Joel Koltner wrote:
Thanks Roy, that's a great summary.

If I started from the vantage point of wanting to design a flat
panel-style (patch-like) antenna for 2m (and let's assume narrow band is
fine for the moment), are there any obvious starting points besides a
big patch that's being operated well below resonance (let's assume I
want my panel to be no bigger than 6"x6")? Just meandered lines are
probably as good (and can be readily simulated in NEC :-) )? (I've read
Randy Bancroft's book on patch antennas and have a reasonably good feel
for how they operate... although he makes it clear there's often plenty
of empirical design involved too, particularly when you want to get
fancy and achieve circular polarization by exciting multiple modes at
once.)

But you'll probably be able to make some QSOs with it and, with the
help of some mystical mumbling about equilibrium, photons, critical
coupling, and reflected power waves, you'd surely be able to collect a
gaggle of true believers.

It's a shame than Nathan Cohen has already largely cornered the market
on overselling the potential of fractal antennas. :-)

---Joel

When the antenna becomes small, connecting wires can become a
significant -- if not the dominant -- part of the radiating structure.
So some attention has to be paid to them, too. Consider a short end
loaded dipole, with large capacity hats at the wire ends. That's what
your "patch" would look like if fed from the center. And it's not a bad
choice for an electrically small antenna. The radiating is done by the
dipole wire, and the end plates serve to make the current uniform along
the wire, raising the radiation resistance and improving the efficiency
over a non-loaded dipole. If you move the "dipole" toward the outside,
some uneven current will flow on the plates and they'll contribute to
the radiation. NEC can do a good job of modeling these structures, with
the plates modeled as wire grids, if some care is taken. Of course it
can't handle dielectrics. Making a planar antenna on a dielectric
material might be advantageous, but putting dielectric between the two
halves as in a conventional patch would likely reduce the efficiency
without providing any advantage.

What you'll be making is just another small antenna, with no special
properties because of its resemblance to a properly functioning patch.
So you have to deal with the same considerations you do with any small
antenna, all directed toward minimizing the I^2 * R loss.

Roy Lewallen, W7EL