Coaxial waveguide feed with reduced outer diameter

Dual waveguide feed apparatus for receiving or transmitting radio signals within dual ranges of frequencies including a lowest frequency, the apparatus comprising:

• a waveguide having an open end and a rear wall opposite said open end positioned along an axis of the waveguide and defining a first waveguide cavity within the waveguide;
• a center conductor positioned within said first waveguide cavity and along the axis of said waveguide, the center conductor defining a second waveguide cavity with a fundamental waveguide mode within the center conductor, the second waveguide cavity being constructed to operate at a first range of frequencies;
• said center conductor and said waveguide defining a coaxial waveguide cavity with a fundamental coaxial-waveguide mode within the coaxial waveguide cavity, the coaxial waveguide cavity being constructed to operate at a second range of frequencies different than the first range of frequencies, and the waveguide being constructed to have a cutoff frequency for the fundamental coaxial-waveguide mode which is at least 95% of the lowest frequency for the apparatus;
• and
• a first waveguide probe mounted within said coaxial waveguide cavity so as to extend through one of the waveguide and the rear wall into the coaxial waveguide cavity for exciting a first primary coaxial waveguide mode electromagnetic signal in the waveguide cavity, the first waveguide probe being oriented to couple to a first primary coaxial waveguide mode of the coaxial waveguide cavity and being oriented substantially orthogonal to a TEM mode of the coaxial waveguide cavity.

Dual waveguide feed apparatus for receiving or transmitting radio signals of C-Band frequencies, the apparatus comprising:

• a waveguide having an open end and a rear wall opposite said open end positioned along an axis of the waveguide and defining a first waveguide cavity within the waveguide, said waveguide being constructed to have an inner diameter of less than 2 inches;
• a center conductor positioned within said first waveguide cavity and along the axis of said waveguide, said center conductor defining a second waveguide cavity with a fundamental waveguide mode within the center conductor, the second waveguide cavity being constructed to operate at C-band frequencies;
• said center conductor and said waveguide defining a coaxial waveguide cavity with a fundamental coaxial-waveguide mode within the coaxial waveguide cavity, the coaxial waveguide cavity being constructed to operate at a second range of frequencies different than the first range of frequencies;
• and
• a first waveguide probe mounted within said coaxial waveguide cavity so as to extend through one of the waveguide and the rear wall into the coaxial waveguide cavity for exciting a first primary coaxial waveguide mode electromagnetic C-Band frequency signal in the coaxial waveguide cavity, the first waveguide probe being oriented to couple to a first primary coaxial waveguide mode of the coaxial waveguide cavity and being oriented substantially orthogonal to a TEM mode of the coaxial waveguide cavity.