Statistical conversion factor between measurements of EMI in different test facilities

The open area test site (OATS) has been in common use for over 20 years since the introduction of electromagnetic interference (EMI) regulations around the world The OATS must have very low RF ambients however the introduction of digital TV broadcasting and the proliferation of mobile telephone transmitters are threatening the validity of the OATS. This paper discusses the increasing difficulties caused by the masking of EMI emissions by new ambient threats at the OATS. The characteristics of ambients are analyzed and recommendations given for EMI measurements in the presence of the more common OATS ambients. Ambient profiles of old and new OATS are compared and the changes discussed. It is shown that validity of OATS in high ambient urban areas is questionable.

At present there are several methods to do EMI measurements in GTEM cell, such as EDM, MDM, Linear, Wilsonpsilas method and so on. But the difference between the calculated results of these methods and the EMI results measured in OATS (open area test site) is very large in some situation. This article provides a new method to calculate electric field intensity in GTEM cell using the equivalent dipole of the radiator. And series of experiments were performed to prove the validity and advantage of this method. The experiment results show that the calculated results of new method is more agree with the measured results in OATS, which means that the new method can be considered as a more approached way to calculate the electric field intensity in GTEM cell for EMI measurements.

A GTD model is proposed to discuss the normalized site attenuation (NSA) associated with an open area test site (OATS) with finite metallic ground plane. In this study, the NSA values for three OATS sites, based on GTD model and measurement, are carefully examined and agreement between calculated and measured results supports the usefulness of the proposed GTD model. The GTD model is then adopted to analyze the deviation in NSA values for several OATS structures. The GTD simulation has revealed that the key factor affecting NSA is the width of rectangle metallic plane which is essential in reducing the NSA deviation under the finite test site condition.

The main purpose of Fully Anechoic Chamber (FAC) as an alternative facility for EMC compliance testing is to accurately measure the radiated emission generated from equipment-under-test (EUT). The Open Area Test Site (OATS) is the standard test facility for radiated emission measurement, thus the FAC data have to be correlated to the OATS results. In this paper, it is statistically verified the newly proposed correlation algorithm between FAC and test facilities with ground plane such as OATS, semi-anechoic chamber (SAC) in order to use a FAC as an alternative facility for EMC compliance test. The algorithm is based on modeling of EUT as an equivalent set of multipoles. A sequence of E field measurements at FAC is then used to determine the equivalent dipole moments and relative phases for EUT. The dipole model then allows one to simulate the radiated emission from EUT over a ground screen. Thus, emission measurements over an OATS as called for by various standards may be simulated. This paper reviews the basics of the multipole model as it relates to FAC, the E field measurement scheme at FAC, and presents the results of EMI measurements at both FAC and SAC. The radiated emission test using the proposed algorithm requires fifteen E field values measured at nine positions around an arbitrary EUT located within FAC. Radiation from the reference radiator has been tested in order to statistically verify the proposed correlation algorithm between a FAC and the test facilities with ground plane.

The paper presents the main factors which contribute to uncertainties in measurements in screened rooms and in open-area test sites (OATS). EMC standards require test measurements to be made on equipment under specified conditions in order to demonstrate compliance with various national and international regulations. In order for these tests to be meaningful it is necessary that the EMC behaviour of equipment under test (EUT) in different environments should be predictable, consistent and repeatable. In particular, it is desirable that measurements done on the same EUT in different vendor's premises are broadly similar and that measurements done in screened rooms and in OATS can be correlated. Unfortunately, these aims cannot be met at present and hence a deeper understanding and control of the various test environments is necessary to improve the accuracy and consistency of measurements. In order to help with this process, the main issues involved are addressed. Conditions encountered in screened rooms, OATS and other test environments are examined.

The Gigahertz Transverse Electromagnetic Cell (GTEM) is gaining widespread acceptance in radiated emissions testing for electromagnetic compatibility (EMC). The FCC now allows for the data taken in the GTEM to be submitted as final compliance radiated data as long as the GTEM has proven to be correlated to a listed OATS for the product family under test. The correlation must be proven and filed with the FCC. The ability to take final compliance measurements in the GTEM can be instrumental in reducing the cycle time of the regulatory compliance approval process, which will lead to shorter time to market for the product. The Compliance Group at Motorola Paging in Boynton Beach, FL primarily tests small belt-worn pagers and their derivatives. A pager can easily fit into the 1 dB field contour region of a 5305 GTEM cell. The objective of this research was to investigate the correlation between the GTEM and the FCC-listed OATS to (1) reduce cycle time of regulatory compliance tests by qualifying the GTEM as an alternate EMC test site with the FCC and (2) to establish confidence that all emissions that are tested and passed in the GTEM will pass on the open area test site. For paging products, there are four primary contributors to variation in readings from GTEM to OATS: (1) unit-to-unit variation, (2) frequency of emissions, (3) product to product, and (4) the differences in the methods. A four-factor analysis of variance (ANOVA) experiment was designed to investigate the effects of these contributors.

The existence of differences between different open area test sites (OATS) in antenna calibration and electromagnetic compatibility (EMC) compliance measurements is still a real issue. To minimize the differences, it is necessary to analyze the influencing factors. To examine the influence of the ground plane geometry on the site attenuation, a comparison of different open area test site geometries and sizes has been carried out. The investigation has been performed numerically with the method of moments in the frequency range 30-130 MHz for test distances of 3 m and 10 m. The deviation of the site attenuation (with receiving antenna height) in relation to the ideal test site has been calculated. The minimal plane, for example, which is suggested in the standards, shows a high deviation. Furthermore, the significant influence of on and off axis measurements is shown and the reasons are explained.

This paper presents adaptive cancelation techniques to suppress ambient noise in electromagnetic interference mea-surements on open area test sites. The measurements are carried out in time-domain to reduce the total measurement time. To achieve optimum cancelation, time-domain as well as frequency domain adaptive filter algorithms have been investigated and compared in respect of their suppression performance. An advanced digital signal processing technique for fast measurements of electromagnetic interference from electronic devices is presented. Fast measurements of electromagnetic interference of electronic devices and systems are carried out on a test site polluted by electromagnetic ambient noise. Frequency domain adaptive filtering using the overlap-save method is applied. Measurements of a personal computer as device under test are carried out on an urban test site showing the successful cancelation of ambient noise in a frequency range from 30MHz to 1GHz.

The author reports on the results of a correlation exercise comparing radiated emissions measurements obtained at three different kinds of facilities: a GHz transverse electromagnetic (G-TEM) cell, a semianechoic chamber (SAC), and an open area test site (OATS). A source with a data cable which must exit the cell is used. The test objects were digital phones. These telephones receive their power and communicate over an unshielded twisted pair cable. The cable must pass out of the cell and to a switch simulator, which maintains the telephone in its operation state. Several steps taken to improve the correlation between these various radiated emissions test facilities are reviewed. The correlation between the G-TEM and OATS is found to be generally better than 4.5 dB. For most frequencies the correlation is better than 2.5 dB. >

Results of many measurements, which show that antenna calibrations in a SAC are feasible, are shown. Measurements include reflections from the ground plane at an open area test site (OATS) comparing them as the site insertion losses (SIL) at antenna height changes without and with electromagnetic absorbers on the ground plane of the OATS at frequencies from 1 to 18 GHz. Similar measurements are carried out in semi-anechoic chambers (SAC) and the results are compared with those of OATS. A substitution method of antenna calibrations at SAC with absorbers on the ground plane is experimented, compared with those of SSM and discussed.

The addition of an OATS (open area test site) radiated emissions correlation algorithm to a GTEM (GHz transverse electromagnetic) cell allows performance of radiated emissions testing, equivalent to that conducted at an OATS in the GTEM. The original correlation model and the computational algorithm based on this model accurately addressed the measurement of radiated emissions to commercial standards, over the frequency range of 30 MHz to 1 GHz. In the present work, the authors examine new additions and expansions to the original model and algorithm. New additions include measurements to telecommunications specifications, measurements from 9 kHz to 30 MHz for electric and magnetic field measurements, and measurements to MIL-STD requirements and measurements above 1 GHz. >

Radiated emissions measurements are commonly performed in open area test sites (OATS), anechoic and semi-anechoic chambers, and GTEM and TEM cells. The OATS test results are typically regarded as the reference standard and all other techniques must be correlatable to the OATS data. The accepted procedures all determine the maximum emissions within some defined solid angle. Reverberation chambers, which measure total radiated power, are not currently accepted in any emission standard. Simple probing of general directional emission patterns can demonstrate what fraction of the total equipment-under-test (EUT) emissions are observed in a particular test technique. In this article, the emissions from two battery-powered laptop computers were investigated using a short wire antenna in the near field.

일반적으로 안테나 이득 또는 인자를 측정하는 방법으로서 3-안테나법, 표준안테나법, 표준시험장법 등이 있다. 이들 방법은 주파수 영역에서 반사파 등을 고려하여 자유 공간 또는 준자유 공간의 값을 측정한다. 본 논문은 시간 영역에서 반사파를 추적 제거함으로써 야외시험장에서 자유 공간 안테나 이득 인자를 측정 및 교정하는 방법을 논의한다. 시간 영역에서 측정한 전송 계수 <TEX>$S_{21}$</TEX>으로부터 직접파 및 반사파가 수신 안테나에 도달하는 시간차로 이들을 구분하고, 게이팅 기능과 역 푸리에 변환으로 직접파의 주파수 응답 만을 추출하였다. 시간 영역 기능을 갖추고 있는 네트워크 분석기로 안테나 높이를 변화시키면서 이들 파의 경로차를 만들어 1~18 GHz 대역 더블리지 혼 안테나의 반응시간을 분석 하였으며, 그 경로차에 의한 응답을 분리 추출하여 자유 공간 안테나 이득을 측정하였다. 이 결과를ANSI C635의 표준시험장법으로 교정한 결과와 상호 비교하여 좋은 일치가 있음을 보였다. There are several antenna calibration methods, so-called 3-Antenna Method, Standard Site Method, and Standard Antenna Method which measure the antenna gains or antenna factors. These methods yield the free space or quasi free space antenna gains in only the frequency domain. In this paper, an antenna calibration method using the time domain in the open area test site is discussed. The reflected waves due to the ground are traced in the time domain. After they are removed by the time gating function of network analyzer, the free space transmission coefficient <TEX>$S_{21}$</TEX> is extracted. Such a way is applied to the broad band horn antenna ranging 1 GHz to 18 GHz, and the free space gains are obtained by Friis transmission equation. The method is checked by Standard Site Method in open area test site. The results show comparatively good agreement except for 18 GHz.

To provide a uniform RF field for immunity testing, a basic understanding of the antenna beamwidth radiation pattern is required. Ground floor and wall reflections and resonance contribute to the field nonuniformity. During the process of developing an automotive RF immunity test requirement, obstacles to meeting this requirement were encountered due to the absence of an absorber lined ground plane and the frequency limitations of the ferrite tiles placed on the walls and ceiling of the test chamber. The frequency range of this test is 200 MHz to 4 GHz. To visualize the actual effects of the floor and wall on beamwidth patterns, a series of measurements were taken in the semi-anechoic room. Mapping of the antenna beamwidth in a semi-anechoic chamber provides a method to determine the optimum distance to antenna and antenna/target orientation. A secondary benefit of beamwidth mapping is that the actual field strength can be measured and compared to the input power. This will help in determining if the intended amplifier is large enough to produce the required field strength. Additional testing using an open area test site (OATS) sheds light on the contributions of floor and absorber wall reflections. Through an experimental study, optimum antenna orientation is determined to obtain the targeted field uniformity.

First this paper will explain the need to reproducibly measure the unintended radiation from handheld battery powered devices. The established test sites like Open Area Test Sites (OATS) fulfil the reproducible requirement but they are to expensive and need a big space. It is shown that the standard farfield conditions can be found in a TEM waveguide. At last it will be demonstrated how to get the same measurement results from a TEM-cell measurements as from an OATS.