referring to the drawings , and initially to fig1 a , 1 b , an exploded view of one embodiment of a multi - beam base station antenna system 10 is shown in fig1 a , and its cross - section is shown in fig1 b . in its simplest form , the multi - beam base station antenna system 10 includes one or more linear arrays of radiating elements 20 a , 20 b , and 20 c ( also referred to as “ antenna arrays ” or “ arrays ” herein ) and a radio frequency lens 30 . arrays 20 may have approximately the same length with lens 30 . the multi - beam base station antenna system 10 may also include a first compensator 40 , a second compensator 42 , a secondary lens 43 ( shown in fig1 b ), a reflector 52 , radome 60 , end caps 64 a and 64 b , absorber 66 and ports ( rf connectors ) 70 . in description below , azimuth plane is orthogonal to axis of radio frequency lens 30 , and elevation plane is in parallel to axis of lens 30 . in the embodiment shown in fig1 a , 1 b , the radio frequency lens 30 focuses azimuth beams of arrays 20 a , 20 b , and 20 c , changing , for example , their 3 db beam widths from 65 ° to 23 °. in the embodiment shown in fig1 a , 1 b , three linear antenna arrays 20 a , 20 b , and 20 c are shown , but any number and / or shape of arrays 20 may be used . the number of beams of a multi - beam base station antenna system 10 is the same as number of ports 70 of arrays 20 a , 20 b , and 20 c . in fig1 a , 1 b , each of arrays 20 has 2 ports , one for + 45 ° and another for − 45 ° polarization . in operation , the lens 30 narrows the hpbw of the antennas arrays 20 a , 20 b , and 20 c while increasing their gain ( by 4 - 5 db for 3 - beam antenna shown in fig1 ). for example , the longitudinal axes of columns of radiating elements of the antenna arrays 20 a , 20 b , and 20 c can be parallel with the longitudinal axis of lens 30 . in other embodiments , axis of antenna arrays 20 can be slightly tilted ( 2 - 10 °) to axis of lens 30 ( for example , for better return loss or port - to - port isolation tuning ), but axis of an array and axis of lens are still located in the same plane . all antenna arrays 20 share the single lens 30 so each antenna array 20 a , 20 b , and 20 c has their hpbw altered in the same manner . the multi - beam base station antenna system 10 as described above may be used to increase system capacity . for example , a conventional 65 ° hpbw antenna could be replaced with a multi - beam base station antenna system 10 as described above . this would increase the traffic handling capacity for the base station . in another example , the multi - beam base station antenna system 10 may be employed to reduce antenna count at a tower or other mounting location . a cross - sectional view of an assembled multi - beam base station antenna system 10 is illustrated in fig1 b . fig1 b is also illustrating how 3 beams are formed ( beam 1 , beam 2 , beam 3 ). the azimuth position angle of the beams provided by the antenna arrays 20 a , 20 b , and 20 c are shown by dotted lines in fig1 b . preferably , the azimuth angle for each beam will be approximately perpendicular to the reflector of the array 20 . for example , in the embodiment shown in fig1 b , − 10 db beamwidth of each beam is close to 40 ° and the directions of beams are − 40 °, 0 °, 40 °, respectively . one difference of lens 30 compared to known luneberg lenses is its internal structure . as shown in fig1 b , the dielectric constant (“ dk ”) of lens 30 is homogenous , in the contrast with known luneberg lenses which have multiple layers with different dk . a lens 30 having a homogenous dk is generally easier and less expensive to manufacture . also , it can be more compact , having 20 - 30 % less diameter . in one embodiment , a lens having a dk of approximately 1 . 8 and diameter of about 2 wavelengths λ focuses beams and provides azimuth patterns with low sidelobes ( less than − 17 db ), as shown in fig1 and 11 . in the case of an antenna system 10 having three beams , a lens 30 having a diameter of approximately 2 wavelengths and dk = 1 . 9 provides a beam width about 30 % less than an equivalent prior art antenna system including a planar array based on the butler matrix type bfn , as one can see from measured hpbw : it was also confirmed that homogeneous cylindrical lens ( when diameter of lens is 1 . 5 - 5 wavelength in free space ) has about 1 db more directivity compare to multi - layer luneberg lens with the same diameter and compare to predicted by geometric optics . performance of dielectric cylinder in this case can be explained as combination of dielectric travelling wave antenna ( end fire mode ) combined with lens mode ( focusing mode ) of operation . the 1 . 5 - 5 wavelength diameter embodiment is applicable for forming 2 to 10 beams , which includes most of current multi - beam applications for base station antennas . compactness is one of the key advantages of a proposed multi - beam base station antenna system ; the antenna is narrower compared to known multi - beam solutions ( based on luneberg lens or butler matrix ). a conventional luneberg lens is a spherically symmetric lens that has a varying index of refraction inside it . here , the lens 30 is preferably shaped as a circular cylinder ( if , for example , each beam need the same shape ) and is homogeneous ( not multilayer ) as shown in fig1 a and 1 b . alternatively , or additionally , the lens 30 may comprise an elliptical cylinder , which may provide additional performance improvements ( for example , the sidelobes reduction of a central beam ). other shapes may also be used . in some embodiments , the lens 30 may comprise a structure such as the ones described in u . s . patent application ser . no . 14 / 244 , 369 , filed apr . 3 , 2014 , which is hereby incorporated by reference in its entirety . as described in that application , the lens 30 may comprise various segmented compartments to provide additional mechanical strength . the lens 30 may be made of particles or blocks of dielectric material . the dielectric material particles focus the radio - frequency energy that radiates from , and is received by , the linear antenna arrays 20 a , 20 b , and 20 c . the dielectric material may be artificial dielectric of the type described in u . s . pat . no . 8 , 518 , 537 which is incorporated by reference . in one example , the dielectric material particles comprise a plurality of randomly distributed particles . the plurality of randomly distributed particles is made of a lightweight dielectric material . the range of densities of the lightweight dielectric material can be , for example , 0 . 005 to 0 . 1 g / cm 3 . at least one needle - like conductive fiber is embedded within each particle . by varying number / orientation of conductive fibers inside particle , dk can be vary from 1 to 3 . where there are at least two conductive fibers embedded within each particle , the at least two conductive fibers are in an array like arrangement , i . e . having one or more row that include the conductive fibers . preferably , the conductive fibers embedded within each particle are not in contact with one another . base station antennas are subject to vibration and other environmental factors . the use of compartments assists in the reduction of settling of the dielectric material particles , increasing the long term physical stability and performance of the lens 30 . in addition , the dielectric material particles may be stabilized with slight compression and / or a backfill material . different techniques may be applied to different compartments , or all compartments may be stabilized using the same technique . antennas with traditional luneburg cylindrical lenses can suffer from high cross - polarization levels . the use of a isotropic ( homogeneous ) dielectric cylinder can also provide depolarization of the incident em wave based on its geometry ( nonsymmetrical for vertical ( v ) and horizontal ( h ) components of the electric field ). when the em wave crosses a cylinder , polarization along the axis of cylinder (“ vv ”) will have a bigger phase delay than polarization perpendicular to cylinder axis (“ hh ”), causing depolarization . this depolarization can be reduced by constructing a radio frequency lens 30 with dielectric materials having different dk for the vv and hh directions . to compensate for depolarization , the dk for vv polarization must be less than the dk for hh polarization . the difference in dk , may depend on a variety of factors including the size of cylinder and the relationship between beam wavelength and the diameter of the cylinder . in other words , reduction of the naturally occurring depolarization caused by a cylindrically shaped lens 30 can be achieved using anisotropic dielectric materials . similarly , circular polarization can be created , if needed , on the other hand by using anisotropic material to create a difference in phase of 90 °. anisotropic material can be , for example , the dielectric particles having conductive fibers inside described in u . s . pat . no . 8 , 518 , 537 , which is incorporated by reference . by mixing , or arranging , different particles with different compositions and / or shapes , different values of dk in direction of parallel and perpendicular to axis of cylinder can be achieved . for example , an incident wave linearly polarized with polarization +/− 45 ° will have a cross - polarization level of about − 8 db after passing through a dielectric cylinder with a dk of 2 and a diameter of approximately two wavelengths , this level may be unacceptable for certain commercial applications where a cross - polarization level of approximately − 15 db is desired . this increased cross - polarization is occurring because the vv component of the electric field has a phase difference of about − 30 ° compare to the hh component and the elliptical polarization is created with an axial ratio of about 8 db . artificial dielectric particles based on conductive fibers such as those described in u . s . pat . no . 8 , 518 , 537 , which is hereby incorporated by reference in its entirety , have a + 20 ° phase difference between h and v field components ( i . e . a phase difference in the opposite direction ). by mixing regular dielectric with artificial dielectric , phase differences between vv and hh components can be obtained close to 0 ° and antenna cross - polarization can be minimized ( see fig1 ) and spec & lt ;− 15 db can be met in wide frequency band , say 1 . 7 - 2 . 7 ghz . in one embodiment , a mix of approximately 40 % regular dielectric and 60 % artificial dielectrics ( called also in literature left handed material for its unusual characteristic ) are used . other ratios also may be used . referring to fig2 , an exemplary linear antenna array 200 for use in a multi - beam base station antenna system 10 is shown in more detail . the array 200 includes a plurality of radiating elements 210 , reflector 220 , phase shifter / divider 230 , and two input connectors 70 . the phase shifter / divider 230 may be used for beam scanning ( beam tilting ) in the elevation plane . each radiating element 210 includes two linear orthogonal polarization ( slant + 1 - 45 ° 311 , 312 ), as shown in more detail in fig3 c , where 4 equivalent dipoles 313 - 316 are shown forming two orthogonal polarization vectors 311 , 312 . four dipoles 310 are arranged in a square , or in the “ box ”, as shown in fig3 a and supported by feed stalks , as illustrated in fig3 b . the configuration of radiating element 210 and reflector 220 provide a special shape of antenna pattern in the azimuth plane with a close to linear dependence of azimuth beamwidth with frequency . for example , for a three beam antenna shown in fig1 , measured − 3 db beamwidth of radiating element 210 is plotted against frequency in fig4 ( plot 410 ) and vary from 62 ° ( 1 . 7 ghz ) to 46 ° ( 2 . 7 ghz ). as a result of lens 30 , the azimuth beamwidth of the total antenna is stabilized in the frequency band ( see plots 430 for 3 db beamwidth and 420 for − 10 db beamwidth ). as one can see from plot 420 , − 10 db beamwidth is very close to desirable 40 °: 40 +/− 3 ° was measured over 45 % bandwidth ). beam width and beam position stabilization is important for multi - beam antennas to provide appropriate cell coverage . if a radiating element without this specific frequency dependence is used , beam variations of total antenna will be too much , i . e ., − 10 db beamwidth may vary from 30 ° to 50 ° as a function of frequency , and illumination of assigned sector will be very poor . for example , these may be big gaps ( up to 30 db at the highest frequency ) between sectors ( drop signal ) or big overlapping between sectors at lower frequency , which is also not acceptable because of interference . the effect of azimuth beam stabilization over frequency can be explained by fig1 b , where azimuth beamwidth of is written φ for antenna arrays 20 and θ for lens 30 . the radio frequency lens is providing a focusing effect , so φ & gt ; θ . θ is in inverse proportion to frequency f and also in inverse proportion to illuminated lens aperture s : θ = k 1 / fs , where k 1 coefficient depends on amplitude and phase distribution ( see j . d . kraus , antennas , mcgraw - hill , 1988 , p . 846 ), and s = r 2 sin ( φ / 2 ) for beam stabilization , the condition θ ( f 1 )= θ ( f 2 ) should be satisfied , or : sin [( φ ( f 1 )/ 2 ]/ sin [( φ ( f 2 )/ 2 ]= f 2 / f 1 ( 1 ) as one can see from equation ( 1 ), for lensed antenna 10 beam stabilization , linear antennas 20 a , 20 b , 20 c should have azimuth beam width monotonically decreasing with frequency . for small φ , φ ( f 1 )/( φ ( f 2 )≈ f 2 / f 1 , i . e ., azimuth beamwidth of antenna element 210 is in inverse proportion to frequency . this simplified analysis illustrates the importance of the frequency dependence of azimuth beam width of linear antennas 20 . for example , to get maximum gain for lowest frequency , the entire focus area of should be used , or s = d , where d is diameter of lens . it means that for optimal wideband / ultra - wideband performance , a full lens should be illuminated for lowest frequency of bandwidth , and central area for highest frequency . another example using a “ box ” or square radiating element is shown in u . s . pat . no . 6 , 333 , 720 , which is hereby incorporated by reference in its entirety . an array of box - type four dipole radiating elements has monotonically decreasing beamwidth with frequency because array factor is linearly reverse to frequency . when a box style radiating element is used without a lens , the array factor primarily contributes to its achieving significant frequency dependence ( see plot 410 in fig4 ). as shown in fig4 , with proper selection of antenna element ( 4 dipoles arranged in square or box element ), the azimuth beamwidth of the lensed antennas can be stabilized ( plots 420 , 430 ). furthermore , linear antenna array can have “ box ” elements of different frequency bands , interleaved with each other as shown in u . s . pat . no . 7 , 405 , 710 ( which is incorporated by reference ), where first box - type dipole assembly is coaxially disposed within a second box - type dipole assembly and located in one line . this allows a lensed antenna to operate in two frequency bands ( for example , 0 . 79 - 0 . 96 and 1 . 7 - 2 . 7 ghz ). for similar beam widths of lensed antenna in both bands , central box - type element ( high band element ) should have directors ( fig6 ). in this case , a low band element may have , for example , a hpbw of 65 - 50 °, and a high band element may have a hpbw of 45 - 35 °, and in the result , the lensed antenna will have stable hpbw of about 23 ° ( and beam width about 40 ° by − 10 db level ) across both bands . the multi - beam base station antenna system may include one or more secondary lenses . these secondary lenses 43 can be placed between array 20 a , 20 b , and 20 c and lens 30 for further azimuth beamwidth stabilization , as shown in fig1 b . the secondary lenses may comprise dielectric objects , such as rods 510 and 520 or cubes 530 as shown in fig5 a - 5 c , respectively . other shapes may also be used . as shown in fig6 , directors 610 can be also placed on the top of radiators for further beamwidth stabilization in the wide frequency band . the directors 610 can vary in length , which can be selected , for example , so as to narrow the radiation pattern for the higher frequency band while leaving the radiation pattern in the lower portion of frequency band unchanged . this configuration can result in more a sharp dependence of azimuth pattern of the arrays 20 a , 20 b , and 20 c against frequency . by utilizing a combination of specially selected element 210 shapes , dielectric pieces / secondary lenses 510 , 520 , 530 , and / or directors 610 above array elements 210 , a stable pattern in the very wide frequency band can be provided ( e . g . greater than 50 %). for example , as shown in fig4 , a − 10 db beamwidth for a three - beam antenna 420 is 40 +/− 4 ° in 1 . 7 - 2 . 7 ghz band ( 40 ° is optimal for sector coverage ). in prior art , this beamwidth can vary from 28 - 45 °, which is not acceptable for cell sectors because too narrow beams can lead to drop signals in beam - crossing directions , and wide beams )(& gt ; 45 ° can lead to undesirable interference between sectors due to overlapping . as shown in fig8 , the use of a cylindrical lens significantly reduces grating lobes ( and other far sidelobes ) in the elevation plane ( compare plot 810 is for antenna without lens , and plot 820 for the same antenna with lens ). typically , 5 db grating lobe reduction was observed for 3 - beam antenna shown in fig1 . the 5 db grating lobe reduction is correlated with 5 db gain advantage of lensed antenna fig1 against original linear arrays 20 . the grating lobe &# 39 ; s improvement is due to the lens focusing the main beam only and defocusing the far sidelobes . this allows increasing spacing between antenna elements . for prior art , the spacing between array elements depends on grating lobe and is selected by criterion : d max / λ & lt ; 1 /( sin θ 0 + 1 ), where d max is maximum allowed spacing , λ — wavelength and θ 0 is scan angle ( see eli brookner , practical phased array antenna systems , artech house , 1991 , p . 4 - 5 ). in lensed antenna , spacing d max can be increased : d max /= 1 . 2 ˜ 1 . 3 [ 1 /( sin θ 0 + 1 )]. so , the lens 30 allows the spacing between radiating elements 210 to be increased for the multi - beam base station antenna system 10 while reducing the number of radiating elements by 20 - 30 % for comparable prior art systems . this results in additional cost advantages for the multi - beam base station antenna system 10 . as shown in fig7 a , compensators 40 and 42 are , in the simplest case , dielectric sheets 710 with certain dielectric constant and thickness . the dk and thickness of the compensator 40 and 42 can be selected for wideband return loss tuning (& gt ; 15 db at ports 70 ) and providing desirable port - to - port isolation between all ports 70 ( usually need & gt ; 30 db ). also , second compensator 42 may also compensate reflection from the outer boundary of lens 30 , for further improvement of port - to - port isolation . compensators 40 and 42 can have a variety of shapes , such as shapes 710 , 720 , 730 , 740 , 750 , and 760 shown in fig7 a - 7 f . alternatively , or additionally , short conductive dipoles ( with length & lt ;& lt ; λ ) may also be used on the surface of compensators 40 and 42 to compensate depolarization of isotropic dielectric cylinder . when an em wave crosses the dipole , maximum phase delay will occur when vector e is parallel to the dipoles and minimum when perpendicular . so , the process of depolarization can be controlled by placing different orientations of wires on compensators 40 and 42 . for example , depolarization of linear polarization can be decreased ( axial ratio & gt ; 20 db ), or , if needed , can be converted to circular ( axial ratio close to 0 db ). for example , compensators 720 and 730 includes short wires printed on a dielectric sheet , as shown in fig7 b and 7 c , respectively ; compensator 720 has lateral wires , 730 has longitudinal wires . referring to fig7 d and 7 e , similar functions for polarization tuning can be achieved with compensators 740 . 750 having slots in the dielectric . in another example , compensator 760 comprises thin dielectric rods , as shown in fig7 f . so , compensators 42 , 40 are used for return loss and port - to - port isolation improvements and ( or ) antenna polarization control . alternatively , or additionally , wires may be disposed on the surface or lens 30 for providing similar benefits . end caps 64 a and 64 b , radome 60 , and tray 66 provide antenna protection . radome 60 and tray 66 may be made as one extruded plastic piece . other materials and manufacturing processes may also be used . in some embodiments , tray 66 is made from metal and acts as an additional reflector to improve antenna back lobes and front - to - back ratio . in some embodiments , an rf absorber ( not shown ) can be placed between tray 66 and arrays 20 a , 20 b , and 20 c for additional back lobes &# 39 ; improvement . the lens 30 is spaced such that the apertures of the antennas arrays 20 a , 20 b , and 20 c point at a center axis of the lens 30 . mounting brackets 53 are used for placing antenna on the tower . in fig8 , radiation patterns of the multi - beam base station antenna system 10 of fig1 is shown , measured in elevation plane ( plot 820 ) for beam tilt 10 ° and d / 2 = 0 . 92 . for comparison , a radiation pattern without a radio frequency lens 30 is shown ( plot 810 ) which has 5 db higher grating lobe . in fig9 , 10 and 11 , radiation patterns of the multi - beam base station antenna system 10 of fig1 are shown , measured in azimuth plane . in fig9 , co - polar ( 910 ) and cross - polar ( 920 ) azimuth patterns are shown for central beam . as one can see from fig9 , good antenna performance is achieved , including low cross - polarization level (& lt ;− 20 db ), low sidelobes (& lt ;− 18 db ) and low back lobes . in contrast , prior art analogous antenna based on classical luneberg has cross - polarization level 10 - 12 db higher . in wireless communications , low cross - polarization of antenna benefits to diversity gain and mimo performance , and reduction of side and back lobes reduce the interference . in fig1 , all three beams are shown together ( 1010 , 1020 , 1030 ). please note that all three beam have the same shape , which is an advantage compared to prior art butler matrix multi - beam solutions , where outer beams are not symmetrical and have different shape and gain compare to central beam . fig1 illustrates a configuration of three multi - beam base station antenna systems of fig1 providing uniform 360 ° cell coverage with low overlap between beams , which is desirable for lte . in fig1 , radio frequency lens 30 has flat top and bottom areas , as it is convenient from mechanical / assembling point of view ( simple flat end cups 64 a , 64 b can be used ). but in some cases , as shown in fig1 , a radio frequency lens 1200 with rounded ( hemispherical ) ends 1210 , 1220 may be used . for simplicity , only one linear array 20 is shown in fig1 , which can be analogous to linear array 20 presented in fig2 . hemispherical lens ends 1210 , 1220 provide additional focusing in elevation plane for edge radiating elements 1230 , 1240 resulting in advantage of obtaining of additional gain δg ≈ 10 log ( 1 + d / l ), [ db ], where d is lens diameter . for a three beam antenna as shown in fig1 , δg ≈ 1 db . configuration of fig1 can be an economically effective way for improving antenna gain , because the additional gain δg is obtained without increasing lengths of arrays 20 and number of their radiating elements . in addition to single band antennas , the dual and / or multiband antennas are in demand . such antennas may include , for example antennas providing ports for transmission and reception in the , 698 - 960 mhz + 1 . 7 - 2 . 7 ghz bands , or , for example , 1 . 7 - 2 . 7 ghz + 3 . 4 - 3 . 8 ghz . use of cylindrical lenses gives good opportunity for creating dual - band multi - beam bsa . a homogeneous cylindrical radio frequency lens works well when its diameter d = 1 . 5 − 6λ ( wavelength in free space ). this is applicable for both bsa dual - band cases mentioned above . a challenge is providing the same the azimuth beamwidth for all bands and all beams . to get this , azimuth beam width of a low band antenna array ( before passing through a radio frequency lens ) should be wider compare to a high band antenna array , approximately in proportion of central frequency ratio between the two bands . in fig1 - 15 , solutions for dual - band antenna arrays ( which are part of multi - beam lensed antenna ) are schematically shown . these dual band arrays contain radiators of 2 different bands and these arrays can be placed around lens in similar way as it is shown in fig1 for single band arrays . in fig1 , lower band ( lb ) radiating elements 1300 and higher band ( hb ) radiating elements 210 are placed in the same line in the center of reflector 1310 . both lb and hb radiating elements are box - type dipole array to provide azimuth beam width monotonically decreasing azimuth beam with increasing of frequency . also , each hb element 210 has directors 610 which help hb azimuth beamwidth to be narrower , than lb azimuth beamwidth . in the result , after passing the radio frequency lens 30 , lb and hb radiation patterns have similar beamwidth ( as it was detailed discussed above ). if , for example , for array 1310 lb azimuth hpbw is 65 °- 75 °, hb can be about 40 °, and the resulting hpbw of multi - beam lensed antenna is about 23 ° in both bands . in fig1 , another dual band array is shown , with another approach for narrowing hb azimuth beam . inside lb element 1300 , single hb element 210 is placed , but between lb elements , a pair of hb elements 1400 are placed . these hb elements 1400 can be , for example , crossed dipoles , as shown in fig1 . by variation of spacing between elements 1400 in azimuth plane , azimuth hb beam can be adjusted to required width , so that beamwidth after passing through the radio frequency lens 30 is of a desired hpbw . in fig1 , one more dual band array is shown . pairs of hb elements 1400 are connected by 1 : 2 power divider 1500 and feedlines 1510 to phase shifter / divider 230 . by variation of spacing between elements 1400 in azimuth plane , azimuth hb beam can be adjusted to required width , for optimal covering of cell sector . while the foregoing examples are described with respect to three beam antennas , additional embodiments including , for example , 1 -, 2 -, 4 -, 5 ,- 6 , n - beam antennas sharing a single lens are also contemplated . additional configurations are also contemplated . so , proposed multi - beam antenna solution , compared to known luneberg lens and butler matrix feed network solutions has reduced cost , has less weight , is more compact and has better rf performance , including inherently symmetrical beams and improved cross - polarization , port - to - port isolation , and beam stability . though the invention has been described with respect to specific preferred embodiments , many variations and modifications will become apparent to those skilled in the art upon reading the present application . for example , the invention can be applicable for radar multi - beam antennas . the invention is therefore that the apprehended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications .