# Patent

## Title
Cellular array with steerable spotlight beams

## Abstract

Cellular array implementations with multiple steerable spotlight beams irradiated from a common aperture are disclosed herein. Such an approach can easily be adapted to suit various geographical population densities and distributions. The array is capable of producing multiple 65-degree cellular coverage beams, which may be used for regular coverage or in MIMO (Multiple Input Multiple Output) mode. The array may also produce multiple steerable beams, or “spotlight” beams. These beams may be relatively narrow and may be steered electronically both in azimuth and elevation directions. By steering the beams in this way, the beams are able to provide cellular services at high-demand “hotspot” regions where high capacity service is required. The spotlight beams may also be used to fill voids or deficiencies caused by regular coverage beams.

## Background
FIELD
The present invention generally relates to the field of antenna arrays. More specifically, the present invention is related cellular array implementations with multiple steerable spotlight beams irradiated from a common aperture.
BACKGROUND
As wireless devices have exploded in popularity, the ability to provide sufficient coverage to more and more users over large areas is more crucial than ever. Current cellular antenna array techniques have reached limiting factors in meeting these demands. As such, there is a growing need to provide wireless coverage with higher capacity in certain regions.
Current standard cellular arrays produce a single azimuth beam with 65-degree or 90-degree beam-width for sectorized cellular coverage. In an urban area, there can exist several densely populated areas, or hot spots, where particularly high capacity of communications are required. In such cases, additional steerable beams with narrow azimuth beam-width can be used to improve capacity in these areas.
One conventional approach for producing several narrow azimuth beams involves use of a Butler matrix with a uniform weight function. However, this approach produces radiation patterns with relatively high sidelobes that waste energy and may cause interference with neighbouring beams. Other approaches use an additional antenna with a relatively large aperture on top of a typical cellular array to produce the narrow beams in a cellular network. This method is undesirable due to limited and expensive real estate on a cellular tower. Furthermore, the narrow beam produced in this manner is often not electronically steerable making this approach only useful in a scenario with fixed geographical density.
SUMMARY
An antenna array architecture is disclosed herein, including multiple rows of discrete radiators. Multiple discrete radiators at the interior of the rows are fed in pair to a first set of hybrid couplers. A first output of the first set of hybrid couplers is fed to a first azimuth phase shifter, and a second output of the first set of hybrid couplers is fed to a second azimuth phase shifter. Radiators at the ends of said rows fed in pair to a second set of hybrid couplers, where a first output of the second set of hybrid couplers at one end of the rows is fed to a first elevation phase shifter to produce a first beam, a first output of the second set of hybrid couplers at another end of the rows is fed to a second elevation phase shifter to produce a second beam, a second output of the second set of hybrid couplers is fed to a third set of hybrid couplers, a first output of the third set of hybrid couplers is fed to the first azimuth phase shifter, and a second output of the third set of hybrid couplers is fed to the second azimuth phase shifter. A third elevation phase shifter is configured to receive the output of the first azimuth phase shifter to produce a third beam, and a fourth elevation phase is configured to receive the output of the second azimuth phase shifter to produce a fourth beam, where the first beam and the second beams are coverage beams for providing service to a large area and the third and fourth beams are spotlight beams for providing high capacity service to a targeted area.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention:
FIG. 1 is an exemplary array architecture of the cellular MIMO array with spotlight beams according to embodiments of the present disclosure.
FIG. 2 is a block diagram illustrating an exemplary feed structure and beam forming configuration of a three-sector cellular MIMO array configuration with spotlight beams according to embodiments of the present disclosure.
FIG. 3 is a diagram of radiation patterns of an exemplary three-sector cellular MIMO array with spotlight beams according to embodiments of the present disclosure.
FIG. 4 is a block diagram of an exemplary orthogonal dual spotlight beam forming scheme according to embodiments of the present disclosure.
FIG. 5 is a graph illustrating an exemplary azimuth radiation pattern of a steerable spotlight beam according to embodiments of the present disclosure.
FIG. 6 is a graph illustrating exemplary azimuth radiation patterns of a 65° coverage beam according to embodiments of the present disclosure.



DETAILED DESCRIPTION
Reference will now be made in detail to several embodiments. While the subject matter will be described in conjunction with the alternative embodiments, it will be understood that they are not intended to limit the claimed subject matter to these embodiments. On the contrary, the claimed subject matter is intended to cover alternative, modifications, and equivalents, which may be included within the spirit and scope of the claimed subject matter as defined by the appended claims.
Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. However, it will be recognized by one skilled in the art that embodiments may be practiced without these specific details or with equivalents thereof. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects and features of the subject matter.
Portions of the detailed description that follows are presented and discussed in terms of a method. Embodiments are well suited to performing various other steps or variations of the steps recited in the flowchart of the figures herein, and in a sequence other than that depicted and described herein.
Some portions of the detailed description are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits that can be performed on computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. A procedure, computer-executed step, logic block, process, etc., is here, and generally, conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a cellular antenna array. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout, discussions utilizing terms such as “accessing,” “writing,” “including,” “storing,” “transmitting,” “traversing,” “associating,” “identifying” or the like, refer to the action and processes of an antenna array or other electronic computing device that manipulates and transforms data represented as physical (electronic) quantities within the system's registers and memories into other data similarly represented as physical quantities within the system memories or registers or other such information storage, transmission or display devices.
Cellular Array with Steerable Spotlight Beams
Cellular array implementations with multiple steerable spotlight beams irradiated from a common aperture are disclosed herein. Such an approach can easily be adapted to suit various geographical population densities and distributions.
According to some embodiments, the array is capable of producing multiple 65-degree cellular coverage beams, which may be used for regular cellular coverage with diversity gain or in MIMO (Multiple Input Multiple Output) mode. The array may also produce multiple relatively narrow steerable beams, or “spotlight” beams. The spotlight beams may be relatively narrow and may be steered (e.g., moved, aimed, or rotated) electronically both in azimuth and elevation directions. By steering the beams in this way, the array is able to provide higher capacity service with greater reliability at high-demand “hotspot” regions where high capacity service is required. The spotlight beams may also be used to fill voids or deficiencies caused by regular coverage beams, for example.
In this way, the cellular arrays of the various embodiments disclosed herein may significantly improve network capacity with MIMO capability for regular cellular services, and the arrays are complemented with multiple steerable beams. The steerable beams may be high-gain and relatively narrow spotlight beam. The antenna beams disclosed in the embodiments herein may be irradiated simultaneously and independently from a common aperture.
It should be noted that the combination of regular cellular beams and spotlight beams result in higher overall aperture efficiency. The various implementation of these array concepts utilizes an orthogonal dual beam former, which allows simultaneous beam forming of multiple coverage beams and spotlight beams using a common aperture. The orthogonal dual beam former allows relatively low-loss integration of regular cellular beams with multiple spotlight beams using simple radio frequency (RF) circuits, resulting in a higher overall aperture efficiency.
The array architecture disclosed herein may be used in a typical three-sector cellular network. The relatively narrow spotlight beams are electronically steerable both in azimuth and elevation directions, independent of the coverage beams. The array contains a plurality of driven radiating elements distributed on a planar aperture. An orthogonal dual beam former is used to allow the radiating elements to be fed simultaneously so that multiple cellular coverage beams and multiple electronically steerable spotlight beams may be produced at the same time from a common aperture.
With regard to FIG. 1, an exemplary multi-beam array architecture 100 is illustrated according to embodiments of the present invention. According to some embodiments, the array has 9 columns and 10 rows of discrete radiators. The radiators may be broadband radiators such as broadband patches or dipoles. Every two rows of radiators (e.g., pairs of rows) may be offset in the azimuth direction by a certain distance (e.g., half of the radiator length) to produce optimal azimuth beam patterns. For example, the first row 101 and second row 102 may be offset from the third row 103 and fourth row 104 in the azimuth direction by half the spacing between elements.
The interior or middle columns are primarily used for forming the two spotlight beams, and the outer or edge columns are shared elements for forming both the 65-degree coverage beams and the spotlight beams. According to some embodiments, the array may produce 2 65-degree coverage beams and 8 spotlight beams for each polarization. According to other embodiments, the array may produce 4 65-degree coverage beams and 16 spotlight beams for two linear polarizations.
With regard now to FIG. 2, an exemplary feed and beam forming structure of a three-sector MIMO configuration with two simultaneous spotlight beams is depicted according to embodiments of the present invention. The general arrangement and interconnections of the radiators is illustrated, where radiators are fed in pair to 90-degree hybrid couplers (e.g., hybrid coupler 205) at each interior column.
Outputs of the 90-degree hybrid couplers are summed at two separate azimuth phase shifters 201 and 200 to form spotlight beams, and radiators at the edge columns are used as shared elements for generating both spotlight beams and coverage beams. Azimuth phase shifter 200 is connected to elevation phase shifter 204, and azimuth phase shifter 201 is connected to elevation phase shifter 203. The radiators at the interior of the rows (e.g., radiator A22) are fed in pair to hybrid couplers which feed one output to azimuth phase shifter 201 and another output to azimuth phase shifter 200. According to some embodiments, the coverage beams formed are 65-degree coverage beams.
The hybrid outputs of the edge column radiators (e.g., radiators 209 and 210) are split between the spotlight beams and the coverage beams. For example, one of the hybrid outputs of the right-most column (e.g., hybrid coupler 211) feeds elevation phase shifter 213 to produce a first 65-degree coverage beam, and the other hybrid output of the right-most column feeds an azimuth phase shifter (e.g., azimuth phase shifter 200) in conjunction with an additional radiator (e.g., radiator 214) and hybrid coupler (e.g., hybrid coupler 208). Similarly, the hybrid output of the left-most column (e.g., hybrid coupler 212) feeds the second spotlight beam and the second coverage beam. Consequently, this array architecture may produce two independent spotlight beams and two independent 65-degree coverage beams within the same aperture for different polarizations.
FIG. 3 illustrates 65-degree coverage beam patterns and associated spotlight beam patterns for an exemplary broadband 3-sector MIMO array according to embodiments of the present invention. According to some embodiments, for each polarization, a narrow beam (e.g., 10° to 14°) is formed for each spotlight beam. In this case, a total of 8 spotlight beams are separated into two groups, with each group consisting of 4 alternating beams as shown in the figures. For example, at any given time, spotlight #1 can be A1, A2, A3, or A4 and Spotlight#2 can be B1, B2, B3, or B4. The frequency of operation typically include both the UMTS and LTE bands ranging from 1710 MHz to 2690 MHz. The beams are dual polarized with +/−45° linear slant polarization and can be used for 4T4R MIMO (>3λ spacing) or gain diversity.
With regard now to FIG. 4, an exemplary orthogonal dual beam forming configuration for producing spotlight beams (e.g., spotlight beam 401) and coverage beams (e.g., coverage beam 402) is illustrated according to embodiments of the present invention. A single column (e.g., column 403) is illustrated, according to some embodiments. As described earlier, rows of beam forming elements are paired together, and pairs of radiators (e.g., radiators 404 and 405) are connected by a 90-degree hybrid coupler (e.g., hybrid 406). Each 0-degree output of the hybrid couplers are fed to a phase shifter (e.g., spotlight phase shifter 408), while each 90-degree output of the hybrids are fed to a coverage phase shifter (e.g., coverage phase shifter 407). As such, two orthogonal beams may be formed simultaneously.
With regard now to FIG. 5, azimuth radiation patterns of exemplary steerable spotlight beams are illustrated according to embodiments of the present invention. The spotlight beams are orthogonal to each other, and the beamwidth of the beams depends on the azimuth size and number of columns in the array. In one planar configuration, the spotlight beam may be steered to approximately ±45° with relatively low azimuth sidelobes (e.g., below −18 dB). Unlike the radiation patterns produced by prior techniques, such as a Butler matrix with uniform weight function, the patterns have relatively low sidelobes due to flexible amplitude taper.
With regard to FIG. 6, azimuth radiation patterns of an exemplary 65-degree coverage beam produced by edge columns for a three-sector MIMO array is illustrated according to embodiments of the present invention.

## Claims

1. An antenna array, comprising:
a plurality of rows of discrete radiators;
a plurality of the discrete radiators at an interior of said rows fed in pair to hybrid couplers, wherein a first output of the hybrid couplers is fed to a first azimuth phase shifter, and a second output of the hybrid couplers is fed to a second azimuth phase shifter;
a plurality of the discrete radiators at ends of said rows to produce a first beam at a first elevation phase shifter, and a second beam at a second elevation phase shifter;
a third elevation phase shifter for receiving an output of the first azimuth phase shifter to produce a third beam; and
a fourth elevation phase shifter for receiving an output of the second azimuth phase shifter to produce a fourth beam,
wherein the first and second beams are coverage beams and the third and fourth beams are steerable spotlight beams for providing service to specific areas.

2. The antenna array of claim 1, wherein the hybrid couplers are 90-degree hybrid couplers.

3. The antenna array of claim 1, further comprising 90-degree hybrid couplers for feeding the first elevation phase shifter, the second elevation phase shifter, the first azimuth phase shifter, and the second azimuth phase shifter.

4. The antenna array of claim 1, wherein gains of the first and second beams are greater than gains of the third and fourth beams.

5. The antenna array of claim 1, wherein the first and second beams are relatively wide.

6. The antenna array of claim 1, wherein the third and fourth beams are narrower than the first and second beams.

7. The antenna array of claim 1, wherein the first and second beam operate in a multiple input multiple output (MIMO) mode.

8. The antenna array of claim 1, wherein the first and second beams are electronically steerable in an elevation direction.

9. The antenna array of claim 1, wherein the third and fourth beams are electronically steerable in azimuth and elevation directions.

10. The antenna array of claim 1, wherein the array is configured to operate in a three-sector cellular network.

11. The antenna array of claim 1, wherein pairs of rows of discrete radiators are offset by a predetermined distance in an azimuth direction.

12. The antenna array of claim 11, wherein the offset distance is roughly half of an element spacing between discrete radiators in an azimuth direction.

13. The antenna array of claim 1, wherein all beams are irradiated from a common aperture.

14. The antenna array of claim 1, wherein the discrete radiators are broadband patch antennas.

15. The antenna array of claim 1, wherein the discrete radiators are broadband dipole antennas.

16. The antenna array of claim 1, further comprising additional discrete radiators at the interior of the rows and additional phase shifters, wherein the additional phase shifters produce fifth, sixth, seventh, and eighth spotlight beams.

17. The antenna array of claim 1, wherein a single polarization is used.

18. The antenna array of claim 1, wherein two polarizations are used.