Mr. Cuthbert is right, the directivity is 3.28 assuming an infinite ground plane. Isotropic radiation into half of space would be a directivity of 2. I think the most important facet of the 41" rod antenna ( or similar device used over a range for which it is electrically very short) is not so much its directivity but the field impedance, which is quite high. It is a fair approximation in fact to say that this antenna radiates not at all, and that what you get is the quasi-static lines of electric force for which the electric field can be calculated as the potential on the rod relative to the ground plane, along the electric field line path, i.e., a simple potential gradient. Note that no current has to flow in the rod to generate this field and therefore there is little or no power to radiate. Shielding against such a field is easy, the same material that could give you 120 dB of electric field SE might only yield 20 dB of magnetic or plane wave shielding effectiveness.
From: [email protected] List-Post: [email protected] Date: Thu, 28 Oct 2004 17:33:26 -0600 To: <[email protected]>, <[email protected]> Subject: RE: Vertical monopole with counterpoise radiation pattern Gary, almost but not quite isotrophically. There is zero radiation straight up- just like off the ends of a dipole. I will send you a WORD document with the radiation pattern of a monopole. Dave Cuthbert Micron Technology From: [email protected] mailto:[email protected]] On Behalf Of Gary McInturff Sent: Thursday, October 28, 2004 5:19 PM To: [email protected] Subject: Vertical monopole with counterpoise radiation pattern Folks, I'm guessing that for a given dimension above the ground plane the above antenna radiates isotrophically, correct. (No - I'm not much of an antenna guy). Just trying to figure out a little about the shielding integrity test for e-fields in Mil-std- 285. Thanks Gary ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [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 Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [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 Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [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
