Near-Field Plane Distribution of Rectangular Waveguide Excited by Dominant and Higher-Order Modes

In this paper, on the basis of Hertz potential technique, the expressions for calculation of the radiation field of aperture antennas with given distribution of field sources in rectangular coordinate system were obtained in the closed form. Derived expressions allow to calculate amplitude, phase and polarization radiation characteristics of canonical radiators, rectangular waveguide and pyramidal horn, on the planes at the different distances from the aperture to the point of observation. The calculation of radiation characteristics was carried out for the case of waveguide excitation by dominant TE₁₀ mode and for the case of TE₂₀ and TE₃₀ higher order mode excitation. The analysis of field distribution at the near-field reactive and "very-near-field" zones was performed. It was shown that for electrically small rectangular waveguides excited by TE₁₀ mode the boundary of far- zone can be defined as 1.8-2.0lambda with satisfactory for practice accuracy. Knowledge of complex amplitude value in near zone for waveguide with separate TE_m0 mode excitation allows to obtain the amplitude and phase near zone characteristics of the waveguide with multimode excitation, for example TE₁₀ + TE₂₀, TE₁₀ + TE₃₀, TE₂₀ + TE₃₀ and so on excited at the same frequency.