Hi Ed, Cool list. For a next list you may want to add the OATS at NIST in Boulder, CO. They had the biggest meanest bull snake living underneath their ground screen. On occasion he would feel like defending his territory and scare us all when we were doing antenna calibrations. I wonder if it's still there after the latest site upgrade.
Just to let you know, what Hans described is not really a novel idea. The concept of other-than-rectangular semi-anechoic chambers has been used many many times, e.g. the boat-shaped chambers and AEMI's doubly horn design. Typically, these concepts have been proven to be fairly impractical and expensive. The performance gain is small and the layout is usually designed through raytracing such that the direct reflection from chamber walls "misses" the critical points on the quiet zone. Howevever, this does not mean that the overall quiet zone performance is better (usually isn't), it just means that the chamber is optimally designed to comply with the ANSI standard measurement method at five points. These techniques are typically used to mask the use of inferior performing absorbers, absorbers which can't perform up to the level required for them to be used in a compliant EMC chamber. Chamber building cost is also an important parameter of superior chamber design and non-rectangular chambers usually turn out to be a LOT more expensive, due to labor and material cost. Improvements in chamber performance are gained by numerically optimized absorber design and improved bulk material measurements. The latest ferrite/foam hybrids outperform older designs by up to 10 dB in the low-frequency range. Other than the geometry issue (ALL modern chambers are built rectangular due to improvements in absorber performance and material costs), the larger chambers are being built with multi-scan capabilities. For the Xerox chamber (built by ETS, where I designed and verified it) the range has been qualified for 5(!) different positions, for quiet zones from 3m to 10m diameter, all with +/- 3dB max. deviation from theoretical NSA. They have two antenna masts in place for multiscan (polarization, frequency bands) capability. Other high-performance chambers (ETS's HP (FtCollins) and Sony (San Diego), and TDK/Lindgren's UL (Melville) ) have multi-range capabilities as well. So chamber builders have already made great strides in making Hans's dreams come true. The superior performance chambers are already out there, more are still to come whenever the larger corporations are willing to shell out the big dollars. Although those chambers use more expensive absorber material than "standard" 10m chambers and are somewhat larger in size, the designs are close to the practical limits on footprint (dictated by measurement range and quiet zone size) and performance. Regards, -Robert Robert Bonsen Principal Consultant Orion Scientific email: [email protected] URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
