Communications: radio wave antennas – Antennas – With spaced or external radio wave refractor
Patent
1998-07-27
2000-07-04
Ho, Tan
Communications: radio wave antennas
Antennas
With spaced or external radio wave refractor
343755, 343756, H01Q 1906, H01Q 1910
Patent
active
06084552&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns an antenna for radiofrequency (r.f.) transmission.
2. Discussion of Prior Art
The requirement for an antenna which provides transmission covering 360.degree. in azimuth is well known in, for example, combat identification systems where combat vehicles etc need to transmit a signal which allows them to be identified by friendly forces. The applicability of the current invention is not, however, restricted to this field and uses may be found in any situation where transmission covering an azimuth of 360.degree. is required, for example, in the area of local area networking where a number of peripheral devices may communicate by r.f. transmission rather than electrical or fibre optic link.
Several types of reflector antenna are known (see for example Kraus, J. D., Antennas, McGraw-Hill, 2nd Ed., 1988.). Conventionally, the reflector is used to direct or focus the energy into a narrow beam, but if the application requires an omnidirectional antenna pattern, then the reflector needs to spread the energy into a wide angle. This has been achieved using a dual reflector system using a parabolic subreflector (Orefice, M. & Pirinoli, P., "Dual reflector antenna with narrow broadside beam for omnidirectional coverage", Elec. Lett., Vol. 29, No. 25, Dec. 9, 1993, pp. 2158-2159.). If just a single reflector is preferred, one can use, for example, a beam having a fundamental Hermite-Gaussian radial intensity to illuminate a cone which reflects the radiation over 360.degree. in azimuth. However, a beam having such a radial intensity to illuminate has its maximum intensity illuminating the point of the cone and this causes scattering and interference which, in turn, causes high sidelobes and a ragged elevation pattern. Such a design is also difficult to model accurately.
SUMMARY OF THE INVENTION
Therefore, in a first aspect of the present invention there is provided a method of transmitting radiofreaquency radiation over an azimuth angle of substantially 360.degree. which is characterised by illuminating a substantially conical reflector with a beam having a Laguerre-Gaussian intensity distribution, the minimum of the Laguerre-Gaussian distribution coinciding with the apex of the reflector, and the arrangement of the beam and relector being such that the radiation reflected from the reflector is divergent.
The term substantially, conical, when used in this specification, is intended to be construed in a broad sense where, in addition to the case of a perfect cone within the strictest meaning, other cases where reflection over 360.degree. in azimuth is provided are included. Such cases would include structures based on a cone shape but with sides which are convex or concave.
According to a second aspect of the invention, an radiofreaquency antenna for providing transmission over substantially 360.degree. in azimuth comprises a conical reflector and means for illuminating said reflector with a beam having a Laguerre-Gaussian intensity distribution, the minimum of the Laguerre-Gaussian distribution coinciding with the apex of the reflector, and the arrangement of the beam and the reflector being such that the radiation reflected from the reflector is divergent.
A further preferred embodiment includes a source of radiation having a Fundamental Hermnite-Gaussian intensity distribution and means for converting said radiation to radiation having a Laguerre-Gaussian intensity distribution.
The means for converting radiation having a Fundamental Hermite-Gaussian intensity distribution may comprise a spiral phaseplate. A further preferred embodiment includes means for collimating the radiation having a Fundamental Hermite-Gaussian intensity distribution.
The means for collimating the radiation having a Fundamental Hermite-Gaussian intensity distribution may comprise at least one lens.
A further preferred embodiment includes means for controlling the angular coverage in elevation of the output radiation of the antenna.
The means for controlling the angular coverage m ele
REFERENCES:
patent: 2045398 (1936-06-01), Massey et al.
patent: 4111564 (1978-09-01), Trice
patent: 4581529 (1986-04-01), Gordon
patent: 5115486 (1992-05-01), Bader et al.
Optical and Quantum Electronics, vol. 24, 1992, pp. S951-S962, XP000195853, N.R. Heckenberg et al: "Laser beams with phase singularities" cited in the application, see p. S961, Paragraph 4.
Optics Communications, vol. 96, 1993, pp. 123-132, XP000195858, M.W. Beijersbergen et al: "Astigmatic laser mode converters and transfer of orbital angular momentum", cited in the application, see abstract.
Optics Communications, vol. 112, No. 5/6, Dec. 1, 1994, pp. 321-327, XP000474724, M.W. Beijersbergen et al: "Helical-wavefront laser beams produced with a spiral phaseplate" cited in the application, see the whole document.
Optical Communications, vol. 127, Jun. 15, 1996, pp. 183-188, XP000195860, G.A. Turnbull et al: "The generation of free-space Laguerre-Gaussian modes at millimetre-wave frequencies by use of spiral phaseplate" cited in the application, see the whole document.
IEE Proceedings, vol. 131, No. 4, Aug. 4, 1984, pp. 258-262, XP000195855, R.J. Wyde: "Millimetre-wave Gaussian beam-mode optics an corrugated feed horns" cited in the application, see p. 262, left-hand column.
Patent Abstract of Japan, vol. 13, No. 46 (E-711), Feb. 2, 1989 & JP 63 240202 A (NEC CORP), Oct. 5, 1988, see abstract.
May Peter B
Robertson Duncan A
Ho Tan
The Secretary of State for Defence in Her Britannic Majesty's Go
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