A new 60 GHz open-resonator technique for precision permittivity and loss-tangent measurement

A new open-resonator technique is described for the determination of loss tangent and dielectric permittivity of low-absorbing materials at 60 GHz, micrometer and the stepping-motor-driven hat mirror in the Fabry-Perot cavity can be scanned at a very small step (to change the cavity length or mirror spacing) to provide a complete interferogram over the entire resonance peak profile. This method is termed here as a new, full cavity-length variation technique. The minimum step size is 20 nm and the variation range of the cavity length is about 25 mm, which can col;er eight fundamental resonance modes. With this technique, all resonance curves in the variation range of the cavity can be studied more completely than with any other previous technique. The technique requires only fixed frequency sources, and eliminates the need for a broader band, stable, continually tunable frequency source.