. The amplitude RP is a three-dimensional spatial surface. For antennas with linear polarization, the vertical plane corresponds to the E-vector plane and the horizontal plane to the H-vector plane (E-plane and H-plane).
Important characteristics of RPs with a pronounced preferred radiation region include the direction of the main maximum. The RP tilt angle (amateur radio jargon) is the angle relative to the horizon at which the maximum of the main lobe of the antenna radiation pattern is directed.
The beamwidth of the radiation pattern is equal to the angular width of the main lobe within which the radiation power is at least half of the maximum power.
One of the main indicators of the RP is the directivity factor (DF) of the antenna.
Polarization Radiation Pattern
The polarization RP is a unit polarization vector aligned with the direction of the antenna's electric field vector, describing the dependence of its orientation on angular coordinates over time.
The type of polarization of the field radiated by the antenna is determined by the shape of the curve traced by the end of the E vector during one period of RF oscillations in a plane perpendicular to the direction toward the observation point:
1) Linear
2) Rotating
a) Circular
b) Elliptical
clockwise – right-handed
counterclockwise – left-handed.
Isotropic radiator, Antenna, Directivity factor, DF, Electromagnetic wave polarization