GB855723A - Improvements in or relating to electromagnetic wave transmission systems - Google Patents

Abstract

855,723. Waveguide couplers. WESTERN ELECTRIC CO. Inc. March 20, 1959 [March 28, 1958], No. 9703/59. Class 40(8). A wave energy distribution system comprises two circular waveguides arranged coaxially one within the other, the larger of the two guides being dimensioned to support a second order mode having an electric field null which coincides with the boundary of the smaller guide. In the directional coupler shown, the inner guide is divided into two sections 11, 12 by a gap d, both sections being dimensioned to support only the H 01 mode at the operating frequency. The outer guide 13 is dimensioned to be just below cut-off for the H 03 mode at the operating frequency so that H 01 mode energy propagating from left to right in the guide 11-will excite both the H 01 and the H 02 modes in the gap d. These modes propagate with unequal phase constants #1, #2, so that if the length of the gap d is such that (# 1 -# 2 )d = (2n-1)# the two modes suffer a differential phase change of 180 degrees. At the end of the guide 12 the field configuration is such that the electric vectors of the two modes are in antiphase within the area defined by the guide 12 and in phase within the area defined by the annular gap 2. Thus the whole of the energy is transferred to the annular gap within which it is propagated in a coaxial mode. By means of the known type of converter shown, this mode may be transformed to the dominant H 01 mode within a rectangular guide 16. Any ratio of power division between the coaxial guide 2 and the inner guide 12 may be achieved by suitably dimensioning the gap d. Thus an equal division of energy is obtained by making (# 1- # 2 )d =(2n-1)<SP>#</SP>/ 2 . The coaxial guide 2 is matched to the H 02 mode by making the boundary of the guide 12 co-incide with the electric field null of this mode. It is stated that reflection of H 01 mode energy from the end of the guide 12 is negligible. Mode converters of the kind shown may be provided at both ends of the coupler. Specification 855,026 and U.S.A. Specification 2,748,350 are referred to.