GB918866A - Improvements in or relating to switched waveguide arrangements - Google Patents

Abstract

918,866. Radio receiving systems; amplitude modulating systems; R.F. couplings. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. April 25, 1961 [July 6, 1960], No. 23621/60. Classes 40 (5) and 40 (7). [Also in Groups XXXVI and XL (b)] A microwave radiometer comprises two waveguide sections side-by-side connected by two 3 db. coupling slots 7, 8, one waveguide end A being connected to an aerial " pointed " as a star, and its other end connected to a passive load L2 producing the same noise level as the aerial in the absence of a signal, the other waveguide having its ends respectively coupled to a radio receiver R and to an open or short-circuit or absorbing load L1 or another receiver. Further, two coaxial rectangular vanes 11, 12 are rotated mid-way between the guide sections by a motor 10 so that alternately the receiver R receives energy from the aerial A, when the vanes are open, and only from the equivalent noise source L2, when the vanes are closed. The receiver inputs are detected as a low-frequency modulation of the microwave energy (of frequency twice the rotation frequency of the vanes) and after amplifying passed to a phasesensitive rectifier with other input (of equal frequency) derived from a photo-cell 14 whose incident light from a lamp 13 is interrupted at twice the speed of the vane shaft by vanes 15 on the shaft. The load L1 may alternatively be a second receiver whose detected output is subtracted from that of receiver R (the two modulations being inverse), or the two receivers may be slightly off-tuned and swept through a frequency band (keeping the frequency difference constant) which includes, e.g., the frequency of the hydrogen spectral line.