On Wed, 18 May 2005 00:47:01 -0700, DaveC wrote:

On Sat, 14 May 2005 11:56:51 -0700, Jeff Liebermann wrote
(in article ):

This might help:
http://802.11junk.com/jeffl/pics/antennas/Biquad/
It's the 4NEC2 output for Trevor Marshall's biquad design. I'll tweak
it to include a VSWR over frequency graph later.

Not to look a gift horse in the mouth, but how about a plot of VSWR vs.
groundplane-to-element spacing?

If I did everything I promised to do, I'd never get anything done.

See:
http://802.11junk.com/jeffl/pics/ant...uad/index.html
I've added a VSWR and reflection coefficient graph, main page, and
NEC2 file.
http://802.11junk.com/jeffl/pics/ant.../biqdfeed2.nec

The 300MHz frequency used is handy because everything is in
wavelengths. In this case, to get 2400MHz, just multiply everything
by 8. For example, the 288-312MHz frequency plot is actually
2304-2496MHz. If you extract dimensions from the model, it's the same
story. Multiple all dimensions that are in wavelengths by 8 to get
something useable at 2400Mhz. If you want to use the design for a
cell phone antenna or other frequency, just use a different scaling
factor.

I think the NEC2 deck I posted is the one that came with the samples
in the 4NEC2 program. (Actually, I'm not sure where it came from.)
You can download the program and sample antennas from:
http://www.si-list.org/swindex2.html#4nec2_

The frequency plot was done by changing the FR card to:
FR 0 7 0 0 288 4
This results in the plots being slightly off the ideal 300MHz
frequency. Therefore, I posted the frequency plot and main page that
was generated with the above frequency scan. There are probably
better ways to do this, but with 9 minutes per compile, I just used
what popped into my foggy brain first.

For construction details and dimensions, see:
http://martybugs.net/wireless/biquad/
The antenna to reflector spacing isn't horribly critical. The above
construction article uses 15mm. I've been adjusting the height during
construction for maximum gain and/or best VSWR and ending up with
about 16mm (measured to center line of copper wire).



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558