microwave resonator optimizations

A project required a resonator with an E-field perpendicular to the sample tube. The purpose was to exploit the resonance of a methyl-group in a sample. Since the frequency of 62.5 GHz was only approximate, a little tuning range of a GHz or so was required. The starting point was a WR15 waveguide with 3.7mm width and 1.85mm height. We decides to have the resonator coupled with a slit as first try.

the resonator displayed in a semitransparent way

A movable part called matcher lets us transform the wave such that it optimally couples into the resonator. The matcher has two lambda quarter wide rings milled into its surface. To the topright. The resonator, left has a dielectric movable part called tuner(not yet inserting), below and the sample tube coming in from above(also not yet inserting).

It was rather simple to find parameters where it resonates

the targetted resonance

as movie
However, rather close by there were more, unwanted resonances

an unwanted resonance

as movie
and another one

another unwanted resonance

as movie
The necessary geometry parameters were made variable and swweps over them helped us tweak the geometry to fit our needs.

The field homogenity was phantastic. Here the cut through the e-field plane

resonator with the E field in the plane

and now a cut in the B field plane.

resonator with the B field in the plane

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last updated 18.Nov.2006

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