Conical horn antenna applicable to plural modes of electromagnetic waves

A plural mode horn antenna having a desired mode of electromagnetic wave generating portion for generating a desired mode(s) of electromagentic wave(s) out of plural modes of electromagnetic waves in a position between a feed waveguide located on a base end side and a conical horn located on a fore end side, said plural mode horn antenna comprising

• a first tapered waveguide connected to the fore end side of said feed waveguide and expanding at a predetermined certain angle while defining an inner peripheral surface of a truncated cone from an inside diameter thereof equal to the inside diameter of said feed waveguide up to an inside diameter certain times as large as a predetermined wavelength of the frequency of an electromagnetic wave of a mode to be generated;
• a first straight cylindrical waveguide connected to the fore end side of said first tapered waveguide and extending forward in the form of a cylindrical inner peripheral surface having an inside diameter larger than 1.22 times the wavelength of a minimum frequency of a high frequency band to which the electromagnetic wave of said mode to be generated belongs, smaller than 1.7 times the wavelength of the maximum frequency of said high frequency band, and smaller than 1.22 times the wavelength of a maximum frequency of a low frequency band;
• a second tapered waveguide connected to the fore end side of said first straight cylindrical waveguide and expanding at a certain angle while defining an inner peripheral surface of a truncated cone from an inside diameter thereof equal to the inside diameter of said first straight cylindrical wave guide up to an inside diameter thereof certain times as large as a predetermined wavelength of a frequency different from that of said mode of electromagnetic wave;
• and
• a second straight cylindrical waveguide connected between the fore end side of said second tapered waveguide and the base end side of said conical horn and having an inside diameter certain times as large as said predetermined wavelength of the frequency different from that of said mode of electromagnetic wave, said inside diameter of said second straight cylindrical waveguide being larger than 1.22 times the wavelength of a minimum frequency of said low frequency band, smaller than 1.7 times the wavelength of the maximum frequency of said low frequency band, and larger than 1.7 times the wavelength of the minimum frequency of said high frequency band.