seeking links info for design and theory of handheld VHF UHF antennas

Question

I've been looking but so far nothing. Even design software with templates for monopoles, end feds

Answer 1

By "handheld VHF/UHF antennas" I'm assuming you mean the rubber ducky and/or whip style antennas.

As you've mentioned, these are monopole antennas, but electrically short ones. Like an electrically short dipole, shortening a monopole increases its capacitive reactance at the feedpoint — i.e. the antenna would begin to react more like a capacitor than a resistor. So it has a lower radiation resistance and is harder to match to a 50Ω source.

To compensate for this, the antennas need to be "loaded". This might be done more efficiently with a "capacitance hat" at the far end but for handhelds use inductive loading starting at the feed end is more typical.

I suspect that with a whip antenna this is mostly in the form of base loading (see also). There are many other ways of loading a short antenna (pdf), and I iiuc a rubby ducky also uses continuous loading — sometimes called "helical loading" but not to be confused with an actual helix antenna which radiates in a completely different fashion!

For a bit more theory re. loading:

• https://www.rainesengineering.com/articles/SimpleFormulasLoadedAntennas.pdf
• https://owenduffy.net/blog/?p=1736 (more on "Q factor" which affects bandwidth)

There's also the issues of balance and ground plane. (Related to the idea of a counterpoise sometimes called a "tiger tail".)

While a 1/4 λ monopole is different than a 1/2 λ end fed, there is still some concern of balancing the feedpoint — anecdotally the understanding seems to be that the user's hand/body capacitively couples to serve as the ground, but there's some missing links here to relevant theory which I haven't found.

And finally, what about the radiation pattern? Similar to other verticals, the height above terrain and ground plane height/quality considerations will also have an effect on the radiation pattern especially in elevation. (In the azimuth surely the user's body effects it, cf. the "body shielding" used as a transmitter hunting technique. Again there are surely missing links here; perhaps in the cell phone engineering literature there are studies of this?)