A waveguide bridge/quasi-optical W-band spectrometer for dielectric measurement of absorbing materials

A spectrometer system is designed and constructed for the precision measurement of dielectric permittivity and loss tangent of absorbing materials. The new instrument is capable of providing the high resolution data for the first time over an extended W-band (68-118 GHz) frequencies for specimens with large range of absorption values, including highly absorbing specimens which otherwise would not be possible. The technique is based on the unbalanced bridge which is developed for the measurement of the phase of the wave passed through the specimen in free space (quasi-optical) with reference provided by a waveguide arm. Precision waveguide and quasi-optical components allowed reliable broad band operation. A number of common dielectrics are measured and data for the real and imaginary parts of dielectric permittivity are presented.