CA1191944A - Shifted focus cassegrain antenna with low gain feed - Google Patents
Shifted focus cassegrain antenna with low gain feedInfo
- Publication number
- CA1191944A CA1191944A CA000414634A CA414634A CA1191944A CA 1191944 A CA1191944 A CA 1191944A CA 000414634 A CA000414634 A CA 000414634A CA 414634 A CA414634 A CA 414634A CA 1191944 A CA1191944 A CA 1191944A
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- subreflector
- feed element
- cassegrain antenna
- reflector
- reflecting surface
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Abstract
ABSTRACT OF THE DISCLOSURE
A new type Cassegrain antenna provides a shifted or ring focus by use of a subreflector having a reflecting surface in the shape of an ellipsoid of revolution or a shape similar to two foci arrangements in combination with a low gain radiating element having a phase center which is relatively-insensitive to frequency. The result is an extremely-compact, axially-symmetrical Cassegrain antenna construction for less than sixty wavelength antenna diameters, maintaining approximately a 10 per cent subreflecter to main reflector diameter ratio.
A new type Cassegrain antenna provides a shifted or ring focus by use of a subreflector having a reflecting surface in the shape of an ellipsoid of revolution or a shape similar to two foci arrangements in combination with a low gain radiating element having a phase center which is relatively-insensitive to frequency. The result is an extremely-compact, axially-symmetrical Cassegrain antenna construction for less than sixty wavelength antenna diameters, maintaining approximately a 10 per cent subreflecter to main reflector diameter ratio.
Description
IMPROVED SHIFTED FOCUS CASSEGRAIN ANTENNA
WITH LOW GAIN FEED
The present invention relates in general to communication antennas, and more particularly, to a Cassegrain antenna which may be considerably reduced in size while providing for efficient operation in the low CHz range without a disabling increase in antenna blockage through use of a secondary reflector of special configuration providing a shifted focus in combination with a low gain feed.
In Cassegrain antennas, a feed element is located in the general region of the vertex of a paraboloidal primary reflector for radiating energy toward an intermediate secondary reflector which is smaller than the primary reflector and is located between the vertex and the focal point of the primary lS reflector. The secondary reflector usually has a hyperboloidal configuration and its focal point is preferably located coincident with the focal point of the primary reflector.
One of the heretofore unsolved problems in the design of Cassegrain antennas is how to provide such an antenna which is small in size~ that is, with a main dish which is less than fifteen feet in diameter, for use at fre~uencies as low as 4 GHz. Conflicting desi~n considerations relating to the size of the feed horn required at frequencies in the low GHz range and the size of the subreflector to be used with such a feed horn if antenna blockage and spillover problems are to be avoided have placed a lower limit on the size of the Cassegrain antenna at approximately fifteen feet. However, there are many applications in which a Cassegrain antenna of smaller size is very desirable for use at frequencies as low as 4 GHz.
One of the long-s~anding problems encountered in the design of the Cassegrain-type antenna relates to antenna blockage, which is affected both by the size of the secondary reflector (subreflector) and the size of the feed element (horn). As one extreme, it is apparent that the subreflector cannot be as large as the main reflector, since this would produce total blockage of the main reflectors while, an extremely-small subreflector produces undesirable spillover problems resulting in loss of power. Thus, a typical ratio between the diameter of the subreflector and the diameter of the main reflector has been selected to be approximately 1:10 in the design cf a Cassegrain antenna. Similarly, a feed horn will typically produce an aperture blockage which is at lea~t equal to the diameter of the horn, and in those cases where the horn is placed in close proximity to the subreflector, the blockage produced by this combination will increase significantly at least for that part of the energy directed to the central portion o the subreflector where the maximum power is generally concentrated.
When it is desired to operate in the lower G~z frequency range, in order to bundle a beam towards the ~ubreflector of the antenna, it is necessary to utilize a high gain horn~
Thus, a flared horn is typically used as the feed element in a Cassegrain antenna in order to provide a high gain feed.
Unfortunately, as the operating frequency of the antenna is reduced, to get a high gain horn, the horn becomes bigger and bigger in size which contributes to an increase in the blockage of the main reflector. For example, at 10 GHz if 30 degrees is the required feed angle to bundle all the energy to the subreflector~ it i~ necessa{y ~o provide at 15 to 25 db gain horn which may have an aperture size of 5iX to eight inches.
On the other hand, if the operating frequency is reduced to 4 S GHz, the same horn will have to have an aperture si~e of about fifteen to twenty inches. ~nder these circumstances, the minimum diameter fGr the subreflector will ~e about eighteen inches or one foot and a half in diameter if undesirable blockage of the main reflector by the horn itself is to be avoided. With a typical ratio of 1:10 between the size of the subreflector and the si~e of the main reflector, it can be seen why at present Cassegrain systems are not capable of being reduced below ifteen feet in diameter for operating at frequencies below 4 GHz, without incurring significant blockage proble~s~
In addition, there is an inherent blockaye based on the offset between the subreflector and the horn. Thus, with a standard hyperboloidal subreflector, the first ray at the center of the horn must be transmitted to the main reflector past the edge of the horn. If the operatiny band of the antenna requires use of a feed horn which is eighteen inches in diameter, this will cause an eighteen inch blockage in itself;
however, the optical geometry of the system will probably make this a two to four foot blockage depending on the spacing of the feed horn from the subreflector~ With this in mind, it can be ~een that any increase in the si~e of the horn for operation at lower frequencies will result in the blockage problem becoming more accute, effectively blocking the inner part o~
the main reflector, where the maximum power is transmitted.
~`''3~
In order to obviate this blockage problem which prevents reduction in size of the Cassegrain antenna for low freguency operation, there has been proposed in British Patent No.
973,583 by J. L. Lee, as well as ln French Patent No. 1,392,013 to G.R.P. Marie, a Cassegrain-type antenna having a subreflec-tor in the shape of an ellipsoidal surface of revolution with one focus of the ellipsoid coincident with the phase center of the feed horn and the other focus o the ellipsoid positioned adjacent the outer edge of the subreflector so as to produce a ring focus in space. With such an arrangement, the phase center of the feed horn effectively shifts to the ring focus so that the origin of the reflected energy i5 apparently disposed along the ring extending around the outes edge of the sub-reflector, thereby totally eliminating blockage by the subreflector or the feed horn~ In this regard the ring focus provides a cross-over of the rays from the feed horn with the result that the center ray representing the maximum power is deflected to the outer edge oE the main reflector and is not in any way blocked by the horn.
While the shifted focus system disclosed by J. L. Lee and G.R.P. Marie effectively has solved the aperture blockage problem created both by the feed horn and the subreflector, and thereby has apparently opened the way to the design of small size Cassegrain antennas~ such a system has a basic drawback in that it requires the precise location of the foci of both the feed horn and the subreflector for proper operation.
Unfortunately,, it has been found that problems arise with this system due to the fact that the phase center of the high gain horn which is normally provided in this type of antenna will move with changes in frequency. Th~ls, at the high end of the frequency range over which the antenna is to operate, the phase center will sit deeper in the horn than at the low frequency end of that range. This movement oE the phase center disrupts the optical geometry of the antenna resulting in deterioration of the operation thereof.
It is therefore a principal object of the present invention to provide a small size Cassegrain-type antenna which 10 is capable of efficient operation in the low GHz range.
It is another object of the present invention to provide a Cassegrain-type antenna which is capable of being produced at a small si~e with a low cost while significantly reducing loss due to shadowing and blockage by the subreflector or the feed 15 element.
It is a further object of the present invention to provide a Cassegrain-type antenna of the shifted focus t~pe having a feed element which is least f~equency dependent.
In accordance with the basic feature of the present 20 invention, there is provided a ~assegrain antenna of the type having a shaped subreflector which produces a shifted ring focus in combination with a low gain feed source having a well-def ined phase center which is relatively insensitive to frequency. In i~s most-basic form, such a low gain feed source 25 can be provided in the form of an open waveguide; however, a prime focal-type horn, such as a horn having a rectangular waveguide section by way of a step portion therebetween, the circular waveguide section having a corrugated section around the periphery and adjacent -to the end thereof or a simple diagaonaLly fed square horn may be utilized for this purpose. Sucll a so~lrce is extremely simple ar~d can be made sufficiently ~mall to eliminate any aperture blockage ~y the horn in a shifted focal point system. This result~ in an extremely-compact antenna feed system which can be manufactured at very-low cost. ~owever, even more importantly, with such an arrange~ent, a Cassegrain antenna as small as four feet in diameter can be effectivel~ designed which has extremely high gain and excellent wide angle pattern performance and is capable of operation at 4 GHz.
These and other objects features and advantages of the present invention will become more apparent from the following detailed description of a preferred embodiment, which is illustrated in the accompanying drawings.
Fi~ure 1 is a schematic diagram of a conven~ional Cassegrain antenna illustrating the problem of aperture blocking by the subreflector and feed horn;
Figure 2 is a ~chematic diagram of a shifted focus Cassegrain antenna having a subreflector formed as an ellipsoidal surface of revolution;
Figure 3 is a schematic diagram of a Cassegrain antenna embodying the features of the present invention;
Figure 4 is a longitudinal sectional view of one type of low gain feed horn which may be used with the present invention; and Figures SA and 5B are elevational views of the subreflector utilized by the present invention having peripheral corrugations in the circumferential and radial directions, respectively, for reduction of side lobe scattering.
The inability to produce a Cassegrain antenna smaller than about fiEteen feet in diameter is directly linked to the problem of antenna blockage by the subreflector and feed horn.
~igure l is somewhat exaggerated in its illustration of such blocking in a typical Cassegrain antenna but is useful in illustrating the problems which have hindered the manufacture of small-size Cassegrain antennas to the present date.
In Figure 1 a high gain flared horn l having a phase cen~er at point A directs microwave energy with an aperture angle ~ toward a subreflector 2 having a hyperboloidal surface from which the microwave energy is reflected onto a parabolic main reflector 3 having an axis X and a diameter D to form a substantially--parallel trans~ission beam in the well-known manner. As can be seen from Figure l, the subreflector 2 provides a primary aperture blockage of the rays reflected from the main reflector 3 by an amount equal to the diameter d of the subreflector 2. Bowever, it is also apparent that only those rays directed at the subreflector 2 which are capable of passing the peripheral edge of the feed horn 1 will reach the main reflector 3. Thus, while the blockage provided by the subreflector 2 is equal to the diameter d, an even greater blockage equal to the distance d' is created by the feed horn l. Unfortunately, this problem is subject to conflicting design considerations, especially where an antenna small size ~5 is desired. Thus, for a standard Cassegrain antenna that is designed to transmit or receive signals in a frequency range of 4 GHz and lower, the typical high gain feed horn regulred at these frequencies is of such a size that significant blockage of the antenna occurs. Therefore, as the transmission frequency is reduced on an antenna of small size, ~ limit is reached beyond which the antenna will no longer operate in a satisfactory manner. It is for this reason that present S Cassegrain systems cannot be designed to operate below 4 GHz a~d that antennas of this type are limited to a diameter no smaller th~n approximately fift:een feet.
Figure 2 illustrates a Ca~segrain antenna having a shaped subreflectc)r 2' which serves to shift the phase center of the microwave energy from the point A within the feed horn 1 to a ring focus O disposed adjacent the periphery of the subreflector 2~o This system, which has been disclosed in British Patent No. 973r583 and French Patent No. 1,392,013, eliminates the blocka~e of the main reflector 3 by the feed horn 1 due to the shifting of the phase center to a ring which is concentric with the axis X of the feed horn 1 and subreflector 2' ancl has a diameter slightly larger than the diameter d of the subreflector 2' so as to eliminate any blockage whatsoever by the feed horn 1. This shifting of the phase center of the feed horn 1 results from the fact that the reflecting surface of the subreflector 2' is formed as an ellipsoidal surface of revolution with one focus of the ellipsoid being coincident with the phase center A of the feed horn and the other ocus of the ellipsoid being coincident with ZS the ring focus O of the subreflector 2'. With a high gain feed horn 1 havinq a feed angle ~ which includes the subreflector
WITH LOW GAIN FEED
The present invention relates in general to communication antennas, and more particularly, to a Cassegrain antenna which may be considerably reduced in size while providing for efficient operation in the low CHz range without a disabling increase in antenna blockage through use of a secondary reflector of special configuration providing a shifted focus in combination with a low gain feed.
In Cassegrain antennas, a feed element is located in the general region of the vertex of a paraboloidal primary reflector for radiating energy toward an intermediate secondary reflector which is smaller than the primary reflector and is located between the vertex and the focal point of the primary lS reflector. The secondary reflector usually has a hyperboloidal configuration and its focal point is preferably located coincident with the focal point of the primary reflector.
One of the heretofore unsolved problems in the design of Cassegrain antennas is how to provide such an antenna which is small in size~ that is, with a main dish which is less than fifteen feet in diameter, for use at fre~uencies as low as 4 GHz. Conflicting desi~n considerations relating to the size of the feed horn required at frequencies in the low GHz range and the size of the subreflector to be used with such a feed horn if antenna blockage and spillover problems are to be avoided have placed a lower limit on the size of the Cassegrain antenna at approximately fifteen feet. However, there are many applications in which a Cassegrain antenna of smaller size is very desirable for use at frequencies as low as 4 GHz.
One of the long-s~anding problems encountered in the design of the Cassegrain-type antenna relates to antenna blockage, which is affected both by the size of the secondary reflector (subreflector) and the size of the feed element (horn). As one extreme, it is apparent that the subreflector cannot be as large as the main reflector, since this would produce total blockage of the main reflectors while, an extremely-small subreflector produces undesirable spillover problems resulting in loss of power. Thus, a typical ratio between the diameter of the subreflector and the diameter of the main reflector has been selected to be approximately 1:10 in the design cf a Cassegrain antenna. Similarly, a feed horn will typically produce an aperture blockage which is at lea~t equal to the diameter of the horn, and in those cases where the horn is placed in close proximity to the subreflector, the blockage produced by this combination will increase significantly at least for that part of the energy directed to the central portion o the subreflector where the maximum power is generally concentrated.
When it is desired to operate in the lower G~z frequency range, in order to bundle a beam towards the ~ubreflector of the antenna, it is necessary to utilize a high gain horn~
Thus, a flared horn is typically used as the feed element in a Cassegrain antenna in order to provide a high gain feed.
Unfortunately, as the operating frequency of the antenna is reduced, to get a high gain horn, the horn becomes bigger and bigger in size which contributes to an increase in the blockage of the main reflector. For example, at 10 GHz if 30 degrees is the required feed angle to bundle all the energy to the subreflector~ it i~ necessa{y ~o provide at 15 to 25 db gain horn which may have an aperture size of 5iX to eight inches.
On the other hand, if the operating frequency is reduced to 4 S GHz, the same horn will have to have an aperture si~e of about fifteen to twenty inches. ~nder these circumstances, the minimum diameter fGr the subreflector will ~e about eighteen inches or one foot and a half in diameter if undesirable blockage of the main reflector by the horn itself is to be avoided. With a typical ratio of 1:10 between the size of the subreflector and the si~e of the main reflector, it can be seen why at present Cassegrain systems are not capable of being reduced below ifteen feet in diameter for operating at frequencies below 4 GHz, without incurring significant blockage proble~s~
In addition, there is an inherent blockaye based on the offset between the subreflector and the horn. Thus, with a standard hyperboloidal subreflector, the first ray at the center of the horn must be transmitted to the main reflector past the edge of the horn. If the operatiny band of the antenna requires use of a feed horn which is eighteen inches in diameter, this will cause an eighteen inch blockage in itself;
however, the optical geometry of the system will probably make this a two to four foot blockage depending on the spacing of the feed horn from the subreflector~ With this in mind, it can be ~een that any increase in the si~e of the horn for operation at lower frequencies will result in the blockage problem becoming more accute, effectively blocking the inner part o~
the main reflector, where the maximum power is transmitted.
~`''3~
In order to obviate this blockage problem which prevents reduction in size of the Cassegrain antenna for low freguency operation, there has been proposed in British Patent No.
973,583 by J. L. Lee, as well as ln French Patent No. 1,392,013 to G.R.P. Marie, a Cassegrain-type antenna having a subreflec-tor in the shape of an ellipsoidal surface of revolution with one focus of the ellipsoid coincident with the phase center of the feed horn and the other focus o the ellipsoid positioned adjacent the outer edge of the subreflector so as to produce a ring focus in space. With such an arrangement, the phase center of the feed horn effectively shifts to the ring focus so that the origin of the reflected energy i5 apparently disposed along the ring extending around the outes edge of the sub-reflector, thereby totally eliminating blockage by the subreflector or the feed horn~ In this regard the ring focus provides a cross-over of the rays from the feed horn with the result that the center ray representing the maximum power is deflected to the outer edge oE the main reflector and is not in any way blocked by the horn.
While the shifted focus system disclosed by J. L. Lee and G.R.P. Marie effectively has solved the aperture blockage problem created both by the feed horn and the subreflector, and thereby has apparently opened the way to the design of small size Cassegrain antennas~ such a system has a basic drawback in that it requires the precise location of the foci of both the feed horn and the subreflector for proper operation.
Unfortunately,, it has been found that problems arise with this system due to the fact that the phase center of the high gain horn which is normally provided in this type of antenna will move with changes in frequency. Th~ls, at the high end of the frequency range over which the antenna is to operate, the phase center will sit deeper in the horn than at the low frequency end of that range. This movement oE the phase center disrupts the optical geometry of the antenna resulting in deterioration of the operation thereof.
It is therefore a principal object of the present invention to provide a small size Cassegrain-type antenna which 10 is capable of efficient operation in the low GHz range.
It is another object of the present invention to provide a Cassegrain-type antenna which is capable of being produced at a small si~e with a low cost while significantly reducing loss due to shadowing and blockage by the subreflector or the feed 15 element.
It is a further object of the present invention to provide a Cassegrain-type antenna of the shifted focus t~pe having a feed element which is least f~equency dependent.
In accordance with the basic feature of the present 20 invention, there is provided a ~assegrain antenna of the type having a shaped subreflector which produces a shifted ring focus in combination with a low gain feed source having a well-def ined phase center which is relatively insensitive to frequency. In i~s most-basic form, such a low gain feed source 25 can be provided in the form of an open waveguide; however, a prime focal-type horn, such as a horn having a rectangular waveguide section by way of a step portion therebetween, the circular waveguide section having a corrugated section around the periphery and adjacent -to the end thereof or a simple diagaonaLly fed square horn may be utilized for this purpose. Sucll a so~lrce is extremely simple ar~d can be made sufficiently ~mall to eliminate any aperture blockage ~y the horn in a shifted focal point system. This result~ in an extremely-compact antenna feed system which can be manufactured at very-low cost. ~owever, even more importantly, with such an arrange~ent, a Cassegrain antenna as small as four feet in diameter can be effectivel~ designed which has extremely high gain and excellent wide angle pattern performance and is capable of operation at 4 GHz.
These and other objects features and advantages of the present invention will become more apparent from the following detailed description of a preferred embodiment, which is illustrated in the accompanying drawings.
Fi~ure 1 is a schematic diagram of a conven~ional Cassegrain antenna illustrating the problem of aperture blocking by the subreflector and feed horn;
Figure 2 is a ~chematic diagram of a shifted focus Cassegrain antenna having a subreflector formed as an ellipsoidal surface of revolution;
Figure 3 is a schematic diagram of a Cassegrain antenna embodying the features of the present invention;
Figure 4 is a longitudinal sectional view of one type of low gain feed horn which may be used with the present invention; and Figures SA and 5B are elevational views of the subreflector utilized by the present invention having peripheral corrugations in the circumferential and radial directions, respectively, for reduction of side lobe scattering.
The inability to produce a Cassegrain antenna smaller than about fiEteen feet in diameter is directly linked to the problem of antenna blockage by the subreflector and feed horn.
~igure l is somewhat exaggerated in its illustration of such blocking in a typical Cassegrain antenna but is useful in illustrating the problems which have hindered the manufacture of small-size Cassegrain antennas to the present date.
In Figure 1 a high gain flared horn l having a phase cen~er at point A directs microwave energy with an aperture angle ~ toward a subreflector 2 having a hyperboloidal surface from which the microwave energy is reflected onto a parabolic main reflector 3 having an axis X and a diameter D to form a substantially--parallel trans~ission beam in the well-known manner. As can be seen from Figure l, the subreflector 2 provides a primary aperture blockage of the rays reflected from the main reflector 3 by an amount equal to the diameter d of the subreflector 2. Bowever, it is also apparent that only those rays directed at the subreflector 2 which are capable of passing the peripheral edge of the feed horn 1 will reach the main reflector 3. Thus, while the blockage provided by the subreflector 2 is equal to the diameter d, an even greater blockage equal to the distance d' is created by the feed horn l. Unfortunately, this problem is subject to conflicting design considerations, especially where an antenna small size ~5 is desired. Thus, for a standard Cassegrain antenna that is designed to transmit or receive signals in a frequency range of 4 GHz and lower, the typical high gain feed horn regulred at these frequencies is of such a size that significant blockage of the antenna occurs. Therefore, as the transmission frequency is reduced on an antenna of small size, ~ limit is reached beyond which the antenna will no longer operate in a satisfactory manner. It is for this reason that present S Cassegrain systems cannot be designed to operate below 4 GHz a~d that antennas of this type are limited to a diameter no smaller th~n approximately fift:een feet.
Figure 2 illustrates a Ca~segrain antenna having a shaped subreflectc)r 2' which serves to shift the phase center of the microwave energy from the point A within the feed horn 1 to a ring focus O disposed adjacent the periphery of the subreflector 2~o This system, which has been disclosed in British Patent No. 973r583 and French Patent No. 1,392,013, eliminates the blocka~e of the main reflector 3 by the feed horn 1 due to the shifting of the phase center to a ring which is concentric with the axis X of the feed horn 1 and subreflector 2' ancl has a diameter slightly larger than the diameter d of the subreflector 2' so as to eliminate any blockage whatsoever by the feed horn 1. This shifting of the phase center of the feed horn 1 results from the fact that the reflecting surface of the subreflector 2' is formed as an ellipsoidal surface of revolution with one focus of the ellipsoid being coincident with the phase center A of the feed horn and the other ocus of the ellipsoid being coincident with ZS the ring focus O of the subreflector 2'. With a high gain feed horn 1 havinq a feed angle ~ which includes the subreflector
2', all energy emanating from the phase center A will be reflected frc>m the ellipsoidal surface of the subreflector 2' ~ t~
through the ring focus O, ~o that the ring focus O effectively beco~es the origin of the microwave energy directed toward the parabolic main reflector 3. Since the ring focus O is positioned outside of the edge of both the feed horn 1 and subreflector 2l, all of the rays emanating from the feed horn l will be reflected by the main reflector 3~y thereby reducing the antenna blockage to substantially zero.
While the antenna system illustrated in Figure 2 serves quite well to eliminate the problem of antenna blockage and opens the way for the production of Cassegrain antennas of ~ignificantly-smaller size than heretofore possible, it i6 apparent that this system has rather rigid constraints on the optical geometry dictated by the specific shape of the subreflector 2'. Thus, the subreflector 2' has a reflecting surface wh~ch requires the precise location of the phase center A and the ring focus O relative thereto in order to produce proper reflection of the microwave energy from the subreflector 2' to the main reflector 3. Because of the close proximity of the two foci between the subreflector and the horn, even slight movements of one of the two focl with respect to the other has a profound effect on the performance of the antenna.
In this regard, if a typical high gain horn is used as the feed horrl l, the performance of the antenna system becomes subject to the dependency of the phase center of the hGrn on changes in frequency. Unfortunately, as the frequency of the antenna is varied across the operating bandwidth thereof, the phase center A of the typical high gain feed horn 1 will shit along the a~i.s X with the result that the geometry of the antenna system wlll be changed producing a drastic deteriora~ion in the operating performance thereof. In effect, the antenna system illustrated in Figure 2 require~ that the two ocl A and O be in relatively-close proximity to one another and be fixed in position relative to one another for the system ~o operate in a satisfactory manner.
One embodiment of the present invention is illustrated in Figure 3 in the form of a Cassegrain antenna system similar to that shown in Figure 2, but with ~ low gain feed horn 1', such as a prime focal horn, provided in place of the high gain horn 1. First of all, the low gain feed horn 1' presents a relatively-fixed phase center which is independent of changes in frequency, eliminating the problem inherent in the system of Figure 2. Secondly, with the arrangement of Figure 3 there is no longer any requirement for a feed angle ~ of twenty to thirty degrees to eliminate spillover at the subreflector 2', since the feed horn l~ can be placed in very-close proximity to the subreflector 2', for example, with the phase center A
approximately one-half to one inch from the peak of the sloping surface, thereby producing a very-compact feed arrangement which is as effective as a direct feed insofar as antenna blockage is concerned. So long as the feed horn l is slightly smaller than the diameter d of the subreflector, there will be absolutely no blockaye in the antenna of the present invention.
Further, since the phase center of the low gain feed horn 1' is relatively insensitive to fre~uency, the optical geometry of the system will be preserved over a wide bandwidth of operating frequencies.
The low gain feed horn 1I may in its most-simple form be provided as an open waveguide of circular or rectangular cross section which typically has no gain whatsoever. Boweverr a horn of the type illustrated in Fi~ure 4 represents one example of a type of low gain horn which may be used in accordance with the present inven~ion~ This type of horn typically provides a gain of 5 to 8 db, as compared to the more conventionally-used flared horn shown in Figure 2, which provides a gain as high as 25 db. As seen in Figure 4, the 10 tlorn is provided as a waveguide 4 having a rectan~ular section 4a extending into a circular section 4b via a step 4c.
A corrugated section 5 is provided around the peri2hery of the circular section 4b adjacent to the end of the waveguide 4.
This type of horn, which has been used heretofore primarily as a prime feed horn, has the advantages of very simple construction and is very light in weight compared to the standard flared horns normally used in Cassegrain antennas, with the result that the system of the present invention as seen in Figure 3 represents an antenna of very simplified construction which can be manuf,actured for low cost in a small size not heretofore attainable in Cassegraln antennas.
As can be seen from Figure 5A, the subreflectoe 2' is generally circular, having a peak P from which the ellipsoidal surface of revolution extends to the outer edge where a plurality of annular corrugations 8 are provided in the subreflector surface. These circumferential corrugations 8, which have a 1/4 wavelength spacing, serve to cut down the currents which cause edge scattering and are particularly useful ln a system such as lllustrated in Figure 3 wherein a low gain feed horn providing a feed angle of 90 degrees or more is provided. Figure 5B shows a subreflector 2' also having edge current control in the form of radial corrugations 8 ' ~
While we have shown and described several embodiments in accordance with the present invention, it is understood that the invention is not limited to the details shown and described herein but ls susceptible of n~merous changes and modifications as obv.ious to one of ordinary skill in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications known to those skilled in the art.
through the ring focus O, ~o that the ring focus O effectively beco~es the origin of the microwave energy directed toward the parabolic main reflector 3. Since the ring focus O is positioned outside of the edge of both the feed horn 1 and subreflector 2l, all of the rays emanating from the feed horn l will be reflected by the main reflector 3~y thereby reducing the antenna blockage to substantially zero.
While the antenna system illustrated in Figure 2 serves quite well to eliminate the problem of antenna blockage and opens the way for the production of Cassegrain antennas of ~ignificantly-smaller size than heretofore possible, it i6 apparent that this system has rather rigid constraints on the optical geometry dictated by the specific shape of the subreflector 2'. Thus, the subreflector 2' has a reflecting surface wh~ch requires the precise location of the phase center A and the ring focus O relative thereto in order to produce proper reflection of the microwave energy from the subreflector 2' to the main reflector 3. Because of the close proximity of the two foci between the subreflector and the horn, even slight movements of one of the two focl with respect to the other has a profound effect on the performance of the antenna.
In this regard, if a typical high gain horn is used as the feed horrl l, the performance of the antenna system becomes subject to the dependency of the phase center of the hGrn on changes in frequency. Unfortunately, as the frequency of the antenna is varied across the operating bandwidth thereof, the phase center A of the typical high gain feed horn 1 will shit along the a~i.s X with the result that the geometry of the antenna system wlll be changed producing a drastic deteriora~ion in the operating performance thereof. In effect, the antenna system illustrated in Figure 2 require~ that the two ocl A and O be in relatively-close proximity to one another and be fixed in position relative to one another for the system ~o operate in a satisfactory manner.
One embodiment of the present invention is illustrated in Figure 3 in the form of a Cassegrain antenna system similar to that shown in Figure 2, but with ~ low gain feed horn 1', such as a prime focal horn, provided in place of the high gain horn 1. First of all, the low gain feed horn 1' presents a relatively-fixed phase center which is independent of changes in frequency, eliminating the problem inherent in the system of Figure 2. Secondly, with the arrangement of Figure 3 there is no longer any requirement for a feed angle ~ of twenty to thirty degrees to eliminate spillover at the subreflector 2', since the feed horn l~ can be placed in very-close proximity to the subreflector 2', for example, with the phase center A
approximately one-half to one inch from the peak of the sloping surface, thereby producing a very-compact feed arrangement which is as effective as a direct feed insofar as antenna blockage is concerned. So long as the feed horn l is slightly smaller than the diameter d of the subreflector, there will be absolutely no blockaye in the antenna of the present invention.
Further, since the phase center of the low gain feed horn 1' is relatively insensitive to fre~uency, the optical geometry of the system will be preserved over a wide bandwidth of operating frequencies.
The low gain feed horn 1I may in its most-simple form be provided as an open waveguide of circular or rectangular cross section which typically has no gain whatsoever. Boweverr a horn of the type illustrated in Fi~ure 4 represents one example of a type of low gain horn which may be used in accordance with the present inven~ion~ This type of horn typically provides a gain of 5 to 8 db, as compared to the more conventionally-used flared horn shown in Figure 2, which provides a gain as high as 25 db. As seen in Figure 4, the 10 tlorn is provided as a waveguide 4 having a rectan~ular section 4a extending into a circular section 4b via a step 4c.
A corrugated section 5 is provided around the peri2hery of the circular section 4b adjacent to the end of the waveguide 4.
This type of horn, which has been used heretofore primarily as a prime feed horn, has the advantages of very simple construction and is very light in weight compared to the standard flared horns normally used in Cassegrain antennas, with the result that the system of the present invention as seen in Figure 3 represents an antenna of very simplified construction which can be manuf,actured for low cost in a small size not heretofore attainable in Cassegraln antennas.
As can be seen from Figure 5A, the subreflectoe 2' is generally circular, having a peak P from which the ellipsoidal surface of revolution extends to the outer edge where a plurality of annular corrugations 8 are provided in the subreflector surface. These circumferential corrugations 8, which have a 1/4 wavelength spacing, serve to cut down the currents which cause edge scattering and are particularly useful ln a system such as lllustrated in Figure 3 wherein a low gain feed horn providing a feed angle of 90 degrees or more is provided. Figure 5B shows a subreflector 2' also having edge current control in the form of radial corrugations 8 ' ~
While we have shown and described several embodiments in accordance with the present invention, it is understood that the invention is not limited to the details shown and described herein but ls susceptible of n~merous changes and modifications as obv.ious to one of ordinary skill in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications known to those skilled in the art.
Claims
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4GHz comprising a main dish reflector, a feed element disposed at the base of said dish reflector in the form of a prime focal horn directed away from said reflector, and a subreflector facing said dish reflector and said feed element and being shaped to focus energy received from said feed element through a locus of points forming a ring disposed adjacent the periphery thereof toward said main dish reflector.
2. A Cassegrain antenna as defined in claim 1 wherein said subreflector has a reflecting surface in the shape of an ellipsoid of revolution about a line coincident with the axes of said dish reflector.
3. A Cassegrain antenna as defined in claims 1 or 2 wherein said feed element is a Gruner horn.
4. A Cassegrain antenna as defined in claims 1 or 2 wherein said feed element is an open-ended waveguide.
5. A Cassegrain antenna as defined in claim 1 wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
6. A Cassegrain antenna as defined in claim 5 wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
7. A Cassegrain antenna as defined in claim 1 wherein said subreflector includes means for effecting edge current control.
8. A Cassegrain antenna as defined in claim 7 wherein said edge current control means comprises one-quarter wave circumferential corrugations in the periphery of the reflecting surface of said subreflector.
9. A Cassegrain antenna as defined in claim 7 wherein said edge current control means comprises radial corrugations in the circumferential edge of said subreflector.
10. A Cassegrain antenna comprising a main reflector, a subreflector and a feed element, said subreflector having a reflecting surface which is shaped to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring concentric with the axis of said main reflector and disposed outside the edge of the reflecting surface of said subreflector, and said feed element being a low gain radiating element.
11. A Cassegrain antenna as defined in claim 10 wherein said feed element is a prime focal horn.
12. A Cassegrain antenna as defined in claim 10 wherein said feed element is a Gruner horn.
13. A Cassegrain antenna as defined in claim 10 wherein said feed element is an open-ended waveguide.
14. A Cassegrain antenna as defined in claim 10 wherein said feed element is disposed in close proximity to the center of said subreflector.
15. A Cassegrain antenna as defined in claim 10 wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
15. A Cassegrain antenna as defined in claim 10 wherein the reflecting surface of said subreflector is formed by rotating an ellipse about the axis of said main reflector with one focus of said ellipse located at the phase center of said low gain horn and the other focus of said ellipse being disposed on said ring.
17. A Cassegrain antenna as defined in claim 10 wherein said subreflector includes means for effecting edge current control.
18. A Cassegrain antenna as defined in claim 17 wherein said edge current control means comprises one-quarter wave corrugations in the periphery of the reflecting surface of said subreflector.
19. A Cassegrain antenna as defined in claim 17 wherein said edge current control means comprises radial corrugations in the circumferential edge of said subreflector.
20. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4 GHz comprising a main reflector having a diameter of sixty wavelengths or less, a subreflector facing said main reflector and a feed element in the form of a prime focal horn facing said subreflector in close proximity thereto.
21. A Cassegrain antenna as defined in claim 20 wherein said feed element is a Gruner horn.
22. A Cassegrain antenna as defined in claim 20 wherein said feed element is an open-ended waveguide.
23. A Cassegrain antenna as defined in claim 20 wherein said subref1ector includes means for effecting edge current control.
24. A Cassegrain antenna as defined in claim 23 wherein said edge current control means comprises radial corrugations in the circumferential edge of said subreflector.
25. A Cassegrain antenna as defined in claim 23 wherein said edge current control means comprises one quarter wave corrugations in the periphery of the reflecting surface of said subreflector.
26. A Cassegrain antenna as defined in claim 20, wherein said subreflector has a reflecting surface which is shaped to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring disposed outside the edge of the reflecting surface of said subreflector.
27. A Cassegrain antenna as defined in claim 26 wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
28. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4GHz comprising a main dish reflector, a feed element disposed at the base of said main dish reflector and having a well-defined phase center which is relatively insensitive to frequency, and a subreflector having a reflecting surface in the shape of an ellipsoid of revolution about a line coincident with the axis of said main dish reflector so as to focus energy received from said feed element through a locus of points forming a ring disposed adjacent to the periphery thereof and towards said main dish reflector, said feed element comprising a rectangular waveguide section adjoining a circular waveguide section by way of a step portion therebetween, said circular waveguide section having a corrugated section around the periphery and adjacent to the end thereof, said corrugated section extending in a direction substantially perpendicular to the axis of said circular waveguide section, and wherein said subreflector contains radial corrugations disposed along the circumferencial edge thereof so as effect edge current control.
29. A Cassegrain antenna according to claim 28, wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
30. A Cassegrain antenna according to claim 28, wherein said corrugations disposed along the periphery of said subreflector are one-quarter wavelength corrugations.
31. A Cassegrain antenna comprising a main reflector, a subreflector and a feed element, said subreflector having a reflecting surface in the shape of an ellipsoid of revolution about a line coincident with the axis of said main reflector, so as to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring concentric with the axis of said main reflector and disposed outside the edge of the reflecting surface of said subreflector, said feed element having a well defined phase center which is relatively insensitive to frequency and being in the form of an open-ended waveguide.
32. A Cassegrain antenna according to claim 31, wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
33. A Cassegrain antenna according to claim 32, wherein said subreflector includes one-quarter wavelength circumferencial corrugations disposed along the periphery of the reflecting surface thereof for performing edge current control.
34. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4GHz comprising a main dish reflector, a feed element disposed at the base of said dish reflector and a subreflector facing said dish reflector and said feed element and being shaped to focus energy received from said feed element through a locus of points forming a ring disposed adjacent the periphery thereof toward said main dish reflector, said feed element having a well-defined phase center which is relatively insensitive to frequency.
35. A Cassegrain antenna as defined in claim 34, wherein said subreflector has a reflecting surface in the shape of an ellipsoid of revolution about a line coincident with the axes of said dish reflector.
36. A Cassegrain antenna as defined in claims 34, wherein said feed element comprises a horn having a rectangular waveguide section adjoining a circular waveguide section via a step portion therebetween, said circular waveguide section having a corrugated section around the periphery and adjacent to the open end thereof, said corrugated section extending in a direction substantially perpendicular to the axis of said circular waveguide section.
37. A Cassegrain antenna comprising a main reflector, a subreflector and a feed element, said subreflector having a reflecting surface which is shaped to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring concentric with the axis of said main reflector and disposed outside the edge of the reflecting surface of said subreflector, and said feed element being a low gain radiating element having a well-defined phase center which is relatively insensitive to frequency.
38. A Cassegrain antenna as defined in claim 37, wherein said feed element comprises a horn having a rectangular waveguide section adjoining a circular waveguide section via a step portion therebetween, said circular waveguide section having a corrugated section around the periphery and adjacent to the end thereof and extending in a direction substantially perpendicular to the axis of said circular waveguide section.
39. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4GHz comprising a main reflector having a diameter of sixty wavelengths or less, a subreflector facing said main reflector and a feed element facing said subreflector in close proximity thereto and having a well-defined phase center which is relatively insensitive to frequency, and wherein said subreflector has a reflecting surface which is shaped to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring disposed outside the edge of the reflecting surface of said subreflector.
40. A Cassegrain antenna as defined in claim 39, wherein said feed element comprises a horn having a rectangular waveguide section adjoining a circular waveguide section via a step portion therebetween, said circular waveguide section having a corrugated section around the periphery and adjacent to the end thereof and extending in a direction substantially perpendicular to the axis of said circular waveyuide section.
41. A Cassegrain antenna as defined in claim 2, wherein said subreflector includes means for effecting edge current control.
42. A Cassegrain antenna as defined in claim 41, wherein said edge current control means comprises one-quarter wave circumferential corrugations in the periphery of the reflecting surface of said subreflector.
43. A Cassegrain antenna as defined in claim 41, wherein said edge current control means comprises radial corrugations in the circumferential edge of said subreflector.
1. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4GHz comprising a main dish reflector, a feed element disposed at the base of said dish reflector in the form of a prime focal horn directed away from said reflector, and a subreflector facing said dish reflector and said feed element and being shaped to focus energy received from said feed element through a locus of points forming a ring disposed adjacent the periphery thereof toward said main dish reflector.
2. A Cassegrain antenna as defined in claim 1 wherein said subreflector has a reflecting surface in the shape of an ellipsoid of revolution about a line coincident with the axes of said dish reflector.
3. A Cassegrain antenna as defined in claims 1 or 2 wherein said feed element is a Gruner horn.
4. A Cassegrain antenna as defined in claims 1 or 2 wherein said feed element is an open-ended waveguide.
5. A Cassegrain antenna as defined in claim 1 wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
6. A Cassegrain antenna as defined in claim 5 wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
7. A Cassegrain antenna as defined in claim 1 wherein said subreflector includes means for effecting edge current control.
8. A Cassegrain antenna as defined in claim 7 wherein said edge current control means comprises one-quarter wave circumferential corrugations in the periphery of the reflecting surface of said subreflector.
9. A Cassegrain antenna as defined in claim 7 wherein said edge current control means comprises radial corrugations in the circumferential edge of said subreflector.
10. A Cassegrain antenna comprising a main reflector, a subreflector and a feed element, said subreflector having a reflecting surface which is shaped to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring concentric with the axis of said main reflector and disposed outside the edge of the reflecting surface of said subreflector, and said feed element being a low gain radiating element.
11. A Cassegrain antenna as defined in claim 10 wherein said feed element is a prime focal horn.
12. A Cassegrain antenna as defined in claim 10 wherein said feed element is a Gruner horn.
13. A Cassegrain antenna as defined in claim 10 wherein said feed element is an open-ended waveguide.
14. A Cassegrain antenna as defined in claim 10 wherein said feed element is disposed in close proximity to the center of said subreflector.
15. A Cassegrain antenna as defined in claim 10 wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
15. A Cassegrain antenna as defined in claim 10 wherein the reflecting surface of said subreflector is formed by rotating an ellipse about the axis of said main reflector with one focus of said ellipse located at the phase center of said low gain horn and the other focus of said ellipse being disposed on said ring.
17. A Cassegrain antenna as defined in claim 10 wherein said subreflector includes means for effecting edge current control.
18. A Cassegrain antenna as defined in claim 17 wherein said edge current control means comprises one-quarter wave corrugations in the periphery of the reflecting surface of said subreflector.
19. A Cassegrain antenna as defined in claim 17 wherein said edge current control means comprises radial corrugations in the circumferential edge of said subreflector.
20. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4 GHz comprising a main reflector having a diameter of sixty wavelengths or less, a subreflector facing said main reflector and a feed element in the form of a prime focal horn facing said subreflector in close proximity thereto.
21. A Cassegrain antenna as defined in claim 20 wherein said feed element is a Gruner horn.
22. A Cassegrain antenna as defined in claim 20 wherein said feed element is an open-ended waveguide.
23. A Cassegrain antenna as defined in claim 20 wherein said subref1ector includes means for effecting edge current control.
24. A Cassegrain antenna as defined in claim 23 wherein said edge current control means comprises radial corrugations in the circumferential edge of said subreflector.
25. A Cassegrain antenna as defined in claim 23 wherein said edge current control means comprises one quarter wave corrugations in the periphery of the reflecting surface of said subreflector.
26. A Cassegrain antenna as defined in claim 20, wherein said subreflector has a reflecting surface which is shaped to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring disposed outside the edge of the reflecting surface of said subreflector.
27. A Cassegrain antenna as defined in claim 26 wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
28. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4GHz comprising a main dish reflector, a feed element disposed at the base of said main dish reflector and having a well-defined phase center which is relatively insensitive to frequency, and a subreflector having a reflecting surface in the shape of an ellipsoid of revolution about a line coincident with the axis of said main dish reflector so as to focus energy received from said feed element through a locus of points forming a ring disposed adjacent to the periphery thereof and towards said main dish reflector, said feed element comprising a rectangular waveguide section adjoining a circular waveguide section by way of a step portion therebetween, said circular waveguide section having a corrugated section around the periphery and adjacent to the end thereof, said corrugated section extending in a direction substantially perpendicular to the axis of said circular waveguide section, and wherein said subreflector contains radial corrugations disposed along the circumferencial edge thereof so as effect edge current control.
29. A Cassegrain antenna according to claim 28, wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
30. A Cassegrain antenna according to claim 28, wherein said corrugations disposed along the periphery of said subreflector are one-quarter wavelength corrugations.
31. A Cassegrain antenna comprising a main reflector, a subreflector and a feed element, said subreflector having a reflecting surface in the shape of an ellipsoid of revolution about a line coincident with the axis of said main reflector, so as to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring concentric with the axis of said main reflector and disposed outside the edge of the reflecting surface of said subreflector, said feed element having a well defined phase center which is relatively insensitive to frequency and being in the form of an open-ended waveguide.
32. A Cassegrain antenna according to claim 31, wherein said feed element is disposed less than three wavelengths from the center of said subreflector.
33. A Cassegrain antenna according to claim 32, wherein said subreflector includes one-quarter wavelength circumferencial corrugations disposed along the periphery of the reflecting surface thereof for performing edge current control.
34. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4GHz comprising a main dish reflector, a feed element disposed at the base of said dish reflector and a subreflector facing said dish reflector and said feed element and being shaped to focus energy received from said feed element through a locus of points forming a ring disposed adjacent the periphery thereof toward said main dish reflector, said feed element having a well-defined phase center which is relatively insensitive to frequency.
35. A Cassegrain antenna as defined in claim 34, wherein said subreflector has a reflecting surface in the shape of an ellipsoid of revolution about a line coincident with the axes of said dish reflector.
36. A Cassegrain antenna as defined in claims 34, wherein said feed element comprises a horn having a rectangular waveguide section adjoining a circular waveguide section via a step portion therebetween, said circular waveguide section having a corrugated section around the periphery and adjacent to the open end thereof, said corrugated section extending in a direction substantially perpendicular to the axis of said circular waveguide section.
37. A Cassegrain antenna comprising a main reflector, a subreflector and a feed element, said subreflector having a reflecting surface which is shaped to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring concentric with the axis of said main reflector and disposed outside the edge of the reflecting surface of said subreflector, and said feed element being a low gain radiating element having a well-defined phase center which is relatively insensitive to frequency.
38. A Cassegrain antenna as defined in claim 37, wherein said feed element comprises a horn having a rectangular waveguide section adjoining a circular waveguide section via a step portion therebetween, said circular waveguide section having a corrugated section around the periphery and adjacent to the end thereof and extending in a direction substantially perpendicular to the axis of said circular waveguide section.
39. A Cassegrain antenna for use in transmitting and/or receiving signals in a frequency range including 4GHz comprising a main reflector having a diameter of sixty wavelengths or less, a subreflector facing said main reflector and a feed element facing said subreflector in close proximity thereto and having a well-defined phase center which is relatively insensitive to frequency, and wherein said subreflector has a reflecting surface which is shaped to focus energy received from said feed element to said main reflector through a locus of points in the form of a ring disposed outside the edge of the reflecting surface of said subreflector.
40. A Cassegrain antenna as defined in claim 39, wherein said feed element comprises a horn having a rectangular waveguide section adjoining a circular waveguide section via a step portion therebetween, said circular waveguide section having a corrugated section around the periphery and adjacent to the end thereof and extending in a direction substantially perpendicular to the axis of said circular waveyuide section.
41. A Cassegrain antenna as defined in claim 2, wherein said subreflector includes means for effecting edge current control.
42. A Cassegrain antenna as defined in claim 41, wherein said edge current control means comprises one-quarter wave circumferential corrugations in the periphery of the reflecting surface of said subreflector.
43. A Cassegrain antenna as defined in claim 41, wherein said edge current control means comprises radial corrugations in the circumferential edge of said subreflector.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000414634A CA1191944A (en) | 1982-11-01 | 1982-11-01 | Shifted focus cassegrain antenna with low gain feed |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000414634A CA1191944A (en) | 1982-11-01 | 1982-11-01 | Shifted focus cassegrain antenna with low gain feed |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1191944A true CA1191944A (en) | 1985-08-13 |
Family
ID=4123866
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000414634A Expired CA1191944A (en) | 1982-11-01 | 1982-11-01 | Shifted focus cassegrain antenna with low gain feed |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1191944A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6911953B2 (en) | 2003-11-07 | 2005-06-28 | Harris Corporation | Multi-band ring focus antenna system with co-located main reflectors |
| US6937201B2 (en) | 2003-11-07 | 2005-08-30 | Harris Corporation | Multi-band coaxial ring-focus antenna with co-located subreflectors |
| WO2015047458A1 (en) * | 2013-09-24 | 2015-04-02 | Northrop Grumman Systems Corporation | Antenna for multiple frequency bands |
-
1982
- 1982-11-01 CA CA000414634A patent/CA1191944A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6911953B2 (en) | 2003-11-07 | 2005-06-28 | Harris Corporation | Multi-band ring focus antenna system with co-located main reflectors |
| US6937201B2 (en) | 2003-11-07 | 2005-08-30 | Harris Corporation | Multi-band coaxial ring-focus antenna with co-located subreflectors |
| WO2015047458A1 (en) * | 2013-09-24 | 2015-04-02 | Northrop Grumman Systems Corporation | Antenna for multiple frequency bands |
| US9246234B2 (en) | 2013-09-24 | 2016-01-26 | Northrop Grumman Systems Corporation | Antenna for multiple frequency bands |
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