RML has developed a desk-top version of the well-known strip line radiated field immunity test method. The product has been enhanced by the inclusion of novel features that improve ease of use and reduce the demands upon ancillary equipment. Ingenious construction allows use in ways that can analyse and eliminate design weaknesses at an early stage, often saving the cost of later palliatives such as shielded enclosures and cable filters.
Firstly, it is possible to subject the Equipment Under Test (EUT) to stress from the E field and H field separately, as well as together as is normally the case. This is achieved by switching the termination of the line. The switch is on the left of this picture. Although this feature is fully effective only at frequencies below 200MHz (100MHz for x4322), it does allow the designer to distinguish between magnetic and capacitive pick-up routes and chose an appropriate improvement strategy.
The second feature is that, by ingenious construction, the strip line may be set in each of the three orthogonal positions relative to the EUT. Contrast this picture with the one above. This allows the designer to determine the orientation of fields that cause troublesome interference without the difficulties that usually accompany movement of the EUT.
The Enhanced version of this strip line includes voltage sensing built-in to the line itself. A dc signal is delivered via a bias tee for measurement whilst the strip line is in use. This novel arrangement improves the accuracy of field measurement and avoids the need to provide a separate field-measuring device. Together with the standard features of compact construction and low power requirement this enhancement makes RML’s strip line ideal for development laboratory, pre-compliance and production line testing.
These strip lines may also be used for emission testing. Comparison with formal methods is possible: See NIS Note No. 1326 ”Theory and Measurement of Radiated Emissions using a TEM cell”. For production control comparison with a “golden sample” is straightforward. For development testing the switched termination may be used to differentiate between electric dipole and magnetic loop sources.
Further technical details and application case studies are available in the paper
“Desk-top radiated –immunity testing of small assemblies”, by R. C. Marshall,
10th International Conference on Electromagnetic Compatibility, IEE, Warwick, 1997.