If I wanted to cut slots I would create an object sized and positioned where I wanted and then use the boolean operator to subtract the slot object from the tube (in your case). There are other schemes so this may not be the best but it is relatively easy to accomplish.
Azulykit
That's what I did, but at one point the box for the slots had to be united with the AirBox (where one puts the radiation boundary). Once that is done, it seems impossible to change anything, as the process of uniting has destroyed any chance of changing the number of slots. But if I don't unite them, I get errors about two intersecting objects, even though they are in fact both vacuum.
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Deborah,
I would first try a long 4-sided box comprising my coaxial cable (filled with dielectric even) as a first iteration try (the design formulas for square coax line to determine dimensions can be found in good text books)
But I'd still need to cut the slots, so it does not really change the situation. Cutting them in round coax is no more difficult (perhaps even easier) than square coax. My problems resolve around the issue of being able to change a design quickly, by changing a few parameters in my model. Once on starts uniting the box used to cut the slots and the Airbox with the radiation boundaries, I seem to lose that flexibility.
I have never seen this type of antenna in commercial production, and there may be a reason for it (perhaps it does produce impractical, usable results compared to other design?) The box design should yield some insight as to characteristics, and if a near-real coax model is worth spending time on.
I agree there are no commercial implementations of it, but that makes it an interesting idea for me. I can see some practical problems, but I'd like to investigate it.
The usual coaxial-colinear design (1/2 wavelength offset pieces of coax)
I assume you mean this sort of thing, first published by Wheeler in the 1950's or so.
**broken link removed**
That design I provided a link to has a vastly exaggerated gain. I think part of the issue is that the radiation from the upper sections is smaller than the lower sections, as the lower sections have already radiated power. My idea with the slots was to control the amount of power radiated.
but I have not seen anything in the way of 'leaky' style radiating sections (to form a vertical 'beam').
All the more reason to investigate it!
Bear in mind the length of the slots will be kind of in accord with 'waveguide beyond cutoff' propagation phenomenon as far as allowing energy to exit and this may also impart a particular 'phase delay' onto the wave near the cutoff frequency (would be my thinking).
Jim
Yes, I'd not considered the "waveguide beyond cutoff" issue. I was thinking that short slots would act similar to a Hertzian dipole. So I could phase a number of dipoles vertically. Idea being to control the amount of radiation from each slot by controlling the length of the slots.
You have got me thinking. Perhaps a better way to approach it is to slots with a length comparable to a half-wave, but control the radiation by controlling the width.
I'm interested in investigating some of these ideas from an academic point of view, even though I am not an academic.
Any further thoughts you have about the possible issues with such a design, I'd be interested to know.
Deborah