Re: NEC-LIST: CFA modeling results

>Jack,
>
>Thank you very much for your reply. I read it with interest and I will
>still follow up any discussion/analysis on the CFA. I realize that our
>modeling results differ quite a bit, including my own two models.
>
>I have come to the conclusion, that my modeling software cannot
>accurarely simulate the actual CFA. Only more expensive modeling
>software may accomplish that ? Therefore, I have decided not to do any
>more modeling of the CFA. Also, I cannot model the phasing network, etc.
>I looked at your model, and I was wondering, how you modeled the phasing
>network ?
>
>I believe now, that only your experimental model will give some concrete
>answers to all the questions we had, even if it is a scaled-down model .
>I certainly wish you luck, and I hope that your test results will
>finally provide the " right " answers to this " mysteriuos " antenna !
>
>Regards, Max

Max,

Thank you for your interest in the CFA. I will say one thing it is a
curious antenna.

With the EZNEC/4D program that I use, I can include series or parallel
loads, and I have tried to include matching and phasing circuitry ---
but gave up. As I said the input port impedances depend strongly on
the amplitude and phase of the source currents (and on whether one
uses current or voltage sources).

The circuitry used by the inventors of the CFA seems to be as
uncertain as is its performance.

The original experiments (in 1989) employed an RF source feeding delay
and advance circuitry, followed by two linear amplifiers powering the
CFA. The ICAP'91 paper shows a simplified method of tuning (as I said
before), viz. a capacitor in series with the cylinder (labelled +45
degrees), an inductor in series with the disc (labelled -45 degrees),
both inputs common, connecting to a 50:25 ohms transformer. This
circuit and the accompanying text suggests that when properly tuned
and phased the antenna system is resonant.

I have searched in vain for resonance. If I set one source current at
1-ampere (or 1-volt), maintain the minus and plus 45-degree phase
relation, and let the other source current (or voltage) be greater and
less than 1-ampere (or 1-volt), I can find no current (or voltage)
relationship that resonates the antenna.

Both ports are capacitive reactive, and the real part of the impedance
depends on the amplitude differences of the source currents (or
voltage).

The first circuit for the 80M reduced size antenna (Antennex CFA) was
balanced. The second alternative circuit is not balanced, and,
curiously the L-netork feeding the disc is reversed. The two circuits
tend to obscure the true operation, and no one seems to know what they
are doing. I want to stay at arm's length from the Antennex muddle.

It will work, according to Brian Stewart, with either circuit and yet
AntenneX says clearly that the first circuit doesn't work. According
to John Stanely it works (efficiently) with neither circuit.

Fathi Kabbary, I have not communicated with him, apparently has a
circuit (according to Brian Stewart) that works, but he does not want
this information disclosed.

So where are we in this never ending discussion loop? Both Brian and
Maurice are firmly convinced that the CFA is a real-antenna working on
a completely new technique, and not on the techniques of the past ---
and that NEC cannot predict the performance of this antenna. I am
convinced that NEC can predict the performance of the CFA.

Let me stick this discussion to phasing. According to NEC, with
quadrature feed, I need to have the phase relationships as follows:

1) Cylinder - 45-degrees; Disc + 45-degrees (opposite to that above); or

2) Cylinder 0-degrees; Disc + 90-degrees; or

3) Cylinder - 90-degrees; Disc 0-degrees.

Otherwise the antenna does not radiate at all, pattern isotropic, Gain
< - 99.99 dBi.

So, we will have to find out how to tune our antenna when we have it
in the field. We will stick with equal currents. A current balun
will force equal currents. An inductor in series (each port) will
resonate the impedances, and additional circuitry in one (or both)
input ports will be adjusted to achieve the quadrature phase
relationship.

We can then validate NEC, by impedance, direction of power flow, and
field strength measurement.

If NEC is validated, we will then have to appeal for help, on how to
realize positive gain, since Hately Antenna Technology says that the
CFA antenna achieves, by Poynting Vector Synthesis, a compact,
broadband and efficient antenna.

Regards, Jack

_____________________________________________
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>
_____________________________________________
Received on Tue Jul 06 1999 - 20:40:37 EDT