US3708795A - Cassegrain antenna mounted in aircraft nose cone - Google Patents

Cassegrain antenna mounted in aircraft nose cone Download PDF

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Publication number
US3708795A
US3708795A US00114320A US3708795DA US3708795A US 3708795 A US3708795 A US 3708795A US 00114320 A US00114320 A US 00114320A US 3708795D A US3708795D A US 3708795DA US 3708795 A US3708795 A US 3708795A
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Prior art keywords
dish
sub
antenna
reflections
antenna according
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Expired - Lifetime
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US00114320A
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English (en)
Inventor
J Lyons
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BAE Systems PLC
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Hawker Siddeley Aviation Ltd
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Assigned to BRITISH AEROSPACE PUBLIC LIMITED COMPANY reassignment BRITISH AEROSPACE PUBLIC LIMITED COMPANY CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). EFFECTIVE JAN. 2, 1981 Assignors: BRITISH AEROSPACE LIMITED
Assigned to BRITISH AEROSPACE reassignment BRITISH AEROSPACE ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: HAWKER SIDDELEY AVIATION LIMITED
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/27—Adaptation for use in or on movable bodies
    • H01Q1/28—Adaptation for use in or on aircraft, missiles, satellites, or balloons
    • H01Q1/281—Nose antennas
    • 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
    • H01Q19/18—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 having two or more spaced reflecting surfaces
    • H01Q19/19—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 having two or more spaced reflecting surfaces comprising one main concave reflecting surface associated with an auxiliary reflecting surface
    • H01Q19/195—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 having two or more spaced reflecting surfaces comprising one main concave reflecting surface associated with an auxiliary reflecting surface wherein a reflecting surface acts also as a polarisation filter or a polarising device

Definitions

  • the forward-looking antennas used in strike and interceptor aircraft over recent years have usually employed a Cassegrain configuration having a parabolic main dish and hyperbolic sub-dish, the whole unit being mechanically scanned.
  • polarization sensitive reflecting surfaces have been used in order to reduce the aperture blocking effect of the subdish to a minimum. Details of such a Cassegrain antenna can be found in the paper by P.W. Hannan: Microwave Antennas derived from Cassegrain Telescope, I.R.E. Trans. A.P., March 61.
  • the swept volume required by the antenna is such that the permissible dish diameter is a good deal less than the radome cross section thus resulting in a valuable loss of aperture area.
  • the need to scan the antenna through large azimuth angles requires that the radome be extended rearwards some distance behind the scanner pivot point thus increasing both the radome surface area and the shell strength requirements.
  • rotating waveguide joints are necessary. When multi-channel and possibly multi-frequency feeds are employed the joints pose installational and mechanical problems and also introduce undesirable attenuation losses.
  • a parabolic sub-dish may be employed, the main dish being a simple flat plate.
  • the main dish acts essentially as a plane mirror, it only needs to be scanned through half the angle required to scan the radar beam.
  • An antenna of this type for a given aperture area, demands a larger radome than the conventional Cassegrain layout. This makes the arrangement extremely unattractive as far as aircraft design is concerned.
  • the present parabolic sub-dish is, by definition, a surface which focusses in a single reflection a wave parallel to its axis to a point (the focus).
  • FIG. 1 is a pictorial view of a Cassegrain antenna
  • FIG. 2 is a diagram of the antenna of FIG. 1 installed in anaircraft
  • FIG. 3 is a similar diagram of a flat plate Cassegrain antenna
  • FIG. 4 is a similar diagram showing a modified flat plate Cassegrain antenna according to the invention.
  • FIG. 5 is a diagram of such an antenna installed as an integrated structure in a large aircraft
  • FIG. 6 illustrates the geometry of the device
  • FIGS. 7, 8 and 9 are plots of various mathematicalequations involved.
  • FIG. 10 is a plot of the surfaces developed.
  • FIG. 1 shows a prior art Cassegrain antenna with a paraboloid main dish 9 and a hyperboloid sub-dish 10.
  • FIG. 2 shows how such an antenna may be installed in the nose of an aircraft 8.
  • FIG. 3 a flat plate Cassegrain antenna is shown similarly installed. This has a parabolic sub-dish 11 and a main dish 12 in the form of a simple flat plate. Polarization sensitive reflecting surfaces are employed.
  • FIG. 4 Corning now to the modified flat plate Cassegrain antenna according to the invention, a scheme employing the two-reflection case is shown in FIG. 4.
  • the general shape of the two-reflection surface 13 resembles that of typical nose radomes.
  • the included angle at the vertex of the'surface is too large for this surface to be used as an external radome.
  • the shape is almost ideal when faired into the aircraft fuselage lines, as shown in FIG. 5.
  • the antenna sub-dish 13 also becomes the external aircraft radome.
  • the losses and phase errors associated with such a surface have also been eliminated and therefore improvements in antenna performance can be expected.
  • This ray path has a section R parallel to the foreand-aft axis of the system and striking the flat plate main dish 12, whence it is reflected back along a parallel path R" to strike the sub-dish 13.
  • the ray is then reflected across the bowl of the sub-dish 13 along a path 11" to strike it again on the opposite side of the fore-and-aft axis, where there is a second reflection from the sub-dish directing the ray along path R"" to the feed horn substantially at the center of the flat plate main dish 12.
  • Equations 2 and 3 are plotted in normalized form in FIG. 7. It is seen that over the forward portion of the surface, the loci of P, P" are identical. As x/F is reduced, however, the two curves diverge, showing that P and P" do not share a common loci for all values of 0. This is no disadvantage as far as the present application to antennas is concerned as will now be shown.
  • Equation (1) describes the relationship between the angular spread of the feed, 0, and the normalized aperture spread function y/F. As such this equation may be used to design a feed horn which will give a specified power distribution across the aperture. From FIG. 7, we see the maximum permissible normalized radius of a flat plate scanner pivoted at the feed point is about 0.65. From H6. 8 which is a plot of equation (1), it is seen that this corresponds to a feed angle of 36 which is nearly the point at which the two loci curves diverge. Thus, if we define our required surface by equation (3) (locus of P"), then for feed angles less than 36 the required two-reflection, common locus curve exists.
  • the present conventional Cassegrain antenna in the strike aircraft has a dish diameter of 26 inches.
  • a inch can be added to the diameter.
  • the diameter can be increased to almost 32 inches representing an aperture area increase of in excess of 45 percent.
  • utilization of the latter configuration enabled the dish diameter to be increased from 23% inches to 26% inches, some 30 percent increase in aperture area.
  • antenna gain is directly proportional to aperture area
  • the extra reflection introduces an additional loss compared with the parabolic sub-dish antenna and hence this loss must be weighed against the extra gain derived from the allowable increase in aperture area.
  • the techniques for designing the required gridded dielectric reflection surface are well documented, e.g. see the article by M.A. Teichman: Designing Wire Grids for Impedance Matching of Dielectric Sheets, Microwave Journal, April 68. Good reflection properties are achievable over a wide range of angles of incidence and losses at each reflection can be kept as low as a few hundredths of a decibel. Thus, it is considered that the improved antenna performance achieved by the permitted aperture area increase far outweigh the effect of additional losses introduced by the second sub-dish reflection.
  • the substantially conically shaped sub-dish because of its reduced surface area, is somewhat lighter than that of the conventional flat plate Cassegrain antenna. For example,for the strike aircraft installation, the weight saving for this item was some 40 percent.
  • a surface of revolution has been evolved which has the property of redirecting radiation from a point source feed, after two reflections, into a plane wavefront which propagation parallel to the surface axis.
  • the above surface has been used in conjunction with a flat plate scanner and polarization sensitive reflection surfaces to form an antenna suitable for nose mounting in aircraft.
  • the sub-dish of the present design can also become the external aircraft radome thus avoiding the requirement for a further dielectric surface.
  • the shape of the sub-dish required for the proposed antenna is such that significant weight savings are possible for the applications outlined in (3) and (4) above.
  • the invention is also of special benefit in the case of the small executive type of civil airliners where fuselage cross sections are small but the aircraft still requires the maximum possible size of scanner for its weather radar.
  • the resulting surface, ogival in shape, although simplifying antenna installation, is not suitable for use as an external radome on supersonic aircraft.
  • a radome shape having a vertex included angle of or less it is necessary to use a radome shape having a vertex included angle of or less.
  • this type of antenna utilizes radome volume as efficiently as electronically-scanned antennas and an installation of comparable performance would cost considerably less than its more complicated counterpart.
  • a forward-looking aircraft antenna of substantially Cassegrain configuration comprising a main dish in flat plate form, and a sub-dish forward of the main dish with a reflecting surface in the form of a surface of revolution generated about a fore-and-aft axis passing through the center of the main dish, said sub-dish surface being chosen from the class of surfaces of revolution that require morethan a single reflection at said sub-dish to bring a wave approaching from said main dish and parallel to said axis of revolution to a substantial point focus on said axis.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Astronomy & Astrophysics (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Remote Sensing (AREA)
  • Aerials With Secondary Devices (AREA)
  • Details Of Aerials (AREA)
US00114320A 1970-02-10 1971-02-10 Cassegrain antenna mounted in aircraft nose cone Expired - Lifetime US3708795A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB641370 1970-02-10

Publications (1)

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FR (1) FR2085590B3 (OSRAM)
GB (1) GB1342892A (OSRAM)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0139482A3 (en) * 1983-09-22 1986-07-16 British Aerospace Public Limited Company Scanning dual reflector antenna
US5175559A (en) * 1991-10-24 1992-12-29 Westinghouse Electric Corp. Combined Radar/ESM antenna system and method
US5526008A (en) * 1993-06-23 1996-06-11 Ail Systems, Inc. Antenna mirror scannor with constant polarization characteristics
US5714947A (en) * 1997-01-28 1998-02-03 Northrop Grumman Corporation Vehicle collision avoidance system
US5775643A (en) * 1996-10-18 1998-07-07 The Boeing Company Passive flow control aero-optical turret assembly
US6404399B1 (en) * 2000-02-04 2002-06-11 Mitsubishi Denki Kabushiki Kaisha Radar antenna

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2334316C1 (ru) * 2007-04-12 2008-09-20 Федеральное Государственное Унитарное Предприятие "Нижегородский Научно-Исследовательский Институт Радиотехники" Антенное устройство

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3084342A (en) * 1957-12-18 1963-04-02 Gen Electric Co Ltd Tracking antenna with gyroscopic control
US3231893A (en) * 1961-10-05 1966-01-25 Bell Telephone Labor Inc Cassegrainian antenna with aperture blocking compensation
US3414904A (en) * 1966-05-16 1968-12-03 Hughes Aircraft Co Multiple reflector antenna

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3084342A (en) * 1957-12-18 1963-04-02 Gen Electric Co Ltd Tracking antenna with gyroscopic control
US3231893A (en) * 1961-10-05 1966-01-25 Bell Telephone Labor Inc Cassegrainian antenna with aperture blocking compensation
US3414904A (en) * 1966-05-16 1968-12-03 Hughes Aircraft Co Multiple reflector antenna

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0139482A3 (en) * 1983-09-22 1986-07-16 British Aerospace Public Limited Company Scanning dual reflector antenna
US5175559A (en) * 1991-10-24 1992-12-29 Westinghouse Electric Corp. Combined Radar/ESM antenna system and method
US5526008A (en) * 1993-06-23 1996-06-11 Ail Systems, Inc. Antenna mirror scannor with constant polarization characteristics
US5775643A (en) * 1996-10-18 1998-07-07 The Boeing Company Passive flow control aero-optical turret assembly
US5714947A (en) * 1997-01-28 1998-02-03 Northrop Grumman Corporation Vehicle collision avoidance system
US6404399B1 (en) * 2000-02-04 2002-06-11 Mitsubishi Denki Kabushiki Kaisha Radar antenna

Also Published As

Publication number Publication date
DE2105995B2 (de) 1972-10-12
FR2085590B3 (OSRAM) 1973-10-19
GB1342892A (en) 1974-01-03
DE2105995A1 (de) 1971-08-19
FR2085590A3 (OSRAM) 1971-12-24

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AS Assignment

Owner name: BRITISH AEROSPACE PUBLIC LIMITED COMPANY, DISTRICT

Free format text: CHANGE OF NAME;ASSIGNOR:BRITISH AEROSPACE LIMITED;REEL/FRAME:004080/0820

Effective date: 19820106

Owner name: BRITISH AEROSPACE PUBLIC LIMITED COMPANY

Free format text: CHANGE OF NAME;ASSIGNOR:BRITISH AEROSPACE LIMITED;REEL/FRAME:004080/0820

Effective date: 19820106

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Owner name: BRITISH AEROSPACE, BROOKLANDS RD., WEYBRIDGE SURRE

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST. AS OF APR. 17,1978;ASSIGNOR:HAWKER SIDDELEY AVIATION LIMITED;REEL/FRAME:003953/0751

Effective date: 19811218

Owner name: BRITISH AEROSPACE, ENGLAND

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:HAWKER SIDDELEY AVIATION LIMITED;REEL/FRAME:003953/0751

Effective date: 19811218