Slot antennas began life as slots in curved surfaces, eg., aircraft
fuselages and wings. Most structural alloys will do fine. Rectangular
tubes are unusual. They are often unsightly protusions.

The maths is more complicated with curved surfaces.

But if you just copy somebody else's slot, and scale dimensions
according
to
frequency, the maths reduces to simple A*B/C schoolboy arithmetic.

I have not found any round rather then square designs on the net. Do you
know of any? If I found one I could scale it down to 33cm. I have not
found any 33cm slotted designs period. I have found a calculator for
rectangular waveguide though which I ran for 33cm. Not sure how I would
adapt its results to round though.

Matt

It should be close, yoy may have to move the slots closer of further apart
by the velocity factor inside the waveguide (going from rectangular to
round, round could be faster so slots may be further apart, but not by
much)
How many slots, how many wavelengths long?

I am wanting 10 slots, 5 per side. I think 7" inch aluminun pipe for
waveguide in 33cm band.

Another question. I have heard for injection into the waveguide you should
use a 1/4 wave stub. I also heard its not supposed to farther then half way
into the waveguide. If I were to use 2" x "8 waveguide how would I do that
since the 1/4 wave stub is 3.2 inches and the waveguide is only 2 inches
wide?

Matt

On Fri, 17 Dec 2004 09:26:51 -0600, "Matt"
wrote:

Another question. I have heard for injection into the waveguide you should
use a 1/4 wave stub. I also heard its not supposed to farther then half way
into the waveguide.

Hi Matt,

What you've "heard" is vague at best. You really need another source
of information, or at least more sources. Try searching the
googlegroups archive of this news group.

In your particular situation (you will eventually have to convert all
this to coax or wire) you either probe excite a waveguide or you loop
excite it.

73's
Richard Clark, KB7QHC

"Matt" wrote in message
...
Slot antennas began life as slots in curved surfaces, eg., aircraft
fuselages and wings. Most structural alloys will do fine.
Rectangular
tubes are unusual. They are often unsightly protusions.

The maths is more complicated with curved surfaces.

But if you just copy somebody else's slot, and scale dimensions
according
to
frequency, the maths reduces to simple A*B/C schoolboy arithmetic.

I have not found any round rather then square designs on the net. Do
you
know of any? If I found one I could scale it down to 33cm. I have not
found any 33cm slotted designs period. I have found a calculator for
rectangular waveguide though which I ran for 33cm. Not sure how I
would
adapt its results to round though.

Matt

It should be close, yoy may have to move the slots closer of further
apart
by the velocity factor inside the waveguide (going from rectangular to
round, round could be faster so slots may be further apart, but not by
much)
How many slots, how many wavelengths long?

I am wanting 10 slots, 5 per side. I think 7" inch aluminun pipe for
waveguide in 33cm band.

Another question. I have heard for injection into the waveguide you
should
use a 1/4 wave stub. I also heard its not supposed to farther then half
way
into the waveguide. If I were to use 2" x "8 waveguide how would I do
that
since the 1/4 wave stub is 3.2 inches and the waveguide is only 2 inches
wide?

Matt

The 2" by 8" sounds wrong for gernic waveguide. it is usally in about a 1:2
ratio
It may be more like 4" by 8" for 900 Mhz.
The field max is in the middle of the waveguide, and the probe end needs to
be there.
ARRL had an article on the rectangular waveguide antenna.
The beam on this antenna if mounted horozontally is very narrow in the
horozontal but wide in the vertical. Fan shaped beam.

Richard Clark wrote:
On Thu, 16 Dec 2004 10:42:48 -0600, "Matt"
wrote:

Can I make a slot antenna out of round pipe rather then rectangular?


Hi Matt,

Round pipe is quite common.

Any URL with examples, plans, calcilations ?
Any book ?

All I find are rectangular WG slot.
Only "Alford Slot" but that isnt what we talk about.

73!

Matt wrote:
Can I make a slot antenna out of round pipe rather then rectangular?

I assume you are referring to a circular waveguide with slot radiators
cut into the surface. The usual arrangement is to use a rectangular
waveguide with dimensions chosen so that only one possible propagation
mode exists for the wavelength in use. This makes it fairly simple to
determine suitable locations and dimensions of the radiating slots for
the desired current distribution.

The problem with circular waveguide is that it does not constrain the
polarization to any particular orientation. Even if the wave is
launched in a known orientation, the presence of the slots may very well
induce a 'twist' in the propagating wave which will affect the
excitation of the slots in a way which may be extremely difficult to
predict, or even measure.

One remedy is to insert features inside the circular waveguide which
constrain the propagating wave to the desired polarization direction.
Specific methods can be found in the microwave literature but I think
you will find fabrication of rectangular waveguide by far the easiest
solution if you're only going to construct a few units.

bart
wb6hqk



I am having a hard time finding inexpensive rectangular tubing for working
in 33cm band. Figure I need 2" x 8" and its not cheap. I can get 7" pipe
much cheaper.

Matt

On Sat, 18 Dec 2004 09:52:07 +0100, Darko
wrote:
Any URL with examples, plans, calcilations ?
Any book ?

All I find are rectangular WG slot.
Only "Alford Slot" but that isnt what we talk about.

Hi OM,

It isn't? Why? This one is available at:
http://www.eta.chalmers.se/~pgp/alfo...lford_eng.html
and seems a perfectly useful introduction to the topic.

http://www.qsl.net/kd2bd/slot.html
discusses other factors, such as the slot length that affects the
elevation gain profile.

http://members.ij.net/packrats/Slot_...a/Slot_ant.pdf
is more the classic discussion using standard waveguide materials with
an array of slots. This in turn offers a link:
http://www.ham-radio.com/sbms/sd/slotant.htm
that leads to a BASIC program for calculating the dimensions for these
standard waveguides.

http://hjem.get2net.dk/ole_nykjaer/o...lotant_sma.jpg
contains another slot array, but this page illustrates the probe
excitation connector construction (one of those things I made a point
of, however, loop coupling is more flexible).

http://www.caron-inc.com/search/103/related.php
contains a lot of individual links that I won't go into.

there were 17,700 hits for the term "slot antenna," and these few were
on page one. I will leave it to you two correspondents to research
further and ask questions (I will anticipate the first: "Scale those
you find interesting to your own frequency").

To respond to Bart's point about modalities (the Alford Slot Antenna
would seem to be immune, whereas these traditional arrays would be
prone to his discussion): there are simple techniques to force modes
through the usages of thin sheet metal diaphragms and masks. Working
with the plumbing in these frequencies is both hands-on and conceptual
visualization friendly - sort of like Fields in a bottle.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Sat, 18 Dec 2004 09:52:07 +0100, Darko
wrote:

Any URL with examples, plans, calcilations ?
Any book ?

All I find are rectangular WG slot.
Only "Alford Slot" but that isnt what we talk about.


Hi OM,

It isn't? Why? This one is available at:
http://www.eta.chalmers.se/~pgp/alfo...lford_eng.html
and seems a perfectly useful introduction to the topic.

Hi Richard !

Yes, this is Alford, kind of slot antenna.
But we searching for "round pipe slot WG antenna" not using usual Wave
Guides.
Just for info, not for build, rectangular, standard WG slot antenna is
much easy to make.

73 !

On Sun, 19 Dec 2004 01:03:10 +0100, Darko
wrote:
But we searching for "round pipe slot WG antenna" not using usual Wave
Guides.

Hi OM,

This is a contradiction.

The Alford type is not the usual waveguide. Round waveguides are more
frequently used for rotating connections (RADAR), and only for short
sections. The Alford type is a classic "Slot Antenna" and, in fact,
is not a waveguide at all.

I did provide square waveguide slot antennas and you did not respond
to them.

If you reject both round and square examples, then there is not much
left to talk about.

73's
Richard Clark, KB7QHC