Friday, March 22, 2019

Fitting a dipole into a smaller space

Take the band (in metres) you wish to make an antenna for. Halve it.

That's the horizontal space you need to accommodate a flat top half wavelength dipole.

But you don't have that room on your property.

What do you do?

Some people are worried that if their dipole isn't quite straight then they will suffer much reduced performance.

This isn't so.

Unlike antennas like magnetic loops, verticals and critically coupled beams, where you do need to be careful to get design performance, half wavelength dipoles are very forgiving with what you do to them. 

Provided you have the centre two thirds relatively straight you can bend their ends to fit.

The ends can be lower than the centre. Ends don't have to be the same height. The only substantial difference is that the length that you obtain resonance on your desired centre frequency might be a little different.

Here's a few (but not all) possible dipole configuration options below. The black blob is the feed point.

Not all bent dipole configurations are equal. Impedances change and losses increase with extreme bending. Read the following links for what antenna modellers and experimenters have to say about this. 

* Bending the dipole (academic paper by Erwin B Daculan)

* KK4OBI's bent Dipoles
* W4RNL on folding bending and mutilating dipoles
* W5ALT's bent dipoles

PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.


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