2.4Ghz vs. 5GHz antenna

[James Knott]

faisal-nMFrlatgk0VeoWH0uzbU5w at public.gmane.org wrote:
> So a normal antenna for any frequency will be of a harmonic fraction 
> of the wavelength of the signal.  For best performance you'd want a 
> 1/2 wavelength antenna.
>
> For 5.4 GHz, the wavelength is 6cm.
> For 2.4 GHz, the wavelength is 12cm.
>
> http://www.csgnetwork.com/freqwavelengthcalc.html
>
> So a 2.4 GHz antenna that is say, a 1/2 wavelength antenna should work 
> well as a 1/4 wavelength antenna.

You'd better go back to school on this.  As I mentioned in another note, 
the simplest antenna is a dipole, which is 1/2 wavelength overall or 1/4 
wavelength either side of the feed point.  A similar antenna would be a 
1/4 wavelength element and ground, with the ground representing the 
other side of the antenna.  In these examples 1/4 wavelength presents a 
low impedance which is easily matched by common radio equipment.  If the 
1/4 wavelength elements were replace with 1/2 wavelength, then you'd 
have a high impedance, which will not match the equipment.  Since 5 GHz 
is just over twice 2.4 GHz, a 1/4 wavelength element @ 2.4 GHz is now a 
1/2 wavelength @ 5 GHz.
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