Space tapered antenna having compressed spacing or feed network phase progression, or both

Information

  • Patent Grant
  • 6353410
  • Patent Number
    6,353,410
  • Date Filed
    Friday, March 19, 1999
    25 years ago
  • Date Issued
    Tuesday, March 5, 2002
    23 years ago
Abstract
A space-tapered antenna has a collinear array of radiating elements coupled via a cable feeding system to a Butler matrix feed system. Either the collinear array has compressed rows spaced in a range of ⅜ to ¼ λ, where λ is the operating wavelength of the antenna, the cable feeding system is a phase progression cable feeding system, or both. One 120° space-tapered antenna has eight compressed rows spaced at ⅜ λ for providing six 20° degree beams with −10 dB side lobe suppression. Another 120° space-tapered antenna has eight compressed rows spaced at ¼ wavelength for providing four 30° beams with −15 dB side lobe suppression. A 60° space-tapered antenna has eight compressed rows spaced at ⅜ λ in combination with a 22 ½° phase progression cable feeding system for providing three 20° beams with −14 dB side lobe suppression. One 90° space-tapered antenna has eight compressed rows spaced at ¼ λ in combination with a 22 ½° phase progression cable feeding system for providing three 30° beams with −17 dB side lobe suppression. Another 90° space-tapered antenna has four rows spaced at ½ λ and a 45° phase progression cabling feeding system for providing three 30° beams with −12 dB side lobe suppression.
Description




BACKGROUND OF THE INVENTION




1. Technical Field




This invention relates to an antenna; and more particularly relates to a multibeam antenna.




2. Description of Related Art





FIG. 1A

shows an antenna


20


of U.S. Pat. No. 5,589,843 having a space tapered multi-beam antenna


24


, a Butler-matrix feed network


28


, and a radio receiver and/or transmitter


37


. The antenna


20


is known as a space tapered one hundred twenty degree antennas having four thirty degree beams.




The radio receiver and/or transmitter


37


receives and/or provides radio receiver and/or transmitter signals from or to the 4-way Butler matrix feed network


28


via cabling


41


. The radio receiver/transmitter equipment


37


is generally shown since the specific type of equipment used in an actual installation can vary widely. The Butler matrix feed network


28


is implemented using a planar microstrip design


39


shown in

FIG. 1B

with no crossovers and is fabricated from a printed circuit board having a dielectric substrate made of low loss ceramic material, such as glass epoxy. In general, the Butler-matrix feed network


28


has N antenna ports


29


and N receiver/transmitter equipment ports


31


, where N is equal to the number of co-linear arrays of the associated antenna. As shown, the 4-way Butler matrix feed network


28


has four antenna output ports


29


and four radio receiver/transmitter input ports


31


. The standard phase shift of the 4-way Butler matrix feed network


28


is as follows:





















ANT1




ANT2




ANT3




ANT4






























BEAM 2L




0




−135




+90




−45







BEAM 1L




0




−45




−90




−135







BEAM 1R




0




+45




+90




+135







BEAM 2R




0




+135




−90




+45















The Butler-matrix feed network


28


is connected to the space-tapered antenna


24


with equally phased cables


35


that provide phase shifting of outgoing signals to electronically steer the radiating pattern of the space-tapered antenna


24


.




In

FIG. 1A

, the space tapered multi-beam antenna


24


has a space-tapered array


26


(ANT1, ANT2, ANT3, ANT4) with rows of radiating elements spaced at about ½ λ (i.e. wavelength), where λ is the wavelength of the electromagnetic energy to be received or transmitted. (In practice, the spacing between adjacent co-linear arrays may actually be approximately 0.47 λ.) The number of radiating elements in outermost rows is less than the number of radiating elements in center rows in order to suppress side-lobes distortion in the antenna signal, which is typically −9 or −10 Db. The space-tapered array


26


includes four co-linear arrays of associated electromagnetic radiating elements


30


. Each antenna output port


29


of the 4-way Butler matrix feed network


28


is respectively connected to a respective antenna ANT1, ANT2, ANT3, ANT4 of the co-linear array


26


by cables


35


and connectors


27


associated with each antenna array. The cables


35


are all the same length (i.e. equal phase cables) so as not to introduce any phase change with respect to the signals carried thereover relative to the other cables


35


. In comparison, the cables


41


need not be equal phase cables since any phase changes introduced by these cables is not relevant to the electronic beam(s) being used.




In

FIG. 1A

, the outermost co-linear antenna arrays ANT1 and ANT4 each comprise two radiating elements


30


, while the innermost antenna arrays ANT2 and ANT3 each comprise four radiating elements


30


. These radiating elements


30


are typically dipole elements, although other types of radiating element can be used. Energy is radiated or received from these dipole elements by means of a feedstrap


43


having a centrally located connector


27


. The dipole elements are spaced from each adjacent dipole element of the same array by a distance approximately equal to λ. The feed strap includes portions


45


extending beyond the lowermost and uppermost dipole element, with the end of these portions connected to the electrically conductive back plate


47


of the antenna. Such a feed strap configuration is known in the art as a Bogner type feed (see U.S. Pat. No. 4,086,598, hereby incorporated by reference).




The phase progression for the antenna beam of the antenna shown in

FIG. 1A

is show in the table below:



















BEAM




ANT1




ANT2




ANT3




ANT4



























2L




0




−135




+90




−45






1L




0




−45




−90




−135






1R




0




+45




+90




+135






2R




0




+135




−90




+45














The one hundred twenty degree antennas


20


suffer from high side-lobe levels that do not meet desired customer specifications of being below −10 dB from the beam peak. Also, the outer beams suffer from a drop in gain as compared to the inner beams.





FIGS. 1C

,


1


D,


1


E show frequency plots for the antenna


20


in

FIG. 1A

that show these problems, including frequency plots respectively at frequencies of 1.850 giga Hertz (hereinafter “GHz”), 1.920 GHz and 1.990 GHZ. As a person skilled in the antenna design art would appreciate, each plot shows various plot characteristics, including four plot overlays (i.e. 1LH, 1RH, 2LH, 2RH), four beam peaks in degrees, four beamwidths in degrees, four front-to-back (hereinafter “f/b”) ratios in decibels (hereinafter “dB”) and four sidelobes in degrees and dBs. In

FIGS. 1C

,


1


D,


1


E, the various “triangles” help to indicate these various plot characteristics.




The technical problem to be solved is to provide an antenna having reduced side-lobe suppression, including a spaced-tapered antenna having outer beam signals that do not have a significant drop in gain as compared to inner beam signals.




SUMMARY OF THE INVENTION




The basic idea of the present invention is to either compress the row spacing of radiating elements in the collinear arrays of the antenna, or use phase progression cables leading from the feed system to the collinear array, or both.




The invention provides a new antenna, including a space-tapered antenna, having a collinear array of radiating elements coupled via a cable feeding system to a Butler matrix feed system. In the antenna, either the collinear array has compressed rows spaced in a range of ⅜ to ¼ of a wavelength, the cable feeding system is a phase progression cable feeding system, or both.




One 120° space-tapered antenna has eight compressed rows spaced at ⅜ wavelength for providing six 20° degree beams with −10 dB side lobe suppression. The six beam antenna is unique in that it provides a way to use an 8-way Butler matrix, because in the prior art there is no 6-way Butler matrix feed system.




Another 120° space-tapered antenna has eight compressed rows spaced at ¼ wavelength for providing four 30° beams with −15 dB side lobe suppression.




A 60° space-tapered antenna has eight compressed rows spaced at ⅜ wavelength in combination with a 22 ½° phase progression cable feeding system for providing three 20° beams with −14 dB side lobe suppression.




A 90° space-tapered antenna has eight compressed rows spaced at ¼ wavelength in combination with a 22 ½° phase progression cable feeding system for providing three 30° beams with −17 dB side lobe suppression.




A 90° space-tapered antenna has four rows spaced at ½ wavelength and a 45° phase progression cabling feeding system for providing three 30° beams with −12 dB side lobe suppression. For this antenna, the phase progression shifts the beams so that a center beam is down the middle, normal to the antenna. This also reduces the number of beams by one such that the radiating pattern of the antenna includes the center beam with an equally balanced number of side beams around the center beam. The phase progression may also be achieved directly in the output of the feed network.




One advantage of the present invention includes improved side-lobe distortion suppression and reduced dropoff in gain of the outer beams as compared to the inner beams. The sidelobe distortion is reduced by about −6 dB which translates into 4× less side lobe distortion in the antenna signal for improved signal transmission.




These embodiments provides improved side-lobe suppression and the outer beams that do not have the gain dropoff associated with prior art space tapered antennas.











A DESCRIPTION OF THE DRAWINGS




For a fuller understanding of the nature of the invention, reference should be made to the following detailed descriptions taken in connection with the accompanying drawings, not in scale, in which:





FIG. 1A

shows a prior art antenna


20


shown and described in U.S. Pat. No. 5,589,843.





FIG. 1B

shows a 4-way Butler matrix feed network


28


that is part of the antenna


20


shown in FIG.


1


A.





FIGS. 1C

,


1


D,


1


E show frequency plots for the antenna


20


in

FIG. 1A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ.





FIG. 2A

shows a block diagram of an antenna that is the subject matter of the present invention.





FIGS. 2B

,


2


C,


2


D show plots for the antenna in

FIG. 2A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ.





FIG. 3A

shows a block diagram of an antenna that is the subject matter of the present invention.





FIG. 3B

shows a diagram of an space tapered multibeam antenna that is part of the antenna shown in FIG.


3


A.





FIGS. 3C

,


3


D,


3


E show frequency plots for the antenna in

FIG. 3A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ.





FIG. 4A

shows a block diagram of an antenna that is the subject matter of the present invention.





FIG. 4B

shows a diagram of an space tapered multibeam antenna that is part of the antenna shown in FIG.


4


A.





FIGS. 4C

,


4


D,


4


E show frequency plots for the antenna in

FIG. 4A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ.





FIG. 5A

shows a block diagram of an antenna that is the subject matter of the present invention.





FIGS. 5B

,


5


C,


5


D show frequency plots for the antenna in

FIG. 5A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ.





FIG. 5E

shows a block diagram of an antenna that is the subject matter of the present invention.





FIGS. 5F

,


5


G,


5


H show frequency plots for the antenna in

FIG. 5E

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ.





FIG. 6A

shows a block diagram of an antenna that is the subject matter of the present invention.





FIGS. 6B

,


6


C,


6


D show frequency plots for the antenna in

FIG. 6A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ.





FIG. 7

shows an 8-way Butler matrix feed network


128


that is part of the antenna


200


shown in FIG.


3


A.











DETAILED DESCRIPTION OF THE INVENTION




Various embodiments of the invention will be described below. For the convenience of the reader, and to the extent possible, the reference numeral system used to describe embodiments of the present invention will substantially track the numeral system used to describe the antenna shown in

FIG. 1A

with the addition of multiples of 100s.




Space Tapered 90° Multi-beam Antenna with Three 30° Beams





FIG. 2A

shows a ninety degree antenna generally indicated as


100


having a 4-way Butler matrix feed network


28


similar to that shown in

FIG. 1A

, having a space tapered multibeam antenna


24


with a 2-4-4-2 configuration and a horizontal spacing of 0.50 λ similar to that shown in

FIG. 1A

, and also having four cables


102


,


104


,


106


,


108


with different cable lengths for connecting the 4-way Butler matrix feed network


28


to the space tapered multibeam antenna


24


. The ninety degree antenna


100


provides three thirty degree beams.




In effect, the ninety degree antenna


100


works similar to the principles used on the four beam antenna


20


shown and described with respect to FIG.


1


A. The space tapered multibeam antenna


24


and the 4-way Butler matrix feed network


28


remain the same as before. As shown, the 4-way Butler matrix feed network


28


has four input ports


101




a


,


101




b


,


101




c


,


101




d


. Only three of the four input ports


101




a


,


101




b


,


101




c


receive antenna input signals from the radio receiver and/or transmitter (not shown). The other input port


101




d


is connected via a resistor


120


to electrical ground. In one embodiment, the resistor


120


is 50 ohm resistors, although the scope of the invention is not intended to be limited to any particular resistor value. The only other change is the cabling that feed the Butler matrix signal to the space tapered multibeam antenna


24


, as discussed below. In

FIG. 1A

, the cables


35


are equally phased. Similar in structure to cable


35


in

FIG. 1A

, each cable


102


,


104


,


106


,


108


connects a respective antenna array ANT1, ANT2, ANT3, ANT4 (see

FIG. 1A

) to a respective Butler matrix output port


29


(see FIG.


1


A). However, in contrast to the cables


35


in

FIG. 1A

, each cable


102


,


104


,


106


,


108


has a different length to introduce a phase progression in the antenna signals provided to the respective antenna array ANT1, ANT2, ANT3, ANT4(see FIG.


1


A). When the cables


102


,


104


,


106


,


108


have a respective different length to provide a phase progression of forty-five degrees (i.e. 0, +45, +90, +135), then the antenna


100


will get the following “total” phase progression:



















BEAM




ANT1




ANT2




ANT3




ANT4



























1L




0




−90




−180




+90






1R




0




+90




+180




−90






C




0




0




0




0















FIGS. 2B

,


2


C,


2


D show frequency plots for the antenna in

FIG. 2A

respectively at frequencies of 1.850 GHZ, 1.920 GHz and 1.990 GHZ. As a person skilled in the antenna design art would appreciate, each plot shows various plot characteristics, including four plot overlays (i.e. Center, Left, Right), three beam peaks in degrees, three beamwidths in degrees, three f/b ratios in dB and three sidelobes in degrees and dBs. In

FIGS. 2B

,


2


C,


2


D, the various “triangles” help to indicate these various plot characteristics.




In operation, beams


2


L,


1


L,


1


R are steered to become beams


1


L, C, and


1


R respectively. As shown, beam


2


R is not used and is terminated with a fifty ohm load. In essence, the beams are steered fifteen degrees in order to get the center beam. Another way to get the extra phase is to add the phase progression directly onto the Butler's outputs.




The scope of the invention is not intended to be limited to any particular phase progression or cable lengths. A person skilled in the art would appreciate how to determine the different cable lengths to achieve the desired phase progression, which would typically depend may on the cable type and the frequency.




One advantage of the ninety degree antenna


100


is that it has side-lobe suppression better than −12 dB. The outer beams do not have the gain drop off associated with the one hundred twenty degree antenna when compared to the frequency plots shown in

FIGS. 1C

,


1


D,


1


E.




The ninety degree antenna


100


can be used wherever the original four beam antenna


20


in

FIG. 1A

is used.




Space Tapered 120° Multi-beam Antenna With Six 20° Beams





FIG. 3A

shows a one hundred and twenty degree antenna generally indicated as


200


having an 8-way Butler matrix feed network


202


, having a space tapered multibeam antenna


224


with a 1-2-4-4-4-4-2-1 configuration and a horizontal spacing of 0.375 λ, and also having eight cables


204


,


206


,


208


,


210


,


212


,


214


,


216


,


218


with the same cable lengths for connecting the 8-way Butler matrix feed network


202


to the space tapered multibeam antenna


224


. The one hundred and twenty degree antenna


200


provides six twenty degree beams.




In effect, the one hundred and twenty degree antenna


200


works with the principles used on the original four beam antenna shown and described with respect to FIG.


1


A. However, instead of four rows of dipoles there are eight rows. When hooked up to the 8-way Butler matrix feed network


202


, eight fifteen degree beams are normally formed.




For the present invention the eight rows are squeezed into the space normally occupied by six rows for providing the six twenty degree beams. This gives the antenna a horizontal spacing of 0.375 wavelengths.




In operation, the one hundred and twenty degree antenna


200


is a six beam antenna that is a compromise between the four and eight beam models. It has the same side-lobe suppression as the four beam antenna with a fifty percent increase in channel capacity. This is not as large an increase as the eight beam antenna, but the side-lobe suppression is much better. (A normal antenna with half wavelength spacing between the dipoles would have eight usable beams. Due to the compressed spacing, only six beams are usable.)




The 8-way Butler matrix feed network


202


is known in the art, is shown and described with respect to

FIG. 7

of U.S. Pat. No. 5,589,843, and is connected to a radio receiver and/or transmitter (not shown) such as


37


shown in FIG.


1


A. As shown, the 8-way Butler matrix feed network


202


has eight input ports


202




a


,


202




b


,


202




c


,


202




d


,


202




e


,


202




f


,


202




g


,


202




h


. Only six of the eight input ports


202




b


,


202




c


,


202




d


,


202




e


,


202




f


,


202




g


receive antenna input signals from the radio receiver and/or transmitter (not shown). The other two input ports


202




a


,


202




h


are connected via a respective resistor


220


,


222


to electrical ground. In one embodiment, the respective resistors


220


,


222


are 50 ohm resistors, although the scope of the invention is not intended to be limited to any particular resistor value.




As shown, the eight cables


204


,


206


,


208


,


210


,


212


,


214


,


216


,


218


provide eight Butler matrix feed network signals to the space tapered multibeam antenna


224


.





FIG. 3B

generally shows the space tapered multibeam antenna


224


having the 1-2-4-4-4-4-2-1 configuration and the horizontal spacing of 0.375 λ. The space-tapered multibeam antenna


224


includes eight co-linear antenna arrays ANT1, ANT2, ANT3, ANT4, ANT5, ANT6, ANT7, ANT8 of associated electromagnetic radiating elements


230


. Similar to that shown and described in

FIGS. 1A and 2A

, these radiating elements


230


are typically dipole elements, although other types of radiating element can be used. Each of the eight Butler matrix feed network signals on the eight cables


204


,


206


,


208


,


210


,


212


,


214


,


216


,


218


is separately provided to a respective antenna ANT1, ANT2, ANT3, ANT4, ANT5, ANT6, ANT7, ANT8 of the space-tapered multibeam antenna


224


by cables and connectors (not shown) associated with each antenna array, which a person skilled in the art would appreciate how to do. For the embodiment in

FIGS. 3A and 3B

, the cables (not shown) are all the same length (i.e. equal phase cables) so as not to introduce any phase change with respect to the signals carried thereover relative to the other cables. Similar to that shown and described in

FIGS. 1A and 2A

, the space tapered multibeam antenna


224


uses a feedstrap configuration that is known in the art as the Bogner type feed.




The one hundred and twenty degree antenna


200


provides six twenty degree beams at the following angles:























BEAM




ANT1




ANT2




ANT3




ANT4




ANT5




ANT6




ANT7




ANT8































3R




0




−112.5




+135




+22.5




−90




+157.5




+45




−67.5






2L




0




−67.5




−135




+157.5




+90




+22.5




−45




−112.5






1L




0




−22.5




 −45




−67.5




−90




−112.5




−135  




−157.5






1R




0




+22.5




 +45




+67.5




+90




+112.5




+135  




+157.5






2R




0




+67.5




+135




−157.5




−90




−22.5




+45




+112.5






3R




0




+112.5




−135




−22.5




+90




−157.5




−45




+67.5















FIGS. 3C

,


3


D,


3


E show frequency plots for the antenna in

FIG. 3A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ. As a person skilled in the antenna design art would appreciate, each plot shows various plot characteristics, including four plot overlays (i.e. 1L, 1R, 2L, 2R, 3L, 3R), six beam peaks in degrees, six beamwidths in degrees, six f/b ratios in dB and six sidelobes in degrees and dBs. In

FIGS. 3C

,


3


D,


3


E the various “triangles” help to indicate these various plot characteristics.




In order to achieve desired side-lobe suppression, a space taper technique is used. The eight rows of dipoles do not have an equal number of elements. The 1-2-4-4-4-4-2-1 configuration supplies a side-lobe suppression of −9 dB. Fine tuning the antenna may eventually get the side-lobe suppression of −10 dB.




In comparison to the present invention, the known prior art space tapered one hundred twenty degree antenna has four thirty degree beams or eight fifteen degree beams. The four beam antennas do not provide as much channel capacity as the eight beam models. The eight beam models suffer from even higher side-lobe levels than the four beam antennas.




The one hundred and twenty degree antenna


200


of the present invention can be used wherever the original four beam antenna is used.




Space Tapered 120° Multibeam Antenna With Four 30° Beams and Suppressed Side-lobes





FIG. 4A

shows a one hundred and twenty degree antenna generally indicated as


300


having an 8-way Butler matrix feed network


302


, having a space tapered multibeam antenna


324


with a 1-2-4-4-4-4-2-1 configuration and a horizontal spacing of 0.250 λ, and also having eight cables


304


,


306


,


308


,


310


,


312


,


314


,


316


,


318


with the same cable lengths for connecting the 8-way Butler matrix feed network


302


to the space tapered multibeam antenna


324


. The one hundred and twenty degree antenna


300


provides four thirty degree beams.




In effect, the one hundred and twenty degree antenna


300


works with the principles used on the original four beam antenna shown and described with respect to FIG.


1


A. However, instead of four rows of dipoles, there are eight rows. When hooked up to a typical 8-way Butler matrix feed network, eight fifteen degree beams are normally formed. However, in the present invention the eight rows may be squeezed into the space normally occupied by four rows for providing four thirty degree beams. This gives the one hundred and twenty degree antenna


300


a horizontal spacing of 0.250 wavelengths.




The 8-way Butler matrix feed network


302


is known in the art, is shown and described with respect to

FIG. 7

of U.S. Pat. No. 5,589,843, and is connected to a radio receiver and/or transmitter (not shown) such as


37


shown in FIG.


1


A. As shown, the 8-way Butler matrix feed network


302


has eight input ports


302




a


,


302




b


,


302




c


,


302




d


,


302




e


,


302




f


,


302




g


,


302




h


. Only four of the eight input ports


302




c


,


302




d


,


302




e


,


302




f


receive antenna input signals from the radio receiver and/or transmitter (not shown). The other four input ports


302




a


,


302




b


,


302




g


,


302




h


are connected via a respective resistor


320


,


321


,


322


,


323


to electrical ground. In one embodiment, the respective resistor


320


,


321


,


322


,


323


are 50 ohm resistors, although the scope of the invention is not intended to be limited to any particular resistor value.




As shown, the eight cables


304


,


306


,


308


,


310


,


312


,


314


,


316


,


318


provide eight Butler matrix feed network signals to the space tapered multibeam antenna


324


.





FIG. 4B

generally shows the space tapered multibeam antenna


324


having the 1-2-4-4-4-4-2-1 configuration and the horizontal spacing of 0.250 λ. The space-tapered multibeam antenna


324


includes eight co-linear antenna arrays ANT1, ANT2, ANT3, ANT4, ANT5, ANT6, ANT7, ANT8 of associated electromagnetic radiating elements


330


. Similar to that shown and described in

FIGS. 1A

,


2


A,


3


A, these radiating elements


330


are typically dipole elements, although other types of radiating element can be used. Each of the eight Butler matrix feed network signals on the eight cables


304


,


306


,


308


,


310


,


312


,


314


,


316


,


318


is separately provided to a respective antenna ANT1, ANT2, ANT3, ANT4, ANT5, ANT6, ANT7, ANT8 of the space tapered multibeam antenna


324


by cables and connectors (not shown) associated with each antenna array, which a person skilled in the art would appreciate how to do. For the embodiment in

FIGS. 4A and 4B

, the cables (not shown) are all the same length (i.e. equal phase cables) so as not to introduce any phase change with respect to the signals carried thereover relative to the other cables. Similar to that shown and described in

FIGS. 1A

,


2


A,


3


A, the space tapered multibeam antenna


324


uses a feedstrap configuration that is known in the art as the Bogner type feed.




In order to achieve further side-lobe suppression, a space taper technique is used. The eight rows of dipoles do not have an equal number of elements. The 1-2-4-4-4-4-2-1 configuration supplies a side-lobe suppression of −15 dB. This antenna is also much broader banded than the original four beam model. It has a working bandwidth of


280


MHz as opposed to the normal 140 MHz.




The one hundred and twenty degree antenna


300


provides four thirty degree beams at the following angles:

























ANT1




ANT2




ANT3




ANT4




ANT5




ANT6




ANT7




ANT8
































BEAM 2L




0




−67.5




−135




+157.5




+90




+22.5




 −45




−112.5






BEAM 1L




0




−22.5




 −45




−67.5




−90




−112.5




−135




−167.5






BEAM 1R




0




+22.5




 +45




+67.5




+90




+112.5




+135




+167.5






BEAM 2R




0




+67.5




+135




−157.5




−90




−22.5




 +45




+112.5















FIGS. 4C

,


4


D,


4


E show frequency plots for the antenna in

FIG. 4A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ. As a person skilled in the antenna design art would appreciate, each plots shows various plot characteristics, including four plot overlays (i.e. 1L, 1R, 2L, 2R), four beam peaks in degrees, four beamwidths in degrees, four f/b ratios in dB and four sidelobes in degrees and dBs. In

FIGS. 4C

,


4


D,


4


E, the various “triangles” help to indicate these various plot characteristics.




The suppressed side-lobe one hundred twenty degree antenna has side-lobe suppression better than −15 dB. The outer beams do not have the gain drop off associated with the one hundred twenty degree antenna as shown in the frequency plots in

FIGS. 4C

,


4


D,


4


E.




In comparison to the present invention, a normal antenna with half wavelength spacing between the dipoles would have eight usable beams. In the present invention, due to the compressed spacing, only four beams are usable. Also, half of the feedlines are on the back side of the reflector. This means the feedlines on the front side of the reflector are two half wavelengths long. For proper side-lobe suppression, an antenna needs to have feedlines which are an even number of half wavelengths long.




The prior art space tapered one hundred twenty degree antennas have four thirty degree beams. These one hundred twenty degree antennas suffer from high side-lobe levels that do not meet customer specifications of being below −10 dB from the beam peak. Also, the outer beams suffer from a drop in gain as compared to the inner beams. See the frequency plots in

FIGS. 1C

,


1


D,


1


E.




The antenna


300


can be used wherever the original four beam antenna is used.




Space Tapered 60° Multibeam Antenna with Three 20° Beams





FIG. 5A

shows a sixty degree antenna generally indicated as


400


having an 8-way Butler matrix feed network


402


, having a space tapered multibeam antenna


424


with a 1-2-4-4-4-4-2-1 configuration and a horizontal spacing of 0.375 λ, and also having eight cables


404


,


406


,


408


,


410


,


412


,


414


,


416


,


418


with the different cable lengths for connecting the 8-way Butler matrix feed network


402


to the space tapered multibeam antenna


424


to provide twenty two and a half degree phase progression. The sixty degree antenna


400


provides three twenty degree beams.




In effect, the antenna works with the principles used on the original four beam antenna. Instead of four rows of dipoles there are eight rows. When hooked up to an eight way Butler matrix, eight fifteen degree beams are normally formed. In the present invention, the eight rows were squeezed into the space normally occupied by six rows for providing the three twenty degree beams. This gives the antenna a horizontal spacing of 0.375 wavelengths.




The 8-way Butler matrix feed network


402


is known in the art, shown and described with respect to

FIG. 7

of U.S. Pat. No. 5,589,843, and is connected to a radio receiver and/or transmitter (not shown) such as


37


shown in FIG.


1


A. As shown, the 8-way Butler matrix feed network


402


has eight input ports


402




a


,


402




b


,


402




c


,


402




d


,


402




e


,


402




f


,


402




g


,


402




h


. Only three of the eight input ports


402




c


,


402




d


,


402




e


receive antenna input signals from the radio receiver and/or transmitter (not shown). The other five input ports


402




a


,


402




b


,


402




f


,


402




g


,


402




h


are connected via a respective resistor


420


,


421


,


422


,


423


,


425


to electrical ground. In one embodiment, the respective resistors


420


,


421


,


422


,


423


,


425


are 50 ohm resistors, although the scope of the invention is not intended to be limited to any particular resistor value.




The phase progression of the 8-way Butler matrix feed network


402


is as follows:























BEAM




ANT1




ANT2




ANT3




ANT4




ANT5




ANT6




ANT7




ANT8































3R




0




−112.5




+135




+22.5




−90




+157.5




+45




−67.5






2L




0




−67.5




−135




+157.5




+90




+22.5




−45




−112.5






1L




0




−22.5




 −45




−67.5




−90




−112.5




−135  




−157.5






1R




0




+22.5




 +45




+67.5




+90




+112.5




+135  




+157.5






2R




0




+67.5




+135




−157.5




−90




−22.5




+45




+112.5






3R




0




+112.5




−135




−22.5




+90




−157.5




−45




+67.5














As shown, the eight cables


404


,


406


,


408


,


410


,


412


,


414


,


416


,


418


provide eight Butler matrix feed network signals to the space tapered multibeam antenna


424


.




The space tapered multibeam antenna


424


is shown in

FIG. 3B

generally having the 1-2-4-4-4-4-2-1 configuration and the horizontal spacing of 0.375 λ. In order to achieve further side-lobe suppression a space taper technique was used. The eight rows of dipoles do not have an equal number of elements. The 1-2-4-4-4-4-2-1 configuration supplies a side-lobe suppression of −14 dB.




When the cables


404


,


406


,


408


,


410


,


412


,


414


,


416




418


have a phase progression of 0, +22.5, +45, +67.5, +90, +112.5, +135, +157.5 together with the standard phase progression of the Butler matrix, then sixty degree antenna generally indicated as


400


provides three twenty degree beams at the following angles:























BEAM




ANT1




ANT2




ANT3




ANT4




ANT5




ANT6




ANT7




ANT8











1L




0




−45




−90




−135




−180




+135




+90




+45






C




0




   0




   0




   0




   0




   0




   0




   0






1R




0




+45




+90




+135




+180




−135




−90




−45















FIGS. 5B

,


5


C,


5


D show frequency plots for the antenna in

FIG. 5A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ. As a person skilled in the antenna design art would appreciate, each plot shows various plot characteristics, including three plot overlays (i.e. 1L, 1R, CH), three beam peaks in degrees, three beamwidths in degrees, three f/b ratios in dB and four sidelobes in degrees and dBs. In

FIGS. 5B

,


5


C,


5


D, the various “triangles” help to indicate these various plot characteristics.




The sixty degree antenna has side-lobe suppression better than −14 dB. The outer beams do not have the gain drop off associated with the one hundred twenty degree antenna as shown in the frequency plots in

FIGS. 5B

,


5


C,


5


D.




The prior art space tapered one hundred twenty degree antennas has four thirty degree beams. The one hundred twenty degree antenna suffers from high side-lobe levels that do not meet the customer specification of being below −10 dB from the beam peak. Also, the outer beams suffer from a drop in gain as compared to the inner beams. See the frequency plots in

FIGS. 1C

,


1


D,


1


E.




A normal antenna would only send beams down either side. To get a middle beam, the equally phased cables normally leading from the Butler matrix to the antennas were replaced with cables having a twenty-two and a half degree phase progression. This shifted the beams so that one was down the middle. This set up actually produces five twenty degree beams, but customer demand was for only three. This could also be done by adding the phase progression directly to the Butler's outputs.




The antenna


400


can be used wherever the original four beam antenna is used.





FIG. 5E

shows a one hundred degree antenna generally indicated as


500


having an 8-way Butler matrix feed network


502


, having a space tapered multibeam antenna


524


with a 1-2-4-4-4-4-2-1 configuration and a horizontal spacing of 0.375 λ, and also having eight cables


504


,


506


,


508


,


510


,


512


,


514


,


516


,


518


with the different cable lengths for connecting the 8-way Butler matrix feed network


502


to the space tapered multibeam antenna


524


to provide twenty two and a half degree phase progression. The antenna


500


provides five twenty degree beams.




The 8-way Butler matrix feed network


502


is known in the art, shown and described with respect to

FIG. 7

of U.S. Pat. No. 5,589,843, and is connected to a radio receiver and/or transmitter (not shown) such as


37


shown in FIG.


1


A. As shown, the 8-way Butler matrix feed network


502


has eight input ports


502




a


,


502




b


,


502




c


,


502




d


,


502




e


,


502




f


,


502




g


,


502




h


. Only five of the eight input ports


502




b


,


502




c


,


502




d


,


502




e


,


502




f


receive antenna input signals from the radio receiver and/or transmitter (not shown). The other three input ports


502




a


,


502




g


,


502




h


are connected via a respective resistor


520


,


522


,


523


to electrical ground. In one embodiment, the respective resistors


520


,


522


,


523


are 50 ohm resistors, although the scope of the invention is not intended to be limited to any particular resistor value.




The phase progression of the 8-way Butler matrix feed network


502


is as follows:























BEAM




ANT1




ANT2




ANT3




ANT4




ANT5




ANT6




ANT7




ANT8































3R




0




−112.5




+135




+22.5




−90




+157.5




+45




−67.5






2L




0




−67.5




−135




+157.5




+90




+22.5




−45




−112.5






1L




0




−22.5




 −45




−67.5




−90




−112.5




−135  




−157.5






1R




0




+22.5




 +45




+67.5




+90




+112.5




+135  




+157.5






2R




0




+67.5




+135




−157.5




−90




−22.5




+45




+112.5






3R




0




+112.5




−135




−22.5




+90




−157.5




−45




+67.5














As shown, the eight cables


504


,


506


,


508


,


510


,


512


,


514


,


516


,


518


provide eight Butler matrix feed network signals to the space tapered multibeam antenna


524


.




The space tapered multibeam antenna


524


is shown in

FIG. 3B

generally having the 1-2-4-4-4-4-2-1 configuration and the horizontal spacing of 0.375 λ. In order to achieve further side-lobe suppression a space taper technique was used. The eight rows of dipoles do not have an equal number of elements. The 1-2-4-4-4-4-2-1 configuration supplies a side-lobe suppression of −12 dB.




When the cables


504


,


506


,


508


,


510


,


512


,


514


,


516


,


518


have a phase progression of 0, +22.5, +45, +67.5, +90, +112.5, +135, +157.5 together with the standard phase progression of the Butler matrix, then one hundred degree antenna generally indicated as


500


provides five twenty degree beams at the following angles:























BEAM




ANT1




ANT2




ANT3




ANT4




ANT5




ANT6




ANT7




ANT8











2L




0




−90




−180  




 +90




0




 −90




−180




+90






1L




0




−45




−90




−135




−180   




+135




 +90




+45






C




0




   0




   0




   0




0




   0




   0




   0






1R




0




+45




+90




+135




+180   




−135




 −90




−45






2R




0




+90




+180  




 −90




0




 +90




+180




−90















FIGS. 5F

,


5


G,


5


H show frequency plots for the antenna in

FIG. 5E

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ. As a person skilled in the antenna design art would appreciate, each plots shows various plot characteristics, including three our plot overlays (i.e. 1L, 1R, CH), three beam peaks in degrees, three beamwidths in degrees, three f/b ratios in dB and four sidelobes in degrees and dBs. In

FIGS. 5F

,


5


G,


5


H, the various “triangles” help to indicate these various plot characteristics.




Space Tapered 90° Multibeam Antenna with Three 30° Beams and Suppressed Side-lobes





FIG. 6A

shows a ninety degree antenna generally indicated as


600


having an 8-way Butler matrix feed network


402


, having a space tapered multibeam antenna


626


with a 1-2-4-4-4-4-2-1 configuration and a horizontal spacing of 0.250 λ, and also having eight cables


604


,


606


,


608


,


610


,


612


,


614


,


616


,


618


with the different cable lengths for connecting the 8-way Butler matrix feed network


602


to the space tapered multibeam antenna


624


to provide twenty two and a half degree phase progression. The ninety degree antenna


600


provides three thirty degree beams.




In effect, the antenna works with the principles used on the original four beam antenna. Instead of four rows of dipoles there are eight rows. When hooked up to an eight way Butler matrix, eight fifteen degree beams are normally formed. For the present invention, the eight rows were squeezed into the space normally occupied by four rows, together with twenty two and a half degree phase progression in the cabling, for providing three thirty degree beams. This gives the antenna a horizontal spacing of 0.250 wavelengths. To get a centered beam, the equally phased cables leading from the Butler to the antenna were replaced with cables having a twenty two and a half degree phase progression. This gives one beam down the middle and one on either side. This could also be done by adding the phase progression directly to the Butler's outputs.




In order to achieve further side-lobe suppression, a space taper technique is used. The eight rows of dipoles do not have an equal number of elements. The 1-2-4-4-4-4-2-1 configuration supplies a side-lobe suppression of −17 dB. This antenna is also much broader banded than the original four beam model. It has a working bandwidth of 280 MHz as opposed to the normal 140 MHz.




The 8-way Butler matrix feed network


602


is known in the art, shown and described with respect to

FIG. 7

of U.S. Pat. No. 5,589,843, and is connected to a radio receiver and/or transmitter (not shown) such as


37


shown in FIG.


1


A. As shown, the 8-way Butler matrix feed network


602


has eight input ports


602




a


,


602




b


,


602




c


,


602




d


,


602




e


,


602




f


,


602




g


,


602




h


. Only three of the eight input ports


602




c


,


602




d


,


602




e


receive antenna input signals from the radio receiver and/or transmitter (not shown). The other five input ports


602




a


,


602




b


,


602




f


,


602




g


,


602




h


are connected via a respective resistor


620


,


621


,


622


,


623


,


625


to electrical ground. In one embodiment, the respective resistors


620


,


621


,


622


,


623


,


625


are 50 ohm resistors, although the scope of the invention is not intended to be limited to any particular resistor value.




The phase progression of the 8-way Butler matrix feed network


602


is as follows:

























ANT1




ANT2




ANT3




ANT4




ANT5




ANT6




ANT7




ANT8
































BEAM 2L




0




−67.5




−135




+157.5




+90




+22.5




 −45




−112.5






BEAM 1L




0




−22.5




 −45




−67.5




−90




−112.5




−135




−167.5






BEAM 1R




0




+22.5




 +45




+67.5




+90




+112.5




+135




+167.5






BEAM 2R




0




+67.5




+135




−157.5




−90




−22.5




 +45




+112.5














As shown, the eight cables


604


,


606


,


608


,


610


,


612


,


614


,


616


,


618


provide eight Butler matrix feed network signals to the space tapered multibeam antenna


624


.




When the cables


604


,


606


,


608


,


610


,


612


,


614


,


616


,


618


have a phase progression of 0, +22.5, +45, +67.5, +90, +112.5, +135, +157.5 together with the phase progression of the Butler matrix, then the ninety degree antenna


600


provides three thirty degree beams at the following angles:























BEAM




ANT1




ANT2




ANT3




ANT4




ANT5




ANT6




ANT7




ANT8











1L




0




−45




−90




−135




−180




+135




+90




+45






C




0




   0




   0




   0




   0




   0




   0




   0






1R




0




+45




+90




+135




+180




−135




−90




−45














The sixty degree antenna


600


also provides a fourth unused beam.





FIGS. 6B

,


6


C,


6


D, show frequency plots for the antenna in

FIG. 6A

respectively at frequencies of 1.850 GHz, 1.920 GHz and 1.990 GHZ. As a person skilled in the antenna design art would appreciate, each plot shows various plot characteristics, including three plot overlays (i.e. 1L, 1R, CH), three beam peaks in degrees, three beamwidths in degrees, three f/b ratios in dB and four sidelobes. In

FIGS. 6B

,


6


C,


6


D, the various “triangles” help to indicate these various plot characteristics.




The suppressed side-lobe ninety degree antenna has side-lobe suppression better than −17 dB. The outer beams do not have the gain drop off associated with the one hundred twenty degree antenna as shown in the frequency plots in

FIGS. 6B

,


6


C,


6


D.




The prior art space tapered one hundred twenty degree antenna having four thirty degree beams suffers from high side-lobe levels that do not meet the customer specification of being below −10 dB from the beam peak. Also, the outer beams suffer from a drop in gain as compared to the inner beams. See frequency plots in

FIGS. 1C

,


1


D,


1


E which show these problems. The normal ninety degree antennas with four rows of dipoles have side-lobe suppression of −12 dB as shown in

FIGS. 1C

,


1


D,


1


E.




A normal antenna with half wavelength spacing between the dipoles would have eight usable beams. Due to the compressed spacing, only four beams are usable. Also, half of the feedlines are on the back side of the reflector. This means the feedlines on the front side of the reflector are two half wavelengths long. For proper side-lobe suppression, an antenna needs to have feedlines which are an even number of half wavelengths long.




The ninety degree antenna


600


can be used wherever the original four beam antenna is used.





FIG. 7

illustrates the layout of the microstrip printed circuit board implementation of a Butler matrix feed network


128


used for connection with the antenna


224


shown in FIG.


3


A. The ports


29


are identified with the 4L, 3L, 2L, 1L, 1R, 2R, 3R, 4R notation corresponding to the co-linear array connections with the ports


31


for connection to the radio receiver(s) and/or transmitter(s) having a similar notation.




SCOPE OF THE INVENTION




Accordingly, the invention comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth.




It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.




It is also to be understood that the invention is intended to be claimed in a regular utility application to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.



Claims
  • 1. An antenna, comprising:a radio receiver/transmitter; a Butler matrix feed system coupled to the radio receiver/transmitter by a cable feeding system; a collinear array having rows of radiating elements spaced at ½ λ and being coupled to the Butler matrix feed system; characterized in that either the collinear array has compressed rows of radiating elements spaced apart in a range of ¼ λ to ⅜ λ, where λ is the operating wavelength of the antenna, or the cable feeding system is a phase progression cable feeding system, or a combination of both.
  • 2. A space tapered multi-beam antenna according to claim 1, characterized in that the antenna is a 120° space-tapered antenna having eight compressed rows spaced at ⅜ λ for providing six 20° degree beams.
  • 3. A space tapered multi-beam antenna according to claim 1, characterized in that the antenna is a 120° space-tapered antenna having eight compressed rows spaced at ¼ λ for providing four 30° beams.
  • 4. A space tapered multi-beam antenna according to claim 1, characterized in that the antenna is a 60° space-tapered antenna having eight compressed rows spaced at ⅜ λ and the cable feeding system is a 22 ½° phase progression cable feeding system for providing three 20° beams.
  • 5. A space tapered multi-beam antenna according to claim 1, characterized in that the antenna is a 90° space-tapered antenna having eight compressed rows spaced at ¼ λ and the cable feeding system is a 22 ½° phase progression cabling feeding system for providing three 30° beams.
  • 6. A space tapered multi-beam antenna according to claim 1, characterized in that the antenna is a 90° space-tapered antenna having four rows spaced at ½ λ and the cable feeding system is a 45° phase progression cabling feeding system for providing three 30° beams.
  • 7. An antenna system, comprising:an N by N butler matrix, responsive to X input signals, where X is an integer greater than 1 and less than N, for providing N butler matrix signals; and a multibeam antenna, responsive to the N butler matrix signals, for providing Y multibeam antenna signals, where Y is an integer greater than 1 and less than N.
  • 8. An antenna system according to claim 7,wherein the antenna system has N cables for coupling the N by N butler matrix to the multibeam antenna; and wherein each of the N cables has a different length for providing a phase progression in the N butler matrix signals.
  • 9. An antenna system according to claim 7,wherein the multibeam antenna has N collinear arrays having compressed spacing therebetween.
  • 10. An antenna system according to claim 7,wherein the less than N multibeam antenna signals include N−1 multibeam antenna signals.
US Referenced Citations (3)
Number Name Date Kind
4086598 Bogner Apr 1978 A
5589843 Meredith et al. Dec 1996 A
6072432 Powell et al. Jun 2000 A