Patent GB-519766-A (GB)
Title: Improvements in or relating to transmission systems for ultra-high frequency electromagnetic waves
IPC: H01Q13/02
Filed: 1939-04-27
Abstract: 519,766. Aerials ; dielectric guides for displacement waves. ELECTRICAL RESEARCH PRODUCTS, Inc. April 27, 1939, No. 12614. Convention date, April 29, 1938. [Class 40 (v)] A wave guide, in the form of a metallic pipe. for transmitting frequencies of the order of 2,000 megacycles, is terminated by a flared extension or horn for radiating or receiving the waves, the flare of the horn being so related to its length as to give maximum axial gain. Fig. 1 shows a construction of horn giving the directional characteristic shown in Fig. 3. The horn may be rectangular in cross-section, as shown in Fig. 8, or it may have a linear, parabolic or exponential flare. Specifications 493,695, 494,835, and 495,977 are referred to. The Specification as open to inspection under Sect. 91 also describes horns of the shape shown in Figs. 10, 14 and 15 (Cancelled) all of which give maximum radiation along the axis of the guide ; if the directive axis is inclined to the guide axis the horns may be asymmetric. The impedances of the feeding and radiating portion of the guide are matched by an intermediate flared portion or by a portion comprising a number of successively-larger sections interconnected by flanges, or by a quarter-wave length of guide of intermediate impedance. Alternatively, the guide may terminate in a reactance chamber closed by an adjustable aperture and piston, the horn branching laterally from the chamber. With large-aperture terminations, secondary radiation lobes are produced due to wave-front distortion in the structures. In the case of horns this is prevented by inserting a co-axial metal disc 5, Fig. 14. (Cancelled) or an annular disc of metal or dielectric material, within the horn, or,. by extending the guide to project a short distance into the horn, Fig. 15 (Cancelled); the constructions of Figs. 14 and 15 (Cancelled) may also be used to match two pipe-guides of different diameter. Alternatively, the mouth of the horn is covered by a lens of dielectic material, or transverse reactance elements may be placed in the horn, Fig. 19 (Cancelled). In the latter case the elements comprise wires w<1>, w<2> mounted parallel to the electric field, the reactance of the wires being adjusted by extending them outside the horn as co-axial lines each short-circuited by an adjustable piston. Wave-front distortion in the termination shown in Fig. 10 (Cancelled) is eliminated by covering its mouth with a zone-plate of metal or dielectric material. When the crosssection is rectangular, a metal grating is provided which sub-divides the end-piece into a number of pipe guides of rectangular section having different dimensions and hence different transmission characteristics, since the velocity of wave propagation is an inverse function of the dimensions. The same principle is applied to compensate distortion produced by a curved guide or horn, the transverse dimensions being reduced along the outside path of the bend. Fig. 23 (Cancelled) shows a " folded " horn in which the waves from the guide 17 follow a zig-zag path between the baffles 21 to the apertures 20, the cross-section of the successive passages changing in a linear or parabolic manner ; the structure is then equivalent to a straight horn with a stepped flare. In a modification, the baffles are set an an angle to the supporting plates 18, 19 to give outwardlyflared passages, the wave source being disposed between the two innermost baffles. In other forms, a radiating horn is placed within and directed towards the closed throat of an outer reflector horn, or a small reflector horn is placed within a larger radiating horn. For uniform horizontal radiation, the system of Fig. 32 (Cancelled) is used comprising a vertical pipe-guide 30 terminating in a flange 31 opposite which is disposed an annular plate 32 forming one end of a pipe resonance chamber 33 the other end being closed by an adjustable piston p<1>, The members 31, 32 may be replaced by suitably-shaped conical or dish-shaped members, maximum radiation in a particular direction being obtained by shaping the members asymmetrically. Suitable dimensions for the various structures are given. This subject matter does not appear in the Specification as accepted.