The spurious-mode filter of a THz-range hollow dielectric waveguide

The spurious HE12and HE−+31modes are brought about not only in the hollow dielectric waveguide inhomogeneities [1,2] (namely, bendings, breaks (or discontinuities), etc),but also when the waveguide (along with an operating HE11 mode) becomes energized from the microwave oscillator and the laser. They, much like HE11, are linearly polarized. In consequence of this, these modes can well be suppressed using the filter built around the resonator acting as a segment bounded by one-dimensional wire gratings. The E vector polarization is parallel to wires. For an arbitrary length of this type of resonator the factor δ of the mode HEnm power transmission through the resonator, including the attenuation constant of the above mode and the phase-change constant ßnm, is determined by the following expression: equations where T and R are the power transmission and reflection factors for a single grating, whereas Φ is the wave phase being reflected from the grating. The peak microwave power transmission through the resonator occurs with a resonator length expressed as equations where q is the half-wave number the HEnmmode for the resonator length of δ, λ is the HEnm mode wavelength in the waveguide.