GB1605279A - Aerials - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO AERIALS (71) We, THE MARCONI COMPANY LIMITED. of Marconi Housc, Ncw Street, Chelmsford, CM1 1PL, Essex, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method y which it is to be performed, to be particularly described in and by the following statement: This invention relates to aerials.

According to the invention, an aerial for radiating and/or receiving electromagnctic waves of a predetermined wavelength I comprises two plane reflectors of different sizes mounted parallel to each other and spaced apart hy a distance substantially equal to N1/2, where N is a positive integer, along a common axis of symmetry, so as to form a resonant structure and an antenna positioned on said axis between said reflectors for exciting vibrations of wavelength I in said resonant structure, thereby causing an output beam of electromagnetic radiation of wavelength I to be produced, directed generally along said axis in the direction of the smaller of said reflectors, said antenna being formed hy a slot in an otherwise closed end of a waveguide which passes along said axis through the larger of said re@lec@@ Preferable @ri@@flectors are circular in shape and preferably they have diameters substantially equal to 21 and 0.41 respectively.

Preferably also said antenna is positioned substantially midway between said reflectors. the invention also provides an aerial array comprising two or more aerials each in accordance with the present invention, mounted together on a common support member. Such aerial arrays are suitable for use with radar or direction-finding equipment @@@ the @@@@ principl The invention @@ls particular application in a tracking radar system for a homing head of a missile.

One embodiment of the @@@@ntion will now be described, by way of example. with reference to the accompanying drawing. of which: Figures I and 7 are respectively a sectional elevation and a plan view of an elementary aerial; ind Figure 3 is a plan view of an aerial array.

Referring to Figures I and 2, the aerial comprises two circular metal reflectors 10 and 12, having diameters respectively equal to 21 and ().41 where 1 is the operating wavelength of the aerial. The larger reflector 10 carrics a tubular metal rim 14, having a depth of 0.51.

The smaller reflector 12 is mounted on this rim 14, by means of a pair of dielectric supports 16.

In this way, the reflectors 10 and 12 are fixed parallel to each other and spaced apart by a distance approximately equal to 0.51, along a common axis IX of symmetry. The two reflectors it), 12 thus form a resonant structure for clcctromagnctic vibrations of wavelength l A rectangular waveguide 20 passes along the axis 18, through the larger reflector 10, and terminates in a slot 22, approximately 0.5l in length. which acts as an exciting antenna for the aerial The Icngth of the waveguide 20 which projects between the reflectors 10 and 12 is approximately equal to 0.25l, so that the exciting slot 22 lics substantially mid-way between the reflectors 10 and 12.

In operation, electromagnetic guided waves are fed down the waveguide 20. These waves are radiated from the s@@ 22, and excite electromagne@ @ib@@ wavelength @ between the reflectors are 12. these vibrations cause an output beam of electromagnetic waves to be produced, directed generally along the axis 18 in the direction of the smaller reflector 12.

Such an aerial providers a high gain factor and yet is simple in construction and is therefore both chcap to produce and reliable in operation.

The rim 14 is not essential, but serves to increase the gain of the aerial still further.

In @odi@@@@tion of the element @@rial, the spacing of the reflectors 10 and 12 may be increased by an integral number of half wavelength. Thus, in general, the spacing between the reflectors is substantially equal to @@@@l@re N is a positive integer.

Referring now to Figure 3, four elementary aerials 24, 26, 2X and 30. each of which is constructed as shown in Figures I and 2, are mounted side-by-side on a common support 32 in a square formation to provide an aerial array suitable for use in a static-split radar system.

The support 32 may be mounted on gimbals (not shown) so that it can be tilted so as to permit the aerial array to track a target.

What we claim is: 1. An aerial for radiating and/or receiving electromagnetic waves of predetermined wavelength 1 comprising two plane reflectors of different sizes mounted parallel to each other and spaced apart by a distance substantially equal to No/2, where N is a positive integer, along a common axis of symmetry, so as to form a resonant structure, and an antenna positioned on said axis between said reflectors for exciting vibrations of wavelength 1 in said resonant structure, thereby causing an output beam of electromagnetic radiation of wavelength I to be produced, directed generally along said axis in the direction of the smaller of said reflectors, said antenna being formed by a slot in an otherwise closed end of a waveguide which passes along said axis through the larger of said reflectors.

Claims (1)

1. 2. An aerial according to Claim 1, wherein said reflectors are circular in shape.

   3. An aerial according to Claim 2 wherein said reflectors have diameters substantially equal to 21 and 0.41 respectively.

   4. An aerial according to Claim 1, Claim 2 or Claim 3, wherein said antenna is positioned substantially midway between said reflectors.

   5. An aerial array comprising two or more aerials mounted together on a common support member, each of these aerials being in accordance with any one of the preceding claims.

   6. An aerial array according to Claim 6, wherein there are four of said aerials mounted side-by-side in a square formation.

   7. An acrial substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawing.

   8. An aerial array substantially as hereinbefore described with reference to Figures 1. 2 and 3 of the accompanying drawing.