Such non-circular waveguides as sectoral

elliptical and semi-ellptical waveguides have been widely used in satellite communication applications in the microwave and in millimeter wave ranges. However they are not fully studied yet. Here we give the data on the attenuation constant of the TE01 wave of the semi-circular waveguides and show that

the TE11 wave of the semi-circular waveguide is the more efficient transmission mode than the TE01 of the same guide. Given also are the characteristic im-pedances of the TE01 wave of the semi-circular waveguide and of the TE20 wave of the rectangular waveguides. These two kinds of waveguides together may build up a multiple branch waveguide coupler. Such coupler might as well be constructed by employing TE11 wave in the semi-circular waveguide and TE10 wave in the rectangular waveguide.We have calculated the attenuation constants of the TEC1l in an elliptical waveguide by a corrected formula other than that of Chu corrected by Lewin. Given also are data on the normalized guide wavelengths of the elliptical waveguide

needed in designing a phase shifter for generating circularly polarized