Group:

The celebrated Numerical Electromagnetic Code (NEC) developed largely at US
taxpayer expense (Let's all Salute the US Taxpayers!) and generally released
to the public for free provides algorithms for numerically integrating
Maxwell's celebrated partial differential equations and so enables one to
obtain numerical solutions to real practical problems such as the antenna
field strengths at points in space due to modelled practical transmitting
antennas.

NEC codes are available for downloading from public WWW sites. The raw NEC
codes however do not have modern GUI based interfaces are required to be
'driven' by Fortran style card decks and profide outputs as files and not in
graphical form.

Several enterprising folks/companies have added GUE capability including
data visualization to enable a more user friendly interaction with the NEC
codes.

For example Roy Lewallen's (W7EL) famous EZNEC programs are one example of
the widespread use of the public NEC codes that have been 'enhanced' by Roy
to provide user friendly graphical (GUI) based input/output (I/O).

Apparently the outputs from the 'raw' NEC codes provide field strengths only
in rectangular co-ordinates and so... one cannot directly obtain readouts of
the circular components for circularly polarized antennas.

Thus it is relatively difficult for non-experts to print out or to plot
field strengths in terms of right hand or left hand circular propagation
co-ordinates. For example if one attempts to model a circularly polarized
antenna such as an axial mode helix, NEC (EZNEC) certainly allows the
modelling to occur by breaking the helix into small segments that
approximate a real helix to whatever degree of accuracy is required. The
difficulty comes when one attempts to plot or graph the circularily
polarized fields resulting from the modelled antenna. NEC only provides
rectangular (x-y-z) components for the fields and not direct circular
components for the fields.

It is relatively simple to calculate the circular components from NEC's
rectangular component outputs, and a simple arithmetic transformation
routine can be written to quickly and easily process the NEC outputs into
circular outputs so that one can then obtain solutions for circularily
polarized antennas expressed in terms of right and left hand circularly
polarized components.

It seems however that none of the extant GUI equipped NEC based programs
such as EZNEC have implemented this (simple) transformation.

I suppose that since the use of circularly polarized antennas is only a very
small fraction of the use of rectilinearly polarized antennas and so the
authors of NEC must have felt that their would not be much call for those
outputs. In fact the output transform from rectilinear to circular
components is trivial compared to most other aspects of NEC codes! But in
truth there is not much (commercial) call or market for the use of
circularly polarized output plots.

Question for our own Roy Lewallen W7EL... Roy do you think that there would
be much of a market for EXNEC to provide circular polarization outputs from
EZNEC, and do you have any plans to implement output plots from EZNEC in
terms of circular polarization?

I can supply you with references to the needed transformations. Just a few
lines of Fortran or Visual Basic should do it...

Just asking? [smile]

-- Pete K1PO
-- Indialantic By-the-Sea, FL

"Peter O. Brackett" wrote in message
m...
Group:

The celebrated Numerical Electromagnetic Code (NEC) developed largely at
US taxpayer expense (Let's all Salute the US Taxpayers!) and generally
released to the public for free provides algorithms for numerically
integrating Maxwell's celebrated partial differential equations and so
enables one to obtain numerical solutions to real practical problems such
as the antenna field strengths at points in space due to modelled
practical transmitting antennas.

NEC codes are available for downloading from public WWW sites. The raw
NEC codes however do not have modern GUI based interfaces are required to
be 'driven' by Fortran style card decks and profide outputs as files and
not in graphical form.

Several enterprising folks/companies have added GUE capability including
data visualization to enable a more user friendly interaction with the NEC
codes.

For example Roy Lewallen's (W7EL) famous EZNEC programs are one example of
the widespread use of the public NEC codes that have been 'enhanced' by
Roy to provide user friendly graphical (GUI) based input/output (I/O).

Apparently the outputs from the 'raw' NEC codes provide field strengths
only in rectangular co-ordinates and so... one cannot directly obtain
readouts of the circular components for circularly polarized antennas.

Thus it is relatively difficult for non-experts to print out or to plot
field strengths in terms of right hand or left hand circular propagation
co-ordinates. For example if one attempts to model a circularly polarized
antenna such as an axial mode helix, NEC (EZNEC) certainly allows the
modelling to occur by breaking the helix into small segments that
approximate a real helix to whatever degree of accuracy is required. The
difficulty comes when one attempts to plot or graph the circularily
polarized fields resulting from the modelled antenna. NEC only provides
rectangular (x-y-z) components for the fields and not direct circular
components for the fields.

It is relatively simple to calculate the circular components from NEC's
rectangular component outputs, and a simple arithmetic transformation
routine can be written to quickly and easily process the NEC outputs into
circular outputs so that one can then obtain solutions for circularily
polarized antennas expressed in terms of right and left hand circularly
polarized components.

It seems however that none of the extant GUI equipped NEC based programs
such as EZNEC have implemented this (simple) transformation.

I suppose that since the use of circularly polarized antennas is only a
very small fraction of the use of rectilinearly polarized antennas and so
the authors of NEC must have felt that their would not be much call for
those outputs. In fact the output transform from rectilinear to circular
components is trivial compared to most other aspects of NEC codes! But in
truth there is not much (commercial) call or market for the use of
circularly polarized output plots.

Question for our own Roy Lewallen W7EL... Roy do you think that there
would be much of a market for EXNEC to provide circular polarization
outputs from EZNEC, and do you have any plans to implement output plots
from EZNEC in terms of circular polarization?

I can supply you with references to the needed transformations. Just a
few lines of Fortran or Visual Basic should do it...

Just asking? [smile]

-- Pete K1PO
-- Indialantic By-the-Sea, FL


The NEC output file lists axial ratio and tilt. Nittany's NecWin Pro, and
GNEC plot these results.

73,

Frank

On Sat, 6 Dec 2008 16:53:28 -0500, "Peter O. Brackett"
wrote:

I suppose that since the use of circularly polarized antennas is only a very
small fraction of the use of rectilinearly polarized antennas and so the
authors of NEC must have felt that their would not be much call for those
outputs.

Take a little experience late in the evening, and in the morning you
will find this supposition will have cleared away.

73's
Richard Clark, KB7QHC

Peter O. Brackett wrote:

Question for our own Roy Lewallen W7EL... Roy do you think that there
would be much of a market for EXNEC to provide circular polarization
outputs from EZNEC, and do you have any plans to implement output plots
from EZNEC in terms of circular polarization?

I can supply you with references to the needed transformations. Just a
few lines of Fortran or Visual Basic should do it...

Just asking? [smile]

Plots and tabular output of circular polarization components has been a
feature of EZNEC+ and EZNEC Pro programs since the introduction of v.
4.0 in May 2004. (The current version is 5.0.) This feature isn't
included in the demo or standard programs. I see it's not properly
indexed in the manual -- I've made a note to correct that at the next
revision. It's described in Getting Started/What Was New in v. 4.0.

Roy Lewallen, W7EL

"Peter O. Brackett" wrote in message
m...
Group:


Question for our own Roy Lewallen W7EL... Roy do you think that there
would be much of a market for EXNEC to provide circular polarization
outputs from EZNEC, and do you have any plans to implement output plots
from EZNEC in terms of circular polarization?

I can supply you with references to the needed transformations. Just a
few lines of Fortran or Visual Basic should do it...

Just asking? [smile]

-- Pete K1PO
-- Indialantic By-the-Sea, FL


Hi Pete

I thought the FF Tab data in EZNEC was very informative for analyzing the
circularity of the antennas i tried to analyze with EZNEC. Perhaps you
know of some additional data that would assist me in better understanding
the polarization of these antennas. Tell me what is left out of Roy's
data in EZNEC.

Jerry KD6JDJ

Roy:

[snip]
Plots and tabular output of circular polarization components has been a
feature of EZNEC+ and EZNEC Pro programs since the introduction of v. 4.0
in May 2004. (The current version is 5.0.) This feature isn't included in
the demo or standard programs. I see it's not properly indexed in the
manual -- I've made a note to correct that at the next revision. It's
described in Getting Started/What Was New in v. 4.0.
[snip]

Oh, OK... as you likely know I am one of your customers, an EZNEC user, but
my version is older. :-(

There are no circular polarization outputs available in my version.

I'll purchase a new version so that I can have that capability.

Did you add the calculations to produce the circular outputs from NEC
rectilinear outputs yourself or is it/was it included in the basic NEC
codes?

Keep an eye out for my order. [smile]

Thanks!

-- Pete K1PO
-- Indialantic By-the-Sea, FL


"Roy Lewallen" wrote in message
...
Peter O. Brackett wrote:

Question for our own Roy Lewallen W7EL... Roy do you think that there
would be much of a market for EXNEC to provide circular polarization
outputs from EZNEC, and do you have any plans to implement output plots
from EZNEC in terms of circular polarization?

I can supply you with references to the needed transformations. Just a
few lines of Fortran or Visual Basic should do it...

Just asking? [smile]

Plots and tabular output of circular polarization components has been a
feature of EZNEC+ and EZNEC Pro programs since the introduction of v. 4.0
in May 2004. (The current version is 5.0.) This feature isn't included in
the demo or standard programs. I see it's not properly indexed in the
manual -- I've made a note to correct that at the next revision. It's
described in Getting Started/What Was New in v. 4.0.

Roy Lewallen, W7EL

Peter O. Brackett wrote:

Oh, OK... as you likely know I am one of your customers, an EZNEC user,
but my version is older. :-(

There are no circular polarization outputs available in my version.

I'll purchase a new version so that I can have that capability.

Did you add the calculations to produce the circular outputs from NEC
rectilinear outputs yourself or is it/was it included in the basic NEC
codes?

Keep an eye out for my order. [smile]

Thanks!

They're calculated from the linearly polarized NEC fields Ephi and
Etheta. As you said, NEC doesn't directly report LHP and RHP components
but the calculation is trivial from the reported linearly polarized fields.

You have v. 3.0. If you don't have either of the upgrade notice I sent,
drop me an email and I'll send you the Customer ID you need to get your
upgrade discount price. You'll need EZNEC+ if you want the circular
polarization features.

Roy Lewallen, W7EL

Jerry:

[snip]
"Jerry" wrote in message
...
..
..
..
I thought the FF Tab data in EZNEC was very informative for analyzing the
circularity of the antennas i tried to analyze with EZNEC. Perhaps you
know of some additional data that would assist me in better understanding
the polarization of these antennas. Tell me what is left out of Roy's
data in EZNEC.

Jerry KD6JDJ
[snip]

Apparently nothing!

Jerry it seems that I have an older version of EZNEC, a version that did not
support CP outputs.

I just contacted Roy todayh and ordered the latest upgrade to EZNEC +
version 5 which
Roy tells me supports CP outputs.

But... one thing about NEC is that it does not support antennas in motion.
NEC and all of the commercial
software that is derived from this (US Taxpayer supported code, God Bless
the US Taxpayer!) do not
support antennas in motion. Rather NEC supports only static antennas in
steady state excitation.

There may be some "multi-physics" programs/software out there that can
calculate radiated fields
for antennas in motion, but I am not aware of them. Of course I'm not an
expert and I have not done any
research on this topic and so I don't personally know of any programs that
can produce
CP outputs for antennas that are in motion, specifically symmetric antennas
that are rotating
at some arbitrary angular rotation velocity with respect to their axis of
symmetry.

BTW... Do you happen to know of any programs/software that can
simulate/emulate antennas in motion?

Just asking...

-- Pete K1PO
-- Indialantic, By-the-Sea, FL

Peter O. Brackett wrote:
Jerry:

[snip]
"Jerry" wrote in message
...
.
.
.
I thought the FF Tab data in EZNEC was very informative for analyzing
the circularity of the antennas i tried to analyze with EZNEC.
Perhaps you know of some additional data that would assist me in
better understanding the polarization of these antennas. Tell me
what is left out of Roy's data in EZNEC.

Jerry KD6JDJ
[snip]

Apparently nothing!

Jerry it seems that I have an older version of EZNEC, a version that did
not support CP outputs.

I just contacted Roy todayh and ordered the latest upgrade to EZNEC +
version 5 which
Roy tells me supports CP outputs.

But... one thing about NEC is that it does not support antennas in
motion. NEC and all of the commercial
software that is derived from this (US Taxpayer supported code, God
Bless the US Taxpayer!) do not
support antennas in motion. Rather NEC supports only static antennas in
steady state excitation.

And, why would this be "important"... it doesn't support arbitrary
terrain surfaces either, nor non-uniform soil properties.

Since the vast majority of "amateur radio" antennas (this is r.r.a.a,
after all) can be modeled adequately by NEC.

If you need more, fork out the bucks for a FEM code that does what you need.




There may be some "multi-physics" programs/software out there that can
calculate radiated fields
for antennas in motion, but I am not aware of them. Of course I'm not
an expert and I have not done any
research on this topic and so I don't personally know of any programs
that can produce
CP outputs for antennas that are in motion, specifically symmetric
antennas that are rotating
at some arbitrary angular rotation velocity with respect to their axis
of symmetry.


As you say, you've not researched it.

I would suggest that the need for such a thing is fairly small, but I'll
bet someone somewhere has done it, just not as a "end user" software
product.




Certainly, there IS a lot of modeling of EM waves from moving objects
(radar reflections being of particular interest).

Depends on the relative scales, too. If you're talking waves from a
meter scale object viewed from kilometers away, then using a point
source approximation for the object will work nicely, and then it's just
simple geometry.

Jim:

Hi, thanks for the inputs...

[snip]
If you need more, fork out the bucks for a FEM code that does what you
need.
[snip]

OK, I have a client who can underwrite such software, do you have a
recommendation
for a particular product?

[snip]
As you say, you've not researched it.

I would suggest that the need for such a thing is fairly small, but I'll
bet someone somewhere has done it, just not as a "end user" software
product.
[snip]

I agree, there are certainly several "commercial" high priced muliti-physics
software packages
available on the market that cost 10's of thousands of dollars per 'seat',
and... I'll bet that there
are a few more "in-house" packages developed within the defense industrial
community.

[snip]
Certainly, there IS a lot of modeling of EM waves from moving objects
(radar reflections being of particular interest).
[snip]

Yep I believe that might be so, again... do you have any specific
recommedations?

[snip]
Depends on the relative scales, too. If you're talking waves from a meter
scale object viewed from kilometers away, then using a point source
approximation for the object will work nicely, and then it's just simple
geometry.
[snip]

For the present investigation, I only need the capability to simulate
antennas that
rotate very fast...

Thanks!

-- Pete K1PO
-- Indialantic By-the-Sea, FL