Antenna
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.
