US3140491A - Diffraction shield consisting of notched ring which frames passive reflector - Google Patents
Diffraction shield consisting of notched ring which frames passive reflector Download PDFInfo
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- US3140491A US3140491A US253622A US25362263A US3140491A US 3140491 A US3140491 A US 3140491A US 253622 A US253622 A US 253622A US 25362263 A US25362263 A US 25362263A US 3140491 A US3140491 A US 3140491A
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- shield
- diffraction
- paraboloid
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- edge
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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
- H01Q19/02—Details
- H01Q19/021—Means for reducing undesirable effects
- H01Q19/022—Means for reducing undesirable effects for reducing the edge scattering of reflectors
Definitions
- the back radiation pattern of a paraboloid antenna is caused by currents induced at the outer edge of the paraboloid principally by its primary feed.
- Most attempts to solve the problem have been based primarily on the reduction of the edge currents by shaping the pattern of the primary radiator, by shielding the edge of the paraboloid by placing it in a tunnel, or by the use of a paraboloid with a very small f/D ratio.
- the more recent efforts in this field, such as disclosed in US. Patents 2,808,586 and 2,942,265, have been to provide means so that the energy radiated directly from the primary feed arrives at the edge substantially out of phase with the energy reflected from the reflector.
- the instantinvention operates on the principle of cancellation by phase control and basically consists of a ring of sheet metal positioned on the periphery of the paraboloid antenna.
- an object of the invention is to provide means for controlling the diffraction of microwaves.
- a further object of the invention is to provide means for controlling the direction of propagation of diffracted electromagnetic waves.
- Another object of the invention is to provide means for substantially reducing the undesirable effects of edge diffraction in antenna systems operating over a broad band of frequencies.
- Another object of the invention is to provide means for substantially reducing unwanted back radiation in paraboloid antennas.
- FIG. 1 is a perspective view of the front side of a typical paraboloid antenna with one embodiment of the invention in place;
- FIG. 2 is a cross-sectional view taken on the line 22 of FIG. 1;
- FIG. 3 is a cross-sectional view similar to FIG. 2 but showing another embodiment of the invention.
- a typical paraboloid antenna 1 composed of conductive material and having a peripheral flange portion 2 is provided with a ditfraction shield 3.
- Antenna 1 is provided with a primary feed 5.
- Shield 3 consists of a ring "Ice of sheet metal having notches 4 and 4' extending around segments thereof, said notches being spaced at approximately one wave-length intervals and having a depth of approximately /2 wavelength, the wavelengths being relative to the transmission frequency.
- the notched shield causes the electric field at the edge of the parabola to be broken into two components which appear to be 180 out of phase when viewed from the rear of the antenna. The result is a broad null in the back radiation pattern.
- the theory of the diffraction shield may be better understood by considering the view of a paraboloid antenna as shown in FIGURE 1.
- Energy is radiated by the primary feed 5 toward the antenna shield 3.
- the electro magnetic field representation is shown in vector form where I is the poynting vector and represents the power density of the field.
- the electric vector 1 is shown normal to the plane of the shield 3.
- the electromagnetic field reaches the shield 3, it must meet the boundary conditions as dictated by Maxwells equation.
- the outer edge of the shield creates a second boundary condition since the current flow must be interrupted. This condition causes the energy entrapped on the shield to be reradiated.
- the radiation pattern tends to be cardioid and hence a substantial amount is reradiated to the rear of the paraboloid.
- the notches 4 provide a means of providing an out-of-phase segment. By cutting the notches M 2 deep, the energy generally reradiated to the rear of the antenna as a result of the current discontinuity at the notch is 180 out of phase from that reradiated from the outer edge or tooth 4. In order to radiate the notches must be at least ) ⁇ /2 wide. On the other hand, the notches should not be too wide or too far apart. Considering the notches as an array, the width and spacing should not be substantially greater than 7 ⁇ to effect good pattern control. A value of A was chosen for test and was found to be adequate.
- FIG. 1 device The following is a description of the operation of the FIG. 1 device:
- the linearly polarized primary feed 5 emits an electromagnetic wave in the direction of the flange portion 2 polarized substantially perpendicular to the aperture plane in the 0 (north) and 180 (south) directions and parallel to the aperture plane in the (east) and 270 (west) directions.
- the plane of polarization rotates uniformly from perpendicular to parallel polarization for directions from 0 (north) to 90 (east) and 180 (south) to 270 (west); but rotates from parallel to perpendicular polarization for directions from 90 (east) to 180 (south) and 270 (west) to 0 (north).
- Diffraction is associated with only the perpendicularly polarized component of the electromagnetic wave.
- a radial component of current is induced in the diiiraction shield 3.
- the discontinuity of this current at the edge of the shield produces a re-radiated electromagnetic wave.
- the current induced in the notch 4 is 180 out of phase with the current induced in tooth 4' due to the one-half wavelength difference in distance from the primary feed 5.
- the notches and the teeth appear as k) two segmented line sources spaced one-half wavelength apart and 180 out of phase.
- the resulting far-field radiation pattern has a null directly to the rear of the paraboloid. Hence back radiation is virtually eliminated.
- FIG. 3 shows another effective type of diffraction shield which consists of a ring of sheet metal attached to the flange portion 2 of the paraboloid as in FIGS. 1 and 2.
- the outer one-half wavelength is bent back at approximately 30 and is not provided with notches as the FIGS. 1 and 2 embodiments.
- the embodiment of FIG. 3 provides a partial current discontinuity to the radial current at the point of bend. This causes the shield to re-rad-iate at this point.
- the reradiatcd energy cannot radiate to the rear of the paraboloid because the outer portion of the shield acts as a barrier. Some current is still present at the shield edge and is radiated as before. This radiation is substantially reduced because of the radiation at the bend.
- FIGS. 2 and 3 can also be combined to provide an effective diffraction shield.
- the invention provides a simple and effective means for reducing the radiation from the back side of a paraboloid antenna.
- a microwave system having means for controlling edge diffraction comprising: reflector means, ring means extending around at least a portion of said reflector means, said ring means being provided with a plurality of notches.
- a microwave system having means for controlling edge diffraction comprising: reflector means having a reflecting surface, ring means extending around at least a portion of said reflector means, said ring means having an outer edge disposed in a direction backwards with respect to the outer periphery of said reflecting surface.
- a device for controlling edge diffraction of a reflecting means comprising: means adapted to be positioned about the edge of at least a portion of a reflecting means, said means including a portion thereof defining two segmented line sources spaced one-half wave length apart and out of phase.
- said portion of said means comprises material having a plurality of notches which have a radial depth of approximately onehalf wave length, said notches being spaced at approximately one wave length intervals.
- said portion of said means comprises material having an outer portion disposed in a direction of approximately 30 from the plane of said material, said portion having a radial depth of approximately one-half wave length.
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Description
y 1964 F. E. ASHBAUGH ETAL 3,140,491
DIFFRACTION SHIELD CONSISTING OF NOTCHEID RING WHICH FRAMES PASSIVE REFLECTOR Filed Jan. 24, 1963 INVENTORS FRED Asf/BAUGH FRANK M Bus/WAN AGENT United States Patent This invention relates generally to electromagnetic wave transmission and reception, and more particularly to the control of edge diifraction in microwave antennas of the paraboloid type.
In certain applications of microwave antennas it is often necessary to minimize the amount of energy radiated in some directions as Well as maximize the amount of energy radiated in other directions.
In other applications, such as radio-astronomy and microwave relay links, it is very important that the radiation from the back side of a paraboloid antenna be as low as possible. In the field of radio astronomy the main beam of the paraboloid scans the sky to record and map areas of RF radiation. The back side of the antenna also picks. up some radiation from the warm earth. This unwanted radiation acts as noise to the desired signal from the sky, the amount being often expressed as noise temperature. For microwave relay links application, unwanted back radiation results in signal distortion.
The back radiation pattern of a paraboloid antenna is caused by currents induced at the outer edge of the paraboloid principally by its primary feed. Most attempts to solve the problem have been based primarily on the reduction of the edge currents by shaping the pattern of the primary radiator, by shielding the edge of the paraboloid by placing it in a tunnel, or by the use of a paraboloid with a very small f/D ratio. The more recent efforts in this field, such as disclosed in US. Patents 2,808,586 and 2,942,265, have been to provide means so that the energy radiated directly from the primary feed arrives at the edge substantially out of phase with the energy reflected from the reflector.
The instantinvention operates on the principle of cancellation by phase control and basically consists of a ring of sheet metal positioned on the periphery of the paraboloid antenna.
Therefore, an object of the invention is to provide means for controlling the diffraction of microwaves.
A further object of the invention is to provide means for controlling the direction of propagation of diffracted electromagnetic waves.
Another object of the invention is to provide means for substantially reducing the undesirable effects of edge diffraction in antenna systems operating over a broad band of frequencies.
Another object of the invention is to provide means for substantially reducing unwanted back radiation in paraboloid antennas.
Other objects of the invention not specifically set forth above will become readily apparent from the accompanying description and drawings in which:
FIG. 1 is a perspective view of the front side of a typical paraboloid antenna with one embodiment of the invention in place;
FIG. 2 is a cross-sectional view taken on the line 22 of FIG. 1; and
FIG. 3 is a cross-sectional view similar to FIG. 2 but showing another embodiment of the invention.
A typical paraboloid antenna 1 composed of conductive material and having a peripheral flange portion 2 is provided with a ditfraction shield 3. Antenna 1 is provided with a primary feed 5. Shield 3 consists of a ring "Ice of sheet metal having notches 4 and 4' extending around segments thereof, said notches being spaced at approximately one wave-length intervals and having a depth of approximately /2 wavelength, the wavelengths being relative to the transmission frequency. The notched shield causes the electric field at the edge of the parabola to be broken into two components which appear to be 180 out of phase when viewed from the rear of the antenna. The result is a broad null in the back radiation pattern.
The theory of the diffraction shield may be better understood by considering the view of a paraboloid antenna as shown in FIGURE 1. Energy is radiated by the primary feed 5 toward the antenna shield 3. The electro magnetic field representation is shown in vector form where I is the poynting vector and represents the power density of the field. The electric vector 1 is shown normal to the plane of the shield 3. In accordance with Maxwells equations, both the electric vector E and the magnetic vector E are normal to the flow of energy and are related to the poynting vector '1? by the vector relationship F=EXFI When the electromagnetic field reaches the shield 3, it must meet the boundary conditions as dictated by Maxwells equation. The significant boundary condition is in this case is defined by the vector relationship J' FXF, where T is the current density induced in the shield 3 in the direction shown in FIGURE 1, and is" is the outward normal to shield 3. It is significant to note that the induced current in the shield flows across the shield 3.
The outer edge of the shield creates a second boundary condition since the current flow must be interrupted. This condition causes the energy entrapped on the shield to be reradiated. The radiation pattern tends to be cardioid and hence a substantial amount is reradiated to the rear of the paraboloid. The notches 4 provide a means of providing an out-of-phase segment. By cutting the notches M 2 deep, the energy generally reradiated to the rear of the antenna as a result of the current discontinuity at the notch is 180 out of phase from that reradiated from the outer edge or tooth 4. In order to radiate the notches must be at least )\/2 wide. On the other hand, the notches should not be too wide or too far apart. Considering the notches as an array, the width and spacing should not be substantially greater than 7\ to effect good pattern control. A value of A was chosen for test and was found to be adequate.
The following is a description of the operation of the FIG. 1 device:
Consider the rim of the paraboloid of FIG. 1 marked as a compass rose. The linearly polarized primary feed 5 emits an electromagnetic wave in the direction of the flange portion 2 polarized substantially perpendicular to the aperture plane in the 0 (north) and 180 (south) directions and parallel to the aperture plane in the (east) and 270 (west) directions. The plane of polarization rotates uniformly from perpendicular to parallel polarization for directions from 0 (north) to 90 (east) and 180 (south) to 270 (west); but rotates from parallel to perpendicular polarization for directions from 90 (east) to 180 (south) and 270 (west) to 0 (north).
Diffraction is associated with only the perpendicularly polarized component of the electromagnetic wave. For this polarization, a radial component of current is induced in the diiiraction shield 3. The discontinuity of this current at the edge of the shield produces a re-radiated electromagnetic wave. The current induced in the notch 4 is 180 out of phase with the current induced in tooth 4' due to the one-half wavelength difference in distance from the primary feed 5. As seen from the rear of the paraboloid, the notches and the teeth appear as k) two segmented line sources spaced one-half wavelength apart and 180 out of phase. The resulting far-field radiation pattern has a null directly to the rear of the paraboloid. Hence back radiation is virtually eliminated.
For a linearly polarized primary feed polarized in the north and south direction, substantial diffraction shielding is provided by only a segment of the shield located at the north and south edges of the paraboloid. Some additional shielding is provided by extending the shield completely around the paraboloid. This also provides shielding for dual polarized primary feeds.
FIG. 3 shows another effective type of diffraction shield which consists of a ring of sheet metal attached to the flange portion 2 of the paraboloid as in FIGS. 1 and 2. However, in this embodiment the outer one-half wavelength is bent back at approximately 30 and is not provided with notches as the FIGS. 1 and 2 embodiments. The embodiment of FIG. 3 provides a partial current discontinuity to the radial current at the point of bend. This causes the shield to re-rad-iate at this point. The reradiatcd energy cannot radiate to the rear of the paraboloid because the outer portion of the shield acts as a barrier. Some current is still present at the shield edge and is radiated as before. This radiation is substantially reduced because of the radiation at the bend.
Based upon the above explained theory, and the well known principle that radiation will occur at points of current discontinuity, which discontinuity may take on the form of slots, probes, or abrupt changes in directions such as a bend, it was determined that the total diffraction pattern is 'a composite of the bend, the length of the bent portion, as well as residual current at the edge of the reflector. As the result of such a determination, satisfactory performance was obtained experimentally with 30 degrees. However, the exact value of 30 degrees is not critical to the operation of the FIG. 3 shield.
The embodiments of FIGS. 2 and 3 can also be combined to provide an effective diffraction shield.
It has thus been shown that the invention provides a simple and effective means for reducing the radiation from the back side of a paraboloid antenna.
Although particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention, and it is intended to cover in the appended claims all such changes and modifications that come within the true spirit and scope of the invention.
What we claim is:
1. A microwave system having means for controlling edge diffraction comprising: reflector means, ring means extending around at least a portion of said reflector means, said ring means being provided with a plurality of notches.
2. The device defined in claim 1 wherein said notches are spaced at approximately one wave length intervals and have a radial depth of approximately one-half wave length.
3. A microwave system having means for controlling edge diffraction comprising: reflector means having a reflecting surface, ring means extending around at least a portion of said reflector means, said ring means having an outer edge disposed in a direction backwards with respect to the outer periphery of said reflecting surface.
4. The device defined in claim 3 wherein the said outer edge is approximately one-half wave length in radial depth and is disposed backwards at approximately 30 from the plane of the ring means.
5. A device for controlling edge diffraction of a reflecting means comprising: means adapted to be positioned about the edge of at least a portion of a reflecting means, said means including a portion thereof defining two segmented line sources spaced one-half wave length apart and out of phase.
6. The device defined in claim 5 wherein said portion of said means comprises material having a plurality of notches which have a radial depth of approximately onehalf wave length, said notches being spaced at approximately one wave length intervals.
7. The device defined in claim 5 wherein said portion of said means comprises material having an outer portion disposed in a direction of approximately 30 from the plane of said material, said portion having a radial depth of approximately one-half wave length.
References Cited in the file of this patent UNITED STATES PATENTS 1,987,780 Latour Jan. 15, 1935 2,460,869 Braden Feb. 8, 1949 2,895,127 Padgett July 14, 1959 2,895,131 Butler July 14, 1959 FOREIGN PATENTS 726,058 Great Britain Mar. 16, 1955 1,020,065 Germany Nov. 28, 1957 1,105,354 France June 29, 1954
Claims (1)
1. A MICROWAVE SYSTEM HAVING MEANS FOR CONTROLLING EDGE DIFFRACTION COMPRISING: REFLECTOR MEANS, RING MEANS EXTENDING AROUND AT LEAST A PORTION OF SAID REFLECTOR
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US253622A US3140491A (en) | 1963-01-24 | 1963-01-24 | Diffraction shield consisting of notched ring which frames passive reflector |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US253622A US3140491A (en) | 1963-01-24 | 1963-01-24 | Diffraction shield consisting of notched ring which frames passive reflector |
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| Publication Number | Publication Date |
|---|---|
| US3140491A true US3140491A (en) | 1964-07-07 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US253622A Expired - Lifetime US3140491A (en) | 1963-01-24 | 1963-01-24 | Diffraction shield consisting of notched ring which frames passive reflector |
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| US (1) | US3140491A (en) |
Cited By (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3599219A (en) * | 1969-01-29 | 1971-08-10 | Andrew Corp | Backlobe reduction in reflector-type antennas |
| US3623115A (en) * | 1968-12-07 | 1971-11-23 | Telefunken Patent | Directional antenna |
| US3631502A (en) * | 1965-10-21 | 1971-12-28 | Univ Ohio State Res Found | Corrugated horn antenna |
| US4115782A (en) * | 1976-06-21 | 1978-09-19 | Ford Motor Company | Microwave antenna system |
| DE2920412A1 (en) * | 1979-05-19 | 1980-11-20 | Licentia Gmbh | Parabolic radio antenna with side screens - minimises scattering and gives antenna shadow region of 85 degrees instead of 115 degrees without screening |
| US4376940A (en) * | 1980-10-29 | 1983-03-15 | Bell Telephone Laboratories, Incorporated | Antenna arrangements for suppressing selected sidelobes |
| US4803495A (en) * | 1985-01-09 | 1989-02-07 | Raytheon Company | Radio frequency array antenna with energy resistive material |
| US5341150A (en) * | 1988-09-28 | 1994-08-23 | Georgia Tech Research Corp. | Low sidelobe reflector |
| WO2005025000A1 (en) * | 2003-08-28 | 2005-03-17 | Peter Bruckmeier | Parabolic antenna provided with an attachment or several attachment elements on the outer edge |
| US20050190116A1 (en) * | 2004-02-27 | 2005-09-01 | Andrew Corporation | Reflector antenna radome with backlobe suppressor ring and method of manufacturing |
| US20100315307A1 (en) * | 2009-06-12 | 2010-12-16 | Andrew Llc | Radome and Shroud Enclosure for Reflector Antenna |
| US20110140983A1 (en) * | 2009-12-11 | 2011-06-16 | Andrew Llc | Reflector Antenna Radome Attachment Band Clamp |
| US9083083B2 (en) | 2009-12-11 | 2015-07-14 | Commscope Technologies Llc | Radome attachment band clamp |
| WO2016073440A1 (en) * | 2014-11-03 | 2016-05-12 | Commscope Technologies Llc | Circumferencial frame for antenna back-lobe and side-lobe attenuation |
| US20160156107A1 (en) * | 2014-12-02 | 2016-06-02 | Ubiquiti Networks, Inc. | Multi-panel antenna system |
| US20170229773A1 (en) * | 2009-06-04 | 2017-08-10 | Jude Lee | Antenna isolation shrouds and reflectors |
| US10205471B2 (en) | 2013-10-11 | 2019-02-12 | Ubiquiti Networks, Inc. | Wireless radio system optimization by persistent spectrum analysis |
| US10312598B2 (en) | 2013-02-04 | 2019-06-04 | Ubiquiti Networks, Inc. | Radio system for long-range high-speed wireless communication |
| US10367592B2 (en) | 2014-06-30 | 2019-07-30 | Ubiquiti Networks, Inc. | Wireless radio device alignment tools and methods |
| US10566676B2 (en) | 2014-04-01 | 2020-02-18 | Ubiquiti Inc. | Compact radio frequency antenna apparatuses |
| US10757518B2 (en) | 2015-09-11 | 2020-08-25 | Ubiquiti Inc. | Compact public address access point apparatuses |
| WO2020260045A1 (en) * | 2019-06-26 | 2020-12-30 | Leax Arkivator Telecom Ab | An antenna with reduced back-lobe radiation |
| US11909087B2 (en) | 2013-02-04 | 2024-02-20 | Ubiquiti Inc. | Coaxial RF dual-polarized waveguide filter and method |
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Cited By (40)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3631502A (en) * | 1965-10-21 | 1971-12-28 | Univ Ohio State Res Found | Corrugated horn antenna |
| US3623115A (en) * | 1968-12-07 | 1971-11-23 | Telefunken Patent | Directional antenna |
| US3599219A (en) * | 1969-01-29 | 1971-08-10 | Andrew Corp | Backlobe reduction in reflector-type antennas |
| US4115782A (en) * | 1976-06-21 | 1978-09-19 | Ford Motor Company | Microwave antenna system |
| DE2920412A1 (en) * | 1979-05-19 | 1980-11-20 | Licentia Gmbh | Parabolic radio antenna with side screens - minimises scattering and gives antenna shadow region of 85 degrees instead of 115 degrees without screening |
| US4376940A (en) * | 1980-10-29 | 1983-03-15 | Bell Telephone Laboratories, Incorporated | Antenna arrangements for suppressing selected sidelobes |
| US4803495A (en) * | 1985-01-09 | 1989-02-07 | Raytheon Company | Radio frequency array antenna with energy resistive material |
| US5341150A (en) * | 1988-09-28 | 1994-08-23 | Georgia Tech Research Corp. | Low sidelobe reflector |
| WO2005025000A1 (en) * | 2003-08-28 | 2005-03-17 | Peter Bruckmeier | Parabolic antenna provided with an attachment or several attachment elements on the outer edge |
| EP1719204A1 (en) * | 2004-02-27 | 2006-11-08 | Andrew Corporation | Reflector antenna radome with backlobe suppressor ring and method of manufacturing |
| US7138958B2 (en) | 2004-02-27 | 2006-11-21 | Andrew Corporation | Reflector antenna radome with backlobe suppressor ring and method of manufacturing |
| EP1719204A4 (en) * | 2004-02-27 | 2008-12-10 | Andrew Corp | REFLECTOR ANTENNA RADLE WITH REAR LOBE SUPPRESSOR RING AND METHOD OF MANUFACTURING THE SAME |
| US20050190116A1 (en) * | 2004-02-27 | 2005-09-01 | Andrew Corporation | Reflector antenna radome with backlobe suppressor ring and method of manufacturing |
| US20170229773A1 (en) * | 2009-06-04 | 2017-08-10 | Jude Lee | Antenna isolation shrouds and reflectors |
| US10756422B2 (en) * | 2009-06-04 | 2020-08-25 | Ubiquiti Inc. | Antenna isolation shrouds and reflectors |
| US20100315307A1 (en) * | 2009-06-12 | 2010-12-16 | Andrew Llc | Radome and Shroud Enclosure for Reflector Antenna |
| US8077113B2 (en) | 2009-06-12 | 2011-12-13 | Andrew Llc | Radome and shroud enclosure for reflector antenna |
| US20110140983A1 (en) * | 2009-12-11 | 2011-06-16 | Andrew Llc | Reflector Antenna Radome Attachment Band Clamp |
| US8259028B2 (en) | 2009-12-11 | 2012-09-04 | Andrew Llc | Reflector antenna radome attachment band clamp |
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| US20160156107A1 (en) * | 2014-12-02 | 2016-06-02 | Ubiquiti Networks, Inc. | Multi-panel antenna system |
| US9698491B2 (en) * | 2014-12-02 | 2017-07-04 | Ubiquiti Networks, Inc. | Multi-panel antenna system |
| US10757518B2 (en) | 2015-09-11 | 2020-08-25 | Ubiquiti Inc. | Compact public address access point apparatuses |
| WO2020260045A1 (en) * | 2019-06-26 | 2020-12-30 | Leax Arkivator Telecom Ab | An antenna with reduced back-lobe radiation |
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