EP0136817A1 - Gregory Antenne mit unterdrückten Nebenkeulen - Google Patents

Gregory Antenne mit unterdrückten Nebenkeulen Download PDF

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Publication number
EP0136817A1
EP0136817A1 EP84305894A EP84305894A EP0136817A1 EP 0136817 A1 EP0136817 A1 EP 0136817A1 EP 84305894 A EP84305894 A EP 84305894A EP 84305894 A EP84305894 A EP 84305894A EP 0136817 A1 EP0136817 A1 EP 0136817A1
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EP
European Patent Office
Prior art keywords
subreflector
main reflector
shield
microwave
antenna
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP84305894A
Other languages
English (en)
French (fr)
Inventor
Charles M. Knop
Edward L. Ostertag
Yuk-Bun Cheng
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Commscope Technologies LLC
Original Assignee
Andrew LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US06/531,069 external-priority patent/US4626863A/en
Application filed by Andrew LLC filed Critical Andrew LLC
Publication of EP0136817A1 publication Critical patent/EP0136817A1/de
Ceased legal-status Critical Current

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    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/001—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems for modifying the directional characteristic of an aerial
    • 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
    • H01Q19/02—Details
    • H01Q19/021—Means for reducing undesirable effects
    • H01Q19/026—Means for reducing undesirable effects for reducing the primary feed spill-over

Definitions

  • the present invention relates generally to microwave antennas and, more particularly, to dual-reflector microwave antennas.
  • Dual-reflector microwave antennas are known which minimise signal blockage at the main reflector dish aperture by utilising small-diameter feed horns and sub- reflectors. These small-diameter feed horn and subreflector combinations produce a good radiation pattern envelope (RPE) in the near-in side lobes between 3° and 10° from the antenna axis.
  • RPE radiation pattern envelope
  • the small-diameter feed horn characteristically displays a wide angle beam which causes an illumination pattern at the surface of the subreflector which is larger in area than the subreflector surface area. Consequently, some portion of the microwave energy fed from the small diameter feed horn spills past the periphery of the subreflector surface. The effect of energy spillover is a degradation in antenna performance in the side lobe region between 10° and 180° from the antenna axis.
  • a related object of this invention is to provide such an improved antenna which minimises side lobes caused by spillover and diffraction while maintaining good gain performance, and which can be efficiently and economically produced at a relatively low cost.
  • Yet another object of the present invention is to provide such an improved dual-reflector microwave antenna which is capable of satisfying the latest RPE specifications set by the U.S. Federal Communications Commission for earth station antennas.
  • a microwave antenna which comprises the combination of a paraboloidal main reflector; a subreflector located such that the paraboloidal main reflector and the subreflector have a common focal point lying between the main reflector and the subreflector; a feed horn for transmitting microwave radiation to, and receiving microwave radiation from, said subreflector; and a shield connected to the peripheral portion of the subreflector and having an absorbing surface which reduces side lobe levels caused by feed horn spillover energy and diffraction of microwave radiation.
  • the shield is preferably formed as a continuous axial projection extending from the periphery of the subreflector toward the main reflector substantially parallel to the axis of the feed horn.
  • the reflective surface of the subreflector is suitably a section of an approximate ellipse.
  • a dual-reflector antenna comprising a paraboloidal main reflector dish 10, a primary feed horn 11 connected to and supported by a circular waveguide 12 extending along the axis of the dish 10, and a subreflector 13 (the paraboloidal axis of the dish is identified as the horizontal line in Fig. 1 from which angles 9 1 , 8 2 and 8 3 are referenced).
  • the axis of the main dish as shown in Fig. 1 is coincident with the longitudinal axis of the waveguide 12 and feed horn 11.
  • feed as used herein, although having an apparent implication of use in a transmitting mode, will be understood to encompass use in a receiving mode as well, as is conventional in the art).
  • the feed horn 11 receives microwave signals via the circular waveguide 12 and launches those signals onto the subreflector 13; the subreflector reflects the signals onto the main reflector dish 10, which in turn reflects the radiation in a generally planar wave across the face of the paraboloid.
  • the paraboloidal main reflector 10 is illuminated by an incoming planar wave and reflects this energy into a spherical wave to illuminate the subreflector 13; the subreflector reflects this incoming energy into the feed horn 11 for transmission to the receiving equipment via the circular waveguide 12.
  • the common focal point F of the paraboloidal surface of the main reflector 10 and the reflecting surface of the subreflector 13 is located between the two reflectors to define what is commonly known as a Gregorian configuration.
  • the subreflector presents a concave reflective surface to the face of the main reflector.
  • the subreflector is mounted on the end of a tripod 14 fastened to brackets 15 on the main reflector dish 10.
  • the tripod 14 is composed of three metal support legs (usually covered with absorber material) which are relatively thin and introduce only a negligible amount of VSWR and pattern degradation into the antenna system. Normally the tripod is arranged so that the support legs are outside the horizontal plane.
  • the subreflector can be supported by a dielectric cone with the small end of the cone mounted on the main reflector 10, or on the waveguide 12, and with the subreflector mounted on the large end of the cone.
  • the subreflector 13 is positioned and dimensioned to intercept a large portion of the radiation launched from the feed horn 11 in the transmitting mode, and an equally large portion of the incoming radiation reflected by the main reflector 10 in the receiving mode, while at the same time minimising blockage of the aperture of the main reflector 10.
  • the subreflector preferably has a maximum diameter of about six wavelengths at the lowband frequency and nine wavelengths at the highband and is positioned sufficiently close to the feed horn to accomplish the desired interception of radiation from the horn.
  • the subreflector 13 is fitted with an absorber- lined shield 30 which intercepts and dissipates a substantial portion of the spillover from the feed horn 11 and also reduces diffraction of microwave radiation at the periphery of the subreflector 13.
  • the inner surface of this shield is lined with an absorber material 31. Spillover radiation is intercepted and dissipated by the shield 30 which projects from the periphery of the subreflector toward the main reflector and parallel to the axis of the feed horn.
  • the shield 30 can be added to the periphery of the subreflector 13 without interfering with the signal path between the subreflector 13 and the main reflector 10.
  • the axial length Ll of the shield 30 is limited by the surface of an imaginary cone whose apex is the common focal point F of the dual reflectors and whose base is the periphery of the main reflector (the cone surface is illustrated by the dotted line A-B, in Fig. 1). In three dimensions, this imaginary cone defines the surface within which the presence of the subreflector shield would interfere with the signal path between the main reflector 10 and the subreflector 13.
  • Diffraction normally occurs at an edge of a subreflector.
  • the only diffracting edge of the subreflector assembly i.e., the edge of the shield 30, is located in a region where the spillover energy level is significantly less than at the periphery of the subreflector 13.
  • the diffraction caused by the subreflector assembly with the shield 30 is much less than without the shield, producing lower side lobes in the region beyond about 10° off axis.
  • the edge of the subreflector shield 30 is shown to be at an angle ⁇ 2 with respect to the axis of the main dish shown in Fig. 1, while the edge of the subreflector 13 is at an angle ⁇ 1 with respect to the axis of the main reflector. Since the radiation beam, as it leaves the feed horn 11, has its peak on the axis of the main reflector 10, the spillover energy level of the beam emanating from the feed horn 11 at angle 92 is significantly lower than it is at angle 8 1 .
  • a shield 32 is provided on the main reflector 10.
  • This shield 32 which has a relatively short axial length L2, is also lined with absorbing material 31.
  • the lengths Ll and L2 of the two shields 30 and 32 are such that their combined effect is to intercept and dissipate substantially all the spillover radiation from the feed horn 11. With these two shields 30 and 32, the antenna exhibits much improved RPE side lobes.
  • the axial length Ll of the subreflector shield 30 is preferably maximised.
  • the upper limit for the length Ll of the subreflector shield is the imaginary cone mentioned earlier, representing the outermost portion of the signal path between the two reflectors.
  • the shield length Ll is made slightly shorter than its maximum permissible length to ensure that it does not interfere with the desired beam.
  • the shield 30 is positioned on the periphery of the subreflector 13. Any number of means for attaching the shield to the subreflector can be used, depending on the materials of construction used for the shield and subreflector.
  • the shield is preferably constructed of a continuous flat metal or fiberglass projection in an annular shape whose inner and outer walls are substantially parallel to the axis of the subreflector. Conventional microwave absorbing material having a pyramidal, flat or convoluted surface, or even "hair” absorber, can be used on the inside surface of the shield.
  • the main reflector shield 32 is constructed in a manner similar to the subreflector shield 30.
  • the shield 32 is also constructed of an annular metal or fiberglass projection whose inner and outer walls are substantially parallel to the axis of the main reflector.
  • the inner wall is lined with microwave absorbing material which can be the same as that used in the subreflector shield 30.
  • the feed horn 11 comprises two straight circular waveguide sections 40 and 41 interconnected by a conical circular waveguide section 42.
  • This feed horn produces substantially equal E-plane and H-plane patterns in two different frequency bands. This is accomplished by selecting the diameter of the horn mouth (aperture) to be approximately equal to one wavelength in the lower frequency band, and then selecting the slope of the conical wall to cancel the radial electric field at the aperture of the horn (of inner diameter Dl) in the upper frequency band.
  • the one-wavelength diameter for the lower frequency band produces substantially equal patterns in the E and H planes for the lower-frequency signals, while the cancellation of the electric field of the higher-frequency signals at the inside wall of the horn aperture produces substantially equal patterns in the E and H planes for the higher-frequency signals.
  • the horn is both small and inexpensive to fabricate, and yet it produces optimum main beam patterns in both the E and H planes in two different frequency bands simultaneously.
  • the small size of the horn means that it minimises horn blockage in reflector-type antennas, even though they are dual frequency band antennas.
  • the feed horn 11 is a conventional smooth-wall TEll mode horn at the low frequency (e.g., 3.95 GHz) with an inside diameter Dl in its larger cylindrical section 40 approximately equal to the wavelength at the center frequency (e.g., 3.95 GHz) of the lower frequency band.
  • the second cylindrical section 41 of the feed horn has a smaller inside diameter D2, and the two cylindrical sections 40 and 41 are joined by the uniformly tapered conical section 42 to generate (at the junction of sections 40 and 42) and propagate the TM 11 mode in the upper frequency band (e.g., 6 GHz). More specifically, the conical section 42 generates (at the junction of sections 40 and 42) a TM 11 mode from the TEll mode propagating from left to right in the smaller cylindrical section 41.
  • the freshly generated TM 11 mode leads the TEll mode by about 90° in phase.
  • the slope of the conical section 42 determines the amplitude of the TM 11 mode signal, while the length L of the larger cylindrical section 4 0 determines the phase relationship between the two modes at the aperture of the feed horn.
  • the open end of the horn is surrounded by a quarter-wave choke (or chokes) 46 comprising a short conductive cylinder 47, concentric with the horn 11, and a shorting ring 48.
  • the inner surface of the cylinder 47 is spaced away from the outer surface of the horn 11 along a length of the horn about equal to a quarter wavelength (at the low band) from the end of the horn, and then the cylinder 47 is shorted to the horn 11 by the ring 48 to form a quarter-wave coaxial choke which suppresses current flow on the outer surface of the horn.
  • the ratio of the mode powers W TM 11 and W TE 11 must be: where the guide wavelength of the TM 11 mode is The guide wavelength of the TE 11 mode is and
  • Equating equations (1) and (5) yields:
  • Equation ( 8 ) Equation ( 8 ) can then be solved for ⁇ :
  • This value of P results, at the high band, in cancellation of the electric field at the aperture boundary, which in turn results in approximately equal E and H patterns of the main beam radiated from the horn in the high frequency band.
  • the diameter Dl must be such that the value of C, which is defined by equation (4) as ; is above the Eigen value of 3.83 for the TM 11 mode in Hthe high frequency band.
  • the diameter Dl must be such that the value of C is below the Eigen value of 5.33 for the TE 12 mode in the high frequency band, and concentricity of sections 40, 41 and 42 must be maintained.
  • the value of C must be within the range of from about 3.83 to about 5.33.
  • the two frequency bands must be selected to satisfy the above criteria.
  • One suitable pair of frequency bands are 4GHz and 6GHz, because ⁇ L and Dl are 2.953 inches, ⁇ H is 1.969 inches, and ⁇ L / ⁇ H is 1.5. This value of the ratio ⁇ L / ⁇ H is, of course, within the prescribed range of 1.22 to 1.61.
  • a flared corrugated feed horn may be used in place of the dual mode smooth-wall horn in the illustrative embodiment of Fig. 3 (e.g., a flare angle of 45° relative to the axis of the paraboloid of the main reflector could be used).
  • a flared corrugated feed horn provides about the same horizontal plane performance (though having more pattern symmetry) when substituted for the feed horn of Fig. 3, but is significantly more expensive than the feed horn of Fig. 3.
  • the corrugated portions of a flared corrugated feed horn are on the inside of the feed horn. Therefore, for the same inside diameter as the feed horn of Fig. 3, the flared feed horn requires a greater outside diameter.
  • the flared corrugated feed horn also casts a larger shadow on the main reflector, thereby requiring an increase in the subreflector size and resulting in higher blockage and higher side lobes. It will be appreciated, therefore, that the particular feed horn used in the antenna of Fig. 1 depends on the desired combination of cost and performance characteristics of the antenna.
  • a paraboloidal main reflector with a diameter of 10 feet is utilised with a focal length-to-diameter ratio of 0.4.
  • the subreflector is 18 inches in diameter.
  • the length Ll of the subreflector shield is 6.302 inches, and the length L2 of the main reflector shield is 41.0 inches.
  • the feed horn is of the type shown in Fig. 3, with an inner diameter of 2.125 inches in its smaller cylindrical section 41 and 2.810 inches in its larger cylindrical section 40.
  • the conical section 42 connecting the two cylindrical sections has a half-flare angle of 30 with respect to the axis of the feed horn.
  • the axial length of the conical section is 0.593 inches.
  • the lengths of the two cylindrical sections 41 and 40 are 1.0 inches and 4.531 inches, respectively, and the mouth of the feed horn is located 24.89 inches from a plane defined by the periphery of the main reflector.
  • the angles 6 1 , e 2 and e 3 are 55°, 80 and 75°, respectively.
  • the axial length L2 of the main reflector shield is chosen such that the angle ⁇ 3 is less than ⁇ 2 . This creates a radial overlap of the two shields 30 and 32 to insure that all of the horn spillover radiation is intercepted by either the main reflector shield 32 or the subreflector shield 30.
  • a preferred surface curvature of the subreflector 13 for the working example described above is shown by way of a Cartesian coordinate graph.
  • the origin of the Cartesian coordinate system is virtually coincident with the common focal point F of the main reflector and the subreflector, and the measured points are taken along a diameter of the subreflector.
  • the surface curvature describes an arc which is approximately, though not exactly, elliptic.
  • the hypothetical example described above is predicted to produce a power pattern as shown in Fig. 5a at 3.95 GHz.
  • the power pattern for the same antenna at 6.175 GHz is shown in Fig. 5b.
  • the power patterns in Figs. 5a and 5b represent amplitude in decibels along an arc length of a circle whose centre is coincident with the position of the antenna.
  • Figs. 5a and 5b also show in dashed lines typical envelopes of the power patterns (so-called RPE's, or radiation pattern envelopes) for a presently commercially available antenna.
  • RPE's radiation pattern envelopes
  • the side lobes in the region between 3° and 10° off axis are considerably lower for an antenna constructed in accordance with the invention.
  • Figs. 7a and 7b also show in dashed lines typical RPE's for a presently commercially available antenna.
  • the antenna of the invention with a flared corrugated feed horn displays predicted RPE's which are comparable to the predicted RPE's of Figs. 5a and 5b in the side lobe region between 5° and 1 0 0 .
  • Both working antenna constructions i.e. with either the Fig. 3 feed horn or the flared corrugated feed horn
  • the dual-reflector microwave antenna utilises a small diameter feed horn and shielded subreflector to achieve a good radiation pattern envelope in the region between 3 0 and 10° off axis, and subreflector and main reflector shields to achieve a superior radiation pattern in the region between 10° and 180° off axis.
  • this antenna minimises side lobes caused by spillover and diffraction while maintaining good gain performance, and the antenna can be efficiently and economically produced at a relatively low cost.
  • This antenna minimises thelength of the main reflector shield, thereby minimising the total antenna shield surface area.
  • this type of antenna is capable of satisfying the latest RPE specification set by the U.S. Federal Communication Commission for earth station antennas.

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  • Aerials With Secondary Devices (AREA)
EP84305894A 1983-09-06 1984-08-29 Gregory Antenne mit unterdrückten Nebenkeulen Ceased EP0136817A1 (de)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US52937583A 1983-09-06 1983-09-06
US529375 1983-09-06
US531069 1983-09-12
US06/531,069 US4626863A (en) 1983-09-12 1983-09-12 Low side lobe Gregorian antenna

Publications (1)

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EP0136817A1 true EP0136817A1 (de) 1985-04-10

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EP84305894A Ceased EP0136817A1 (de) 1983-09-06 1984-08-29 Gregory Antenne mit unterdrückten Nebenkeulen

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0284897A1 (de) * 1987-03-19 1988-10-05 Siemens Aktiengesellschaft Zweireflektor-Microwellen-Richtantenne
EP0859427A1 (de) * 1997-02-14 1998-08-19 Andrew A.G. Doppelreflektormikrowellenantenne
US7898491B1 (en) 2009-11-05 2011-03-01 Andrew Llc Reflector antenna feed RF seal
EP2493018A1 (de) * 2011-02-25 2012-08-29 Honeywell International Inc. Apertur-Moden-Filter

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3314071A (en) * 1965-07-12 1967-04-11 Gen Dynamics Corp Device for control of antenna illumination tapers comprising a tapered surface of rf absorption material
DE1296221B (de) * 1965-09-30 1969-05-29 Siemens Ag Richtantenne, bestehend aus einem ueber einen Fangreflektor ausgeleuchteten Hauptreflektor
EP0005487A1 (de) * 1978-05-11 1979-11-28 CSELT Centro Studi e Laboratori Telecomunicazioni S.p.A. Antenne mit Parabolreflektor und optimaler Strahlungscharakteristik

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3314071A (en) * 1965-07-12 1967-04-11 Gen Dynamics Corp Device for control of antenna illumination tapers comprising a tapered surface of rf absorption material
DE1296221B (de) * 1965-09-30 1969-05-29 Siemens Ag Richtantenne, bestehend aus einem ueber einen Fangreflektor ausgeleuchteten Hauptreflektor
EP0005487A1 (de) * 1978-05-11 1979-11-28 CSELT Centro Studi e Laboratori Telecomunicazioni S.p.A. Antenne mit Parabolreflektor und optimaler Strahlungscharakteristik

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 2, no. 75, 14th June 1978, page 3004 E78; & JP-A-53-41154 (MITSUBISHIDENKI) 14-04-1978 *
THE MARCONI REVIEW, Second quarter 1980; A.D. MONK "The prediction and control of the wide-angle sidelobes of satellite earth station antennas", pages 74-95 *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0284897A1 (de) * 1987-03-19 1988-10-05 Siemens Aktiengesellschaft Zweireflektor-Microwellen-Richtantenne
EP0859427A1 (de) * 1997-02-14 1998-08-19 Andrew A.G. Doppelreflektormikrowellenantenne
US7898491B1 (en) 2009-11-05 2011-03-01 Andrew Llc Reflector antenna feed RF seal
WO2011055167A1 (en) * 2009-11-05 2011-05-12 Andrew Llc Reflector antenna feed rf seal
EP2493018A1 (de) * 2011-02-25 2012-08-29 Honeywell International Inc. Apertur-Moden-Filter
CN102683772A (zh) * 2011-02-25 2012-09-19 霍尼韦尔国际公司 孔径模式滤波器
US9112279B2 (en) 2011-02-25 2015-08-18 Honeywell International Inc. Aperture mode filter
CN102683772B (zh) * 2011-02-25 2016-03-23 霍尼韦尔国际公司 孔径模式滤波器

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