Calculation of transmitted characteristics for metal waveguides in terahertz range

We have studied theoretically and experimentally the spectral features of circular metal waveguides at terahertz wavelengths. For the first time it is shown that in the far region of the terahertz frequency range, where the conductivity of metal is high, at a wavelength of the transmitted radiation more than 50 µm spectrum of the waveguide can be represented by classical modal composition in the approximation of the ideal metal. In the near part of the terahertz range, where the conductivity of the metal substantially lower spectrum of waveguide modes of a hollow metallic waveguide can be described by a set of hybrid modes. The presence of the transition region in the behavior of electrodynamic properties of metallic waveguides in the wavelength range λ = 20 − 50 µm is founded. In this range the key parameter for estimation of the applica-bility of the mode approaches is the ratio of the exciting beam radius w to the waveguide radius a (w0 = w/a). Thus, when analyzing the transmission of terahertz laser radiation on small sized metal waveguide (a/γ ≤ 50) using in calculating the approximation of hybrid modes can only be justified if the excitation waveguides relatively high in relation to the radius of the waveguide beam radiation (w0 > 0,4). In the case of excitation of waveguides by narrow beams of radiation (w0 < 0,4), metal waveguides can retain electromagnetic properties inherent in the ideal metal waveguides.