Slot antennas began life as slots in curved surfaces, eg., aircraft
fuselages and wings. Most structural alloys will do fine. Rectangular
tubes are unusual. They are often unsightly protusions.

The maths is more complicated with curved surfaces.

But if you just copy somebody else's slot, and scale dimensions according
to
frequency, the maths reduces to simple A*B/C schoolboy arithmetic.

I have not found any round rather then square designs on the net. Do you
know of any? If I found one I could scale it down to 33cm. I have not
found any 33cm slotted designs period. I have found a calculator for
rectangular waveguide though which I ran for 33cm. Not sure how I would
adapt its results to round though.

Matt


I doubt if you are interested in an exceptionally well-defined beam. So
the
differences between a rectangular and a circular tube of roughly the same
perimeter will probably be of no great consequence.

( Hi Richard - so we meet again!
----
Acqured nom-de-plume, Punchinello.)