  Open single-mode metallic cavities operating in nonradiative configurations
are proposed and demonstrated. Starting from well-known dielectric resonators,
possible nonradiative cavities have been established; their behavior on the
fundamental TE011 mode has been predicted on the basis of general
considerations. As a result, very efficient confinement properties are expected
for a wide variety of open structures having rotational invariance. Test
cavities realized having in mind practical millimeter wave constraints have
been characterized at microwave frequencies. The field distribution of some
relevant configurations has been modeled by means of a finite-element numerical
method. The obtained results confirm the expected high performances on widely
open configurations. A possible excitation of the proposed resonators
exploiting their nonradiative character is discussed, and the resulting overall
ease of realization enlightened in view of millimeter wave employments.
