GB656200A - Improvements in or relating to radiating or receiving devices for electromagnetic waves - Google Patents

Abstract

656,200. Aerials. ELECTRIC & MUSICAL INDUSTRIES, Ltd. May 28, 1948, No. 14400. [Class 40 (vii)] In a wave-guide horn for radiating or receiving radio waves, the cross-sectional dimensions of the horn increase in a series of steps from its throat to its mouth. The wave-guide 1 feeding the horn is of such dimensions as to propogate H 10 waves only and the successive stepped portions 2 of the horn are so dimensioned as to be matched with respect to one another to prevent the production of higher order modes. Each step behaves as a transformer, the first and the last step having a particular value for the equivalent turns ratio, e.g. r, the turns ratio for the intermediate step being then arranged to have a value r<SP>2</SP>. The stepped portions are so dimensioned that each has the same value of characteristic impedance Z o , and are each a quarter wavelength long, the wavelengths being as measured at the appropriate points in the horn. The transformer action of the first step produces an input impedance to the corresponding section of Z o /r<SP>2</SP>, which is converted by the quarter-wave transformer to Z o r<SP>2</SP> at the foot of the succeeding step. The input impedance at the succeeding section is transformed by the step to Z o /r<SP>2</SP> and this process is repeated until at the last section the input impedance becomes Z o , so that stepped-horn arrangement is matched to its output section. When the horn is used for receiving purposes, conducting slats may be arranged across the mouth of the horn perpendicular to the direction of polarization of the radiation it is desired to receive, to prevent the reception of unwanted radiation polarized perpendicularly thereto.