Electronics > RF, Microwave, Ham Radio

What are your most innovative but still humble HF vertical antenna designs?

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cdev:
The most simple environment for an antenna, a small rectangular lot with either  a tree or space for a vertical mast monopole (made with wire or a mast) in the middle. How to make it sing? I am assuming that people want a low angle of radiation.

bob91343:
Time to hit the books.  Get a copy of Kraus' famous old book Antennas.  He gives some good information on such devices.

MartinL:
Some details that would be helpful:

1. What bands do you want to work - in particular, what's the largest wavelength you want to use - 40m? 80m? 160m?

2. How big is the lot?

3. How tall are you willing, able or allowed to make the antenna?

4. What is the ground conductivity like at the site?

If you're targeting a single band, and have enough space, then the best choice for horizontal gain is a 5/8 wavelength monopole. 1/2 wave and 1/4 wave would be second and third choices in that order:

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Beyond those basic monopoles, the "innovative" design work is generally about trying to either make do with less space, and/or having the antenna be effective over multiple bands. There's no best answer for all cases - you need to give your constraints to get useful suggestions.

TheSteve:
I'd look at the Cushcraft R5/R7 type vertical antenna's for inspiration.

T3sl4co1l:
Omnidirectional to the horizon?  Colinear.

In general, you need length along the axis you want a narrower beam on.

A colinear is long along the vertical direction, so gives a narrow beam, to the horizon.  It is horizontally narrow (and rotationally symmetrical), so gives a broad beam in those directions (indeed, a whole torus in the 3D plot).

It's not always exactly the physical cross-section, for example the long-wire and Yagi antennas have directivity parallel to the long axis.  There's some hackery between effective aperture and physical geometry, which I don't know much about.

It's more explicit with something like a phased array, where the aperture is literally the array itself, and this effectively defines the resolution of the radiation pattern (as projecting the array's grid onto the radiation sphere), as well as the main lobe to side lobe ratio, or something like that.  I forget offhand what angles a phased array can reach, can beams be made in (or nearly to) the plane of the array (for a planar configuration)?  The Yagi would seem to suggest it can.

The underlying truth is, directivity in whatever direction is limited by the bounding sphere (or semisphere for ground plane types) versus wavelength: you simply need a bigger antenna for better directivity.  But also bandwidth (the limitation is all three factors together, I think?), so a Yagi isn't terribly wide but can be fairly compact, whereas a wideband dish needs to be, well, a whole-ass dish.  Or compare Yagi to log periodic, which are similar in directivity, but the log periodic is much wider (longer elements).

Tim

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