|
Slot Antenna
Can I make a slot antenna out of round pipe rather then rectangular?
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 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. 73's Richard Clark, KB7QHC |
Sure! |
Matt,
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 doubt if you are interested in an exceptionally well-defined beam. So the differences between a rectangular and a circular tube of roughly the same perimeter will probably be of no great consequence. ( Hi Richard - so we meet again! ---- Acqured nom-de-plume, Punchinello.) |
"Matt" wrote in message ... Can I make a slot antenna out of round pipe rather then rectangular? 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 I used gutter pipe (3 by 5 or so) in one band and built one out of brass @ 2.5 Ghz worked like a champ. Slots were 1/4 wave (freespace) and seperated by 1/2 wave (speed of waveguide, not freespace) Feed was 1/4 wave sticking into the rect pipe, in the middle. Round pipe should work just fine. |
I used gutter pipe (3 by 5 or so) in one band and built one out of brass
@ 2.5 Ghz worked like a champ. Slots were 1/4 wave (freespace) and seperated by 1/2 wave (speed of waveguide, not freespace) How do you figure the speed in waveguide rather then free space? Matt Feed was 1/4 wave sticking into the rect pipe, in the middle. Round pipe should work just fine. |
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 I doubt if you are interested in an exceptionally well-defined beam. So the differences between a rectangular and a circular tube of roughly the same perimeter will probably be of no great consequence. ( Hi Richard - so we meet again! ---- Acqured nom-de-plume, Punchinello.) |
"Matt" wrote in message ... I used gutter pipe (3 by 5 or so) in one band and built one out of brass @ 2.5 Ghz worked like a champ. Slots were 1/4 wave (freespace) and seperated by 1/2 wave (speed of waveguide, not freespace) How do you figure the speed in waveguide rather then free space? It is in several books, called lambda sub-g you could probably google it, starting with waveguide transmission. I can't remember, but I think is is about 75 to 85% It is determined by the dimentions of the waveguide, (same with coax, and material slows it down further) lambda is wavelength in free space. Matt Feed was 1/4 wave sticking into the rect pipe, in the middle. Round pipe should work just fine. |
"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? |
zaashy wrote:
"Matt" wrote in message ... How do you figure the speed in waveguide rather then free space? It is in several books, called lambda sub-g you could probably google it, starting with waveguide transmission. I can't remember, but I think is is about 75 to 85% It is determined by the dimentions of the waveguide, (same with coax, and material slows it down further) lambda is wavelength in free space. The phase velocity in a hollow, air filled waveguide is always faster than the speed of light, so the velocity factor is always 100%. The amount faster depends on the operating frequency relative to the waveguide's cutoff frequency. The velocity factor in a hollow, air-filled guide = 1 / sqrt(1 - (fc/f)^2) where fc = cutoff frequency f = operating frequency Too bad you can't get information through a waveguide that fast. It goes at the group velocity, which of course is always slower than the speed of light. Sigh. Roy Lewallen, W7EL |
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 |
| All times are GMT +1. The time now is 07:24 AM. |
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
RadioBanter.com