Re: Radiation formula
Re: Radiation formulaLooks like Ott formulas. Personally I have trouble with those equations. There's obviously some trig functions that should be included in those equations to denote directionality or directivity, or there's some assumption(s) going on not stated. Those equations in general form are highly directional. It is true that one can use those equations to show that the E-field produced by a Hertzian magnetic dipole is proportional to the square of the frequency and that the E-field produced by a Herztian electric dipole is proportional to the frequency, but the magnitudes of the coefficients could erronously show which is of greater concern depending upon the situation and obviously do not give any information about directivity. Personal opinion only. This post is NOT to be construed as a criticism of the great pioneer himself, Mr. Ott. Regards, Doug McKean --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Radiation formula
I'll bet I could work it out, but you need to understand sever limitations of these models. The loop model is a low frequency model. It might work at 30 MHz for a physically small radiator, but it only works when the loop size is small relative to a wavelength. If there is a cable connected tot he EUT, then you have to look at cable radiation, which is more efficient at low frequencies. And that brings up a major limitation of the second equation. It only works at frequencies where the cable is electrically short. Off the top of my head I don't know the exact form of the real equation, but in this low frequency model someone has used the small angle approximation that sin x = x for small x to substitute the ratio of cable length to wavelength instead of the sine of that ratio. -- From: Dave Wilson davewilson...@yahoo.com To: emc-p...@ieee.org Subject: Radiation formula List-Post: emc-pstc@listserv.ieee.org Date: Wed, Aug 14, 2002, 1:53 PM Hi Group, I found a source which states that radiated emissions can be modeled as a small loop antenna (i.e. less than 1/4 wavelength), where the maximum E-field strength at 10m is proportional to the square of the frequency:- E = 263 x 10^-12 (F^2 x A x Is) V/m where A = loop area in sq cm, F in MHz, Is = source current in mA For cable radiation, we can model as a monopole antenna over a ground plane, whereby the maximum field strength at 10m (allowing for +6dB ground reflections) is direectional proportional to the frequency:- E = 1.26 x 10^-4 (F x L x Icm) V/m where L = cable length in m, Icm is cm current at F MHz in the cable My question is this - does anyone out there know how the constants in these formulae are derived? Thanks in advance, Dave Wilson Do You Yahoo!? HotJobs, a Yahoo! service http://rd.yahoo.com/careers/mailsig/new/*http://www.hotjobs.com - Search Thousands of New Jobs
Radiation formula
Hi Group, I found a source which states that radiated emissions can be modeled as a small loop antenna (i.e. less than 1/4 wavelength), where the maximum E-field strength at 10m is proportional to the square of the frequency:- E = 263 x 10^-12 (F^2 x A x Is) V/m where A = loop area in sq cm, F in MHz, Is = source current in mA For cable radiation, we can model as a monopole antenna over a ground plane, whereby the maximum field strength at 10m (allowing for +6dB ground reflections) is direectional proportional to the frequency:- E = 1.26 x 10^-4 (F x L x Icm) V/m where L = cable length in m, Icm is cm current at F MHz in the cable My question is this - does anyone out there know how the constants in these formulae are derived? Thanks in advance, Dave Wilson - Do You Yahoo!? HotJobs, a Yahoo! service - Search Thousands of New Jobs
