Tri-band feed horn

A radio frequency (RF) coaxial horn can comprise an inner RF horn disposed inside a larger outer RF horn. An interior surface of the inner horn can comprise a pattern of irregular, aperiodic features that excite modes in first and second RF signals each at a different frequencies that produce substantially Gaussian beam profiles of the first and second signals at the output aperture of the inner horn. The waists of the beam profiles of the first and second signals can be outside the inner horn but inside the outer horn. An interior surface of the outer horn and/or an outer surface of the inner horn can similarly excite modes in a third RF signal at a frequency different than the first and second RF signals to produce a substantially Gaussian beam profile of the third signal at the output aperture of the outer horn. The waist of the beam profile of the third signal can be aligned with the waists of the beam profiles of the first and second signals. Even though the signals are at different frequencies, the illumination pattern of the three RF signals on a reflector antenna at which the horn is directed can be substantially the same.