SMALL CELL ANTENNA

An antenna structure is disclosed. The antenna structure comprises: a plurality of supports; and a plurality of antennas, each of at least two antennas of the plurality of antennas being mounted on a respective one of the supports; wherein each of the at least two antennas are mounted on a side of their respective supports so as to face away from each other; and wherein at least two of the plurality of supports are laterally displaced from each other along one of their respective edges by a prescribed distance and are arranged to form a prescribed angle between themselves. Multiple ones of the antenna structure may be placed so as to provide full space coverage with sectorization, and some embodiments provide for at least partially overlapping coverage.

TECHNICAL FIELD

This invention relates to cellular wireless communication, and more particularly, to antenna structures for use in small cells.

BACKGROUND

Uniform signal strength is a desired but difficult to achieve characteristic of wireless signals used for communication, especially where the angle of coverage is greater than what a single directional antenna can cover. In this regard, it should be appreciated that when the signal from a directional antenna drops off by3dB from the maximum signal, such a reduced signal level is insufficient to claim that coverage is being provided. The maximum signal typically occurs in the direction straight ahead of the center of the antenna and signal drop off occurs as one moves laterally away from the antenna center.

Attempts by the prior art to achieve such uniform coverage required many antennas and complex arrangements, thus, undesirably, increasing the cost of such prior art wireless systems.

SUMMARY

Certain embodiments disclosed herein include an antenna structure. The antenna structure comprises: a plurality of supports; and a plurality of antennas, each of at least two antennas of the plurality of antennas being mounted on a respective one of the supports; wherein each of the at least two antennas are mounted on a side of their respective supports so as to face away from each other; and wherein at least two of the plurality of supports are laterally displaced from each other along one of their respective edges by a prescribed distance and are arranged to form a prescribed angle between themselves.

Certain embodiments disclosed herein include an antenna structure, comprising: at least two antenna arrangements, wherein each antenna arrangement comprises: two supports; and a plurality of antennas, each of at least two antennas of the plurality of antennas being mounted on a respective one of the supports; wherein each of the at least two antennas are mounted on a side of their respective supports so as to face away from each other; and wherein at least two of the plurality of supports are laterally displaced from each other along one of their respective edges by a prescribed distance and are arranged to form a prescribed angle between themselves; wherein each support of the at least two antenna arrangements has an edge opposite to the edge along which it is displaced from the other supports of the antenna arrangement of which it is a part, and wherein each such opposite edge is arranged to be substantially adjacent to an opposite edge of another one of the antenna arrangements so that the at least two antenna arrangements appear to form a simple polygon.

Other embodiments disclosed herein include an antenna structure, comprising: at least two antenna arrangements, wherein each antenna arrangement comprises: two supports; and a plurality of antennas, each of at least two antennas of the plurality of antennas being mounted on a respective one of the supports; wherein each of the at least two antennas are mounted on a side of their respective supports so as to face away from each other; and wherein at least two of the plurality of supports are laterally displaced from each other along one of their respective edges by a prescribed distance and are arranged to form a prescribed angle between themselves; and wherein at least a portion of another side of each support of each of the at least two antenna arrangements faces at least partly toward a portion of a support of another one of the at least two antenna arrangements.

DETAILED DESCRIPTION

We have recognized that a substantially uniform signal strength may be achieved where the angle of coverage is greater than a single directional antenna can cover using at least two directional antennas mounted on a low-cost support, e.g., made of plastic, where the antennas face away from each other and the supports are displaced from each other laterally and being arranged to have an angle between themselves.

FIG.1shows an azimuthal view of an illustrative embodiment of an antenna structure100employing two directional antennas in the horizontal direction that are arranged to provide uniform coverage over180degrees, in accordance with the principles of the disclosure. Shown inFIG.1are supports101and103which are connected by connector105and on which are mounted, respectively, antennas107and109.

Supports101and103may be made of plastic to keep costs low. However, other materials may be employed, e.g., rubber or metal. Supports101and103should be made of a material capable of withstanding the elements that are expected at the location at which antenna structure100is to be deployed. Supports101and103may each have the same length, width, and thickness. The length of each of supports101and103needs to be sufficient to at least be able to support antennas107and109mounted thereon. The length of each of supports101and103needs to be sufficient to at least be able to support a number of antennas107and109mounted thereon one adjacent to the other, this number being, for example 1, or 2, or 4, or 8. The width of each of supports101and103needs to be sufficient to at least be able to support antennas107and109mounted thereon. The width of each of supports101and103may range, for example, from 1 cm to 20 cm. The thickness of each of supports101and103needs to be sufficient to substantially prevent supports101and103from flexing under the conditions expected at the location at which antenna structure100is to be deployed. As will be readily apparent, the thickness will therefore depend upon the type of material employed to form supports101and103. The thickness of each of supports101and103may range from, for example, 0.5 mm to 1 cm when plastic is employed to form supports101and103.

In some embodiments, antennas107and109may be made separately and then affixed to supports101and103, respectively. In other embodiments, antennas107and109may be formed integral with supports101and103.

One or more of antennas107and109may employ the structure of any of the antennas disclosed in U.S. patent application Ser. No. 17/807,046 filed on Jun. 15, 2022, which is incorporated by reference as if fully set forth herein. However, as a quick overview, note that each of antennas107and109when employing the structure of an antenna disclosed in U.S. patent application Ser. No. 17/807,046 may be realized monolithically, i.e., in single-dielectric printed circuit board (PCB), utilizing three metal layers, “top” metal layer M1, also referred to herein as an antenna element, “intermediate” metal layer M2, also referred to herein as a coupler element, and “bottom” metal layer M3, also referred to herein as the ground plane. Top and bottom as used herein are relative to each other and defined with respect to supports101and103, where bottom is the closest layer to the one of supports101and103on which the antenna is mounted. The metal employed for the metal layers may be copper, e.g., as generally employed for wiring traces and pads in PCBs, in some embodiments.

Note that in some embodiments each of the metal layers M1and M2may be circular in shape. In some embodiments, metal layer M3is typically, but need not be, square or oblong with respect to square, which is referred to herein generally as rectangular. The shape of metal layer M3need not be the same as that of metal layer M1and/or metal layer M2. Also, typically, metal layer M3is larger than either of metal layer M1and metal layer M2.

Generally, antenna element metal layer M1, which is the patch antenna, and coupler element, i.e., metal layer M2may be any polygon that has a symmetry under a 90° rotation around the central axis that goes perpendicular to, and through, metal layers M1, M2, and M3. Illustrative examples of such polygons include a square, a regular octagon, a 4-point star, an 8-point star, and so forth. Also, antenna element metal layer M1and coupler element metal layer M2need not have the same shape, so long as in embodiments where different shapes are employed both antenna element M1and coupler element M2respect the above-noted symmetry requirement. It will be appreciated by those of ordinary skill in the art that the circular shapes shown herein have the highest degree of symmetry.

Between top metal layer M1and intermediate metal layer M2is a dielectric layer of printed circuit board (PCB) and between intermediate metal layer M2and bottom metal layer M3is another dielectric layer of PCB. In various embodiments, the dielectric layers are made of the same dielectric material but they each have a different thickness as will be explained further hereinbelow. In an embodiment, a Rogers Corporation, now owned by Dupont, RO4003C low-loss dielectric or a standard FR4 PCB containing ISOLA FR408 dielectric may be employed, where FR4 is a National Electrical Manufacturers Association (NEMA) grade designation for glass-reinforced epoxy laminate material and where “FR” stands for “Flame Retardant”. The number “4” indicates a type 4 woven-glass-reinforced epoxy resin.

In various embodiments, as suggested above, top metal layer M1is employed as a patch antenna element and is fabricated on top of a PCB. Intermediate metal layer M2operates as a coupler that couples signal for transmission from at least one of radio frequency (RF) feeding ports of the antenna structure to the antenna element without conductive direct contact, i.e., an electrical connection, to the antenna element, and hence may be referred to herein as a coupler. Bottom metal layer M3is the ground, i.e., the ground plane, of the antenna. As noted, intermediate metal layer M2is conductively connected to at least one of the feeding ports by a respective one of vertical vias V. At least one of the feeding ports is fed the signal to be transmitted by antenna structure, e.g., from respective coaxial cables, not shown, in the conventional manner.

Each signal is then transported from its one of the feeding ports by a respective one of vias V to the coupler, i.e., intermediate layer M2. Each of antennas107and109may have two vias, each one for a different polarization. Corresponding respective feeding ports, i.e., feeding ports located in the same relative position in one of antennas107and109, are considered as a group. One group may be designated to contain the odd feeding ports while the other group may be designated to contain the even feeding ports.

Supports101and103are displaced from each other by distance D and are held in position by connector105. Illustrative values of D are about 1 cm. It is desirable that D be smaller than the wavelength of the center frequency employed, i.e., λ, divided by 2, e.g., λ/2. D is measured at the closest point of the two antennas. In addition, supports101and103are maintained at an angle A, which may be in the range of between 60 and 90 degrees. Parameters D and A determine generally how wide the coverage is as well as how uniform it is.

The arrangement ofFIG.1is said to have two antennas placed in a 2×1 setup, the notational convention being the Y-Z plane is horizontal with X the vertical axis.

FIG.2is a top view of the structure shown inFIG.1.

FIG.3shows a trimetric view of an illustrative embodiment of an antenna structure300in which four antennas107-1to107-4are mounted on support101and four antennas109-1to109-4are mounted on support103. Such an arrangement may be said to have eight antennas placed in a 2×4 setup, again, the notational convention being the Y-Z plane is horizontal with X the vertical axis. The vertical axis, i.e., elevation, is along the X-axis.

Antennas107-1to107-4and antennas109-1to109-4typically would have the same structure. For example, any of the antenna structures disclosed in U.S. patent application Ser. No. 17/807,046 filed on Jun. 15, 2022 maybe employed.

FIG.4is a top view of antenna structure300ofFIG.3.

FIG.5shows three-dimensional profile500of the total gain 3-D radiation pattern in true shape, logarithmic scale, of antenna array structure300at a center frequency of 3.5 GHz, with the even numbered ports firing, i.e., being supplied with a signal for transmission, in-phase while the odd-numbered ports are inert. The maximum gain, broadside, is 10.28 dBi.

FIG.6shows a polar plot of the radiation gain pattern in dBi on two principal planes with only the even feeding ports being supplied with a signal for transmission, i.e., firing, and no signal being supplied to the odd feeding ports, i.e., being inert. More specifically,FIG.6shows the radiated gain pattern cuts in dBi on two principal planes, the X-Z and the Y-Z planes ofFIG.3, with only even feeding ports being supplied with a signal for transmission and no signal being supplied to the odd feeding ports.

The plot is for half-space coverage, and in particular in the azimuth angle range from −90 degrees to +90 degrees.

The gain obtained from the electric field component directed along the X-axis are GX (θ, φ=0°) for the X-Z cut and GX (θ, φ=90°) for the Y-Z cut. These are very much suppressed. On the other hand, the gain obtained from the electric field component directed along the Y-axis which is GY (θ, φ=0°) for the X-Z cut and GY (θ, φ=90°) for the Y-Z cut, are the ones accounting for the total gain. The electromagnetic radiation emitted from antenna structure300is also very highly linearly polarized, with curves633and634ofFIG.6showing the gain obtained from the electric field component directed along the Y-axis accounting for the total gain of the system.

For pedagogical purposes, the two independent polarizations have been chosen to be along the directions X and Y ofFIG.3. As will be appreciated by those of ordinary skill in the art, the two independent polarizations may be aligned along two different mutually orthogonal directions that are rotated by an angle φ0 relative to the antenna structure300by rotating the antenna structure300by an angle φ0 with respect to the fixed coordinate system ofFIG.1.

FIG.7shows an illustrative embodiment of an antenna structure700which employs a pair of antenna structures100, i.e.,100-1and100-2to achieve a full space coverage. There are four horizontal antennas, and the per-pair coverage is about 180 degrees, so that antenna structure700can be used in order to cover 360 degrees with two sectors, each covering 180 degrees.

FIG.8shows an illustrative embodiment of an antenna structure800which employs four of antenna structures100, i.e.,100-1to100-4to achieve a full space coverage, i.e., 360 degrees. There are eight horizontal antennas, and the per-pair coverage is about 90 degrees with another 90 degrees coverage overlapping redundantly with the corresponding coverage of adjacent pairs. Thus, antenna structure800can be used in order to cover 360 degrees with four sectors, each covering 90 degrees and providing redundant adjacent overlapping coverage.

FIG.9shows an illustrative embodiment of an antenna structure900which employs three of antenna structures100, i.e.,100-1to100-3to achieve a full space coverage. There are six horizontal antennas, and the per-pair coverage is about 120 degrees with another 60 degrees coverage overlapping redundantly with the corresponding coverage of adjacent pairs. Thus, antenna structure900can be used in order to cover 360 degrees with three sectors, each covering 120 degrees and providing redundant adjacent overlapping coverage.

The foregoing merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope.

As used herein, the phrase “at least one of” followed by a listing of items means that any of the listed items can be utilized individually, or any combination of two or more of the listed items can be utilized. For example, if a system is described as including “at least one of A, B, and C,” the system can include A alone; B alone; C alone;2A;2B;2C;3A; A and B in combination; B and C in combination; A and C in combination; A, B, and C in combination;2A and C in combination; A,3B, and2C in combination; and the like.