English: The first modern horn antenna and its inventor, Wilmer L. Barrow in 1938. A horn antenna is a flaring metal horn used to direct microwaves from a waveguide into a beam. Although Jagadish Chandra Bose invented the horn antenna during his pioneering 1897 experiments with microwaves, subsequent development of radio used much lower frequencies at which horns were unsuitable, and the concept of a horn to direct radio waves was forgotten. Around 1933 Barrow at Massachusetts Institute of Technology reinvented the horn antenna during research into microwave detection of aircraft, and published his work in 1938.

Caption: "Metal horn recently devised and successfully used by Prof. Wilmer L. Barrow in focusing ultra-short waves; waves in the range 300 to 4300 megacycles (wavelengths from 1 meter to 7 centimeters)."