When wireless products open the era of personal communication, the carrier of EUT has changed. Should the radiated emission test standards be changed? how to change?
It is no longer ANSI and CISPR that answer this question, but the International Telecommunication Union Radiocommunication Sector (ITU-R), a subsidiary of the United Nations, and the famous mobile communication organization 3GPP (3rd Generation Partnership Project, 3rd Generation Partnership Project).
one,
ITU-R Unconventional
ITU-R took another approach and proposed a new radiated emission test idea, which is no longer based on the RE two-wire model, nor does it measure the noise reaching the receiving antenna, but directly measures the noise source.
ITU-R systematically discusses the method of transmitter nuisance emission measurement in the reference recommendation document Rec. ITU-R SM329. This is an overall plan for RF measurement, not only for the radiated emission of the product as a whole, but also for the conducted emission of the RF port.
spurious domain
The most important content of SM.329 is the introduction of the concept of spurious emission (SpuriousEmission). It divides the entire measurement frequency band into three domains according to the distance from the center frequency point of the main frequency signal: working domain, out-of-band domain and spurious domain. The center frequency point of the main frequency signal is f0, and the working bandwidth (or occupied channel bandwidth) is B. Taking f0 as the reference, the frequency range beyond +/-2.5B is the spurious domain (Spurious domain). Unwanted signals whose frequency falls within the spurious domain are called spurious signals.
(Definition of three domains in SM.329)
surrogate measure
Another very key content in SM.329 is the proposed method to measure radiated emission by substitution. To put it simply, it is to replace the EUT with a signal source plus a transmitting antenna (with known gain) at the same position, and adjust the output of the signal source so that the readings obtained on the measuring instrument are the same as those when measuring the EUT. After measuring one frequency point after another, the size of the EUT radiation disturbance at each frequency point can be calculated from the output power of the signal source and the gain of the antenna. This idea later evolved into the path loss (Tranducer) calibration that must be done when building an RSE test system.
(ITU-R SM.329-10, Alternative method for measuring radiated spurious)
Crazy SM.329
There are many ambiguities in SM.329. For example, when discussing the measurement units of spurious signals, it is pointed out that the test results can be used:
- Field strength, measured in µV/m or dB(µV/m) or A/m or dB(µA/m)
- Power (erp or eirp), measured in W or mW or dBW or dBmW
- Power spectral density pdf, measured in W/m2 or dB(W/m2)
(I'm a little dizzy, which one to use~)
Regarding the test site, SM.329 said that in the 30MHz~1GHz frequency band, OATS and semi-anechoic chambers are still used. As for other test sites, such as full anechoic chambers, reverberation chambers, and TEM, can they be used to measure radiation strays? , to discuss later...
(When I saw this, my heart was broken: use a semi-anechoic chamber below 1GHz?? Should the antenna scan up and down? The company is now using a full-anechoic chamber for RSE measurement. Tell me whether it can be used is still to be determined~ T_T)
When I first read SM.329, I often had the urge to ask the big cow who wrote this standard to clarify. Later, I gradually realized that SM.329 is a reference proposal document, which is responsible for proposing various possibilities, and the specific details need to be implemented in product standards.
This task falls on 3GPP body.
two,
Lamor 3GPP
According to the road planned by ITU-R, 3GPP, known for its diligence, began to work hard. In the test standards formulated for different mobile communication systems, two types of spurious emission tests are further specified:
- Use the antenna joint between the RF link and the EUT antenna as a test reference point to measure the amplitude of the spurious signal output from the RF transmission link. conducted spurious test
- The EUT is regarded as a black box (enclosure), and the measurement antenna receives the spurious emissions from the entire black box, without distinguishing which is the noise radiated from the mobile phone antenna and which is the noise radiated from other parts. That is, the radiation spurious test (Radiated Spurious Emission, RSE)
According to the definition of spurious domain in ITU-R SM.329, 3GPP specifies in detail the RBW settings for RSE testing of different mobile communication systems; the limits on different measurement frequency bands are given; the measurement results are determined as power values , the unit is dBm; the test site is determined to be a full anechoic chamber; the same as the usual RF power test, the measuring instrument is a spectrum analyzer, and PK detection is basically used.
full anechoic chamber
The Fully Anechoic Room (FAR) has been mentioned above. FAR is to add a layer of absorbing material on the ground of the semi-anechoic room to eliminate the ground reflection and form an electromagnetic wave propagation environment without any reflection. FAR simulates free space. Since there is no ground reflection path, only direct waves reach the receiving antenna. The receive antenna no longer needs to scan up and down to find noise maxima.
(Compact fully anechoic chamber has great advantages in space requirements and construction costs)
The measurement reference point for the RSE is at the phase center of the EUT - while the measurement reference point for the RE is at the phase center of the receive antenna. This difference determines that the RSE measurement result has nothing to do with the test distance when the far-field condition is satisfied. We can use the substitution method to measure RSE at any distance (meeting the far-field condition).
At this point, we can stop and focus on the RSE test:
- The measurement site is FAR
- The measuring instrument is a spectrum analyzer
- The measurement reference point is at the EUT, and the measurement result is the power value (dBm)
- It is not necessary to specify the test distance when measuring with the substitution method (need to meet the far-field conditions)
- Measuring antenna without scanning up and down
- PK detection is used in most cases
- Site inspection adopts SVSWR method
whose territory
From the definition of RSE, it can be seen that RSE measures not only the noise produced by the transmitter, but also covers the entire spurious domain, including both intentional emissions and unintentional emissions from other circuits in the EUT that have nothing to do with the transmitter. emission.
After the promulgation of the 3GPP standard, the RSE test has become an important test to measure the EMI performance of wireless products. At the same time, it is not difficult to find that there is an overlap in the scope of the RE and RSE tests...
(RE test: you, you are robbing my territory~ RSE test: blame me~)
So how to find a suitable position for the RE test of wireless products?
In the EU wireless product standard EN301489 series, the RE test is clearly defined as measuring the unintentional emission of the EUT. When the measured disturbance noise comes from the transmitter, even if it exceeds the standard, it will be ignored. At the same time, the practice of focusing on cables and other accessories in RE testing in the traditional ITE era has also been inherited. In the RE testing of wireless products, the EUT needs to bring accessories such as chargers and earphones, and focus on the overall radiated emission performance—the test can even Carried out without the EUT establishing a communication link.
three,
Go back to the two pictures at the beginning of the last article.
The units of measurement and limits give away the identities of these two graphs - the first is the RSE test, the second the RE test. Are you right?
Not only do the test results look similar, but in actual operation, the test layouts of RE tests and RSE tests are often unclear on the outside:
- In the research and development tests of some companies, in order to speed up the test and reduce the cost, the RE test below 1GHz is also carried out in the full anechoic chamber, and only the measurement results are converted to the half anechoic chamber;
- When building an RSE test system, the substitution method is usually used to calibrate the path loss (Tranducer) at a fixed test distance. After that, the RSE test does not need to use the substitution method to measure frequency points one by one. Perform frequency sweep while maintaining a fixed test distance (eg 3m)
。。。
The result is that the longer the RE and RSE tests we see on the surface, the more they look like...
(Guess, is this the RE test? Or the RSE test? The answer is at the end of the article)
epilogue
We have used two issues to describe the RE test and RSE test of wireless products respectively. If we put their details together, it is not difficult to find that RSE is more important in terms of test time, darkroom space, construction cost and comprehensiveness of investigation. Better than RE testing - so much so that both ETS and R&S later introduced small shielded boxes for RSE pre-testing.
Questions arose naturally: why are two test items needed for wireless products? Why not in the RSE test, also bring the EUT as an accessory, and then cancel the RE test?
This is what I have always wondered about.
Here, let me talk about my views, hoping to throw bricks and spark jade:
- From a technical point of view:
If it is only based on theoretical derivation, the limit of RE test below 1GHz is lower than that of RSE, that is to say, when measuring unintentional emission in the frequency band below 1GHz, RE test is more stringent
- From a practical point of view:
RE test and RSE test are two tests formulated by different standard organizations with completely different sources. For example, when doing domestic certification, the RE test belongs to 3C, and the RSE test belongs to the model approval. Cancel one? Uh, when I didn't say...
A generation goes, a generation comes, the sun goes down, the sun rises as usual.
The evolution of test standards is a slow and unstoppable process. CISPR32 replaces CISPR22, RED instructions replace R&TTE instructions... those old friends who were printed in textbooks when they were in school have slowly become history.
The carrier has changed, how can the standard remain the same.
5G commercialization, the global planned working frequency band is from 20 GHz to 80 GHz; the operating frequency of Tesla electric vehicle autopilot active radar system is 77 GHz; Inherent understanding of high frequency. Faced with such a high frequency, how to carry out electromagnetic compatibility research and testing? Existing electromagnetic compatibility sites, equipment and testing methods are stretched. Just as we once stood before the critical point of 1GHz, we are once again standing in front of the singularity of frequency.
New technology is brewing a new revolution, and the electromagnetic compatibility test standard is no exception.
The future has come, let us wait and see.
( Reveal the answer : In the above picture, although it is a fully anechoic chamber, EUT with accessories test, it is really not a RE test above 1GHz.
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