Conformity Magazine

See this article in our Digital Edition
Download a pdf of this article (right click to save the pdf)

In a previous article (see Conformity, February 2008), we described how to select the right chamber for different EMC tests. CISPR standards have evolved at an ever increasing rate since the original publication of that article and, while methods below 1GHz are established, work continues on developing measurement methods above 1 GHz. CISPR is also looking to harmonize CISPR 16 measurement methods between product groups, and this is leading to an increased level of coordination between the committees responsible for the standards.

As a consequence, current and future versions of CISPR standards, such as CISPR 11, 14 and 22, may refer to the measurement methods in CISPR 16 rather than write their own, and in fact CISPR 22 already does so. The new proposed multimedia standard CISPR 32 that will replace CISPR 13 and 22 is looking to introduce ideas not yet included in CISPR 16, including the controversial idea of accepting alternative methods. We will discuss the likely impact of all these changes in this article.

CISPR 16 Standards Series
The IEC manages a number of different EMC standards committees. Emission methods come under CISPR as shown in Table 1, and IEC committees working on immunity methods are grouped under TC 77/SC77B and work on the IEC 61000 series of standards.

Sub Committee	Standard
CISPR A	CISPR 16
CISPR B	CISPR 11
CISPR D	CISPR 12 and 25
CISPR F	CISPR 14
CISPR I	CISPR 13 and 22

Table 1: CISPR standards and their sub-committees

The CISPR 16 series of publications are basic standards for the measurement of radio disturbance in the frequency range 9kHz - 18GHz. Before 2003, the series of standards was divided into 4 parts, CISPR 16-1, 16-2, 16-3, and 16-4, and totalled 1015 pages. A re-organization took place to divide the series of standards into smaller subject-related publications, so that the basic structure was kept, and new parts designated 16-1-X , 16-2-X, etc., where the x values range from 1-5, as shown in Table 2.

Table 2: Reorganization of CISPR 16

This reorganization of the standard in the last five years has seen a huge increase in the workload for CISPR/A. The wide scope of the CISPR 16 standards series as a basic standard means that not all its content is relevant to us in this article. Instead, we will primarily focus on particular parts of 16-1 and 16-2 that concern radiated measurements and anechoic chambers, and their subsequent impact on a number of CISPR product standards.

CISPR 16-1-5 [1] Antenna Calibration
In order to perform chamber validation, the antennas to be used must be calibrated, and here we need to start with a number of definitions.

First, CISPR 16-1-5 defines an antenna calibration test site (CALTS) as an open area test site (OATS) with a tightly specified site attenuation (SA) performance for horizontal electric field polarization only. A CALTS can be used to determine the free space antenna factor (FSAF) of an antenna. CISPR 16-1-5 also defines a reference test site (REFTS) as an OATS with a tightly specified SA performance in horizontal and vertical electric field polarisation. Finally, a COMTS is defined as a compliance test site which is used for the demonstration of product compliance to radiated emission limits. The COMTS will therefore be in our case the anechoic chamber we are validating.

The SA measurements of an REFTS are used to compare corresponding SA measurements of a COMTS, in order to evaluate the performance of a COMTS. Alternatively, the measured SA of a COMTS can be compared to theoretical values. The CALTS in CISPR 16-1-5 is validated using calculable dipole antennas which provide an absolute traceable reference to an expected performance based on theory. Close agreement between measurement and theory has been obtained on a number of prime calibration sites worldwide, thus allowing the calculable dipole antenna to become an acceptable method of traceability. While traceability for antenna calibration and site validation have been established, we will discuss later the remaining traceability problem for emission measurements.

A project for revision of CISPR 16-1-5 was initiated to add antenna calibration methods to the standard. Due to a significant number of technical issues that require further study and resolutions, this project was deactivated to allow sufficient time for the necessary work to be completed. A complete revision of this standard is not to be expected in the near future. However, amendments to the current version may be available sooner, as we will see in the next section.

We should not forget to mention at this point the existence of the American standard ANSI C63.5 [2], which is related to CISPR 16-1-5 and has largely dominated the area of antenna calibration for many years. Although some U.S. members of ANSI C63 subcommittee 1 (which is responsible for ANSI C63.5) are also participating in the CISPR work on antenna calibration, there remain key differences between the two documents. The key differences are the use of theoretical computations and geometric-specific correction factors in ANSI C63.5, as compared to the validation of an REFTS using analytically calculable dipoles in CISPR 16-1-5.

There are also issues common to both standards described in [4] in more detail that include the lack of definition of a reference antenna. This ultimately introduces variability to the normalized site attenuation (NSA) measurements used to validate chambers. Therefore, validation of a chamber may lead to different results depending on the standard used. Harmonization between these two standards would be ideal but may still be some way off.

CISPR 16-1-4 [5] Chamber Validation
Once the antennas have been calibrated per ANSI C63.5, it is then possible to move on to the validation of the COMTS, or in our case the anechoic chamber. CISPR has divided the specification into two different frequency ranges, below and above 1GHz.

Below 1GHz, there are two different chamber validation methods, depending on whether the chamber being validated is a semi-anechoic chamber (SAC) or a fully anechoic room (FAR). Semi-anechoic chambers will have absorbers on all walls and ceiling, but none on the floor which is designated as a ground plane as these chambers are fundamentally an indoor OATS. The origin of the use of the ground plane is well documented and the chamber validation method is the NSA method. The American standard ANSI C63.4 [6] also defines the NSA method and also calibrates antennas according to ANSI C63.5.

Using the same pair of antennas (typically, to cover the full frequency range, a pair of biconical and a pair of log-periodic antennas are used) that has been calibrated on the REFTS, the COMTS is validated over the range 30-1000 MHz, with the transmit antenna positioned at various locations in the test volume (Figure 1) of the chamber and the receive antenna scanned in height from 1-4m. The measurement distance required will be 3m and/or 10m, depending on the size of the test volume, with any volume larger than 2m normally having to be tested at 10m. Most CISPR standards require a 10m distance, except for CISPR 22 which allows 3m measurements only for Class B (domestic) equipment. In reality, many chambers will test at 3m anyway if the equipment under test (EUT) is not larger than 2m in diameter. We will see later that a new standard will specifically define the NSA test distance as a function of the size of the EUT in order to harmonize this issue.

Figure 1: NSA measurement in a semi-anechoic chamber

The design of SACs today is based on sufficient experience with ferrite tile technology that has been gained over the last 15 years. Nowadays, 3m and 10m chambers are built that vary significantly in regard to test volume size and NSA specifications (ï¿½4dB NSA is not always appropriate for some implementations). The SAC is one of two chamber types described in CISPR 16-1-4, with the other being the fully anechoic room (FAR). The FAR eliminates the ground plane effect with the introduction of an absorber covered floor, and this will be described in the next section. For SACs, the challenge will come if they must also be used as a FAR and also meet the requirements above 1GHz, as we will see later in the article.

Figure 2: FSNSA measurement in a FAR with walkway absorbers covering the whole floor

In terms of the future of the method, we need to first look back. The NSA method validates the site in a similar way that the EMC test is performed, using the same measurement distance, height scanning and the same types of antennas. There are, however, two main problems with the NSA method, which has led CISPR/A to look at what is called the reference site method (RSM). First, there was no regulation of the site on which the antennas were calibrated, and therefore the antenna factors were only as good as the site on which they were calibrated, so that the validation of another site by the NSA method would include the errors of the original calibration site. At one point it was actually claimed by some that poor OATS were intentionally being built to make it easier for chambers to pass the NSA test. The introduction of the CALTS method in CISPR 16-1-5 solved this.

A second problem with the NSA method is that the published three-antenna method assumed that the three antenna factors could be obtained from three site attenuation (SA) measurements, whereas in fact one of the antennas is height scanned in one measurement and at a fixed height in a second measurement. There are four unknowns because this antenna is in two states, due to effects of mutual coupling with its ground plane image and the attenuation via the radiation pattern at different heights. The introduction of dual antenna factors, in which the antenna factors of individual antennas were not determined during the calibration process, solved this problem. Having accepted that the NSA method is a comparison of the validation site to the calibration site, we can demonstrate by working through the NSA equations that the antenna factors are redundant.

Therefore, as an amendment to CISPR 16-1-4 and CISPR 16-1-5, CISPR/A is currently considering the use of the RSM. This is an alternative method for the validation of compliance test sites. As with NSA, the determination of Vdirect and Vsite is required. These are obtained with the exact same geometry and polarization that is defined for the NSA method. The difference between the two methods is the calculation of the site attenuation deviation:

âˆ†SA = V_direct - V_site ï¿½ SA_APR

Instead of the two antenna factors and the NSA, the antenna pair reference site attenuation (SAAPR) is required, where SAAPR includes the antenna factors as well as the coupling of each antenna to the ground plane and the coupling between antennas. In addition, the radiation patterns of the antennas are included, unlike the NSA method in which the radiation patterns are only approximated to those of Hertzian dipoles. Even though RSM retains the same antenna geometry configurations as the NSA method, it reduces uncertainties due to fewer number of steps in the measurement process. In many cases ï¿½primeï¿½ sites do have a ground plane size and test setup that has an impact on the accuracy of the measurements.

Therefore, the RSM method may require carrying out several measurements at different locations on the groundplane, and the determination of the result may involve an averaging technique. The advantage of RSM is that the achievable accuracy is higher compared to the NSA method, since the uncertainty introduced by the antenna factors is eliminated. That could lead to a reduction of the acceptance criterion. If this is not done then sites which have a worse performance could actually pass with RSM.

The NSA method avoids the use of hybrid antennas for site validation mainly because their phase centres vary over the frequency range, leading to difficulties in keeping the uncertainties as low as for separate biconical and log-periodic antennas. The advantages of RSM will therefore lie in the reduction in the number of measurements because antenna factors are not required. In the place of multiple measurements in NSA, only one site attenuation measurement per geometric configuration is required for the RSM. Furthermore, it is conceivable that hybrid (instead of biconicals and log-periodic) antennas could be used for RSM with an acceptable uncertainty.

It is important to note at this point that, while traceability for antenna calibration and site validation has been solved, emission measurements still do not define reference antennas, and this problem remains to be solved.

Fully anechoic rooms (FARs) are defined as having all six surfaces treated with absorbing materials and therefore do not have a ground plane floor like their counterparts, the semi anechoic chambers. CISPR 16-1-4 describes the chamber validation method known as the Free Space NSA, or FSNSA method.

The FSNSA test uses a pair of antennas to validate the FAR, but differs from NSA in that there are restrictions on the antennas that can be used. The transmit antenna is specified by the standard as having to be a small biconical, no larger than 40cm in length covering the whole frequency range of 30-1000MHz. Although the receive antenna type is not specified by the standard, it must be the same antenna that will subsequently be used for product testing and is therefore most likely to be a single antenna, combining biconical/log-periodic elements, that will also cover the range 30-1000MHz. The reference site method described in the standard results in a single free space antenna factor that can be used for all positions, and which is therefore a relatively quick and simple calibration to carry out.

FSNSA is a volumetric test that requires the transmit antenna to be placed at 3 different heights (planes) and 5 different positions (Figures 3 and 4). FSNSA is measured at a 3m or 5m separation, with the separation remaining constant between the transmit and receive antennas. In addition both antennas are aligned towards each other at each position during the test, thus making the calibration much simpler by allowing the use of one individual antenna rather than the multiple geometric factors required for NSA tests. From experience however, it does not simplify the chamber validation.

Figure 3: E-plane requirement of the TX antenna

Figure 4: H-plane requirement of the TX antenna

The FSNSA pass criteria from 30-1000MHz are the same as for the NSA measurement, and set at +/-4dB. Although the number of FAR sites is still low compared to SACs, it is generally accepted now that a compliant 3m FAR can be similar in size to a compliant 3m SAC, thus allowing a 3m SAC to be easily converted when lined with the appropriate floor absorber. Larger FARs are rare, with potential 10m type measurements preferring a 5m FAR, mostly due to cost and currently a lack of agreement on limits from the standards committees. Practical issues, such as the handling of large floor standing EUTs typical of 10m sites, have tended to limit the application of FARs to table top equipment. But, as CISPR 16-1-4 now allows both SAC and FAR to co-exist, there should be a method for everyone.

Considerations for the Frequency Range Above 1GHz
Above 1 GHz, CISPR 16-1-4 specifies a method known as the site voltage standing wave ratio (SVSWR) test for the validation of EMC anechoic chambers. Since this method was only very recently introduced, it had been common historically for another method, known as the free space transmission loss (FSTL) test, to be applied in the absence of any standard.

The FSTL method is very similar to the FSNSA method described previously, and typically transmit and receive antennas were both double ridged horns. For many years, critics of the FSTL method saw the use of highly directive antennas as making it too easy to pass, as their high gain meant that the chamber was not really being tested but, instead, the quality of the antenna calibration, and that that alone played the main role in the chamber validation result. In addition, as an unintentional radiator, the EUT would normally have a more complex and less directive radiation pattern and so it was felt that the horn antenna did not give a true representation of this pattern at these frequencies.

As a consequence, one of the main differences in the new SVSWR method described by CISPR 16-1-4 is the use of a more isotropic antenna type as the transmitting antenna. The receive antenna is specified to be of the same type that is used subsequently for the product testing, and is typically a broadband horn antenna. A specification of the radiation pattern for the transmit antenna is included in the standard and shown in the Figures 3 and 4.

Unfortunately, no calibration method is given for determining the pattern of the transmit antenna. This is something that should be developed in future versions of the standard, although many calibrations laboratories can already offer such a service. Currently, the only available data is supplied by the manufacturer of the antenna, of which there are unfortunately too few, and the lack of calibration method leaves the door open to disparity in the uncertainty of the subsequent measurements. It is hoped that CISPR 16-1-5 will address this in future editions.

Clearly, as a result of using an isotropic antenna, the SVSWR method exposes more of the chamber to the antenna beam and therefore requires taking greater care of the anechoic layout. In both the SAC and FAR configuration, this leads us to increasing the coverage of the foam part of the hybrid absorber in chambers where only a partial lining had been sufficient until now, and many chambers will need upgrading as a result.

The method itself is a volumetric test (Figures 5 and 6), involving the positioning of the transmit antenna along the line of sight of the receive antenna (which remains fixed) to 6 specified test points, starting at a 3m distance referenced to the front of the test volume, and then moving further away to 5 other positions as specified by the standard. This is repeated at the centre, right and left positions. The SVSWR for each position is calculated, so that this becomes a relative measurement that compares a set of data points at one location to itself, and not to data points at another location. The acceptance criterion is SVSWR < 6dB.

Figure 5: Top view of SVSWR test positions

Figure 6: Side view of SVSWR test positions

The implications so far are that compliant FARs will pass easily, while SACs may require additional floor absorbers between the antenna and the turntable, and possibly on the turntable itself. It should be noted that wall and/or ceiling absorbers may be required in those SACs that were constructed with partial absorber lining, sufficient to meet the NSA criterion below 1GHz.

CISPR Product Measurements
While CISPR 16-1-4 defines chamber validation methods below and above 1GHz, CISPR 16-2-3 [9] defines measurement methods for products. Methods are well described for both FAR and SAC below 1GHz, but agreement has yet to be established on the methods above 1GHz.

Radiated emission standards now cover the range 30 MHz - 5 GHz. In most cases, the approach above 1GHz is simply a continuation of the methods used below 1GHz. Since typically the same antenna and set up is used, this is convenient and does not require a major reconfiguration of the chamber (although some would also say that any change in the floor absorber set up is a major reconfiguration). Even though most would agree that there cannot be a huge change in the wavelength between say 999 MHz and 1.01 GHz, it has often been the natural break point for defining new measurement methods. There are of course clear RF reasons for this, including the different type of antennas typically used in this frequency range, the increasing impact of the reflection properties of the test environment and positioning equipment, and the increasing complexity of the EUT radiation pattern.

First, below 1GHz we use antennas that can normally illuminate the test equipment within their 3dB beam width. However, semi-anechoic chambers cannot take advantage of this as a result of the ground plane, and have to height scan the antenna in emission tests, while FARs and all radiated immunity tests take full advantage of this and this therefore simplifies the tests. This however assumes that, below 1GHz, a typical radiation pattern of the EUT (a so called unintentional radiator) will also be relatively simple and not require a high degree of spatial sampling and height scanning.

Figure 7: SVSWR Test in SAC with TX antenna

Figure 8: SVSWR Test in FAR

Above 1GHz, we start to see an issue in that the radiation pattern of both antennas and EUTs start to become more directive and complex, thus making it necessary to measure a greater number of positions than below 1GHz. This fact will probably lead to a scanning requirement as can be seen in Figures 9 and 10 in the future. As the equipment under test becomes electrically large compared to the wavelength, we will have to determine the number of positions to sample in order to achieve an acceptable uncertainty during product testing, without having to measure at every possible angle.

Figure 9: CISPR 16-2-3 discussion height scanning with tilting

Figure 10: CISPR 16-2-3 discussion height scanning without tilting

In principle, the higher the test frequency, the larger the number of positions that would need to be measured. CISPR/A is currently looking at data from measurements using height scan and tilting and comparing log periodic and horn antenna measurements. Currently, the results show significant differences which also introduces the question of the necessity for specifications for receive antennas. More data is to be collected before a resolution can be determined. The Joint Task Force on Fully Anechoic Rooms, comprised of experts from CISPR/A and SC77B, is currently developing the standard IEC 61000-4-20 that will be discussed later in this article. The draft standard has included an informative annex on sampling size that the reader is recommended to read.

Finally, it should be noted that an amendment to CISPR 16-1-4 [9] will be introduced on evaluation of the set-up table in the frequency range above 1 GHz. The purpose of this amendment is to provide a process to determine the impact of the setup table on the overall measurement uncertainty. At higher frequencies, the reflection properties of positioning equipment becomes more critical because it becomes electrically large.

CISPR Product Standards
Basic standards like the CISPR 16 series serve a wide base of requirements, one of which is to define measurement methods that are not specifically defined by product standards. Historically, there has not been a general practice of harmonization between the product groups, and this has led to some disparity in measurement methods. However, this is changing, and CISPR/I decided that CISPR 22 [10] in its 2005 revision would be one of the first product standards to remove much of its own text on chamber measurement methods and product measurement methods, and refer instead to CISPR 16-1-4 and CISPR 16-2-3.

For radiated emission measurements above 1GHz, the following references are included: The measuring antennas shall be as defined in subclause 4.6 of CISPR 16-1-4, the measuring site shall be as described in subclause 8 of CISPR 16-1-4, the measurement method shall be as specified in subclause 7.3 of CISPR 16-2-3. More recently, this work has been progressed with the formation of a Joint Task Force between CISPR/A and CISPR/I that is working on the broader transfer of test methods from both CISPR 13 [11] and CISPR 22 into the CISPR 16 standards series. This will clearly serve as a pre-cursor to the proposed new Multimedia standard CISPR 32 [12], that will ultimately replace 13 and 22. We will discuss this standard later in the article.

Other key CISPR standards, such as CISPR 11 [13] and CISPR 14 [14], are beginning to coordinate with the CISPR/A to harmonize methods and also to avoid the parallel development of different methods that could otherwise introduce different requirements.

One standard remaining slightly isolated from this trend is CISPR 25 [15] for automotive products, for which CISPR/D is responsible. Measurement methods used by the automotive industry have traditionally been somewhat different in order to meet specific requirements. These differences cause chambers that meet the requirement called out in CISPR 25 to probably not comply with CISPR 16-1-4, with the result that these chambers can only be used for automotive testing.

The recently published Edition 3 of the standard has simplified the dimensional requirements for the chamber, but still does not define a chamber validation method. A joint task force between CISPR/A and CISPR/D is working on such a method to be published within the next 5 years. However, it is unlikely that CISPR 25 would eventually refer chamber validation to CISPR 16-1-4; the needs of the automotive industry will require the development of an independent method and therefore define different chamber requirements.

Future Developments
The framework for the future structure of EMC standards is constantly being developed and, from the anechoic chamber perspective, this is no exception. Before we discuss the work of CISPR/I and the proposed CISPR 32 standard, we need to look at the work of a number of different joint task forces (JTFs) that have been formed by the CISPR/A and the IEC SC77B organizations.

The three JTFs of interest to us are working on 3 different standards as follows: fully anechoic room (Draft IEC 61000-4-22) [16]; TEM cell (IEC 61000-4-21 [17]); and mode-stirred/reverberation chamber (IEC 61000-4-20 [18]). While TEM cell and mode-stirred chamber standards are published and already going through maintenance updates, they define well known existing methods for these particular technologies and we will assume the reader is familiar with them.

The draft FAR document however, ï¿½IEC 61000-4-22 Ed.1: Radiated emissions and immunity measurements in fully anechoic rooms (FARs),ï¿½ will be published in the future. Its purpose is to address both radiated emissions and immunity measurements in a single document, and thus reduce measurement times without compromising the integrity of the either test. The reciprocity between radiated emissions and immunity measurements is underlined by the harmonization of the chamber validation method, validation criteria, required equipment, EUT setup requirements, and measurement/scanning techniques wherever possible between emissions and immunity tests.

This standard does not propose any limits for measurements performed in FARs, and does not require any new technology to be developed. Limits appropriate for the methods described in this standard will have to be defined by subcommittees responsible for product measurements, if they choose to adopt the methods defined in the new standard. Since only one calibration/validation procedure is performed, and a calibrated field probe or reference antenna is used as the traceable reference instrument for the entire test system, the expenditure of applying this standard for both emissions and immunity tests is believed to be less, compared to applying the separate emission and immunity requirements and procedures contained in the CISPR 16 standard series and IEC 61000-4-3 [19].

The validation method (Figure 11) is a volumetric test similar to that of the FAR method below 1GHz defined in CISPR 16-1-4, and measures the field strength and the forward power at each position to determine a system transducer factor at each point. The validation is carried out by either measuring with two antennas and a vector network analyzer system, or by using an antenna and field probe system. The average system transducer factor and the standard deviation (SdB) are calculated over all points for each polarization and compared to the acceptance criterion.

Figure 11: IEC 61000-4-22 FAR proposed volumetric method

Measurements are currently being carried out to assess whether the pass/fail criteria produce similar results to those of CISPR 16-1-4 and IEC 61000-4-3 to determine if chambers that do meet the different acceptance criteria in these standards will also meet the newly introduced acceptance criteion in the future IEC 61000-4-22. The proposal is quite different and may require some comparisons with the methods called out in the established standards CISPR 16-1-4 and IEC 61000-4-3 to gain credibility.

Now that we have introduced the methods of the CISPR 16 standards series and also IEC 61000-4-20, 21 and 22, we can introduce the proposed replacement for CISPR 13 and 22 that will be called CISPR 32: ï¿½EMC ï¿½ Multimedia Equipment ï¿½ Radio disturbance - characteristics - Limits and methods of measurement.ï¿½ The document has been prepared by CISPR/I and is based on the current best practices for EMC measurements, rather than being based directly on those standards it is replacing. CISPR/I also states that the new standard has been prepared in accordance with the principle of equivalent protection of the radio spectrum rather than strict equivalence of test procedures and results and, as a consequence, the reader familiar with CISPR 13 and CISPR 22 may not find all of the tests described in those two documents carried forward to CISPR 32.

One of the interesting points to note for anechoic chambers is the introduction of limitations in the size of the equipment that can be tested for a given distance. The maximum EUT sizes at 3m, 5m and 10m distances are respectively 1.5m, 2.5m and 5m. By restricting the EUT size per measurement distance, the anechoic chamber designs will become less diverse. However, it is unclear how chambers that already test EUTs beyond the proposed maximum dimensions will fit into this concept.

The importance of this new document is that it is introducing the notion of alternative methods. We have previously discussed the future standard IEC 61000-4-22, introducing an alternative chamber verification method to the one described in CISPR 16-1-4, and CISPR 32 will allow this method to co-exist with TEM cell (IEC 61000-4-21) and mode-stirred/reverberation chamber (IEC 61000-4-20) requirements as well as CISPR 16-1-4 SAC requirements. Of course, each method has its own well known advantages. GTEMs are very practical for small devices with simple cable setup and their correlation to OATS has been accepted by the FCC, although not worldwide.

On the other hand, mode-stirred chambers lack directivity information, but provide significant improvement of emissions testing efficiency by avoiding cable manipulations and FARs simplify measurement setup. Some see this as technically unsound because there is not enough evidence so far that the methods provide equivalent protection while determining different measurements. As a result, there is still no consensus that the inclusion of different test methods can be a way forward for the industry. At the moment, the new standard is scheduled for publication in 2010. After its publication, it was determined that either CISPR 22 and CISPR 13 or CISPR 32 can be used for product testing until 2015.

Conclusions
The CISPR 16 basic standard series has been significantly revised and amended in recent years to accommodate new measurement methods and the evolution towards higher frequencies. One of these parts, CISPR 16-1-4, now includes chamber validation techniques below and above 1GHz that impact the design of anechoic chambers today. Meanwhile, another part, CISPR 16-2-3, is extending measurement methods above 1GHz that are introducing new challenges. CISPR subcommittees are trying to harmonize these methods between basic and product standards, such that the CISPR 16 standards series can become the single reference for test methods and chamber validation processes. However, with alternative methods such as TEM cell, FAR and mode-stirred chambers being proposed by the draft CISPR 32 standard, a better understanding and further investigation of the implications of alternative test methods in a single standard is required. n

Martin Wiles is a Senior RF Engineer at ETSâ€‘Lindgren, and can be reached by eâ€‘mail at martin.wiles@etsâ€‘lindgren.com.

The author would like to thank Mr. Werner Schaefer of CISCO Systems (USA) and Mr. Martin Alexander of NPL (UK) for their highly valued critical review of this article. Both are CISPR/A experts, and have made significant contributions to the development and progress of CISPR 16 over the last ten years.

References

CISPR 16-1-5 Ed 1, ï¿½Specification for radio disturbance and immunity measuring apparatus and methods - Part 1-5: Radio disturbance and immunity measuring apparatus - Antenna calibration test sites for 30 MHz to 1000 MHz,ï¿½ 2003.
CIS/A/644/CD Committee Draft Ed 2, ï¿½Specification for radio disturbance and immunity measuring apparatus and methods - Part 1-5: Radio disturbance and immunity measuring apparatus - Antenna calibration test sites for 30 MHz to 1 000 MHz,ï¿½ 2006.
ANSI C63.5, ï¿½American National Standards for EMC- Radiated Emission Measurements in Electromagnetic Interference (EMI) Control ï¿½ Calibration of Antennas (9KHz- 40GHz),ï¿½ 2006.
Z.Chen, A. Enders. ï¿½CISPR 16-1-5 A Critique on Traceability in Site Validation Measurements,ï¿½ IEEE EMC Hawaii, 2007.
CISPR 16-1-4.Ed 2, ï¿½Specification for radio disturbance and immunity measuring apparatus and methods ï¿½ Part 1-4: radio disturbance and immunity measuring apparatus ï¿½ Ancillary equipment- radiated disturbances,ï¿½ 2007.
ANSI C63.4, ï¿½American National Standards for EMC- Methods of measurement of radio noise emissions from low voltage electrical and electronic equipment in the range 9KHz- 40GHz ),ï¿½ 2003.
CISPR 16-2-3, ï¿½Specification for radio disturbance and immunity measuring apparatus and methods - Part 2-3: Methods of measurement of disturbances and immunity ï¿½ Radiated disturbance measurements,ï¿½ 2006.
CIS/A/774/CD CISPR 16-1-4 Amd. 2 f1 Ed. 2.0, ï¿½Evaluation of set-up table in the frequency range above 1 GHz,ï¿½ 2007.
CISPR 22, ï¿½Information technology equipment ï¿½ Radio disturbance characteristics- limits and methods of measurement,ï¿½ 2005.
CISPR 13, ï¿½Sound and television broadcast receivers and associated equipment - Radio disturbance characteristics - Limits and methods of measurement,ï¿½ 2006.
CIS/I/224/CD, ï¿½CISPR 32: Electromagnetic Compatibility (EMC) ï¿½ Multimedia Equipment ï¿½ Radio disturbance - characteristics - Limits and methods of measurements,ï¿½ 2007.
CISPR 11. Ed 4, ï¿½Industrial, scientific and medical (ISM) radio-frequency equipment - Electromagnetic disturbance characteristics - Limits and methods of measurement,ï¿½ 2006.
CISPR 14 Ed 5, ï¿½Electromagnetic compatibility - Requirements for household appliances, electric tools and similar apparatus - Part 1: Emission,ï¿½ 2006.
CISPR 25 Ed 3, ï¿½Vehicles, boats and internal combustion engines - Radio disturbance characteristics - Limits and methods of measurement for the protection of on-board receivers,ï¿½ 2008.
CIS/A/780/CD ï¿½ IEC 61000.4.22 Ed 1, ï¿½Radiated Emissions and Immunity measurements in fully anechoic rooms,ï¿½ 2007.
IEC 61000.4.21, ï¿½Electromagnetic Compatibility Part 4.21 Testing and measurement techniquesï¿½Reverberation chamber test methods,ï¿½ 2006.
IEC 61000.4.20, ï¿½Electromagnetic Compatibility Part 4.20.Testing and measurement techniques ï¿½ Emission and immunity testing in transverse electromagnetic (TEM) waveguides,ï¿½ 2006.
IEC 61000.4.3, ï¿½Electromagnetic Compatibility Part 4.3 Testing and measurement techniques radiated radio frequency electromagnetic field immunity test equipment ï¿½ Radiated Disturbances,ï¿½ 2006.