Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
  • H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
  • H01Q19/12—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave
  • H01Q19/13—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave the primary radiating source being a single radiating element, e.g. a dipole, a slot, a waveguide termination
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q1/00—Details of, or arrangements associated with, antennas
  • H01Q1/42—Housings not intimately mechanically associated with radiating elements, e.g. radome
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
  • H01Q15/14—Reflecting surfaces; Equivalent structures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
  • H01Q15/14—Reflecting surfaces; Equivalent structures
  • H01Q15/141—Apparatus or processes specially adapted for manufacturing reflecting surfaces
  • H01Q15/142—Apparatus or processes specially adapted for manufacturing reflecting surfaces using insulating material for supporting the reflecting surface
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
  • H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
  • H01Q19/12—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave
  • H01Q19/13—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are concave the primary radiating source being a single radiating element, e.g. a dipole, a slot, a waveguide termination
  • H01Q19/132—Horn reflector antennas; Off-set feeding

Definitions

• Reflektor antenna with off set feeding
• This invention relates to a millimetre wave antenna, and to methods of forming a millimetre wave antenna; particularly, but not exclusively, a millimetre-wave video signal reception antenna.
• 25 antennas apply equally to mm-wave reflector antennas.
• 3G provided a micro- or millimetre wave antenna comprising a reflector portion, a cylindrical skirt portion surrounding the reflector portion, the reflector portion being - ? -
• Figure 1 illustrates a millimetre wave transmission system
• Figure 2 is a sectional view of an antenna according to a preferred embodiment of the invention
• Figure 3 is an exploded view of an antenna according to a preferred embodiment of the invention
• Figure 4 illustrates a first method of manufacturing an antenna according to the invention.
• Figure 5 illustrates a second method of manufacturing an antenna according to the invention.
• a millimetre-wave transmission system comprises the transmitter (1), sited at a local high point and associated with the head-end (la) which controls a programme mix drawn from: - TVRO/DBS satellites at several orbit positions;
• the transmitter Using mm-wave transmission, eg at 29 GHz or 39 GHz, the transmitter would serve an area approximately 3km in diameter. Typically, this will encompass between 5,000 and 10,000 households. Coverage will be determined by considerations of transmitter power, antenna gain, receiver sensitivity, grade of performance required, and line-of-sight limitations due to trees, buildings etc. A customer at the edge of the coverage area would receive a picture quality better than CCIR Grade 4 for 99.9% of all time (compare the DBS target of better than Grade 4 for 99% of the worst month). Under normal conditions, a Grade 4.5 picture (or better) would be achieved. If neither 0 HDTV nor extended definition TV (EDTV) were required, then the s-ame performance could be achieved over about 3.5 km diameter.
• EDTV extended definition TV
• the receiver antenna (2a, 2b, 2c) is a small unobtrusive reflector of about 15 cm diameter or a printed 5 array of similar area.
• the signal passes via a downlead to the indoor receiver, which is of the type already in volume production for satellite reception.
• channels can be carried, selected to meet market requirements whilst remaining compatible with 0 channel spacing, spectrum availability, and frequency re-use objectives. For example, 20 channels spaced at multiples of 19.18 MHz, as used for direct broadcast satellite (DBS) service, could be chosen.
• the mm-wave spectrum offers sufficient bandwidth potential to handle EDTV and HDTV transmissions when these become available.
• an embodiment of an antenna according to the invention and suitable for use in the G above system comprises a single plastics moulding having a rear dish portion 3, and a cylindrical surrounding skirt portion 4, the dish portion 3 being disposed non-axisymmetrically about the long axis of the cylindrical skirt portion 4.
• the shape of the dish portion follows the formula for an offset parabola, as follows:
• f is the focal length (which may be, for example, 77.5 mms). It is not, of course, possible to produce non-axisymmetrical structures of this kind by spinning (the normal process used to fabricate antennas).
• a mating flange 5 may be provided, to which a radome 6 is sealed.
• a feed horn 7 is mounted, offset relative to the dish portion 3 through a hole in the skirt portion 4, so as to illuminate a considerable proportion of the dish.
• the exterior surface of the reflector dish may be metallised, so as to act as the reflecting surface. From a technical viewpoint, the effectiveness of this arrangement is somewhat surprising since a signal has to pass through plastics layers three times (once through the radome, and twice through the reflector), each time at a different angle - and the dielectric constants of plastics are significantly non-unity.
• skirt portion 4 is mounted on a conformal mounting block 8 by screws 9a, 9b etc passing through slots in skirt portion 4; the mounting is slideable to allow the antenna to be aligned during assembly on the block 8 using an alignment key, so as to accurately position the antenna relative to the feed horn 7.
• the feed horn 7 is rigidly fixed to an integrated down-converter module 10, to which mounting block 8 is also fixed, and the whole assembly is unobtrusively affixed at a suitable location using suitable supporting brackets. It will be seen that the skirt portion 4 performs several useful functions.
• the antenna as a whole has a much-simplified structure, with a small number of parts to be assembled together, thus reducing misalignment problems.
• the feed horn 7 may conveniently be fabricated as a single die-casting integral with its waveguide, giving manufacturing advantages over prior feeds which are formed as separate parts and then assembled together.
• the plastic radome 6 may be attached to the flange 5, as shown, using a sealing strip.
• the antenna may be formed as a single unitary whole, including the radome, thus further reducing the assembly time and providing a weathertight seal.
• the face of the radome 6 is inclined so as to have an overhang in use, to prevent the accumulation of rain, snow or ice in the radiation path.
• the invention therefore provides an antenna which can be accurately and cheaply formed, with sufficient rigidity and robustness for long term outdoors mounting at residential premises and a method of manufacturing such an antenna.
• the features of the antenna also lend themselves to the provision of attractive features of appearance (such as a streamlined appearance in the farings between the portions) which enhance the attractiveness of the product for the domestic consumer.
• the dimensions of the mould are slightly bigger than those required in the antenna, so as to allow for the degree of shrinkage which is common with thermo-plastic materials; with a 155 mm diameter antenna, for example, a half millimetre shrinkage is not uncommon.
• a sheet of plastics material 12 for example, Acrylonitrile-Butadiene Styrene (AE3) r having a thickness of, for example, 2.5 mm, is clamped over the mould in known fashion and heated to its softening point.
• a pressure differential is created across the sheet, for example by connecting a vacuum pump to an orifice or orifices 13 in the mould, so that the softened sheet is drawn down into close contact with the mould. Both heat and vacuum are then removed, and the sheet is allowed to cool on the mould; in so doing, it shrinks to the required dimensions.
• suitable thermo-forming techniques such as drape moulding or billow moulding, may equally be applied to manufacturing antennas according to the invention.
• the antenna it is possible to form the antenna with either a female or a male mould. If the plastics material in question is non-reflective (and therefore has to be metallised) then the reflecting layer should then be applied to the inner surface of the reflector dish portion 3, as this is the surface which has been accurately formed against the mould 11. This is somewhat problematic, for two reasons - firstly, it is physically less accessible than the outer surface, and secondly, it is necessary to accurately control the evenness of the metallising layer since the outer surface of that layer will be the actual reflecting surface. Satisfactory results are obtained, however, using spray-paint or vacuum metallising - provided care is taken.
• this process is improved by forming the sheet 12 into a female mould 11 as described above, and then metallising the outer (convex) surface of the moulding.
• the coating may be simply applied as a spray paint. It is, however, necessary (as mentioned above) to employ a slightly non-parabolic reflector profile (or a non-flat radome surface).
• blow moulding is employed to form a one-piece antenna including radome.
• the mould is formed in two parts; a preferred arrangement is as shown in Figure 5, where mould part 11a has the same shape as mould 11 in Figure 4, and mould part lib is essentially cylindrical.
• Two sheets of plastics material 12a, 12b are cut to size and introduced side by side into the moulds as shown? the moulds are then clamped together.
• a strong hollow needle 14 is placed between them, and connected to a source of compressed air. Heat is applied to the mould 11a, lib, so that the plastics sheets soften, as before. Compressed air is then introduced between the sheets 12a, 12b, so as to create a pressure differential across each sheet, and force them out into the mould.
• the mould is cooled (eg by cooling water) and the pressure is released; when they are cold, the moulds 11a, lib are separated, and the moulding removed (the heat having welded the sheets together at their edges) to be metallised as described above. Both these processes are relatively cheap to set up.
• cylindrical does not indicate necessarily a circular cross-section, but includes similar tubular shapes (which need not have a constant cross-section), although a circular cross-section is preferred so as to present an even radiation pattern. It will equally be understood that the invention is capable of operating either as a transmitter or a receiver (although it is primarily intended to be a domestic receiver).

Landscapes

• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Aerials With Secondary Devices (AREA)
• Details Of Aerials (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10641196

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (5)

Citations (5)

Family Cites Families (4)

• 1988
  • 1988-07-27 GB GB888817885A patent/GB8817885D0/en active Pending
• 1989
  • 1989-07-25 GB GB8916938A patent/GB2221351B/en not_active Expired - Lifetime
  • 1989-07-27 DE DE8990076U patent/DE8990076U1/de not_active Expired - Lifetime
  • 1989-07-27 AU AU40487/89A patent/AU634485B2/en not_active Ceased
  • 1989-07-27 JP JP1990600007U patent/JPH03500004U/ja active Pending
  • 1989-07-27 WO PCT/GB1989/000856 patent/WO1990001223A1/en unknown

Patent Citations (5)

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