Apparently I didn't express myself clearly. Let me try again. If instead of leveling on the x^2+y^2+z^2 output of the field sensor(s) when you calibrate the quiet zone you instead verify that the desired field intensity appears in the one desired polarization/orientation at each point in the 1.5 meter square, then you are absolutely guaranteeing the establishment of a plane wave. Further, the coupling to a wire of any specific orientation is fully determined which nails down the threshold of susceptibility, if one exists at the field intensity established.
The EN61000-4-3 antenna-quiet zone separation of 3 meters was determined for a lower frequency of 80 MHz. At that frequency, a 3 meter separation is greater than a half wavelength, which for a dipole radiator such as a biconical is sufficient to approach far field conditions. If you push the lower frequency to 27 MHz, two bad things happen, NEITHER OF WHICH IS TEST CHAMBER RELATED. The far field separation criteria is now greater than the antenna-quiet zone separation, although this is likely mitigated by the fact that the radiator has not increased in physical length as would a tuned dipole. Instead, the biconical has become electrically shorter, which means it appears to be a high impedance load on the rf power source and therefore not much current flows. The biconical at 27 MHz will radiate a near field that, relative to a plane wave has a higher electric and lower magnetic field intensity. This can and will have a dramatic effect on coupling to cables, especially shielded ones. Another effect is room-related, and that is that the absorber tile-lining is reaching its performance limit at 20 MHz, and it is not as absorbent at 27 MHz as at 80 MHz. But this has nothing to do with chamber dimensions either. All the above is classical electromagnetics, I don't think any of it will generate controversy. But this might. I can't see any justification for pushing the lower 80 MHz limit to 27 MHz, except when the test sample is physically large. Then you have an analogous situation to a large test sample on an OATS, which requires a 10 m site to get accurate readings. So if your company builds and/or tests large floor standing racks of equipment, and needs to test at 27 MHz, then you bite the bullet and build the larger chamber and buy the more powerful amps. > From: [email protected] > Reply-To: [email protected] > Date: Wed, 23 Jul 2003 03:01:05 +0000 > To: <[email protected]> > Subject: Re: 3m vs. 10m chamber for radiated immunity > > > Thanks Ken. > > I would expect that 300+ MHz isn't much of a problem. I know that lower > frequencies are a problem, especially if you start at ~27 MHz in a small > chamber. I am not sure how much the small chamber loads the antenna, and how > it > affects the distribution of BOTH (i.e., E and H) EM field components in the > intermediate range, about 80-150 MHz. > > My concern is that the difference in the entire field distribution (E and H > and > their relation) between a small chamber and a large chamber is probably > substantial up to some frequency, which depends in the first place on the > characteristics of the chamber and the absorbers. Thus, the interfering EM > field may be quite different in the two chambers, even though the E-field > component is identical (within the E-field uniformity requirement). Knowing > only the E-field seems not to be enough in case of non-plane non-uniform > propagation. Ultimately, I believe that it may result in very different > susceptibility thresholds in different chambers, when measured relative to the > E-field only. > > It seems that there isn't much, if any, data published and available. > > Neven >> >> I made some measurements once in a 3 meter anechoic chamber built for >> EN61000-4-3. I was interested in the disturbance a wire causes in a field >> due to picking up the field, the resultant currents flowing in such a way as >> to cancel the field that caused them, etc. In order to assess the effect, I >> needed to monitor the undisturbed field. While EN61000-4-3 allows a x-y-z >> field sensor total output to represent the field intensity, I needed to >> measure the relative vector components. I found that in this tile-lined >> chamber, that the only vector of any magnitude was that parallel to the >> radiating antenna. I would say that given this kind of performance, a plane >> wave has been established. >> >> But I was working at 300 MHz. I am suggesting that this simple test could >> be performed at all frequencies of interest to assess the anechoic >> properties of the room. >> >>> From: [email protected] >>> Reply-To: [email protected] >>> Date: Tue, 22 Jul 2003 02:35:08 +0000 >>> To: [email protected] >>> Cc: [email protected] >>> Subject: 3m vs. 10m chamber for radiated immunity >>> >>> >>> Has anyone investigated the difference in performance of different chamber >>> sizes when performing the radiated immunity (-3) test at low frequencies >>> (e.g., >>> between 80 MHz and 100-150 MHz)? The field uniformity is calibrated in >>> E-field, >>> but I would expect the total EM field (E and H components) to have different >>> distribution as a function of different chamber sizes. Specifically, keeping >>> the distance between the antenna and the DUT constant at 3 m, I still expect >>> different performances due to size (chamber loading the antenna and >>> reflections/near field). Consequently, it seems that the interfering signal >>> can >>> be quite different in a small chamber vs. large chamber, with possibly large >>> variations in the H-field components, even though they are both calibrated >>> for >>> the E-field uniformity, and both tests performed at the antenna distance of >>> 3m. >>> >>> I know of a case in which testing in a smaller (3m) chamber makes product >>> consistently fail at significantly lower level than in a larger, 10 m >>> chamber >>> (6 V/m vs. nearly 10 v/m). Fixing a product to pass the 10 V/m level >>> (required >>> by the customer) in the large chamber seems to be relatively easy and >>> inexpensive, while fixing it to pass the same level in a small chamber may >>> be >>> very costly and time consuming. >>> >>> Is there any precedence like in case of the radiated emission, where 10m >>> results prevail in case of a dispute? Any papers to support or dismiss my >>> expectation from above? >>> >>> Thanks, Neven >>> >>> ------------------------------------------- >>> This message is from the IEEE EMC Society Product Safety >>> Technical Committee emc-pstc discussion list. >>> >>> Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >>> >>> To cancel your subscription, send mail to: >>> [email protected] >>> with the single line: >>> unsubscribe emc-pstc >>> >>> For help, send mail to the list administrators: >>> Ron Pickard: [email protected] >>> Dave Heald: [email protected] >>> >>> For policy questions, send mail to: >>> Richard Nute: [email protected] >>> Jim Bacher: [email protected] >>> >>> Archive is being moved, we will announce when it is back on-line. >>> All emc-pstc postings are archived and searchable on the web at: >>> http://www.ieeecommunities.org/emc-pstc >>> >> >> >> ------------------------------------------- >> This message is from the IEEE EMC Society Product Safety >> Technical Committee emc-pstc discussion list. >> >> Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ >> >> To cancel your subscription, send mail to: >> [email protected] >> with the single line: >> unsubscribe emc-pstc >> >> For help, send mail to the list administrators: >> Ron Pickard: [email protected] >> Dave Heald: [email protected] >> >> For policy questions, send mail to: >> Richard Nute: [email protected] >> Jim Bacher: [email protected] >> >> Archive is being moved, we will announce when it is back on-line. >> All emc-pstc postings are archived and searchable on the web at: >> http://www.ieeecommunities.org/emc-pstc > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
