The increase in gain of a fixed length wire antenna is given in the ARRL handbook and is less than monotonic with increasing frequency, further it comes at a high price for a broadcast antenna: the main lobe veers away from an optimal toroidal pattern and begins to align with the wire.
But I am not sure that has any bearing whatsoever on the issue of deriving a microwave radiated emission limit. The issue as I see it is this: If I build a 900 MHz link, and a 2.4 GHz link, the antennas for the 2.4 GHz link will be shorter by the ratio of their wavelengths, for the same gain. That means the shorter antenna's effective aperture has decreased, and it is less efficient as a receiver. In turn that means it can stand a higher level of radiated rfi. Which means to me, other things equal, that the radiated rfi limit should increase with increasing frequency. What am I missing? ---------- >From: Cortland Richmond <[email protected]> >To: Ken Javor <[email protected]>, ieee pstc list <[email protected]> >Subject: Re: Clock frequencies >Date: Wed, Sep 18, 2002, 8:34 PM > > An antenna of some physical size will indeed have gain increasing with > frequency. There is some justification, a 1 GHz antenna being reasonably > small, for assuming that antennas will have similar sizes -- and increasing > gain -- above 960 MHz. However, I suspect that the original limit was > simply an extrapolation, not many users existing there to be affected by > Part 15 devices, from the limit _below_ 960 MHz. > > Cortland > ------------------------------------------- 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] 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"
