Frequency shift in millimeter wave Gaussian beam antenna using two dimensional metal grid mirror

Partially transparent mirrors formed with a one or two dimensional metal grid are commonly used in quasi-optical devices. Quasi-optical coupling at the operating wavelength in those devices is highly sensitive to grid parameters as well as to the quality and thickness of the metal film. Information about the millimeter wave properties of the metal grid is quite important for theoretical analysis as well as for applications in millimeter wave communications. The power reflectance Q or power transmittance T, of the metal grid mirror can be controlled by optimizing of the grid parameters and by using advanced thin-film fabrication techniques. However, the phase shift due to reflection on the metal grid is the dominant effect in determining the relevant center frequency of the quasi-optical cavity. We set up an experiment at 60 GHz using a plane parallel Fabry-Perot cavity where we employed on both sides of the cavity two dimensional metal-grid mirrors. The frequency shift in the 60 GHz band was obtained by resonance measurement using the Fabri-Perot cavity and by varying the pattern repetition as well as the grid width.