LUNEBURG LENS-BASED SYSTEM FOR MASSIVE MIMO

Disclosed is a system for performing Massive MIMO or Multi-User MIMO using a gradient index sphere (such as a Luneburg Lens). The gradient index sphere may have a plurality of radiators disposed along its outer surface such that each radiator radiates inward toward the center of the sphere so that the sphere focuses the energy from each radiator to form a tight beam. This provides for improved uplink gain for detecting and locating a mobile device within range of the system, and it enables high performance with reduced signal processing required for array-based beamforming.

BACKGROUND

Field of the Invention

The present invention relates to wireless communications, and more particularly, to systems for performing Massive MIMO (Multiple Input Multiple Output) in cellular communications.

Related Art

In order to increase capacity of modern cellular communications systems, techniques and systems have been developed to reuse spectrum resources among multiple mobile devices or UEs (User Equipment). This is done by use of phased array antennas whereby two different UEs (for example) that have sufficient angular separation may each be allocated a single beam. If these beams do not overlap where they engage with their respective UEs, each may transmit and receive using the same spectrum resources. There are two established methods for doing this: Massive MIMO, and Multi-User MIMO.

FIG.1Aillustrates a conventional Massive MIMO scenario100. Conventional Massive MIMO scenario100involves an antenna array105having a plurality of antenna elements110a-n. Each antenna element110a-nhas a respective individual gain pattern115a-n. Within range of antenna array105is a UE120, which is transmitting a pilot tone125that is detected by each of the antenna elements110a-n. Each RF receiver (not shown) coupled to a corresponding antenna element110a-ndetects the pilot tone125with a corresponding amplitude and phase ax∠θx. This occurs for each element a-n. According to conventional beamforming techniques, a processor (not shown) calculates the complex conjugates of the set of amplitudes and phases aa-n∠θa-nand applies those amplitude and phase weights to elements110a-nto form a beam directed toward UE120.

FIG.1Billustrates a resulting beamformed beam130, which is formed by the superposition of each of the individual gain patterns115a-nthat have had their respective amplitudes and phases altered according to the calculated weights based on the complex conjugates of the received amplitude and phase aa-n∠θa-nof pilot tone125.

It will be understood that this process may be repeated with each additional UE (not shown) within range of antenna array105. In this case, each UE may have a dedicated beam. Accordingly, the same spectral resources may be used for each beam for communicating with each UE, enhancing the capacity of the system, provided that the corresponding beams do not overlap to an extent to create excessive noise and therefore limiting the capacity as governed by the Shannon-Hartley Theorem.

FIG.2illustrates a conventional Multi-User MIMO scenario200. As illustrated, antenna array105may be identical to that of scenario100. According to scenario200, predetermined amplitude and phase weights are applied to a plurality of signals applied to each of the elements100a-n. This results in a plurality of individual beams230-236. Given that each beam230-236is the result of a particular pattern of amplitude and phase weights aa . . . n∠θa . . . nfor the corresponding antenna elements110a-n. Accordingly, there need not be a correlation between the number of beams230-236and the number of elements110a-n.

According to conventional Multi-User MIMO procedures (3GPP conventional Beamforming code book1) under scenario200, UE120measures the strength of each beam230-236that it receives and determines which beam has the strongest reception. In the illustrated example, beam233is the strongest, although UE120may also detect and measure beams232and234. Given this information, UE120transmits a response to the base station (not shown) connected to antenna array105that beam233is the strongest. Accordingly, the base station performs necessary processing to only transmit to UE120on beam233. It will be understood that additional UEs (not shown) within range of antenna array105may transmit information to the base station indicating its corresponding strongest received beam among beams230-236.

There are disadvantages to the conventional approaches described above. For example, in scenario100, each antenna element100a-nhas a limited individual gain115a-n. Accordingly, until a beamformed beam130is created based on the complex conjugates of the measured amplitudes and phases of each antenna element110a-n, the pilot tone125received by each antenna element110a-nwill be faint towards the cell edge, i.e., toward the edge of antenna105signal coverage. This may limit the performance and range of antenna array105under conventional Massive MIMO techniques for uplink transmission. Further, in scenario200, under conventional Multi-User MIMO, there is a limited number of precoded beams230-236, each of them having fixed gain patterns. Accordingly, there is a limit to the extent to which spectral resources may be reused among different UEs; and if a UE is located between any given pair of fixed pre-coded beams230-236, then not only may there be interference between adjacent beams, but the quality of the signal received by that UE will be diminished for being at the periphery of whichever beam is used for communication. Additionally, in both scenarios100and200, antenna array105has performance limitations because beams that are increasingly off-axis suffer from a distortion of their beam patterns such that the beam becomes “squashed”: wider with notably reduced gain at wide scan angle, with more energy becoming relegated to the beam's sidelobes further reducing directivity and hence peak gain. Increased sidelobe levels place noise into adjacent beams thereby limiting throughput capacity within that adjacent beam. Accordingly, referring toFIG.2, beams230and236, considered as maximum scan angle beams, will have notably lower gain profile than that of axial beam232. Further, the gain reduction at extreme scan angles, e.g., beams230,231,235and236, is affected by single element pattern gain roll off as a function of angle and the limited number of array elements, typically eight in the azimuth plane. The number of elements is typically limited due to antenna size, cost and weight constraints, giving rise to a performance compromise.

Planar antenna array pattern distortion at extreme scan angles occurs due to factors including the following: first, as illustrated inFIG.7, single element gain drops off at extreme scan angles; and second, the ‘Array Factor’ pattern distortion, shown inFIG.9at extreme scan angles, is a product of limiting the number of antenna array elements. The single element pattern and array factor components are multiplied together, as shown inFIG.8, to give an actual antenna array pattern.

Note, pattern distortion is quantified as the deterioration of typical key parameters such as gain, beamwidths, sidelobes, Front to Back Ratios and cross polarization signal strength. In addition, it is recognized that the single element pattern varies across the planar array face due to mutual coupling effects and therefore using a single element pattern to represent all is a simplification, one which is adequate for this discussion.

FIG.3illustrates an exemplary deployment300of cellular antennas305. Depending on the frequency for which the deployment300was designed, the gain patterns and coverage areas310of each cellular antenna305extend to where they slightly overlap. This provides contiguous coverage and opportunities for UEs (not shown) to engage with two cellular antennas for the purpose of handoff. Under conventional deployments, such as deployment300, the physical spacing of cellular antennas305may be designed for conventional cellular frequencies, such as 1900 MHz. However, with the advent of 5G and CBRS (Citizens Broadband Radio Service), higher frequencies are used, on the order of 3.5 GHz. Given that higher frequencies generally have shorter propagation distances, deploying a conventional antenna array105intended for 3.5 GHz with conventional Multi-User MIMO and Massive MIMO techniques may result in large gaps in coverage between cellular antennas305. This problem becomes exacerbated by the weak individual gain115a-nof antenna elements110a-nof a deployment of conventional antenna arrays105. Relying on traditional antenna arrays105may require deploying additional antenna arrays105to fill the gaps in coverage between cellular antennas305, incurring considerable expense.

Accordingly, what it needed is an improved antenna and system for performing Massive MIMO that does not incur the disadvantages of the conventional approaches discussed above.

SUMMARY OF THE DISCLOSURE

An aspect of the present disclosure involves a method for establishing a link between a base station and a UE (User Equipment), the base station having a plurality of radiators disposed on an outer surface of a gradient index sphere, each radiator configured to generate a unique beam having a corresponding unique boresight. The method comprises simultaneously transmitting a downlink signal on each beam; simultaneously receiving, by a subset of radiators, an uplink signal transmitted by the UE; and implementing beamforming to generate a UE-specific beam using only the subset of radiators.

Another aspect of the present disclosure involves a method for establishing a link between a base station and a UE (User Equipment), the base station having a plurality of radiators disposed on an outer surface of a gradient index sphere, each radiator configured to generate a unique beam having a corresponding unique boresight. The method comprises simultaneously transmitting a downlink signal on each beam; simultaneously receiving, by a subset of radiators, an uplink signal transmitted by the UE; measuring a signal strength corresponding to each received uplink signal; determining if the measured signal strength of one of the received uplink signals has a sufficient strength; and depending on the determining, designating a sole radiator for communication with the UE, the sole radiator corresponding to the uplink signal having a sufficient strength.

Another aspect of the present disclosure involves a method for establishing a link between a base station and a UE (User Equipment), the base station having a plurality of radiators disposed on an outer surface of a gradient index sphere, each radiator configured to generate a unique beam having a corresponding unique boresight. The method comprises simultaneously transmitting a downlink signal on each beam; simultaneously receiving, by a subset of radiators, an uplink signal transmitted by the UE; measuring a signal strength corresponding to each received uplink signal; depending on the determining, designating a second subset of radiators based on their measured signal strength; and implementing beamforming to generate a UE-specific beam using only the second subset of radiators.

Another aspect of the present disclosure involves an antenna for use in a Massive MIMO (Multiple Input Multiple Output). The antenna comprises a gradient index sphere having a diameter; and a plurality of radiators disposed on the gradient index sphere along an azimuthal plane and at an angular spacing, each of the radiators having a corresponding beamwidth, wherein the diameter and the angular spacing are configured whereby the beamwidth of each of the plurality of radiators is substantially uniform and whereby the beamwidth is substantially equal to the angular spacing.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG.4illustrates an exemplary system400, which includes a gradient index sphere (e.g., Luneburg lens)405, on which are disposed a plurality of radiators410a-h. Each radiator410a-his coupled to an RF (Radio Frequency) processor440, which may have an RF processing channel for each radiator410a-h. Each RF processor440may have an individual channel for each radiator410a-h, whereby each channel may include filters, power amplifiers (for transmitting downlink signals), low noise amplifiers (for receiving uplink signals), up/down frequency conversion circuitry, and A/D (analog-to-digital) and D/A (digital-to-analog) converters. The A/D converters convert the analog uplink signals into digital signals for transmission to a digital processor450; and the D/A converters convert downlink digital signals received from the digital processor450. Digital processor450may have one or more processors that implement one or more communication protocol stacks and may in turn be coupled to one or more core networks460via a backhaul connection465. Different implementations of digital processor450and RF processor440are possible and within the scope of the disclosure. For example, digital processor450may be an LTE eNodeB and RF processor440may be a radio remote unit coupled to it over a fronthaul connection470. Alternatively, digital processor450may be a 5G gNodeB and the RF processor440may be a radio remote unit coupled to it over an eCPRI or 7.2× connection470; or digital processor450may be a 5G gNodeB Central Unit (CU) and RF processor may include a 5G gNodeB Distributed Unit (DU) coupled to the CU over an F1 connection470. It will be understood that such variations are possible and within the scope of the disclosure.

For background, a Luneburg lens (e.g., gradient index sphere405) is a sphere having a concentrically-graded refractive index. Gradient index sphere405may have a continuous grading of refractive index from the sphere's center (max. refractive index) to its outer surface (min. refractive index). In an exemplary embodiment, the refractive index at the center of the sphere may be 2.0, and the index at the sphere surface may be 1.19, inclusive of a protective thin shell of dielectric material for physical protection of the lens. It will be understood that variations to these max and min indices are possible, and within the scope of the disclosure. Gradient index sphere405may have a step gradient in refractive index. A Luneburg lens (such as gradient index sphere405) serves to substantially focus and planarize the RF wavefront emitted by each radiator410a-hin response to each radiator410a-hradiating inward toward the spherical center of the gradient index sphere405. As such, each radiator410a-hemits a beam from the gradient index sphere405having a boresight defined by the orientation of the radiator relative to the center of the sphere. As a receiver, gradient index sphere405focuses a received substantially planar wavefront that impinges onto it into an aperture defined by a given radiator410a-h, substantially in reverse of the focusing and planarizing done to transmitted energy and having the same boresight. Further discussion of Luneburg lens configurations and variations may be found in co-owned PCT application PCT/US2019/052930 (publication number WO2020/190331) SPHERICAL LUNEBURG LENS-ENHANCED COMPACT MULTI-BEAM ANTENNA, which is incorporated by reference is if fully disclosed herein.

As illustrated, each radiator410a-hmay independently transmit a dedicated signal that the gradient index sphere405focuses into a corresponding beam415a-h. As illustrated, each radiator410a-hhas a distinct beam415a-hhaving a unique boresight. Although each beam415a-his illustrated as having a beamwidth that is narrower that the diameter of the gradient index sphere405, it will be understood that this is done for the convenience of illustration, and that the width of the beam415a-hmay encompass the diameter of the gradient index sphere405as the energy is focused. Further, the frequency at which a given radiator410a-hradiates and the diameter of gradient index sphere405may dictate the angle of divergence of the corresponding beam415a-has it leaves the surface of the gradient index sphere405. As illustrated, there may be substantially designed consistent overlap between adjacent beams415a-hafter a reasonably short propagation distance from gradient index sphere405. As well as consistent beam overlap, sidelobes may be consistent between beams with minimum change for each beam scan. This minimizes their effect of placing interference into adjacent beams even under large scan angle conditions, thereby enabling consistent channel hardening across the scanned beams within system400. Each beam415a-hmay carry an independent signal to the UEs within its corresponding gain pattern without interference from adjacent beams. In the illustrated example, UE120a, which is within the coverage of beam415c, may communicate with system400independently and without interference from signals propagating in beams415band415d.

Depending on the angular spacing of radiators410a-hon gradient index sphere405, there may be gaps between adjacent beams410a-h. In the example illustrated inFIG.4, UE120bis located in a coverage gap between beams415dand415e. In this case, two or more beams may be combined using known beamforming techniques to create a targeted beam420. In this example, UE120bmay transmit a pilot tone (not shown) like that described above with regard toFIG.1A, and radiators (e.g.,410d/e, or410c/d/e/f) may receive the pilot tone with individual signal amplitudes and phases. These received signals may be coupled to RF processor440and may subsequently be sent to digital processor450. Depending on whether beamforming processing is performed in the analog or digital domain, RF processor440or digital processor450may compute the values of the received signals and use computed weights for applying to the signal to be transmitted by radiators410d-eor410c-f. Depending on the strength of the pilot tone received by radiators410a-h, it may be that only a few radiators410are required for communicating with UE120b. In one example, forming a targeted beam420may only require weighted signal contributions from a subset of radiators, such as radiators410dand410e, or alternatively from radiators410c,d,e,f.

Variations of gradient index sphere405may have different radii as well as a different number of radiators410and angular spacing. Further, gradient index sphere405may have multiple rings of radiators410for azimuth and elevation beam differentiation. Fewer radiators410may be used with more inter-beam beamforming. Alternatively, more radiators410may reduce the angular spacing of the boresights of beams415a-hand thus reduce or eliminate any gaps in coverage between adjacent beams. This may obviate the need for inter-beam beamforming, in which there is sufficient coverage to operate like a Multi-user MIMO, similar to that described above with reference toFIG.2. A smaller gradient index sphere405may be used in locations having space constraints, such as in urban environments or indoor deployments. In this case, more beamforming may be relied upon (still using only a subset of the radiators) to compensate for reduced sphere-based beam focusing. It will be understood that such variations are possible and within the scope of the disclosure.

FIG.5illustrates another exemplary Luneberg lens-based system500for performing Massive MIMO according to the disclosure, in which the beams have greater overlap. This may be done in different ways. For example, gradient index sphere505may have a smaller diameter than that of sphere405. which would increase the width of each beam415a-h; or the angular spacing between radiators410a-hmay be reduced, which would bring adjacent beams510a-hcloser together; or a combination of these two approaches may be used. With the gradient index sphere505being smaller, each resulting beam510a-hmay be broader in gain pattern, leading to greater beam overlap, but also providing coverage such that a given UE120may have a sufficiently strong RF link to a given radiator (410eor410f, in this example) such that beamforming might not be necessary. In this case, the UE may operate in Multi-user MIMO mode, providing a beam index (not shown) to digital processor450, whereby UE120may be solely serviced by one radiator (410eor410f).

Examples of radiators410a-hmay include quad ridge horns, flared-notch radiators, Vivaldi radiators, log-periodic radiators, dipole or patch radiators. Each illustrated radiator410a-hmay be two collocated radiators that operate in orthogonal polarizations, such as +/−45 degrees. In this case, each beam410a-hmay be two concentric beams, each at a different polarization. It will be understood that such variations are possible and within the scope of the disclosure.

FIG.6illustrates an exemplary process600for performing MIMO using system400according to the disclosure. In step605, radiators410a-hsimultaneously and independently radiate their respective beams415a-h. As used herein, ‘simultaneously and independently’ may mean that the beams are not scanned or transmitted at different times in a coordinated manner. The actual signal transmitted on each beam415a-hmay be different or shared among radiators410a-h.

In step610, a subset of the radiators410a-hreceives a signal transmitted by UE120b. In the example scenario illustrated inFIG.4, radiators410dand410ereceive the signal at different signal strengths. The other radiators410a-cand410f-hmay receive no discernable signals from UE120b. Further to step610and the example illustrated inFIG.4, radiator410csolely receives a signal transmitted by UE120avia beam415c.

In step615, the signals respectively received by UE120aand120bare measured by either RF processor440or digital processor450to determine if one of the receiving radiators410d/e(UE120b) or410c(UE120a) is receiving a signal strong enough to have that radiator act solely in establishing a link with the UE. For each UE120a/b, if the signal received by one radiator is sufficiently strong, then (for that UE) process600proceeds to step625. In the illustrated example, the signal from UE120areceived by radiator410cis sufficiently strong. However, if none of the received signals is strong enough on its own (e.g., radiators410d/ereceiving the signal from UE120b), then (for UE120b) process600proceeds to step620.

Step615may be implemented by one or more processors (not shown) associated with either RF processor440or digital processor450. In doing so, the processor(s) may execute machine readable instructions that are encoded within one or more non-transitory memory devices and executed by one or more processors that perform their respective described functions. As used herein, “non-transitory memory” may refer to any tangible storage medium (as opposed to an electromagnetic or optical signal) and refers to the medium itself, and not to a limitation on data storage (e.g., RAM vs. ROM). For example, non-transitory medium may refer to an embedded volatile memory encoded with instructions whereby the memory may have to be re-loaded with the appropriate machine-readable instructions after being power cycled.

In step625, digital processor450executes instructions to designate radiator410aas the sole communication path with UE120a. This may be done in a way substantially similar to that done as described above with reference toFIG.2.

In step620, digital processor450executes instructions to implement beamforming using radiators410dand410e. In doing so, the digital processor450may employ known beamforming techniques like that described above in reference toFIGS.1A and1B. In a variation, more radiators410may be used to form beam420. For example, radiators410c-fmay be employed, but may still be a subset of radiators410a-h. In this step, the digital processor450may measure the received signal strength of each of the subset of radiators, and based on the result of the measuring, may further designate a new subset of radiators410a-hfor beamforming, wherein the new subset of radiators410a-hhave a sufficient received signal strength to properly contribute to a beamforming solution. In doing so, the new subset may be the same as the subset of received signals in step610, or it may include more or fewer radiators. It will be understood that such variations are possible and within the scope of the disclosure.

Process600may be performed by digital processor450for each detected UE, in which case digital processor450may include one or more processors coupled to a non-transitory memory encoded with instructions to perform process600. It will be understood that the action of transmitting in step605and receiving in step610may be performed in part by one or more processors associated with digital processor450, in conjunction with RF processor440and radiators410a-h. As used herein, “non-transitory memory” may refer to any tangible storage medium (as opposed to an electromagnetic or optical signal) and refers to the medium itself, and not to a limitation on data storage (e.g., RAM vs. ROM). For example, non-transitory medium may refer to an embedded volatile memory encoded with instructions whereby the memory may have to be re-loaded with the appropriate machine-readable instructions after being power cycled. Further, if an action is described herein as being done by a referenced component (e.g., digital processor450) it will be understood that this implies a processor of the referenced component executing machine-readable instructions to perform the action. All of the steps of process600that may be implemented in software may be implemented within a software implementation of a 3GPP LTE or 5G protocol stack. In an example, process600may be implemented by software implementing the MAC (Medium Access Control) scheduler function. In doing so, in an LTE eNodeB or 5G gNodeB implementation that employs multiple MIMO layers, it may be possible under the disclosure to use the same set of Resource Elements of each layer's resource grid for different UEs. For example, if system400is communicating with two UEs that are angularly spaced such that each has a distinct subset of corresponding radiators410a-h, then one subset of layers may be dedicated to the first UE and another subset of layers may be dedicated to the second UE, allowing the same set of Resource Elements to be used by the same two UEs.

The system400/500of the disclosure offers the following advantages. For example, the quality of each beam415a-h/510a-his independent of its orientation, providing even and consistent gain performance for the entire coverage area. This is in contrast to a conventional linear or planar phased array, whereby beam quality (and thus connection capacity) diminishes with increasing angle off boresight (i.e., as angle increases from a vector normal to the plane of the array). Further, the system400/500does not rely on scanning, thereby eliminating a source of latency problems. Also, as described above, given that only a subset of radiators410a-h may be needed to communicate with a given UE, power reduction may be achieved by only having to activate a subset of radiators (and they associated amplifiers) to communicate with a given UE. Additionally, given that that only a subset of radiators410a-hmay be needed to communicate with a given UE, multiple UEs may share the same Resource Elements in a multi-layer MIMO implementation, providing simultaneous independent beamforming to two UEs using the same spectrum.

FIG.10illustrates another exemplary antenna configuration1000, which has a plurality of radiators1010angularly spaced around a gradient index sphere1005to provide consistent gain throughout the sector of coverage of antenna1000. Gradient index sphere1005may be similar in construction to gradient index sphere405of system400. The perspective ofFIG.10is looking along the elevation axis of antenna1000.

Antenna1000has twelve radiators1010disposed within its angular range of coverage in azimuth, which in this example is a 120 degree sector. As illustrated inFIG.10, the perspective viewed along the elevation axis, showing radiators1010arrayed in the azimuth plane around the ‘equator’ of gradient index sphere1005. Accordingly, the twelve radiators1010are evenly spaced along the azimuth plane of antenna1000. Exemplary antenna1000is configured for operation in the C-Band (3700-3980 MHz), and radiators1010may be configured to radiate a beam (not shown) with a 10 degree beamwidth. In an exemplary embodiment of antenna1000, gradient index sphere1005may have a diameter (d) of 550 mm, and may have disposed on it C-Band radiators1010that are placed at a regular angular spacing (a) of 10 degrees, which corresponds to a physical spacing of 48 mm along the surface of gradient index sphere1005. As illustrated, the two radiators1010at the ends are designated end radiators1010aand1010b. End radiator1010ais disposed at −60 degrees of azimuth, and end radiator1010bis disposed at +60 degrees azimuth, forming the beams at the cell edges of a 120 degree sector.

As with radiators410a-hof system400, the radiators1010of antenna1000may each have two radiators that are oriented to radiate in two orthogonal polarizations (e.g., +/−45 degrees).

Although not shown, antenna1000may be integrated into system400whereby each of the radiators1010is coupled to RF processor440, digital processor450, and core network460as illustrated inFIG.4.

FIG.11illustrates a partial beam pattern plot1100corresponding to antenna1000. In plot1100, the x-axis is the angular orientation of a subset of radiators1010(and their corresponding beams) as disposed on gradient index sphere1005. Referring toFIGS.11and10, beam1105a, which is oriented (i.e., has an azimuth boresight) at −60 degrees azimuth, corresponds to end radiator1010ainFIG.10. Adjacent beam1105corresponds to the radiator1010that is adjacent to end radiator1010aand has an azimuth boresight of −50 degrees. As illustrated, the next adjacent beam is at −40 degree of azimuth and corresponds to the next radiator1010, etc. Each of the beams1105has a 10 degree angular separation (ref1115), a 10 degree beamwidth, and a peak gain of 25 dBi (25 dBi being typical of current competing technologies but not restricted in this implementation for future requirements) at boresight (−60 degrees for beam1105aand −50 degrees for adjacent beam1105). Accordingly, the beams intersect at their respective 3 dB points in their gain profiles. Accordingly, if two adjacent beams (e.g.,1105aat −60 degrees and1105at −50 degrees) are transmitting the same signal, the gains of the two beams1105/1050sum such that beam1105adominates at −60 degrees azimuth. As azimuth shifts from −60 degrees (to the right along the x-axis), the gain of beam1105afalls off as the gain of adjacent beam1105increases. This summation, depicted by summation line1120, continues until the azimuth reaches −50 degrees, where adjacent beam1105dominates. Throughout this azimuth translation, the sum1120in gain of beams1105aand1105remains constant at 25 dBi.

An advantage of the arrangement in antenna1000is that the gain remains consistent throughout the sector right up to the cell edges at +/−60 degrees. This may be accomplished by having the resources (time and frequency) for a given UE shared between two radiators1010(and thus corresponding adjacent beams1105) while making those resources available to a UE that is within the sector coverage of antenna1000but in a different set of adjacent beams1105.

Variations to antenna1000are possible. For example, antenna1000may be designed to use a different frequency band than C-Band. In this case, the diameter d of gradient index sphere1105may scale accordingly and the radiators1010may have a different specific configuration to operate in the different frequency band. However, the ten degree spacing and ten degree beamwidth may still be used to provide consistent gain across the sector of antenna1000right to the cell edge. It will be understood that such variations are possible and within the scope of the disclosure.