
353Microwave Measurements
To have a closed dc circuit it is sometimes necessary to add a dc return on the
input side of the crystal. In a waveguide system, it is often convenient to use
a waveguide to coaxial transition and a coaxial crystal mount. Germanium
or silicon is commonly used as the material in construction for the crystal.
The silicon type IN-21 and IN-23 crystals are suitable for use at the X-band.
This crystal is a low-voltage device. The output voltage (or current) is not
directly proportional to the input voltage but follows a square law. The out-
put of the crystal is fed to an indicating instrument such as a galvanometer
or