HORIZONTALLY POLARIZED OMNI-DIRECTIONAL ANTENNA APPARATUS AND METHOD

An Alford antenna array having at least three driven elements disposed on a substrate, a first portion of each driven element being disposed on one side of the substrate, and a second portion of said each driven element being disposed on a second side of the substrate. At least one of the driven elements has a bent-dipole Alford loop coupled to two feed points and has an acute-angle dipole feed point and acute-angle loaded ends. In other embodiments, the driven elements may comprise any combination of bent-dipoles and/or folded-and-bent dipoles. In further embodiments, six dipoles are concentrically disposed about a central point, where three of the dipoles may operate at a different frequency than the other three dipoles.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail because they may obscure the invention in unnecessary detail. The present invention relates to an innovative Alford antenna array that may be coupled to, or integrated with, an Access Point (AP) or other communication device to enhance Wi-Fi and pico-cellular operation with multiple clients in an interference-limited environment. The present invention may find particular utility in strand-mount APs for Tier One cable operators building small-cell networks, such as the BelAir 100NE. Such APs preferably incorporate dual 802.11n-2009 Wi-Fi radios with 3×3 MIMO and 3 spatial stream support. Each AP preferably integrates a DOCSIS® 3.0, Euro-DOCSIS 3.0, or Japanese-DOCSIS 3.0 cable modem.

For this disclosure, the following terms and definitions shall apply:

The terms “IEEE 802.11” and “802.11” refer to a set of standards for implementing WLAN computer communication in the 2.4, 3.6 and 5 GHz frequency bands, the set of standards being maintained by the IEEE LAN/MAN Standards Committee (IEEE 802).

The terms “communicate” and “communicating” as used herein include both conveying data from a source to a destination, and delivering data to a communications medium, system, channel, network, device, wire, cable, fiber, circuit, and/or link to be conveyed to a destination; the term “communication” as used herein means data so conveyed or delivered. The term “communications” as used herein includes one or more of a communications medium, system, channel, network, device, wire, cable, fiber, circuit, and/or link.

The term “omnidirectional antenna” as used herein means an antenna that radiates radio wave power uniformly in all directions within a preferred plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis, thereby producing a doughnut-shaped radiation pattern.

The term “processor” as used herein means processing devices, apparatus, programs, circuits, components, systems, and subsystems, whether implemented in hardware, tangibly-embodied software or both, and whether or not programmable. The term “processor” as used herein includes, but is not limited to, one or more computers, hardwired circuits, signal modifying devices and systems, devices, and machines for controlling systems, central processing units, programmable devices, and systems, field-programmable gate arrays, application-specific integrated circuits, systems on a chip, systems comprised of discrete elements and/or circuits, state machines, virtual machines, data processors, processing facilities, and combinations of any of the foregoing.

The terms “storage” and “data storage” and “memory” as used herein mean one or more data storage devices, apparatus, programs, circuits, components, systems, subsystems, locations, and storage media serving to retain data, whether on a temporary or permanent basis, and to provide such retained data. The terms “storage” and “data storage” and “memory” as used herein include, but are not limited to, hard disks, solid state drives, flash memory, DRAM, RAM, ROM, tape cartridges, and any other medium capable of storing computer-readable data.

The present invention provides a horizontally polarized, omni-antenna with high gain, low spatial ripple, in a planar (flat) design. The preferred embodiments feature folded dipoles and folded, rounded, or straight directors. Preferably, the folded dipoles have an impedance of 300 ohms each, so that three parallel folded dipoles have an impedance of 100 ohms. A transformer circuit is used to match to the RF 50 ohms line.

The folded dipole also gives a highly uniform current distribution across the outward facing portion of the element. The present embodiments preferably have three locations where the back-to-back dipoles fold in on each other, causing a drop in current density. The ripple is quite small, approximately 0.4 dB. In contrast, the Moller device appears to have six locations where the current density will vary, and three of these locations have a small tail so their ripple will be significantly higher. The present invention also contemplates the use of mixed folded or non-folded dipoles with the advantage of minimizing impedance mismatch.

The use of directors and/or reflectors in certain embodiments helps to improve the gain of the antenna. As is known, an antenna may have a reflector and one or more directors. Such a design operates on the basis of electromagnetic interaction between these parasitic elements and the driven element. The reflector element is typically slightly longer than the driven element, whereas the directors are typically somewhat shorter. This design achieves a substantial increase in the antenna's directionality and gain, compared to a simple dipole.

InFIG. 1, a three-driven-element Alford omni-directional antenna array10comprises a first driven element (dipole)12, a second driven element14, and a third driven element16. Each driven element is disposed on opposite sides of a substrate, inFIG. 1, the side1elements121,141, and161, are on the top of the substrate, and the side2elements122,142, and162are on the bottom. Preferably, the driven elements comprise copper (or other suitable metal such as gold, titanium, etc.) deposited on a printed circuit board (PCB) substrate by known PCB-forming techniques such as photo-etching, chemical vapor deposition, etc. The driven elements ofFIG. 1are shaped with bent dipole feed points123,143, and163, and with transmission line loaded ends124,144, and164. In theFIG. 1embodiment, both the feed points and loaded transmission ends are shaped with acute angles. The array ofFIG. 1is useful with 2.4 Ghz cellular telephone signals, and the array will likely be 1-5 inches in diameter, more preferably, 2-4 inches in diameter, and most preferably 3 inches in diameter; although any size may be used depending on the signals to be transmitted/received. As presently conceived, each antenna array according to the present invention will be mounted in a Access Point (AP) enclosure, together with the AP circuitry190. However, for Multiple Input Multiple Output (MIMO) systems two, three, or more antenna arrays may be mounted in each AP enclosure. The antenna arrays may be mounted in different enclosure corners, at different heights, to avoid signal interference. It is also possible that the two or more antenna arrays be stacked on top of one another, again to avoid interference.

One advantage of the three-driven-element Alford antenna array depicted inFIG. 1is that the current distribution around the outer perimeter of the array is more uniform than in the prior art, leading to reduced spatial ripple and higher effective gain. In particular, the present embodiment provides six ripple sections around the perimeter, but the ripple amplitude is lessened, producing a more uniform signal. A beam-strength diagram of theFIG. 1embodiment would show the three signal lobes extending over the dipole feed points123,143, and163, with lower signal-strength areas over the loaded ends124,144, and164.

The feed points181and182are preferably coupled to an RF cable183, which is coupled to control circuitry190having at least one processor191, ROM192, RAM193, transmitter194, receiver195(or, equivalently a transceiver), power supply196, and other not-shown elements such as interfaces, splitters, heating/cooling structures, etc.

FIG. 2shows a three-element, folded-dipole antenna array according to another preferred embodiment. A folded dipole is a half-wave dipole with an additional wire connecting its two ends. If the additional wire has the same diameter and cross-section as the dipole, two nearly identical radiating currents are generated. The resulting far-field emission pattern is nearly identical to the one for the single-wire dipole described above; however, at resonance its input (feed point) impedance is four times the radiation resistance of a single-wire dipole. This is because for a fixed amount of power, the total radiating current is equal to twice the current in each wire and thus equal to twice the current at the feed point. Like inFIG. 1, the dipoles are bent, but inFIG. 2, the dipoles are also folded, leading to a reduces footprint on the PCB: each array having a diameter of 1-2 inches, more preferably 1.5 inches. This smaller size and folded-dipole arrangement produces even lower ripple, trending close to a 1:1 ratio of high-current to low-current around the periphery of the array. The three-element Alford omni antenna array20comprises a first driven element22, a second driven element24, and a third driven element26. Each driven element is disposed on opposite sides of a substrate, inFIG. 2, the side1elements221,241, and261, are on the top of the substrate, and the side2elements222,242, and262are on the bottom. Alford feed points281and282are preferably driven by circuitry coupled via an RF cable. The driven elements ofFIG. 2are shaped with bent dipole feed points223,243, and263. In theFIG. 2embodiment, the feed points are shaped with obtuse angles.

InFIG. 3, a three-element, combined folded-dipole and bent-dipole antenna array30is shown on a planar PCB substrate. WhileFIG. 3depicts one bent-dipole34and two folded dipoles32and36, the array30could comprise two bent-dipoles and one folded-dipole. The use of combined bent and folded-dipoles allows for more accurate impedance-matching of the array. Alford feed points381and382are used to drive the array, as described above.

FIG. 4is a top view of a three-element, folded and rounded dipole antenna array40according to a most preferred embodiment. As withFIG. 1, each dipole42,44, and46is disposed on opposite sides of a planar PCB substrate, with the side1elements421,441, and461on the top of the substrate, and the side2elements422,442, and462on the bottom. InFIG. 4, the “spoke” elements of the bottom layer dipole elements are not shown, as they are occluded inFIG. 4by the top layer “spokes.” The driven elements ofFIG. 4are shaped with bent and rounded dipoles. The dipole feed points423,443, and463, are shown, together with with transmission line loaded ends424,444, and464. The Alford feed points are not shown inFIG. 4, but are centrally-disposed as in the other Figs.

FIG. 5depicts a four-element, folded and rounded dipole antenna array50according to another embodiment. Similar toFIG. 4, each dipole52,54,56, and57is disposed on opposite sides of the PCB substrate, with the top side elements521,541,561, and577and bottom side elements522,542,562, and571. InFIG. 5, the “spoke” elements of the bottom layer dipole elements are not shown, as they are covered by the top layer “spokes” in the Fig. The driven elements ofFIG. 5are shaped with bent and rounded dipoles. The dipole feed points523,543,563, and573are shown, together with transmission line loaded ends524,544,564, and572. The Alford feed points are not shown, but are centrally-disposed. Of course, any number of dipoles could be formed on the planar substrate, depending upon the IEEE 82.11 signal to be transmitted/received, and the particular use for which the antenna array is designed. TheFIG. 5embodiment will provide a higher gain than theFIG. 4embodiment.

FIG. 6shows the four-element, folded and rounded dipole antenna array50shown inFIG. 5, but with rounded directors60coaxially disposed outward of the array50, according to yet another preferred embodiment. The directors are preferably comprised of copper (or other suitable materials) formed on the top and bottom sides of the PCB substrate with known PCB-forming techniques. The top-side director610is disposed outward of the loaded end524, the top-side director612is disposed outward of the loaded end544, the top-side director614is disposed outward of the loaded end564, and top-side director616is disposed outward of the loaded end572. In similar fashion, the bottom-side director620is disposed outward of the feed point523, the bottom-side director622is disposed outward of the feed point543, the bottom-side director624is disposed outward of the feed point563, and the bottom-side director626is disposed outward of the feed point573. Note that the top and bottom-side directors have similar arc lengths, but are overlapped by most of their lengths, as shown inFIG. 6.

FIG. 7depicts two, three-element, folded and rounded dipole antenna arrays70for dual-mode use, according to a further preferred embodiment. The arrays70comprise the three-element array40ofFIG. 4, having an array71coaxially disposed outward of the array40. In use, the array40may transmit/receive 2.4 GHz signals, while the array71may transmit/receive 5.0 GHz signals. As array40was described in detail above, no further description will be provided here. The array71comprises dipoles712,714, and716. As withFIG. 5, the bottom-side “spokes” of these dipoles are not shown in the Figure, for clarity. The dipole712extends through the loaded end424, the dipole714extends through the loaded end444, and dipole716extends through the loaded end464, as shown. The dipoles712,714, and716are constructed similarly to those dipoles described above and will not be further described here. It is sufficient to note that the 5 GHz dipoles are smaller, with a sharper curvature suitable to the higher frequency signal.

FIG. 8depicts two, three-element, folded and rounded dipole antenna arrays80for dual-mode use, similar toFIG. 7, but with the 5 GHz antenna array81disposed coaxially inward of the array40. Thus, dipole812is disposed inward of loaded end424, the dipole814is disposed inward of the loaded end444, and the dipole816is disposed inward of loaded end464. Again, the construction of the dipoles is similar to that described above and will not be further described here.

In this manner, an innovative antenna system according to a preferred embodiments of the present invention has been designed and field-tested to verify functional operation.

While the foregoing detailed description has described particular preferred embodiments of this invention, it is to be understood that the above description is illustrative only and not limiting of the disclosed invention. While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention.