ABOUT THIS BOOKOpen resonators, open waveguides and open diffraction gratings are used extensively in modern millimetre and submillimetre technology, spectroscopy and radio engineering. The physical principles of open electrodynamic structures are different from those of closed ones because of radiation loss, edges, multiconnected cross-sections and the need to take into account the behaviour of electromagnetic fields at infinity. The eigenoscillation and eigenwave spectra become complex, there are additional demands on the energy relations and the statements of spectral problems change.