Theory, Design and Tests on a Prototype Module of a Compact ...

92 5. RADIOFREQUENCY MEASUREMENT
In all the cases it is clear that the differences respect the reference
case of figure 5.21 were acceptable.
In figure 5.23 is shown the effect of a perturbation on the CCs which
are nearest to the bridge coupler. From first bead pulling, which are
the reference, it is apparent that the level of field in the last AC of
tank #1 is high respect to the mean of the tank, the theory says that
if the nearest CC is changed the level in the following AC (respect to
the feeder) changes also.
Figure 5.23. The effect of local perturbations in the
CCs at the end of a tank.
7. Measurement of the coupling between the module <strong>and</strong>
the waveguide through an iris
In this paragraph the procedure to measure the coupling between
the power waveguide <strong>and</strong> the LIBO module is explained [34]. The procedure
is exportable to other cases, as the case of multi-cells structures
feeded by one cavity through an iris.
First, we introduce some basic concepts <strong>and</strong> the equivalent circuit,
then we introduce some figures of merit to evaluate the correct matching,
next we explain the RF procedure to get the numerical data with
the help of a Network Analyzer; last we introduce a numeric MATLAB
program that, starting from the measurement data, is able to deduce
the desired figures of merit, <strong>and</strong> finally we comment the results.
7.1. The equivalent circuit for one cavity. In the previous
chapters we already introduced the concept of equivalent lumped elements
circuit for resonant cavities. Of course, we know that the equivalent
description is rather difficult because, as in wave-guides, the ordinary
concept of voltage <strong>and</strong> current does not play its usual role.
ω 2 0 = 1/LC, Q0 = ω0L
2 (ω0L)
, R0 = ω0LQ0 =
Rs
Rs
(5.14)
The three quantities defined by these relations can be measured experimentally,
as it is shown in the previous sections, <strong>and</strong> can be used to
establish the lumped elements
L = R0
, C =
ω0Q0
Q0
, Rs =
ω0R0
R0
Q2 . (5.15)
0