What is the radiation pattern?

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What Is The Radiation Pattern?
Antenna radiation pattern is also called antenna pattern, far-field pattern. The antenna gain
cannot be obtained from the radiation pattern, but the directivity coefficient is obtained from the
radiation pattern. Antenna gain = directivity factor * antenna efficiency. Therefore, it is certain
that the directional coefficient is greater than the gain.
The antenna gain is mainly manifested through the test of the radiation pattern. There are many
kinds of test systems for testing the pattern. That is the microwave chamber. And the result of the
test in the darkroom is only a result of comparison with the ideal symmetrical vibrator. It is
known that the gain of an ideal symmetrical oscillator is 2.15dB. In this way, the gain of the
antenna can be calculated according to the test level.
G=D*N%.
In general, the efficiency of the antenna is not 100%, so G<d. When calculating the directional
coefficient D of the antenna, it is usually calculated based on the lobe width of the main lobe
shown on the directional pattern, such as the half-power lobe width, that is, the lobe width at
which the level drops by 3dB.
Antenna gain
Antenna gain refers to the ratio of the power density of the signal generated by the actual
antenna and the ideal radiating unit at the same point in space under the condition of equal
input power. It quantitatively describes the degree to which an antenna concentrates the input
power and radiates it.
The gain obviously has a close relationship with the antenna radiation pattern. The narrower
main lobe of the pattern ,and the smaller the side lobe, the higher the gain. Antenna gain is used
to measure the ability of an antenna to send and receive signals in a specific direction. It is one of
the most important parameters for selecting a base station antenna.
The increase in gain mainly relies on reducing the beamwidth of the radiation on the vertical
plane, while maintaining the omnidirectional radiation performance on the horizontal plane. The
antenna gain is extremely important to the operating quality of the mobile communication
system because it determines the signal level at the edge of the cell. Increasing the gain can
increase the coverage of the network in a certain direction, or increase the gain margin within a
certain range.
Any cellular system is a two-way process. Increasing the gain of the antenna can reduce the
margin of the two-way system gain budget at the same time. In addition, the parameters
representing the antenna gain are dBd and dBi. DBi is the gain relative to the point source
antenna, and the radiation in each direction is uniform; dBd relative to the gain of the
symmetrical array antenna is dBi=dBd+2.15.
Under the same conditions, the higher the gain, the farther the radio wave travels. Generally, the
antenna gain of a GSM directional base station is 18dBi, and the omnidirectional antenna gain is
11dBi.
Characteristic parameters of the antenna radiation pattern

C&T RF Antennas Inc
 Coco Lu (+86)13412239096
In order to facilitate the comparison of the pattern characteristics of various antennas, some
characteristic parameters need to be specified. Mainly include main lobe width, sidelobe level,
front-to-back ratio, direction coefficient, etc.
1. Main lobe width
It is a physical quantity that measures the sharpness of the antenna's maximum radiation area.
The width between the two half-power points of the main lobe of the antenna pattern is usually
taken.
2. Sidelobe level
Refers to the level of the first side lobe closest to the main lobe and the highest level, generally
expressed in decibels.
3. Front-to-back ratio
Refers to the ratio of the maximum radiation direction (forward) level to the opposite direction
(backward) level, usually in decibels.
4. Directivity coefficient
At a certain distance from the antenna, the ratio of the radiation power flow density of the
antenna in the maximum radiation direction to the radiation power flow density of an ideal
non-directional antenna with the same radiation power at the same distance.
Antenna radiation pattern drawing
The antenna radiation pattern is a graph that characterizes the relationship between the
antenna's radiation characteristics (field strength amplitude, phase, polarization) and the spatial
angle. The complete pattern is a three-dimensional space figure, as shown in the figure below.
It is drawn by taking the antenna phase center as the sphere center (coordinate origin) and
measuring its radiation characteristics point by point on a spherical surface with a sufficiently
large radius r. Measure the amplitude of the field strength to obtain the field strength pattern;
measure the power to get the power pattern; measure the polarization to get the polarization
pattern; measure the phase to get the phase pattern.
The surveying and mapping of the three-dimensional spatial pattern are very troublesome. In
actual work, it is generally only necessary to measure the pattern of the horizontal plane and the
vertical plane (that is, the XY plane and the XZ plane).

C&T RF Antennas Inc
 Coco Lu (+86)13412239096
Figure 1 Coordinates of the measurement pattern
The antenna pattern can be drawn in polar coordinates or rectangular coordinates. The
characteristics of the polar coordinate pattern are intuitive and simple, and the spatial
distribution characteristics of the antenna radiation field strength can be directly seen from the
pattern.
But when the main lobe of the antenna pattern is narrow and the sidelobe level is low, the
Cartesian coordinate drawing method shows greater advantages. Because the abscissa
representing the angle and the ordinate representing the radiation intensity can be arbitrarily
selected, for example, even the width of the main lobe of less than 1°can be clearly expressed,
but the polar coordinates cannot be drawn.
Figure 2 shows two coordinate representations of the same antenna radiation pattern.

C&T RF Antennas Inc
 Coco Lu (+86)13412239096
Figure 2 Representation of the pattern (a) Polar coordinates (b) Cartesian coordinates
Generally, when drawing a directional diagram, it is normalized, that is, the radial length (polar
coordinates) or the ordinate value (rectangular coordinates) is the relative field strength
E(θ,φ)/Emax, where E(θ,φ) Is the field strength value in any direction, and Emax is the field
strength value in the maximum radiation direction.
Therefore, the normalized maximum value is 1. For the antenna pattern of extremely low
sidelobe level, most of them are expressed in decibels, and the normalized maximum value is
taken as zero decibels.
Figure 3 shows the same antenna radiation pattern in rectangular coordinates with normalized
field strength and decibel values.

C&T RF Antennas Inc
 Coco Lu (+86)13412239096
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