Abstract:
A horizontally polarized antenna array allows for the efficient distribution of RF energy into a communications environment through selectable antenna elements and redirectors that create a particular radiation pattern such as a substantially omnidirectional radiation pattern. In conjunction with a vertically polarized array, a particular high-gain wireless environment may be created such that one environment does not interfere with other nearby wireless environments and avoids interference created by those other environments. Lower gain patterns may also be created by using particular configurations of a horizontal and/or vertical antenna array. In a preferred embodiment, the antenna systems disclosed herein are utilized in a multiple-input, multiple-output (MIMO) wireless environment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation-in-part of U.S. patent application Ser. No. 11/041,145 filed Jan. 21, 2005 now U.S. Pat. No. 7,362,280 and entitled “System and Method for a Minimized Antenna Apparatus with Selectable Elements,” which claims the priority benefit of U.S. provisional patent application No. 60/602,711 filed Aug. 18, 2004 and entitled “Planar Antenna Apparatus for Isotropic Coverage and QoS Optimization in Wireless Networks” and U.S. provisional patent application No. 60/603,157 filed Aug. 18, 2004 and entitled “Software for Controlling a Planar Antenna Apparatus for Isotropic Coverage and QoS Optimization in Wireless Networks”; the present application also claims the priority benefit of U.S. provisional patent application No. 60/753,442 filed Dec. 23, 2005 and entitled “Coaxial Antennas with Polarization Diversity.” The disclosures of the aforementioned applications are incorporated herein by reference. 
   This application is related to U.S. provisional patent application No. 60/865,148 filed Nov. 9, 2006 and entitled “Multiple Input Multiple Output (MIMO) Antenna Configurations,” the disclosure of which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to wireless communications and more particularly to antenna systems with polarization diversity. 
   2. Description of the Related Art 
   In communications systems, there is an ever-increasing demand for higher data throughput and a corresponding drive to reduce interference that can disrupt data communications. For example, in an Institute of Electrical and Electronics Engineers, Inc. (IEEE) 802.11 network, an access point such as a base station may communicate with one or more remote receiving nodes such as a network interface card over a wireless link. The wireless link may be susceptible to interference from other access points and stations (nodes), other radio transmitting devices, changes or disturbances in the wireless link environment between the access point and the remote receiving node and so forth. The interference may be such to degrade the wireless link by forcing communication at a lower data rate or may be sufficiently strong as to completely disrupt the wireless link. 
   One solution for reducing interference in the wireless link between the access point and the remote receiving node is to provide several omnidirectional antennas in a ‘diversity’ scheme. In such an implementation, a common configuration for the access point includes a data source coupled via a switching network to two or more physically separated omnidirectional antennas. The access point may select one of the omnidirectional antennas by which to maintain the wireless link. Because of the separation between the omnidirectional antennas, each antenna experiences a different signal environment and each antenna contributes a different interference level to the wireless link. The switching network couples the data source to whichever of the omnidirectional antennas experiences the least interference in the wireless link. 
   One problem with using two or more omnidirectional antennas for the access point is that typical omnidirectional antennas are vertically polarized. Vertically polarized radio frequency (RF) energy does not travel as efficiently as, for example, horizontally polarized RF energy inside an office or dwelling space. To date, prior art solutions for creating horizontally polarized RF antennas have not provided adequate RF performance to be commercially successful. 
   SUMMARY OF THE INVENTION 
   The gain of an antenna is a passive phenomenon as antennas conserve energy. Power is not added by an antenna but redistributed to provide more radiated power in a certain direction than would be transmitted by, for example, an isotropic antenna. Thus, if an antenna has a gain of greater than one in some directions, the antenna must have a gain of less than one in other directions. High-gain antennas have the advantage of longer range and better signal quality but require careful aiming in a particular direction. Low-gain antennas have shorter range but antenna orientation is generally inconsequential. 
   With these principles in mind, embodiments of the present invention allow for the use of both vertically and horizontally polarized antenna arrays. The horizontally polarized antenna arrays of the present invention allow for the efficient distribution of RF energy into a communications environment through, for example, selectable antenna elements, reflectors and/or directors that create and influence a particular radiation pattern (e.g., a substantially omnidirectional radiation pattern). In conjunction with the vertically polarized array, a particular high-gain wireless environment may be created such that one wireless environment does not interfere with other nearby wireless environments (e.g., between floors of an office building) and, further, avoids interference created by the other environments. 
   One embodiment of the present invention provides for an antenna system. The antenna system may be a multiple-input and multi-output (MIMO) antenna system. The antenna system includes a plurality of horizontally polarized antenna arrays coupled to a vertically polarized antenna array. Each polarized array may be coupled to a different radio. The vertically polarized antenna array may generate a radiation pattern substantially perpendicular to a radiation pattern generated by one of the horizontally polarized antenna arrays. The horizontally polarized antenna arrays may include antenna elements selectively coupled to a radio frequency feed port. 
   In some embodiments, the radiation pattern generated by one of the horizontally polarized antenna arrays is substantially omnidirectional and substantially in the plane of the horizontally polarized antenna array when a first and second antenna element are coupled to the radio frequency feed port. In some embodiments, the horizontally polarized antenna array may include a reflector or director to restrain or otherwise influence the radiation pattern generated by the antenna elements coupled to the radio frequency feed port. In other embodiments, one or more of the antenna elements include loading structures that slow down electrons and change the resonance of the antenna elements. The antenna elements, in one embodiment, are oriented substantially to the edges of a square shaped substrate. In another embodiment, the antenna elements are oriented substantially to the edges of a triangular shaped substrate. 
   Some embodiments of the present invention may implement a series a parasitic elements on an antenna array in the system. At least two of the elements may be selectively coupled to one another by a switching network. Through the selective coupling of the parasitic elements, the elements may collectively operate as a reflector or a director, whereas prior to the coupling the elements may have been effectively invisible to an emitted radiation pattern. By collectively operating as, for example, a reflector, a radiation pattern emitted by the driven elements of an array may be influenced through the reflection back of the pattern in a particular direction thereby increasing the gain of the pattern in that direction. 
   In some embodiments of the present invention, the radio frequency feed port of the horizontally polarized antenna array is coupled to an antenna element by an antenna element selector. The antenna element selector, in one embodiment, comprises an RF switch. In another embodiment, the antenna element selector comprises a p-type, intrinsic, n-type (PIN) diode. 
   In one embodiment of the antenna system, the horizontally polarized antenna arrays are coupled to the vertically polarized antenna array by fitting the vertical array inside one or more rectangular slits in the printed circuit board (PCB) of the horizontal arrays. Connector tabs on the vertical array may be soldered to the horizontal arrays at the one or more rectangular slits in the PCBs of the horizontal arrays. 
   In another embodiment of the presently disclosed antenna system, the horizontal and vertically polarized antenna arrays may be coupled by a PCB connector element. A portion of the PCB connector element may fit inside the one or more rectangular slits formed within the PCB of the horizontally polarized antenna array. A connector tab on the PCB connector element may be soldered to the horizontally polarized array at a rectangular slit. The PCB connector may also be soldered to the vertically polarized antenna array. For example, soldering may occur at a feed intersection on the PCB of the horizontal and/or vertical arrays and/or the PCB connector. A zero Ohm resistor placed to jumper the RF trace may also be used to effectuate the coupling. 
   A still further embodiment of the present invention discloses an antenna system that includes horizontally polarized antenna arrays with plural antenna elements configured to be selectively coupled to a radio frequency feed port. A substantially omnidirectional radiation pattern substantially in the plane of the horizontally polarized antenna arrays is generated when a first antenna element and a second antenna element of the plurality of antenna elements are coupled to the radio frequency feed port. The system further includes vertically polarized antenna arrays coupled to the horizontally polarized antenna arrays. The vertically polarized antenna arrays generate a radiation pattern substantially perpendicular to a radiation pattern generated by the plurality of horizontally polarized antenna arrays. 
   In one alternative embodiment, each of the horizontally polarized antenna arrays are coupled to one of the vertically polarized antenna arrays by fitting each one of the vertically polarized antenna arrays inside a rectangular slit formed within the printed circuit board of one of the horizontally polarized antenna arrays. In another alternative embodiment, each of the horizontally polarized antenna arrays are coupled to one of the vertically polarized antenna arrays by fitting a portion of a printed circuit board connector element inside a rectangular slit formed within the printed circuit board of one of the horizontally polarized antenna arrays. Each of the vertically polarized antenna arrays are soldered to a printed circuit board connector element at a connector tab. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an exemplary dual polarized, high-gain, omnidirectional antenna system in accordance with an embodiment of the present invention. 
       FIG. 2A  illustrates the individual components of antenna system as referenced in  FIG. 1  and implemented in an exemplary embodiment of the present invention including a vertically polarized omnidirectional array, two horizontally polarized omnidirectional arrays, and a feed PCB. 
       FIG. 2B  illustrates an alternative embodiment of the antenna system disclosed in  FIG. 1 , which does not include a feed PCB. 
       FIG. 3  illustrates an exemplary vertically polarized omnidirectional array as may be implemented in an embodiment of the present invention. 
       FIG. 4A  illustrates a square configuration of a horizontally polarized antenna array with selectable elements as may be implemented in an exemplary embodiment of the present invention. 
       FIG. 4B  illustrates a square configuration of a horizontally polarized antenna array with selectable elements and reflector/directors as may be implemented in an alternative embodiment of the present invention. 
       FIG. 4C  illustrates an exemplary antenna array including both selectively coupled antenna elements and selectively coupled reflector/directors as may be implemented in an alternative embodiment of the present invention. 
       FIG. 4D  illustrates a triangular configuration of a horizontally polarized antenna array with selectable elements as may be implemented in an alternative embodiment of the present invention. 
       FIG. 4E  illustrates an exemplary set of dimensions for one antenna element of the horizontally polarized antenna array shown in  FIG. 4A  and in accordance with an exemplary embodiment of the present invention. 
       FIG. 5  illustrates a series of low-gain antenna arrays in accordance with alternative embodiments of the present invention. 
       FIG. 6  illustrates a series of radiation patterns that may result from implementation of various embodiments of the present invention. 
       FIG. 7  illustrates plots of a series of measured radiation patterns with respect to a horizontal and vertical antenna array. 
       FIG. 8  illustrates exemplary antenna structure mechanicals for coupling the various antenna arrays and PCB feeds disclosed in various embodiments of the present invention. 
       FIG. 9  illustrates alternative antenna structure mechanicals for coupling more than one vertical antenna array to a horizontal array wherein the coupling includes a plurality of slots in the PCB of the horizontal array. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates an exemplary dual polarized, high-gain, omnidirectional antenna system  100  in accordance with an embodiment of the present invention. Any reference to the presently disclosed antenna systems being coaxial in nature should not be interpreted (exclusively) as an antenna element consisting of a hollow conducting tube through which a coaxial cable is passed. In certain embodiments of the antenna systems disclosed herein (such as antenna system  100 ), two horizontal antenna arrays sharing a common axis including a vertical antenna array are disclosed. Such systems are coaxial to the extent that those horizontal arrays share the aforementioned common vertical axis formed by the vertical array although other configurations are envisioned. Notwithstanding, various cabling mechanisms may be used with respect to a communications device implementing the presently disclosed dual polarized, high-gain, omnidirectional antenna system  100  including a coaxial feed. 
   While perpendicular horizontal and vertical antenna arrays are disclosed, it is not necessary that the various arrays be perpendicular to one another along the aforementioned axis (e.g., at a 90 degree intersection). Various array configurations are envisioned in the practice of the presently disclosed invention. For example, a vertical array may be coupled to another antenna array positioned at a 45 degree angle with respect to the vertical array. Utilizing various intersection angles with respect to the two or more arrays may further allow for the shaping of a particular RF emission pattern. 
     FIG. 2A  illustrates the individual components of antenna system  100  as referenced in  FIG. 1  and implemented in an exemplary embodiment of the present invention. Antenna system  100  as illustrated in  FIG. 1  includes a vertically polarized omnidirectional array  210 , detailed in  FIG. 3  below. Antenna system  100  as illustrated in  FIG. 1  also includes at least one horizontally polarized omnidirectional antenna array  220 , discussed in detail with respect to  FIGS. 4A-4D . Antenna system  100  as shown in  FIG. 1  further includes a feed PCB  230  for coupling, for example, two horizontally polarized omnidirectional antenna arrays like array  220 . A different radio may be coupled to each of the different polarizations. 
   The radiation patterns generated by the varying arrays (e.g., vertical with respect to horizontal) may be substantially similar with respect to a particular RF emission pattern. Alternatively, the radiation patterns generated by the horizontal and the vertical array may be substantially dissimilar versus one another. 
   In some embodiments, the vertically polarized array  210  may include two or more vertically polarized elements as is illustrated in detail with respect to  FIG. 3 . The two vertically polarized elements may be coupled to form vertically polarized array  210 . In some embodiments, the vertically polarized array is omnidirectional. 
   Feed PCB  230  (in some embodiments) couples the horizontally polarized antenna arrays  220  like those illustrated in  FIG. 1 . In such an embodiment, the feed PCB  230  may couple horizontally polarized omnidirectional arrays at a feed slot  240  located on horizontal array  220 . In alternative embodiments, the feed PCB  230  may couple each horizontally polarized omnidirectional antenna array  220  at any place on, or slot within, the antenna or supporting PCB. The feed PCB  230  may be soldered to horizontal antenna array  220  at intersecting trace elements in the PCB. For example, an RF trace in the horizontal array may intersect with a similar trace in the vertical array through intersecting of the arrays as discussed, for example, in the context of  FIG. 8 . 
   In some embodiments that omit the aforementioned feed PCB  230 , an intermediate component may be introduced at the trace element interconnect such as a zero Ohm resistor jumper. The zero Ohm resistor jumper effectively operates as a wire link that may be easier to manage with respect to size, particular antenna array positioning and configuration and, further, with respect to costs that may be incurred during the manufacturing process versus, for example, the use of aforementioned feed PCB  230 . Direct soldering of the traces may also occur. While the feed PCB  230  illustrated in  FIGS. 1 and 2A  couples two horizontal antenna arrays  220 , the horizontal arrays  220  may be further coupled or individually coupled to the vertically polarized antenna array  210  or elements thereof utilizing the techniques discussed above and in the context of  FIG. 8 . The coupling of the two (or more) arrays via the aforementioned traces may allow for an RF feed to traverse two disparate arrays. For example, the RF feed may ‘jump’ the horizontally polarized array to the vertically polarized array. Such ‘jumping’ may occur in the context of various intermediate elements including a zero Ohm resistor and/or a connector tab as discussed herein. 
     FIG. 2B  illustrates an alternative embodiment of the antenna system disclosed in  FIG. 1 , which does not include a feed PCB. The embodiment of  FIG. 2B  includes the aforementioned horizontal arrays  220   a  and  220   b  and the vertical arrays  210   a  and  210   b . Instead of utilizing feed PCB  230 , the various arrays may be coupled to one another through a combination of insertion of arrays through various PCB slits as discussed in the context of  FIG. 8  and soldering/jumping feed traces as discussed herein. The inset of  FIG. 2B  illustrates where such array-to-array coupling may occur. 
     FIG. 3  illustrates an exemplary vertically polarized omnidirectional array  210  like that shown in  FIGS. 1 and 2  and including two antenna elements  310  and  320  as may be implemented in an embodiment of the present invention. The vertically polarized omnidirectional antenna elements  310  and  320  of antenna array  210  may be formed on substrate  330  having a first side  340  and a second side  350 . The portions of the vertically polarized omnidirectional array  210  depicted in a dark line  310   a  in  FIG. 3  may be on one side ( 340 ) of the substrate. Conversely, the portions of the vertically polarized omnidirectional array  210  depicted as dashed lines  320   a  in  FIG. 3  may be on the other side ( 350 ) of the substrate  330 . In some embodiments, the substrate  330  comprises a PCB such as FR4, Rogers 4003, or other dielectric material. 
   The vertically polarized omnidirectional antenna elements  310  and  320  of antenna array  210  in  FIG. 3  are coupled to a feed port  360 . The feed port is depicted as a small circle at the base of the vertically polarized omnidirectional array element  310  in  FIG. 3 . The feed port  360  may be configured to receive and/or transmit an RF signal to a communications device and a coupling network (not shown) for selecting one or more of the antenna elements. The RF signal may be received from, for example, an RF coaxial cable coupled to the aforementioned coupling network. The coupling network may comprise DC blocking capacitors and active RF switches to couple the radio frequency feed port  360  to one or more of the antenna elements. The RF switches may include a PIN diode or gallium arsenide field-effect transistor (GaAs FET) or other switching devices as are known in the art. The PIN diodes may comprise single-pole single-throw switches to switch each antenna element either on or off (i.e., couple or decouple each of the antenna elements to the feed port  360 ). 
     FIG. 4A  illustrates a square configuration of a horizontally polarized antenna array  400  with selectable elements as may be implemented in an exemplary embodiment of the present invention. In  FIG. 4A , horizontally polarized antenna array  400  includes a substrate (the plane of  FIG. 4A ) having a first side (solid lines  410 ) and a second side (dashed lines  420 ) that may be substantially parallel to the first side. The substrate may comprise, for example, a PCB such as FR4, Rogers 4003 or some other dielectric material. 
   On the first side of the substrate (solid lines  410 ) in  FIG. 4A , the antenna array  400  includes a radio frequency feed port  430  and four antenna elements  410   a - 410   d . Although four modified dipoles (i.e., antenna elements) are depicted in  FIG. 4A , more or fewer antenna elements may be implemented with respect to array  400 . Further, while antenna elements  410   a - 410   d  of  FIG. 4A  are oriented substantially to the edges of a square shaped substrate thereby minimizing the size of the antenna array  400 , other shapes may be implemented. In some embodiments, the elements may be positioned substantially to the middle or center of the substrate. 
   For example,  FIG. 4D  illustrates a triangular configuration of a horizontally polarized antenna array with selectable elements as may be implemented in an alternative embodiment of the present invention. Each side of the triangular horizontally polarized antenna array may be equal or proportional to a side of the square horizontally polarized antenna array  400  as shown in  FIG. 4A . Other embodiments may implement unequal or otherwise non-proportional sides with respect to the exemplary square configurations illustrated in, for example,  FIG. 4A . The antenna elements on the triangular array, like its square-shaped counterpart, may be positioned substantially to the edge or the middle/center of the array. 
   Returning to  FIG. 4A , although the antenna elements  410   a - 410   d  form a radially symmetrical layout about the radio frequency feed port  430 , a number of non-symmetrical layouts, rectangular layouts, and/or layouts symmetrical in only one axis, may be implemented. Furthermore, the antenna elements  410   a - 410   d  need not be of identical dimension notwithstanding FIG.  4 A&#39;s depiction of the same. 
   On the second side of the substrate, depicted as dashed lines in  FIG. 4A , the antenna array  400  includes a ground component  420 . A portion of the ground component  420  (e.g., the portion  420   a ) may be configured to form a modified dipole in conjunction with the antenna element  410   a . As shown in  FIG. 4A , the dipole is completed for each of the antenna elements  410   a - 410   d  by respective conductive traces  420   a - 420   d  extending in mutually opposite directions. The resultant modified dipole provides a horizontally polarized directional radiation pattern (i.e., substantially in the plane of the antenna array  400 ), as illustrated in, for example,  FIG. 7 . 
   To minimize or reduce the size of the antenna array  400 , each of the modified dipoles (e.g., the antenna element  410   a  and the portion  420   a  of the ground component  420 ) may incorporate one or more loading structures  440 . For clarity of illustration, only the loading structures  440  for the modified dipole formed from the antenna element  410   a  and the portion  420   a  are numbered in  FIG. 4A . By configuring loading structure  440  to slow down electrons and change the resonance of each modified dipole, the modified dipole becomes electrically shorter. In other words, at a given operating frequency, providing the loading structures  440  reduces the dimension of the modified dipole. Providing the loading structures  440  for one or more of the modified dipoles of the antenna array  400  minimizes the size of the antenna array  440 . 
     FIG. 4B  illustrates a square configuration of a horizontally polarized antenna array  400  with selectable elements and reflector/directors as may be implemented in an alternative embodiment of the present invention. The antenna array  400  of  FIG. 4B  includes one or more reflector/directors  450 . The reflector/directors  450  comprise passive elements (versus an active element radiating RF energy) that constrain the directional radiation pattern of the modified dipoles formed by antenna elements  415   a  in conjunction with portions  425   a  of the ground component. For the sake of clarity, only element  415   a  and portion  425   a  are labeled in  FIG. 4B . Because of the reflector/directors  450 , the antenna elements  415  and the portions  425  are slightly different in configuration from the antenna elements  410  and portions  420  of  FIG. 4A . Reflector/directors  250  may be placed on either side of the substrate. Additional reflector/directors (not shown) may be included to further influence the directional radiation pattern of one or more of the modified dipoles. 
   In some embodiments, the antenna elements may be selectively or permanently coupled to a radio frequency feed port. The reflector/directors (e.g., parasitic elements), however, may be configured such that the length of the reflector/directors may change through selective coupling of one or more reflector/directors to one another. For example, a series of interrupted and individual parasitic elements that are 100 mils in length may be selectively coupled in a manner similar to the selective coupling of the aforementioned antenna elements. 
   By coupling together a plurality of the aforementioned elements, the elements may effectively become reflectors that reflect and otherwise shape and influence the RF pattern emitted by the active antenna elements (e.g., back toward a drive dipole resulting in a higher gain in that direction). RF energy emitted by an antenna array may be focused through these reflectors/directors to address particular nuances of a given wireless environment. Similarly, the parasitic elements (through decoupling) may be made effectively transparent to any emitted radiation pattern. Similar reflector systems may be implemented on other arrays (e.g., the vertically polarized array). 
   A similar implementation may be used with respect to a director element or series of elements that may collectively operate as a director. A director focuses energy from source away from the source thereby increasing the gain of the antenna. In some embodiments of the present invention, both reflectors and directors can be used to affect and influence the gain of the antenna structure. Implementation of the reflector/directors may occur on both arrays, a single array, or on certain arrays (e.g., in the case of two horizontal arrays and a single vertical array, the reflector/director system may be present only on one of the horizontal arrays or, alternatively, on neither horizontal array and only the vertical array). 
     FIG. 4C  illustrates an exemplary antenna array including a series of antenna elements that are selectively coupled to a radio feed port. Additionally, the antenna array includes a series of selectively coupled parasitic elements that may collectively operate as, for example, a reflector. Depending on the particular length of the selectively coupled elements, the selectively coupled elements may also function as a director. Selective coupling of both the antenna and parasitic elements may utilize a coupling network and various intermediate elements (e.g., PIN diodes) as discussed above. Through selective coupling control of both antenna and parasitic elements, further control of an RF emission pattern and a resulting wireless environment may result. 
     FIG. 4E  illustrates an exemplary set of dimensions for one antenna element of the horizontally polarized antenna array  400  shown in  FIG. 4A  and in accordance with an exemplary embodiment of the present invention. The dimensions of individual components of the antenna array  400  (e.g., the antenna element  410   a  and the portion  420   a ) may depend upon a desired operating frequency of the antenna array  400 . RF simulation software (e.g., IE3D from Zeland Software, Inc.) may aid in establishing the dimensions of the individual components. The antenna component dimensions of the antenna array  400  illustrated in  FIG. 4E  are designed for operation near 2.4 GHz based on a Rogers 4003 PCB substrate. A different substrate having different dielectric properties, such as FR4, may require different dimensions than those shown in  FIG. 4E . 
   Returning to  FIGS. 4A and 4B , radio frequency feed port  430  (in conjunction with any variety of antenna elements) receives an RF signal from and/or transmits an RF signal to a communication device (not shown) in a fashion similar to that of the feed port  360  illustrated in  FIG. 3 . The communication device may include virtually any device for generating and/or receiving an RF signal. The communication device may include, for example, a radio modulator/demodulator. The communications device may also include a transmitter and/or receiver such as an 802.11 access point, an 802.11 receiver, a set-top box, a laptop computer, an IP-enabled television, a PCMCIA card, a remote control, a Voice Over Internet telephone or a remote terminal such as a handheld gaming device. In some embodiments, the communication device may include circuitry for receiving data packets of video from a router and circuitry for converting the data packets into 802.11 compliant RF signals as are known in the art. The communications device may comprise an access point for communicating to one or more remote receiving nodes (not shown) over a wireless link, for example in an 802.11 wireless network. The device may also form a part of a wireless local area network by enabling communications among several remote receiving nodes. 
   As referenced above, an antenna element selector (not shown) may be used to couple the radio frequency feed port  430  to one or more of the antenna elements  410 . The antenna element selector may comprise an RF switch (not shown), such as a PIN diode, a GaAs FET, or other RF switching devices as known in the art. In the antenna array  400  illustrated in  FIG. 4A , the antenna element selector comprises four PIN diodes, each PIN diode connecting one of the antenna elements  410   a - 410   d  to the radio frequency feed port  430 . In this embodiment, the PIN diode comprises a single-pole single-throw switch to switch each antenna element either on or off (i.e., couple or decouple each of the antenna elements  410   a - 410   d  to the radio frequency feed port  430 ). 
   A series of control signals may be used to bias each PIN diode. With the PIN diode forward biased and conducting a DC current, the PIN diode switch is on, and the corresponding antenna element is selected. With the diode reverse biased, the PIN diode switch is off. In this embodiment, the radio frequency feed port  430  and the PIN diodes of the antenna element selector are on the side of the substrate with the antenna elements  410   a - 410   d , however, other embodiments separate the radio frequency feed port  430 , the antenna element selector, and the antenna elements  410   a - 410   d.    
   In some embodiments, one or more light emitting diodes (LED) (not shown) are coupled to the antenna element selector. The LEDs function as a visual indicator of which of the antenna elements  410   a - 410   d  is on or off. In one embodiment, an LED is placed in circuit with the PIN diode so that the LED is lit when the corresponding antenna element  410  is selected. 
   In some embodiments, the antenna components (e.g., the antenna elements  410   a - 410   d , the ground component  420 , and the reflector/directors  450 ) are formed from RF conductive material. For example, the antenna elements  410   a - 410   d  and the ground component  420  may be formed from metal or other RF conducting material. Rather than being provided on opposing sides of the substrate as shown in  FIGS. 4A and 4B , each antenna element  410   a - 410   d  is coplanar with the ground component  420 . In some embodiments, the antenna components may be conformally mounted to a housing. In such embodiments, the antenna element selector comprises a separate structure (not shown) from the antenna elements  410   a - 410   d . The antenna element selector may be mounted on a relatively small PCB, and the PCB may be electrically coupled to the antenna elements  410 - 410   d . In some embodiments, the switch PCB is soldered directly to the antenna elements  410   a - 410   d.    
   In an exemplary embodiment for wireless LAN in accordance with the IEEE 802.11 standard, the antenna arrays are designed to operate over a frequency range of about 2.4 GHz to 2.4835 GHz. With all four antenna elements  410   a - 410   d  selected to result in an omnidirectional radiation pattern, the combined frequency response of the antenna array  400  is about 90 MHz. In some embodiments, coupling more than one of the antenna elements  410   a - 410   d  to the radio frequency feed port  430  maintains a match with less than 10 dB return loss over 802.11 wireless LAN frequencies, regardless of the number of antenna elements  410   a - 410   d  that are switched on. 
   Selectable antenna elements  410   a - 410   d  may be combined to result in a combined radiation pattern that is less directional than the radiation pattern of a single antenna element. For example, selecting all of the antenna elements  410   a - 410   d  results in a substantially omnidirectional radiation pattern that has less directionality than the directional radiation pattern of a single antenna element. Similarly, selecting two or more antenna elements (e.g., the antenna element  410   a  and the antenna element  410   c  oriented opposite from each other) may result in a substantially omnidirectional radiation pattern. In this fashion, selecting a subset of the antenna elements  410   a - 410   d , or substantially all of the antenna elements  410   a - 410   d , may result in a substantially omnidirectional radiation pattern for the antenna array  400 . Reflector/directors  450  may further constrain the directional radiation pattern of one or more of the antenna elements  410   a - 410   d  in azimuth. Other benefits with respect to selectable configurations are disclosed in U.S. patent application Ser. No. 11/041,145 filed Jan. 21, 2005 and entitled “System and Method for a Minimized Antenna Apparatus with Selectable Elements,” the disclosure of which has previously been incorporated herein by reference. 
     FIG. 5  illustrates a series of low-gain antenna arrays in accordance with alternative embodiments of the present invention. In antenna array  510 , a horizontally polarized omnidirectional array  520  is coupled to two vertically polarized omnidirectional arrays  530   a  and  530   b . The vertically polarized omnidirectional arrays ( 530   a  and  530   b ) may produce a higher gain radiation pattern while the horizontally polarized omnidirectional arrays  520  may produce a lower gain radiation pattern. 
   In antenna array  540 , a feed PCB  550  is coupled to the two horizontally polarized omnidirectional arrays  560   a  and  560   b , which are (in turn) coupled to the one vertically polarized omnidirectional array  570 . The feed PCB  550  and two horizontally polarized omnidirectional arrays  560   a  and  560   b  may produce a higher gain radiation pattern while the vertically polarized omnidirectional array  570  produces a lower gain radiation pattern. 
   In yet another embodiment ( 580 ), a single horizontally polarized omnidirectional array  590  may be coupled to one vertically polarized omnidirectional array  595 . The horizontally polarized omnidirectional array  590  and the vertically polarized omnidirectional array  595  may each produce a lower gain radiation pattern. 
     FIG. 6  illustrates a series of possible radiation patterns that may result from implementation of various embodiments of the present invention. In pattern  610 , a single vertical antenna array  620  emits a low-gain radiation pattern. In pattern  630 , a single horizontal array  640  emits a similar low-gain radiation pattern. A dual vertical array of antenna elements  660   a  and  660   b  emits a higher gain radiation pattern  650  as does a pair of horizontal antenna elements  680   a  and  680   b  coupled by a PCB feed line  690  with respect to pattern  670 . 
     FIG. 7  illustrates plots of a series of measured radiation patterns  700 . For example, plot  710  illustrates exemplary measured radiation patterns with respect to an exemplary horizontal array. By further example, plot  720  illustrates exemplary measured radiation patterns with respect to an exemplary vertical antenna array. 
     FIG. 8  illustrates exemplary antenna structure mechanicals for coupling the various antenna arrays and PCB feeds disclosed in various embodiments of the present invention. Small rectangular slits  810   a - 810   c  may be formed within the PCB of a horizontally polarized omnidirectional array  820 . Similarly, small rectangular slits may be formed within the PCB of a vertically polarized omnidirectional array  830 . The vertically polarized omnidirectional array  830  may fit inside one of the slits  810   c  of the horizontally polarized omnidirectional array  820 . Connector tabs  840   a  of the vertically polarized omnidirectional array  830  may be soldered to connector tabs  840   b  of the horizontally polarized omnidirectional array  820 . In some embodiments, the connector tabs comprise copper. One or more vertically polarized omnidirectional arrays  830  may fit within the horizontally polarized omnidirectional array  820  via the slits  810   a - 810   c . The coupling of the two (or more) arrays via the connector tab (or any other coupling mechanism such as direct soldering) may allow for an RF feed to traverse two disparate arrays. For example, the RF feed may ‘jump’ the horizontally polarized array to the vertically polarized array. 
   One or more feed PCBs  850  may also fit into a small slit  860  within the horizontally polarized omnidirectional array  820 . Specifically, a specifically configured portion  870  of the feed PCB  850  fits within small slit  860 . One or more feed PCBs  850  may be coupled to the horizontally polarized omnidirectional array  820  in this fashion. In other embodiments, one or more feed PCBs  850  may be coupled to the vertically polarized omnidirectional array  830 . The aforementioned connector tab/soldering methodology may also be used in this regard. Similarly, one or more horizontally polarized omnidirectional arrays  820  may be coupled to one or more vertically polarized omnidirectional arrays  830  in any number of ways. Similarly, those skilled in the art will appreciate that the feed PCB  850  may be coupled to one or more horizontally polarized omnidirectional arrays  820  and/or one or more vertically polarized omnidirectional arrays  830 . 
     FIG. 9  illustrates alternative antenna structure mechanicals for coupling more than one vertical antenna array to a horizontal array wherein the coupling includes a plurality of slots in the PCB of the horizontal array. As seen in  FIG. 9 , the horizontal array  910  includes multiple slots  920  for receiving a vertical array  930 . The actual coupling of the horizontal  910  and vertical array  930  may occur in a fashion similar to those disclosed above (e.g., direct soldering at a trace and/or use of a jumper resistor). 
   The embodiments disclosed herein are illustrative. Various modifications or adaptations of the structures and methods described herein may become apparent to those skilled in the art. For example, embodiments of the present invention may be used with respect to MIMO wireless technologies that use multiple antennas as the transmitter and/or receiver to produce significant capacity gains over single-input and single-output (SISO) systems using the same bandwidth and transmit power. Examples of such MIMO antenna systems are disclosed in U.S. provisional patent application No. 60/865,148, which has previously been incorporated herein by reference. Such modifications, adaptations, and/or variations that rely upon the teachings of the present disclosure and through which these teachings have advanced the art are considered to be within the spirit and scope of the present invention. Hence, the descriptions and drawings herein should be limited by reference to the specific limitations set forth in the claims appended hereto.