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Electromagnetic compatibility (EMC) RF electromagnetic field radiation immunity test plan
1. What is RF electromagnetic field radiation immunity test?
In recent years, the use of wireless phones and other radio frequency transmitting devices has increased significantly. The frequencies used are between 0.8 GHz and 6 GHz. Many of these devices use non-constant envelope modulation techniques.
The electromagnetic environment depends on the strength of the electromagnetic field within the environment. Due to the influence of surrounding buildings and other nearby equipment, electromagnetic waves will be reflected and/or distorted. Without advanced instruments, the field strength is difficult to measure and difficult to calculate using classical formulas or equations.
The Radiated Immunity Test of Radio Frequency Electromagnetic Field is based on the international standard IEC61000-4-3 Electromagnetic Compatibility Test and Test Technology Radio Frequency Electromagnetic Field Radiated Immunity Test. GB/T 17626.3-2016 is the latest national standard.
The standard specifies the test scope and environment for RF electromagnetic field radiation immunity testing, specifies the test level and necessary test procedures, the corresponding test equipment required, test level, requirements for test signals, test frequency range, size of the field uniform domain, method of uniformity calibration, test layout, etc.
2. What are the general test levels?
Test levels related to general purpose devices, digital wireless telephones and other RF transmitting devices
The table shows the unmodulated signal field strength. In formal tests, a 1kHz sine wave is used to modulate the unmodulated signal to an amplitude of 80% depth.
(1) General test level
The general frequency range is 80MHz ~ 1000MHz.
(2) Test levels set for RF radiation from digital wireless phones
The following table gives the priority test levels for the frequency ranges 800MHz to 960MHz and 1.4GHz to 2.0GHz.
In the general test level preference table, the test levels are divided into 1, 2, and 3, and the corresponding test field strengths are 1V/m, 3V/m, and 10V/m respectively.
Level 1 is a low-level electromagnetic radiation environment, such as the radiation situation 1 km away from a radio or television station.
Level 2 is a medium electromagnetic radiation environment, such as when low-power mobile phones are in use nearby. This is a typical business environment.
Level 3 is a harsh electromagnetic radiation environment, such as when a mobile phone is used close to the device (at a distance of not less than 1m), or when high-power broadcast transmitters and industrial, scientific and medical equipment are working nearby. This is a typical industrial environment.
Level × is an open level that can be negotiated between the user and the equipment manufacturer, or specified in the product standard or equipment manual.
3. What are the main test environments and test equipment?
This is a schematic diagram of the test site that is preferred as specified by the standard. Radio frequency electromagnetic field radiation immunity testing is usually carried out in an anechoic chamber, which requires that the size of the chamber should be large enough to ensure a uniform field relative to the size of the object being tested. There is also an auxiliary shielded room for placing field strength generating equipment (signal generator, power amplifier), monitoring equipment, and control equipment for the test product.
In addition to the anechoic chamber, the following instruments are required to complete the RF radiation electromagnetic field test:
1. Electromagnetic interference filter : Care should be taken to ensure that the filter does not cause oscillation effects on the connection line.
2. RF signal generator : Rohde & Schwarz RF signal generator, model SMA100B, frequency range 8 kHz to 67GHz. The selection is mainly to generate signals that can cover all test frequency bands and can be modulated by 1KHz sine wave amplitude with 80% modulation depth. There should be manual control functions, such as controlling frequency, amplitude, modulation depth, or in the case of frequency synthesizers, they should have programmable functions for frequency stepping and dwell time. In order to avoid problems caused by harmonics, low-pass filters or loan filters must be used when necessary.
3. Power amplifier : Nanjing Nat RF power amplifier, mainly used for amplifying signals, frequency range: 80MHz-1000MHz; output power: 100W, built-in directional coupler; to modulate or debug the signal and provide the antenna with the power to reach the required field strength level, the harmonic field strength of the power amplifier product measured in a uniform field should be at least 6dB lower than the fundamental wave field strength.
4. Field strength transmitting antenna : biconical, log-periodic, horn or other linear polarization antenna system that can meet the frequency requirements.
5. Isotropic strong sensor : It is equipped with a preamplifier and a photoelectric conversion device with sufficient immunity to the measured field strength and an optical cable connected to the indicator outside the darkroom. Other signal connection methods can also be used as long as they are fully filtered.
6. Auxiliary equipment: used to record the power level required for the test specified field strength and control the level of the test field strength. Care should be taken to ensure that the auxiliary equipment has sufficient immunity to interference.
The configuration scheme can be configured according to the test frequency of the instrument. You can consult Antai engineers to obtain the specific configuration.
4. Is system integration development required?
System integration is very necessary, which mainly involves building a system of instruments and equipment, integrating the RF of these instruments in a cabinet and controlling them through customized software to form a RF radiation immunity test system.
The cabinet can be placed in the amplifier room outside the darkroom, or in the darkroom to reduce the attenuation of long cables on high-power signals. Some users may also need to conduct field tests and take the system out for testing. They can use a portable box to make it detachable and portable, or use a modular instrument.
System software development is also a must for the system, which is convenient for operators to remotely control. It has the following main features:
1. The system uses software to set signal parameters for the RF signal source and spectrum analyzer, eliminating the need for researchers to waste time and resources studying and learning the use of the instruments;
2. The system can save the received signal data in Excel format locally, providing researchers with the basic conditions and massive data for mathematical modeling to study the law of signal attenuation;
3. The system can automatically compare the data of the transmitted signal with the data of the received signal
, and generate an experimental report, which is the basis for the research and analysis of the signal attenuation law;
4. The system can be used for research in the laboratory, and at the same time it is portable, making it convenient for the research institute to conduct field experiments outdoors, combining theory and practical use to provide a strong scientific basis for testing and research.
The above-mentioned RF electromagnetic field radiation immunity test plan is compiled by Antai test engineers. It is also some experience sharing, so that we can learn from each other and solve practical test problems together.
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