Millimeter-wave quadrature interferometer

A simple, low-cost millimeter-wave (70GHz) interferometer with a phase accuracy better than +/- 2 degrees, and a response time of 10ns has been developed and implemented as a diagnostic tool at the LAPD.

The simplicity of this interferometer makes it ideal for measurement of electron densities in a laboratory plasma.

The relative high accuracy and low cost are attained by a homodyne system with a quadrature intermediate frequency (IF) mixer, now commercially available in millimeter-wave frequency bands. Since the system isolator operates near a magnetically-confined plasma, it has been protected by magnetic shielding.