"Dave (from the UK)"
wrote in message ...
Wimpie wrote:

Hi Dave,

Hi Wim

Whether or not the formula is applicable, depends on many factors as
mentioned in my previous posting.

For a broadside array, the formula holds with same accuracy as for
continuous aperture antennas. In my antenna courses I use the
broadside array approach to derive the 2B^2/lambda formula.

My situation is very odd. As I said at the start, this is not an amateur
antenna.

The array of "antennas" are not designed to work as one nice antennas, but
are an essentially random(ish) collection of radiating centres. (However,
they are all energised from the same signal source). So they can be
considered like a phased array, as they are regularly spaced all in one
long line.

Hence my original diagram

A---A---A---A---A---A---A---A---A---A

accurately describes the situation. Each "A" is an antenna. The amplitude
and phase can be arbitrary.

I do *not* want them to behave as a nice phased array with decent gain and
low side-lobes! Each antennas is radiating an *unwanted* signal. But the
fact remains that the gain could conceivably be high under some
circumstances, which would create interference.

Hence I need to test this.

I would reserve the term "far field distance" for that distance where
the complete radiation pattern does not change with measuring
distance. In that case, the 2B^2/lambda formula is a good rule of
thumb.

In this case, I am interested in any direction. The direction of the main
lobe will be essentially random.

--
Dave (from the UK)


Hi Dave

I'm curious about two things.

1 - Do you intend to actually make and record measurements of the
radiated field, or do you want to determine the minimum distance at which
the measurements can be made?
2 - What prevents the use of a computer modeling program to predict the
pattern?

Jerry

Jerry Martes wrote:

Hi Dave

I'm curious about two things.

1 - Do you intend to actually make and record measurements of the
radiated field, or do you want to determine the minimum distance at which
the measurements can be made?

yes

2 - What prevents the use of a computer modeling program to predict the
pattern?

nothing. I think that will be done. But a theoetical analysis would be
nice if possible.


Jerry




--
Dave (from the UK)

Please note my email address changes periodically to avoid spam.
It is always of the form:
Hitting reply will work for a few months only - later set it manually.

http://chessdb.sourceforge.net/ - a Free open-source Chess Database

On 22 abr, 12:25, "Dave (from the UK)" see-my-signat...@southminster-
branch-line.org.uk wrote:
Wimpie wrote:
Hi Dave,

Hi Wim

Whether or not the formula is applicable, depends on many factors as
mentioned in my previous posting.
For a broadside array, the formula holds with same accuracy as for
continuous aperture antennas. In my antenna courses I use the
broadside array approach to derive the 2B^2/lambda formula.

My situation is very odd. As I said at the start, this is not an amateur
antenna.

The array of "antennas" are not designed to work as one nice antennas,
but are an essentially random(ish) collection of radiating centres.
(However, they are all energised from the same signal source). So they
can be considered like a phased array, as they are regularly spaced all
in one long line.

Hence my original diagram

A---A---A---A---A---A---A---A---A---A

accurately describes the situation. Each "A" is an antenna. The
amplitude and phase can be arbitrary.

I do *not* want them to behave as a nice phased array with decent gain
and low side-lobes! Each antennas is radiating an *unwanted* signal. But
the fact remains that the gain could conceivably be high under some
circumstances, which would create interference.

Hence I need to test this.

I would reserve the term "far field distance" for that distance where
the complete radiation pattern does not change with measuring
[all text deleted]

Hi Dave,



I don't know what you are going to do with the array. As long as you
understand how a radiation pattern (whether within or outside the far
field distance) can be calculated based on the array elements, you
should be able to find a comfortable distance. I think references to
scientific documents will not help you any further, maybe a physics
book on electromagnetism or a specialized book on beam forming
antennas may help you.

If your organization is not able to do this in-house, you might hire
an expert.

Best regards,

Wim
PA3DJS

"Dave (from the UK)"
wrote in message ...
Jerry Martes wrote:

Hi Dave

I'm curious about two things.

1 - Do you intend to actually make and record measurements of the
radiated field, or do you want to determine the minimum distance at which
the measurements can be made?

yes

2 - What prevents the use of a computer modeling program to predict
the pattern?

nothing. I think that will be done. But a theoetical analysis would be
nice if possible.


Jerry


--
Dave (from the UK)

Hi Dave

Would you consider building a scale model of this array to allow a polar
orbiting satellite to be the illuminator?
I get some pretty good radiation pattern plots at VHF, using Patrik Tast's
SignalPlotter program and NOAA satellites.

Jerry

Jerry Martes wrote:
Hi Dave

Would you consider building a scale model of this array to allow a polar
orbiting satellite to be the illuminator?

It's not really practical to do that for various reasons. The structure
is not a nice conventional antenna that can be scaled up/down size.

I get some pretty good radiation pattern plots at VHF, using Patrik Tast's
SignalPlotter program and NOAA satellites.

Jerry

That's a concept I have not heard of before. But for me to work at VHF,
I'd need to make the structure larger by a factor of 10, so it would be
several hundred metres long.


--
Dave (from the UK)

Please note my email address changes periodically to avoid spam.
It is always of the form:
Hitting reply will work for a few months only - later set it manually.

http://chessdb.sourceforge.net/ - a Free open-source Chess Database

"Dave (from the UK)"
wrote in message ...
Jerry Martes wrote:
Hi Dave

Would you consider building a scale model of this array to allow a
polar orbiting satellite to be the illuminator?

It's not really practical to do that for various reasons. The structure is
not a nice conventional antenna that can be scaled up/down size.

I get some pretty good radiation pattern plots at VHF, using Patrik
Tast's SignalPlotter program and NOAA satellites.

Jerry

That's a concept I have not heard of before. But for me to work at VHF,
I'd need to make the structure larger by a factor of 10, so it would be
several hundred metres long.


--
Dave (from the UK)

Hi Dave

You are not restricted to VHF. It is possible that there is a polar
orbiting satellite transmitting continuously on the frequency you are
interested in. NOAA satellites transmit continuously at about half the
frequency range you refer to.

Jerry

Dave (from the UK) wrote:
Jerry Martes wrote:

Hi Dave

I'm curious about two things.

1 - Do you intend to actually make and record measurements of the
radiated field, or do you want to determine the minimum distance at
which the measurements can be made?


yes


An interesting problem. What you're presumably trying to do is
determine how far do I need to be to bound the uncertainty on a
measurement in an arbitrary direction. Or, another way, at what distance
is the collective effects of the phase error for each of the signals
(due to path length differences) smaller than your measurement
uncertainty (so you don't care anymore).

This can be quite challenging if you want to worry about -40dB nulls,
for instance, because a very small phase error can result in a -40dB
null becoming a -30 dB null.

Complicating it a bit is that what you're probably really concerned with
is a statistical problem.. you've got multiple sources, a random
direction of observation, (and practically speaking, some propagation
uncertainties between antenna and observation point).

You might want to look for a paper by Dybdal and Ott: "Coherent RF
Error Statistics", IEEE Trans MTT, v34,n12, Dec 86, pp1413-1420 which
discusses this in some detail, and, as well, provides some nice
approximations that are useful in practical systems.



2 - What prevents the use of a computer modeling program to
predict the pattern?


nothing. I think that will be done. But a theoetical analysis would be
nice if possible.

One can come up with a "bound" for the performance from analytical
means, and a Monte Carlo analysis can give you some statistics.

Jim

Jerry Martes wrote:
"Dave (from the UK)"
wrote in message ...

Jerry Martes wrote:

Hi Dave

Would you consider building a scale model of this array to allow a
polar orbiting satellite to be the illuminator?

It's not really practical to do that for various reasons. The structure is
not a nice conventional antenna that can be scaled up/down size.


I get some pretty good radiation pattern plots at VHF, using Patrik
Tast's SignalPlotter program and NOAA satellites.

Jerry

That's a concept I have not heard of before. But for me to work at VHF,
I'd need to make the structure larger by a factor of 10, so it would be
several hundred metres long.


--
Dave (from the UK)


Hi Dave

You are not restricted to VHF. It is possible that there is a polar
orbiting satellite transmitting continuously on the frequency you are
interested in. NOAA satellites transmit continuously at about half the
frequency range you refer to.

Jerry



One can also use Ku-band DBS satellites as an illuminator.

HOWEVER, if you're looking for gnat's eyelash precision, watch out for
atmospheric irregularities/inhomogeneity dominating the measurement.
When you start to get to many km as your "distance to adequately
replicate plane wavefront" the propagation uncertainty will probably be
the greatest source of error. You get "bubbles" of air with local
variations on the scale of meters.

A more practical approach (depending on the precision required) is some
form of near field measurement (or a measurement where the different
path lengths from the radiator to the observation point are explicitly
taken into account).

"Jim Lux" wrote in message
...
Jerry Martes wrote:
"Dave (from the UK)"
wrote in message ...

Jerry Martes wrote:

Hi Dave

Would you consider building a scale model of this array to allow a
polar orbiting satellite to be the illuminator?

It's not really practical to do that for various reasons. The structure
is not a nice conventional antenna that can be scaled up/down size.


I get some pretty good radiation pattern plots at VHF, using Patrik
Tast's SignalPlotter program and NOAA satellites.

Jerry

That's a concept I have not heard of before. But for me to work at VHF,
I'd need to make the structure larger by a factor of 10, so it would be
several hundred metres long.


--
Dave (from the UK)


Hi Dave

You are not restricted to VHF. It is possible that there is a
polar orbiting satellite transmitting continuously on the frequency you
are interested in. NOAA satellites transmit continuously at about
half the frequency range you refer to.

Jerry

One can also use Ku-band DBS satellites as an illuminator.

HOWEVER, if you're looking for gnat's eyelash precision, watch out for
atmospheric irregularities/inhomogeneity dominating the measurement. When
you start to get to many km as your "distance to adequately replicate
plane wavefront" the propagation uncertainty will probably be the greatest
source of error. You get "bubbles" of air with local variations on the
scale of meters.

A more practical approach (depending on the precision required) is some
form of near field measurement (or a measurement where the different path
lengths from the radiator to the observation point are explicitly taken
into account).


Hi Jim

Is the DBS satellite polar orbiting?

Jerry

Jerry Martes wrote:
"Jim Lux" wrote in message
...

Jerry Martes wrote:

"Dave (from the UK)"
wrote in message ...


Jerry Martes wrote:


Hi Dave

Would you consider building a scale model of this array to allow a
polar orbiting satellite to be the illuminator?

It's not really practical to do that for various reasons. The structure
is not a nice conventional antenna that can be scaled up/down size.



I get some pretty good radiation pattern plots at VHF, using Patrik
Tast's SignalPlotter program and NOAA satellites.

Jerry

That's a concept I have not heard of before. But for me to work at VHF,
I'd need to make the structure larger by a factor of 10, so it would be
several hundred metres long.


--
Dave (from the UK)


Hi Dave

You are not restricted to VHF. It is possible that there is a
polar orbiting satellite transmitting continuously on the frequency you
are interested in. NOAA satellites transmit continuously at about
half the frequency range you refer to.

Jerry

One can also use Ku-band DBS satellites as an illuminator.




Hi Jim

Is the DBS satellite polar orbiting?

Jerry

no.. Clarke orbit (e.g. for Dish Network or DirecTV)

There are some orbiting TV satellites in Molniya orbits for covering
Siberia that might be useful. They radiate in C band, and perhaps Ku?

The GOES polar orbiters radiate at 1.6 GHz, and I'm sure there's
others out there. GPS radiates at several L-band frequencies.

ISS radiates in S and Ku bands and is in LEO, as is the Shuttle when
it's up. I don't know if they would be useful as a source though,
because the antenna is directional and probably pointed at TDRSS or a
ground station.