I have successfully constructed various 2400 Mhz antennas using the
4nec2 antenna modelling software (really great application, warm tnx
to the author should he read this!)

What I would like now is to get a rough idea as to how close I can put
the antenna elements to a PVC casing without disturbing the radiation
pattern, SWR etc.

E.g. by putting a 2 mm lossless PVC sheet (with dielectricity constant
= 7) 1 cm in front of the antenna element.

Is it possible to simulate this?

Alex

I have successfully constructed various 2400 Mhz antennas using the
4nec2 antenna modelling software (really great application, warm tnx
to the author should he read this!)

What I would like now is to get a rough idea as to how close I can put
the antenna elements to a PVC casing without disturbing the radiation
pattern, SWR etc.

E.g. by putting a 2 mm lossless PVC sheet (with dielectricity constant
= 7) 1 cm in front of the antenna element.

Is it possible to simulate this?

Alex


Not with a freebie NEC based program.

Also, Why are you using PVC? This stuff is horrible as a base substrate at 2.4
GHz.

73,
Chip N1IR

On 14 Sep 2004 12:38:36 GMT, (Fractenna) wrote:
Also, Why are you using PVC? This stuff is horrible as a base substrate at 2.4
GHz.

Because I can get a cheap PVC case which is otherwise suitabel for
weatherproofing the antenna. And because I have seen reported (I have
not tried it myself) that such material does not get heated in a
microwave oven.

The antenna elements themselves are sandwiched between (1 cm)
styrofoam sheets which should be lossless and have a dielectric
constant = 1 (almost). So the antenna elements would not be in direct
contact with the PVC case.

Have you got any other suggestions for a weatherproof case material?

73 & tnx fer ur answer
Alex

"Alex" wrote in message
...
On 14 Sep 2004 12:38:36 GMT, (Fractenna) wrote:
Also, Why are you using PVC? This stuff is horrible as a base substrate
at 2.4
GHz.

Because I can get a cheap PVC case which is otherwise suitabel for
weatherproofing the antenna. And because I have seen reported (I have
not tried it myself) that such material does not get heated in a
microwave oven.
You should try this yourself. I think you will be surprised.

Because I can get a cheap PVC case which is otherwise suitabel for
weatherproofing the antenna. And because I have seen reported (I have
not tried it myself) that such material does not get heated in a
microwave oven.

This is a good, first-order test. But, as warned, different pvc manu's give
different results. It wasn't made for s-band RF. You must test it thoroughly
without extrapolating. Some is almost OK; others are really poor. Sure ain't
kidex.

73,
Chip N1IR

Who told you PVC was lossless? Stick a sample of it in a (2.4 GHz) microwave oven and see what happens. You could
simulate it with a sheet of carbon impregnated foam, but I guess 4nec2 doesn't handle that either. If you need a
radome, use foam polystyrene, commonly known as Styrofoam®.

--
Crazy George
Remove N O and S P A M imbedded in return address
"Alex" wrote in message ...
I have successfully constructed various 2400 Mhz antennas using the
4nec2 antenna modelling software (really great application, warm tnx
to the author should he read this!)

What I would like now is to get a rough idea as to how close I can put
the antenna elements to a PVC casing without disturbing the radiation
pattern, SWR etc.

E.g. by putting a 2 mm lossless PVC sheet (with dielectricity constant
= 7) 1 cm in front of the antenna element.

Is it possible to simulate this?

Alex

On Tue, 14 Sep 2004 10:23:18 -0500, "Crazy George"
wrote:

Who told you PVC was lossless? Stick a sample of it in a (2.4 GHz) microwave oven and see what happens. You could
simulate it with a sheet of carbon impregnated foam, but I guess 4nec2 doesn't handle that either. If you need a
radome, use foam polystyrene, commonly known as Styrofoam®.

many tnx for your answer

actually I am using styrofoam already for the indoor model. But
styrofoam is too soft and vulnerable to make weatherproof so I shall
have to put it in a case made of something more rugged.

Evidently 4nec2 does not handle the needed simulation so I shall look
around for other software or maybe make a SWR meter and some practical
experiments...

Alex

PVC is not lossless, however...

I used PVC drainage pipe (white, 3 mm thick maybe) to make radome for 900MHz
antenna. Specifically, directional patch arrays. It tuned them down a little
bit (2 mm maybe over half-wave length.) I did not measure significant
decrease of gain. The cover did not touch the radiator. When it touches,
loading get significantly worse.

Andrey


It"Alex" wrote in message
...
On Tue, 14 Sep 2004 10:23:18 -0500, "Crazy George"
wrote:

Who told you PVC was lossless? Stick a sample of it in a (2.4 GHz)
microwave oven and see what happens. You could
simulate it with a sheet of carbon impregnated foam, but I guess 4nec2
doesn't handle that either. If you need a
radome, use foam polystyrene, commonly known as Styrofoam®.

many tnx for your answer

actually I am using styrofoam already for the indoor model. But
styrofoam is too soft and vulnerable to make weatherproof so I shall
have to put it in a case made of something more rugged.

Evidently 4nec2 does not handle the needed simulation so I shall look
around for other software or maybe make a SWR meter and some practical
experiments...

Alex

On Tue, 14 Sep 2004 11:31:29 -0700, "Andrey"
wrote:

PVC is not lossless, however...

I used PVC drainage pipe (white, 3 mm thick maybe) to make radome for 900MHz
antenna. Specifically, directional patch arrays. It tuned them down a little
bit (2 mm maybe over half-wave length.) I did not measure significant
decrease of gain. The cover did not touch the radiator. When it touches,
loading get significantly worse.

tnx for your reply

But it seems to me that what you describe is not so much that the PVC
absorbs energy ("loss") but instead: that it unavoidably de-tunes the
antenna because of its high dielectric constant (about 5 to 9 I
understand). Especially when the PVC touches the radiators the
capacitance between radiator parts is markedly reduced because of this
phenomenon (anyway that is how I intuitively understand it...)

Alex

But it seems to me that what you describe is not so much that the PVC
absorbs energy ("loss") but instead: that it unavoidably de-tunes the
antenna because of its high dielectric constant

PVC is L-O-S-S-Y at 2.4 GHz. The amount varies according to manufacturer. CPVC
has the least loss of a lossy lot.

OK?:-)

73,
Chip N1IR