[TenTec] cone Antenna Wheeler Cap efficiency measurement

[Stuart Rohre]

John,
No, the Wheeler cap does not appear in the ARRL books. It is something from
professional antenna practice back to Wheeler of Hazeltine and Brown et al
at RCA.  It was likely in RCA Reviews their technical magazine back in the
40's.  Wheeler did a group of seminal papers for IEE on Wheeler Cap
Efficiency measurements, and underwater propagation of RF, etc.

The Wheeler Cap is a big shield can , big enough to hold the entire antenna
and the edge of the can shorts to the ground plane.  You measure the antenna
R and jX terms, or S parameters, with the cap on, and out in the antenna
open range field with cap off.  The comparison of the results shows the loss
resistance which is not contributing to radiation and the radiation
resistance which does help radiation.  That is how efficiency of an antenna,
(small antennas of kr 0.1 wavelength to 0.01 wavelength) is determined.
Wheeler published the first curves of antennas in that range and predicted
you could build them down to 0.01 wavelength.  Well, let me qualify the word
predicted, he might have built some small antennas demonstrating the theory.

The back issues of the IEEE, (IRE) Institute of Radio Engineers, when these
papers were published have all the theory and details.  More recent work
with Wheeler cap is in the IEEE publication, "Antennas and Propagation"
magazine available at electrical engineering libraries of colleges, and by
inter-library loan to Public Library, or by reprint fee to IEEE, NY.

72, Stuart K5KVH