Resonators for Millimeter and Submillimeter Wavelengths

Further considerations on the mm-wave Fabry-Perot interferometer are presented. Computed Q values for parallel metal plate resonators indicate that at spacings around 2.5 cm, values ranging from 60,000 at 3 mm, to 300,000 at 0.1 mm wavelengths are possible. The plates must, however, be quite flat. These results are important for many investigations, and in particular for mm and sub-mm wave maser research. For the aperture per wavelength ratios possible here, diffraction effects should be small. Consideration is given to using curved reflectors or focused radiation in applications where the fields must be concentrated. For this purpose, re-entrant conical spherical resonators are treated in detail, as regards operation in the TEM mode at high orders of interference. Expressions for the Q and shunt impedance are given, and high values are possible at mm and sub-mm wavelengths. Quasi-optical methods of coupling into and out of such a resonator are proposed, and the higher modes possible in such a resonator are considered. Results indicate that it could have application to the mm-wave generation problem, and that it represents a good resonant cavity for solid state research at mm and sub-mm wavelengths, and for maser applications in particular.