Study On Planar Whispering Gallery Dielectric Resonators. II. A   Multiple-Band Device
  The basic theory underlying the realization of simple multiple-band non-homogeneous dielectric resonators, whose spectral response is the overlap of single-resonator frequency bands, is developed exploiting a general approach discussed in the previous companion paper. The limit frequencies of the proposed devices, given only by the dielectric properties of the involved materials, can differ in principle by several decades. Experimental confirmations have been obtained on a composite structure built up with teflon and polyethylene; as predicted by the theory, the overall band includes frequencies which range about from 20 GHz to more than 400 GHz, when high frequency resonances are selectively excited. The localization of the higher frequency radiation between the positive steps of the dielectric constant, which is the basic properties of these non-homogeneous resonators, has been experimentally verified by mapping the electromagnetic field intensity. Possible applications of multiple-band Whispering Gallery dielectric resonators are finally outlined. 
G. Annino, M. Cassettari, and M. Martinelli