Shinichi Okuyama

Improvement of radiated emission measurement reproducibility with VHF-LISN obtained from final results of international inter-laboratory comparison on termination control of power line

At present, power supply impedance of radiated emission measurement site is not specified in any testing standards. In measurement of radiated emission from desktop equipment, noise emitted from power line of the EUT is a factor that worsens site correlations because the noise varies with the impedance between power line and the ground. Under such circumstances, VCCI developed VHF-LISN to stabilize power supply facilities for the purpose of improving the reproducibility of radiated emission measurement. To assess its effectiveness, an international inter-laboratory comparison program was carried out, provided with EUTs and termination control devices including the VHF-LISN to ensure identical setup across sites. Until February 2014, this international program was promoted at 16 sites in 9 countries. From the final results, we conclude that the VHF-LISN is the best device to improve the reproducibility of radiated emission measurement.

Investigation on the effect of impedance changes in broadband antennas with varying antenna height on radiated emission measurement below 1 GHz

According to the standard method for calibration of receive antennas to be used in radiated emission measurement below 1 GHz, the sensitivity of receive antenna is defined as a free-space antenna factor obtained by applying a given correction factor to a near free-space factor that is determined by horizontally polarized antenna calibration at a 2 m antenna height. In actual radiated emission measurement performed while varying the receive antenna height, however, the sensitivity of receive antenna varies with antenna impedance changes at different antenna heights. In this situation, the authors measured how the antenna impedance changes with the antenna height and examined how such impedance changes affect radiated emission measurement results, using biconical, log-periodic dipole, and hybrid antennas under test that are typical below 1 GHz. The authors also studied on a method to estimate an antenna height free from antenna impedance changes and suitable for obtaining free-space factors.

Investigation into the influence of ground plane insulation thickness on radiated emission from mains cable of EUT

In the emission standard CISPR32 for multimedia equipment (MME), the specification provided for cabling on the reference ground plane (RGP) stipulates that the thickness of the insulation shall not be more than 150 mm. However, the emission standard does not specify a minimum insulation thickness. Therefore, it is assumed that measurements will be conducted at various insulation thicknesses across various test sites. Thus, the cable impedance varies with the degree of coupling with the RGP, which may significantly degrade the reproducibility of measurements. This investigation verifies that varying insulation thickness does impact AC cable-radiated emission. A very high frequency Une impedance stabilization network (VHF-LISN) representing the common-mode impedance of an AC outlet supplying power to the equipment under test (EUT) in the actual test site was used. The test results have verified that the radiated emission changes much at an insulation thickness of 2 mm or less and the change gradually decreases as the thickness increases (5 dB or less at a thickness of 12 mm or more and 2 dB or less at a thickness of 30 mm).

Evaluation of present limit for radiated emission measurement in FAR Test Site and proposal for new limits according to the polarization plane

Radiated emission test in a FAR (Fully Anechoic Room) site has been adopted as the latest version of CISPR32, IEC61000-6-3 and IEC61000-6-4 standards. Test in a FAR site without metal ground plane is expected to the measurement time reduction, since the height scan is not required to find the maximum emission because there is no reflective wave from the floor. Consequently, the severe limit of 5 dB than a test in OATS (Open Area Test Site) / SAC (Semi Anechoic Chamber) has been introduced to a test below 1 GHz in FAR. However, based on the comparative simulation results, the radiated emission limit in FAR site has been relaxed to plus 7 dB at 30 MHz from the 5 dB severe value at 230 MHz linearly with respect to the logarithm of the frequency, since the disturbance source in the equipment is affected by a metal ground plane of the test in OATS/SAC. The rationale of FAR test limit was indicated as a calculation result, but actual measurement data are not enough. Under this situation, we have performed comparison experiment measurement between SAC site and FAR site by using a same equipment to investigate the validity of the relaxed limit based on the calculation. From the experiment measurement result, the limit according to the polarization plane should be specified because it has a high possibility to mislead the product conformity assessment in a polarization of vertical to the ground plane.

Improvement in the reproducibility of radiated emission measurements in a fully anechoic room by using VHF-LISN to control the termination condition of the AC mains cable leaving the EUT

In radiated emission measurements, the radiated disturbance from the AC mains cable leaving the equipment under test (EUT) significantly differs with the termination condition of the AC mains cable. Because this condition was not defined in applicable test standards, VCCI developed a device called the very high frequency line impedance stabilization network (VHF-LISN) that controls the termination impedance at the end of the power line in the test site connecting the AC mains cable of the EUT. Since then, VCCI has verified the effectiveness of VHF-LISN in the reproducibility of radiated emission measurements in semi anechoic chambers (SACs) while making proposals to CISPR, leading to discussions on the conditioning of the AC mains cable termination currently under way in CISPR SC-I/WG2. Now, VCCI has completed a new series of tests on the VHF-LISN in a fully anechoic room (FAR) according to the test method adopted in CISPR 32 Edition 2.0. This paper reports the results of these new tests and concludes that the reproducibility of radiated emission measurements in the FAR is also verified to improve significantly by controlling the termination condition of the AC mains cable through the use of VHF-LISN.

Comparison experiments on hybrid and biconical/LPD antennas in radiated emission measurement below 1 GHz

In radiated emission measurement below 1 GHz, it is a common practice to use broadband antennas such as biconical antennas and LPD antennas. Another practice is to use hybrid antennas because they do not require replacement of the antenna throughout the frequency range below 1 GHz. While the use of a hybrid antenna at a 10 m distance is viewed as a viable option, its use at a 3 m distance is sometimes questioned because of technical issues. Comparison experiments in this paper aim to validate these issues and study the viability of hybrid antennas in radiated emission measurement below 1 GHz at a 3 m distance.