Height scanning at frequencies above 1 GHz is a serious mixed bag of effects. Most folks use horns for the measurement antenna which increased the directivity, especially when compared to a LPDA. This has been the argument for "bore-sighting" antenna masts which keep the major lobe of the antenna aligned with the EUT. Since bore-sighting isn't required, the manufacturer puts themselves at something of a disadvantage when trying to meet the spirit of the law rather than the letter of it.
The second effect is the directivity of the EUT source. If the EUT were isotropic in radiation pattern, then height scanning would be largely unnecessary, but this is not the case. Apertures and aperture arrays can be highly directive as frequencies go up. For this reason alone, I believe height scanning is necessary to provide a complete picture of the EUT emissions. Brent DeWitt Loveland, CO From: [email protected] [mailto:[email protected]]On Behalf Of [email protected] Sent: Friday, February 13, 2004 3:33 AM To: [email protected] Subject: Re: High Frequency Measurements Also above 1 GHz directivity comes more and more into play (another reason for hieght-scanning). Bob Heller 3M EMC Laboratory, 76-1-01 St. Paul, MN 55107-1208 Tel: 651- 778-6336 Fax: 651-778-6252 ======================================================= "Luke Turnbull" <[email protected] To: <[email protected]> > <[email protected]> Sent by: cc: owner-emc-pstc@majordo Subject: Re: High Frequency Measurements mo.ieee.org 02/13/2004 03:34 AM Please respond to "Luke Turnbull" The reason for height-scanning is that there are unavoidable reflections >from the groundplane, and the only way to ensure that your measurement geometry is not causing a deep null is to scan the height. The reason that reflections are unavoidable is that at 30MHz, absorber would have to be 2.5 m deep which is not practical or economic.k At frequencies above 1 GHz, absorber is practical and economic, and I is easy to put absorber on the ground to minimise the small effect that there might be on your measurement due to ground reflections, and not bother with height scanning. Luke Turnbull >>> "Wiz" <[email protected]> 12/02/2004 15:36:41 >>> Hello, I have a need to make radiated measurements up to 40 GHz. I uses a low loss cable that gives me enough dynamic range up to 18GHz. The cable is very short and I have to move my measurements equipment out to the antenna. I know I need to get a pre-amp and mixer, but what do I do about the cable loss? I have called many places and I cannot find good enough cable to measure to 40 GHz. The other alternative is waveguides as I understand. Those would, I assume, be coupled directly to the input of the mixer. This does not allow for antenna height adjustments form 1 to 4m as required. I have seen other test reports where high frequency data was taken where the antenna was held at about 1meter. I can understand this since emissions will likely be very directional at those frequencies. Is it acceptable to make measurements with the receive antenna at 1 meter only? Thanks for any information you can provide. Wiz This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ 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] 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.ieee-pses.org/ 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] 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.ieee-pses.org/ 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
