Re: NEC-LIST: VHF CFA Paper

Brian,

In what follows, I should have done before hitting the send button on
the message I just sent you.

Changing the phases by + and minus 10-degrees makes little difference
in computed gain.

This TOTALLY disagrees with the result shown in the previously
referenced Hatley et. al. paper, which shows that if we change the
phase by + and minus 0.1 degrees the output power decreases to
60-percent.

In the real world we cannot hold phase to within + and - 0.1
degrees!!!

Does a perfectly circular plate make it work?? I cannot believe that
it does.

If you can tell me how the antenna system I modelled is grounded, I
can put the CFA over a 10 m wire grid, elevated by about 7.3 m (the
estimated building height) and grounded in some way --- i.e. an
antenna over real ground.

The *best* performance for my CFA model is found by feeding the
cylinder and the plate IN PHASE. But here we have two co-located very
simple antenna systems. We have an electrically small monopole (the
cylinder); and a heavily top loaded very-very-very short monopole (the
0.6 m feed conductor top loaded by the plate.

For the tuned version (the untuned version has high gain since there
are no losses with a PEC ground other than conductor losses) the
impedance of the cylinder is 3 ohms; the impedance of the plate is 1.7
ohms; and the gain is -8.8 dBi. Inductor Q-factors 300.

These resistive components are largely the loss resistances in the
inductors tuning the elements ( j 860 and j 498 ohms for the cylinder
and the plate respectively), since the untuned resistances are
very-very low: 0.16 and 0.06 ohms respectively.

John S. Belrose
26 March 1999

_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
Communications Research Centre
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2779
FAX 613-998-4077
e-mail <john.belrose_at_crc.ca>
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Received on Sun Mar 28 1999 - 15:12:59 EST