...about the only compact antenna nobody has much bad to say about is a HexBeam...
You can find people saying bad things about almost any antenna: that doesn't mean it is
a bad one, or that it doesn't do exactly what it claims to do. In this case the performance
claims are perhaps a bit better than modeling would indicate, but we also don't know what
type of quad it was being compared against or the accuracy with which differences could
Basically it works about as well as such a shortened antenna can be expected to work.
Probably the best way to proceed is to determine the limiting dimensions (width and height)
that you have to work within and see what the options are in the space available. Also give
some thought to what characteristics of a beam are most important: Is it the reduced QRM
on receive due to the F/B ratio, or the strongest signal at the other end, or some trade-off
between the two? How much of the 10m band do you regularly use where you want maximum
performance? (Bandwidth probably isn't an issue for a CW operator, or one who uses
phone over a relatively small portion of the band.)
Once you have an idea of what factors are most important and what your limits are, then
we can look at which options best fit them.
Are there any decent books / resources to get me going with modelling?
The late W4RNL had an extensive website with a lot of information on modelling, but it
is now behind the AntenneX paywall. It may be worth paying for access, or looking at
some of the compilations they have available for sale. He also wrote an online training
class on the topic for ARRL, but I don't know if it is still available.
I got started with EZNEC by reading the tutorial, and about 1 1/2 chapters into it
I was off doing my own antennas. You can download a free demo version (which limits
the size of models you can save) to get a sense of the behavior, and also what file
formats it supports for input and output.
Another option is 4NEC2, a very complete package that is available as freeware. I find it
a bit more confusing to use, but then, I've never read any of the documentation on it, and,
given the number of features, that may be my fault more than that of the program. It
includes options for defining antennas with variables and an optimizer, as well as quite a
number of demo files.
All the modeling programs have some limitations, and part of building a successful model
is knowing when to expect problems and what to do about them. The NEC2 equations (used
in EZNEC and 4NEC2) require care with parallel wires (the segmentation has to match on each)
and most programs have problems when wires meet at very sharp angles because of how they
model intersections of wires. MININEC is an older version designed for smaller computers that
couldn't run the original NEC program: it has a number of differences, and its ground model
is famously poor for low horizontal antennas. The newer NEC4 core is available as an option
in EZNEC and some other programs, but requires that one pay for a license to use it (as well
as getting permission from the US Government - apparently it is still categorized as a weapon
But I suspect that either 4NEC2 or EZNEC will be sufficient for most of your needs, and would
be my recommended places to start.
While there are some limitations to model accuracy, I'm still surprised sometimes how well
they can work. I modeled a quad with a gamma match, and was surprised to see the
polarization rotated by about 45 degrees in the output plot. Since I had several 2m quads
that used a gamma match, I immediately took one outside, connected it to a transmitter,
and probed the polarization with a yagi. Sure enough, the polarization was rotated just
as EZNEC had suggested. Changing to a different feed method for the same antenna
shifted it back to where I expected it to be.