On Sat, 11 Jun 2005 10:42:44 -0700, "RST Engineering"
wrote:

We think we know that the impedance at the center of a thin wire antenna in
free space is something on the order of 70 ohms at resonance (quarter-wave
ears with the end fringing factor thrown in).

We think we know that the VSWR bandwidth increases as that thick wire
becomes fat. We think we know that the end fringing factor goes up as the
antenna gets fatter.


What I'm suspecting the further I look into it is that the NEGATIVE image of
that dipole antenna (a slot cut into an infinite sheet of conductor fed at
the center across the slot) is also resonant, but the impedance is going to
be something on the order of 350 ohms. Jasik shows a method of off-center
feeding that reduces the impedance to something on the order of 100 ohms.

What is NOT mentioned is the aforementioned VSWR "goodness factor" going up
with a fatter (wider?) slot.

Is there a better reference to slot antennas than Jasik?


"Antennas" by Krause and Marhefka (ISBN 0-07-232103-2) has a useful
section on slot antennas, They suggest an off-center feedpoint of
lamda/20 will provide 50 Ohms. They don't specifically cover your VSWR
question, but a couple of trials will provide an easy answer.

Barry Lennox