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Basic knowledge of antenna measurement
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The basic knowledge of antenna measurement
involves multiple aspects, including antenna functions, performance parameters,
measurement methods, and testing environments. The following is a detailed
explanation of the basic knowledge of antenna measurement:
1、 The function of
the antenna
Antenna is a key component of wireless
communication systems, and its main functions include:
Directional radiation or reception of radio
wave signals: In the transmitting state, the antenna converts high-frequency
electromagnetic energy in the transmission line into electromagnetic waves in
free space; In the receiving state, the electromagnetic waves in free space are
converted into high-frequency electromagnetic energy in the transmission line.
Energy Conversion: Antennas need to
efficiently convert the guided wave energy propagated by the feeder system into
electromagnetic wave energy, or convert the received electromagnetic wave
energy into current signals.
• Directionality: Antennas can radiate or
receive electromagnetic waves in a directional manner, concentrating them in
the desired direction as much as possible.
Polarization: The antenna should be able to
emit or receive electromagnetic waves of the specified polarization.
2、 Performance
parameters of the antenna
The performance parameters of an antenna
are important indicators for measuring its performance, mainly including:
Gain: Refers to the ability of an antenna
to amplify the received signal, usually closely related to directionality.
Directionality: Describes the radiation
power intensity of an antenna in a specific direction relative to its
omnidirectional radiation state.
Efficiency: includes antenna radiation
efficiency and overall efficiency, with the former considering antenna losses
and the latter considering overall losses such as conductor and dielectric
losses of the antenna.
Impedance: The ratio of voltage to current
at the antenna input terminal, which is the load of the feeder system and
requires good impedance matching with the feeder system.
Standing wave ratio (VSWR): reflects the
degree of matching between the antenna and the feeder system.
Polarization: The polarization method by
which an antenna emits or receives electromagnetic waves.
Operating Frequency Band: The frequency
range within which an antenna can operate normally.
3、 Antenna
measurement method
The measurement of antenna parameters is
usually carried out using instruments such as field strength meters, power
meters, impedance meters, or network analyzers, as well as specialized testing
equipment such as standard antennas. The measurement methods include:
Radiation directional pattern measurement:
By using fixed antenna method or rotating antenna method, measure the radiation
intensity of the antenna in different directions and draw the radiation
directional pattern.
Gain measurement: Using the comparison
method, compare the tested antenna with a standard antenna with known gain to
determine the gain of the tested antenna.
Impedance measurement: Use bridge method,
measurement line method, or sweep frequency method to measure the input
impedance of the antenna.
4、 Test environment
In order to accurately measure the
performance parameters of an antenna, it is necessary to provide an ideal
testing environment, which usually requires:
• Flat and open ground: No metal barriers
or reflectors to reduce the impact on electromagnetic wave propagation.
• Sufficient testing distance: The distance
between the tested antenna and the auxiliary antenna must be greater than the
minimum testing distance of the antenna to reduce measurement errors caused by
phase differences of electromagnetic waves incident on the aperture of the
tested antenna. • Non reflective chamber (microwave
anechoic chamber): The lining of the room is made of sharp tooth shaped
absorbing materials, which can absorb most of the electromagnetic energy
incident on the six walls of the room and simulate free space testing conditions
well.
Antenna principle
The antenna principle mainly involves the
radiation and reception of electromagnetic waves, as well as the conversion of
energy between guided waves and free space waves. The following is a detailed
explanation of the antenna principle:
1、 Definition and
Function
Definition: An antenna is a device that can
effectively radiate electromagnetic waves in a specific direction in space or
effectively receive electromagnetic waves from a specific direction in space.
Function: Antennas play a core role in
wireless communication systems, responsible for converting high-frequency
currents (or guided waves) into electromagnetic waves and radiating them into
space, or receiving and converting electromagnetic waves in space into
high-frequency currents.
2、 Working
principle
1. Electromagnetic induction and
electromagnetic radiation:
The working principle of the antenna is
mainly based on the principles of electromagnetic induction and electromagnetic
radiation. When high-frequency current passes through an antenna, it generates
varying electric and magnetic fields around it. According to Maxwell's
electromagnetic field theory, "a changing electric field generates a
magnetic field, and a changing magnetic field generates an electric
field." By continuously exciting it, wireless signal propagation is
achieved.
At the transmitting end, the antenna
converts high-frequency current into electromagnetic waves and radiates them
into space; At the receiving end, the antenna captures electromagnetic waves in
space and converts them into high-frequency currents.
2. Energy Conversion:
The antenna serves as an energy converter,
completing the energy conversion between guided waves (or high-frequency
currents) and free space waves. The transmitting antenna converts guided waves
into free space waves, while the receiving antenna converts free space waves
into guided waves.
3. Directionality and polarization:
Antennas have a certain directionality and
can radiate or receive electromagnetic waves in a directional manner. This
means that the antenna has stronger radiation or reception capabilities in
specific directions, while weaker capabilities in other directions.
The polarization mode of the antenna is
also one of its important characteristics, which determines the polarization
state of the antenna when emitting or receiving electromagnetic waves.
3、 Antenna type and
characteristics
Antennas can be classified according to
different classification criteria, including working nature, purpose, antenna
characteristics, current distribution, frequency band, carrier, and shape.
Common antenna types include mobile base
station antennas, broadcast antennas, radar antennas, WIFI antennas, mobile
phone antennas, etc. Each antenna has its specific application scenarios and
performance characteristics.
4、 Antenna Design
and Optimization
The shape, size, material, and other
factors of an antenna can all affect its performance. Therefore, the design of
antennas needs to comprehensively consider multiple factors, including
operating frequency, radiation direction, polarization mode, gain requirements,
etc.
In the design process, simulation software
is usually used for simulation and optimization to ensure that the antenna can
meet the design requirements.
What is an antenna?
An antenna is an electronic device used to
effectively radiate or receive electromagnetic waves in wireless communication.
It is an indispensable component in wireless systems, responsible for
converting guided waves (such as the flow of current in transmission lines)
into radio waves (electromagnetic waves propagating in free space), or
converting radio waves into guided waves.
The specific functions of an antenna
include:
1. Radiation and reception: At the
transmitting end, the antenna converts high-frequency currents in electronic
devices into radio waves and radiates these waves into the surrounding space.
At the receiving end, the antenna captures radio waves in space and converts
them into high-frequency currents for further processing by electronic devices.
2. Energy Conversion: Antennas are the
medium for energy conversion, which can convert the electrical energy of
electronic devices into the energy of radio waves, or convert the energy of
radio waves into electrical energy.
3. Directionality: Many antennas are
designed with specific directionality, which means they can more effectively
radiate or receive radio waves in specific directions. Directional antennas can
help improve communication efficiency, reduce interference, and increase
communication distance.
4. Polarization: The polarization of an
antenna refers to the direction of the electromagnetic field in which it
radiates or receives radio waves. Common polarization methods include
horizontal polarization, vertical polarization, circular polarization, and
elliptical polarization. Different polarization methods may have different
advantages and limitations in communication.
5. Impedance matching: In order to
effectively transmit and receive radio waves, antennas need to be impedance
matched with transmission lines (such as feeders). This means that the input
impedance of the antenna should match the characteristic impedance of the
transmission line to reduce energy reflection and loss during transmission.
There are various types of antennas,
including but not limited to dipole antennas, loop antennas, parabolic
antennas, spiral antennas, array antennas, etc. Each antenna has its specific
application scenarios and performance characteristics, such as gain,
directionality, frequency response, polarization mode, etc.
