## Resonant n>0 Modes Trapped by a Dielectric in a Coaxial Line

Lawrence R. Doolittle

Tunnel Dust, Inc.

Walnut Creek, California, USA

January 14, 2002

Scaling laws provide an incentive to make a high power window as large
as possible, since losses scale inversely
with radius, and both heat flux and temperature rise scale inversely
with the radius squared. One phenomenon that limits how large a window
can be made is the presence of higher order
modes in the structure. Conventional wisdom is to limit the average
circumference to one wavelength, so that these modes cannot propagate.
An analysis of the resonant mode properties of low impedance
coaxial windows shows how to design a window to keep these modes
from interfering with power transmission.

You may download this Tech note in its entirety in
PostScript (187K) or
PDF (129K). The PostScript version
can be printed on any PostScript printer, or previewed with
the Ghostscript suite.
The PDF version can be viewed and printed using any of
xpdf (font problems),
the Ghostscript suite,
or (untested) Adobe Acrobat,

You may download a kit (8K) that
allows a complete regeneration of the note, including all
calculations. This kit is tested on a Linux box with
Octave and LaTeX installed.
Unpack it, and type "make" to get as far as the .dvi and .eps files.
Other choices include "make print" and "make web".

You may look at the individual pieces:

- LaTeX source file
- Figure 1, Coaxial window geometry
- Figure 2, Bessel function ratios
- Figure 3, Normalized transverse separation constants
- Figure 4, Normalized resonant frequencies for epsilon=10
- Figure 5, Longitudinal H_z dependence of resonant modes
discussed in the example

*Larry Doolittle*

January 14, 2002