# Patent

## Title
Multi-function array for access point and mobile wireless systems

## Abstract

A multi-function array is described where several communication system functions are realized using the same antenna architecture. An array of antenna elements where each antenna element can generate multiple radiation patterns is described; the multiple radiation patterns from each antenna element provides increased capability and flexibility in generating a phased array, a MIMO antenna system, a receive diversity antenna system, as well as direction finding feature by way of an interferometer function provided by one or multiple elements. The small volume attributes of the antenna elements populating the array lend this technique to mobile wireless devices as well as access points.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. Ser. No. 13/612,833, filed Sep. 13, 2012, titled “MULTI-FUNCTION ARRAY FOR ACCESS POINT AND MOBILE WIRELESS SYSTEMS;
which is a continuation in part (CIP) of U.S. patent application Ser. No. 13/029,564, filed Feb. 17, 2011, titled “ANTENNA AND METHOD FOR STEERING ANTENNA BEAM DIRECTION”,
which is a CON of U.S. patent application Ser. No. 12/043,090, filed Mar. 5, 2008, titled “ANTENNA AND METHOD FOR STEERING ANTENNA BEAM DIRECTION”, now U.S. Pat. No. 7,911,402, issued Mar. 22, 2011;
the contents of each of which are hereby incorporated by reference.


BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to wireless communications; and more particularly to antenna arrays for integration with access points, wireless mobile devices, and communication systems, to service a multitude of functions including phased arrays, multiple input multiple output (MIMO), receive diversity, and direction finding.
Related Art
There is a current need for improved connectivity at cellular and data transmission bands for mobile wireless devices and access points to accommodate the increasing demand for data rates for mobile wireless systems. Improved antenna performance, such as increased efficiency, will translate into increased data rates. Another effective method of improving data rates is to increase the signal to interference plus noise ratio (SINR); the antenna system can significantly improve SINR by increasing directivity. Directivity can be improved by arraying multiple antennas together to form an array. This arraying of antennas increases the effective aperture of the antenna resulting in a more directional beam. The directional antenna radiation pattern or beam can be utilized to direct the signal to the desired direction of communication, or conversely point the antenna radiation pattern in the direction for desired reception. As the antenna radiation pattern narrows, increased transmission and reception in the direction of the main beam is realized, while decreased transmission and reception in other directions is reduced. A resulting improvement in SINR from this narrowing of the antenna beam is realized.
An additional benefit from arraying antenna elements together is the ability to change radiation pattern shape of the array by changing the number of antennas that are combined, or by introducing amplitude and or phase shifts in the feed lines used to connect and combine the various antenna elements together. Changing the radiation pattern of the antenna system during communications provides the ability to improve the communication link quality by optimizing the array pattern; this optimization can take the form of fine tuning the direction of the maxima of the radiation pattern, or can be implemented by increasing the number of antennas connected to increase the directivity of the antenna system. An additional benefit from modifying the radiation pattern can be realized by forming a null in the array pattern and then steering the null in the direction of an interfering source. This will result in improved SINR.
Recent developments in the art have provided for steering of antenna radiation characteristics as is described in commonly owned U.S. Pat. No. 7,911,402 titled “ANTENNA AND METHOD FOR STEERING ANTENNA BEAM DIRECTION”, and issued Mar. 22, 2011; the contents of which are hereby incorporated by reference.
More recently, “beam steering antennas” have evolved toward applications for correcting situations where a wireless device may enter a location having little to no signal reception, otherwise known in the art as a “null” or “null field”. When the device enters a null, the beam steering mechanism activates to steer antenna radiation characteristics into a useable state or mode. More specifically, these Modal antennas are adapted with two or more modes of operation, wherein each mode exhibits unique radiation characteristics across the uniform antenna structure.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates typical antenna connection topologies for four different antenna systems: MIMO, array, receive diversity, and direction finding
FIG. 2 illustrates an array of Modal antenna elements.
FIG. 3 illustrates a modal antenna, wherein an Isolated Magnetic Dipole (IMD) antenna element is shown with two parasitic elements, a first parasitic positioned within the volume of the IMD antenna which is used for frequency adjustment, and the second parasitic which is offset from the IMD antenna and is used to alter the current mode on the IMD antenna.
FIG. 4 illustrates a two element array of Modal antennas in a wireless device.
FIG. 5 illustrates an M element array of Modal antennas in a wireless device.
FIG. 6 illustrates a three element array of Modal antennas in a wireless device.
FIG. 7 illustrates an M element array of Modal antennas in a wireless device.
FIG. 8 illustrates a three element array of Modal antennas in a wireless device.
FIG. 9 illustrates an M element array of Modal antennas in a wireless device.
FIG. 10 illustrates a three element array of Modal antennas in a wireless device.
FIG. 11 illustrates two basic combining circuit topologies to connect multiple Modal antennas to a transceiver port.
FIG. 12 illustrates a combining circuit configured to allow the four individual antenna elements to be accessed in the transceiver or for two, three, or four of the antenna elements can be combined for use by the transceiver.
FIG. 13 illustrates a practical realization of a two element Modal array.
FIG. 14A shows a modal antenna in accordance with embodiments.
FIG. 14B shows the frequency characteristics associated with the modal antenna of FIG. 14A.
FIGS. 14(C-D) show two distinct radiation patterns associated with the modal antenna of FIG. 14A.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This patent describes an antenna system comprising an array of antenna elements, wherein one or more of the antenna elements is adapted to generate multiple unique radiation patterns. The Modal antenna described in U.S. Pat. No. 7,911,402 titled “ANTENNA AND METHOD FOR STEERING ANTENNA BEAM DIRECTION” is an example of an antenna adapted to generate several unique radiation patterns from a single antenna structure. By combining one or several Modal antennas into an array configuration several novel features come to light. For example, an array of modal antennas provides the ability to increase the number of unique radiation beams that can be generated by the array. The combining circuit or “feed circuit” of an array along with the number of antenna elements populating the array will define the number of unique beams that can be generated. The introduction of Modal antennas which possess N unique radiation modes will significantly increase the number of unique radiation beams.
In one embodiment of the present invention, the array can be configured to provide a unique receive diversity solution where one or both receive radiation patterns are generated by combining radiation patterns from multiple arrayed Modal antennas. This additional flexibility of arraying elements together to form receive diversity patterns provides reduced correlation and increased isolation between pairs of elements. Using the array to steer the radiation pattern of one or both antennas in the receive diversity scheme provides the ability to reduce the time one or both antennas are situated in a “null” or reduced signal level region. Steering the radiation pattern will point the array beam in a direction of impinging radiation being scattered into the beam to reduce or eliminate the null region.
In another embodiment of the present invention, the array can be configured to provide multiple antenna patterns for a multiple input multiple output (MIMO) application where one or more radiation patterns are generated by combining radiation patterns from multiple arrayed Modal antennas. The use of and combination of Modal antennas to form combined radiation patterns can be used to improve MIMO antenna system performance by selecting modes of specific Modal antennas and combining or arraying modal antennas to reduce a correlation coefficient between the antennas in the MIMO system, as well as increase isolation between pairs of antennas in the system. Improved signal to interference plus noise ratio (SINR) per channel will result when beam forming is provided for one or more MIMO antennas.
FIG. 14A illustrates a modal antenna in accordance with the '402 patent, where an antenna 50 is comprised of an ISOLATED MAGNETIC DIPOLE (IMD) radiating element 51, which is situated above a ground plane 56 forming an antenna volume therebetween, a first parasitic element 52 (steering conductor) that is coupled with an active element 53, and a second parasitic tuning element 54 (tuning conductor) that is coupled with a second active element 55. In this exemplary embodiment, the active elements 53 and 55 may comprise two state switches that either electrically connect (short) or disconnect (open) the parasitic elements to the ground. The antenna 50 can advantageously provide the frequency splitting and beam steering capabilities and a frequency shifting capability. FIG. 14B illustrates the frequency characteristic 59 associated with the exemplary embodiment of antenna 50 shown in FIG. 14A in three different states. The first state is illustrated as frequency characteristic 57 of a simple IMD radiating element, obtained when both parasitic elements 52 and 54 are open, leading to a resonant frequency f0. The second state is illustrated as frequency shifted characteristic 58 associated with antenna 50 of FIG. 14A, obtained when second parasitic element 54 is shorted to ground through switch 55, leading to a resonant frequency f3. The third state is illustrated as a double resonant frequency characteristic 59 with resonant frequencies f4 and f0, obtained when both parasitic elements 52 and 54 are shorted to ground through switches 53 and 55. This combination enables two different modes of operation, but with a common frequency, f0. As such, operations such as beam switching and/or null-filling may be readily effected using the exemplary configuration of FIG. 14A. It has been determined that the null-filling technique produces several dB signal improvement in the direction of the null. FIG. 14C illustrates the radiation pattern 60 at frequency f0 associated with the antenna 50 of FIG. 14A in the third state (all short), which exhibits a ninety-degree shift in direction as compared to the radiation pattern 61 of the antenna 50 of FIG. 14A in the first state (all open) (shown in FIG. 14D). Such a shift in radiation pattern may be readily accomplished by controlling (e.g., switching) the antenna mode through the control of parasitic element 52, using the active element 53. By providing separate active tuning capabilities, the operation of the two different modes may be achieved at the same frequency.
In another embodiment, two or more antennas in the array can be used to generate an interferometer for determining angle of arrival (AOA) of incoming signals. The receive phase from two or more antennas in the system can be analyzed to discern AOA, wherein additional beams are available for use due to the use of Modal antennas in the antenna system, along with the ability of combining two or more antennas in the system in an array for one or more of the elements required for the interferometer.
Now turning to the drawings, FIGS. 1(A-D) describe current and future requirements for antenna systems in communication devices, including: (i) high directivity beams for high data rate communications; (ii) receive diversity function; (iii) MIMO function; (iv) interference suppression capability; and (v) direction finding. Current solutions describe antenna systems that can typically only address one or two of the four required or desired antenna functions. Typical antenna connection topologies are shown for four different antenna systems: multi-element array for smart antenna function; multiple elements for MIMO function; two antenna system for receive diversity function; and for interference suppression, multiple antenna elements required. More functionality per antenna element is needed to overcome current limitations.
FIG. 2 illustrates an array of Modal antenna elements. Four Modal antennas are shown in a mobile wireless device configuration; alternately the Modal antennas can be integrated into fixed communication devices such as access points, with an access point with two Modal antennas shown. Each Modal antenna can generate multiple radiation patterns, with N modes shown in this example. Thus, “M” Modal antennas with “N” modes per antenna provides: (i) MN array beams for phased array function; (ii) multiple mode combinations for receive diversity function; (iii) M element MIMO antenna system with variable patterns; and (iv) M element interferometer for direction finding function.
FIGS. 3(A-C) show the configuration and operation of a Modal antenna described in the '402 patent. An Isolated Magnetic Dipole (IMD) antenna is shown with two parasitics, one within the volume of the IMD antenna which is used for frequency adjustment, and the second parasitic which is offset from the IMD antenna and is used to alter the current mode on the IMD antenna. As shown in FIG. 3A, the second parasitic is used to tune the antenna frequency to f3 when shorted to ground. Now, when the first parasitic is shorted to ground the resonances occure at f4 and f0 (same frequency as with both parasitics open). As shown in FIG. 3B, when both first and second parasitics are disconnected from the ground plane (both in “OFF” state) a specific radiation pattern “A” is generated. When both parasitics are connected to the ground plane (both in “ON” state) a second unique radiation pattern “B” is generated. Two different radiation patterns at the same frequency f0 are achieved. FIG. 3C shows a plot of frequency vs. return loss for each state of the antenna.
FIG. 4A illustrates a two element array of Modal antennas in a wireless device, including Modal Antenna 1, and Modal Antenna 2. Each Modal antenna has two unique radiation patterns. A combination of the two Modal antennas in the array will generate four unique radiation patterns or modes. Additional radiation patterns can be generated using the array by applying phase shifts to the various antenna elements to steer the array radiation pattern. FIG. 4B shows unique radiaitn omodes for the two-element array of Modal antennas prior to phase shifting to beam steer (22=4 modes).
FIG. 5A illustrates an M element array of Modal antennas in a wireless device. Each Modal antenna has N unique radiation patterns or modes. A combination of the M Modal antennas in the array will generate MN unique radiation patterns or modes. Additional radiation patterns can be generated using the array by applying phase shifts to the various antenna elements to steer the array radiation pattern. FIG. 5B shows MN unique radiation modes for M element arrat of Modal antennas with N modes prior to phase shifting to steer beam.
FIG. 6A illustrates a receive diversity configuration with three antenna elements configured in a three element array of Modal antennas in a wireless device. Each Modal antenna has two unique radiation patterns or modes. Twenty eight combinations of pairs of radiation patterns can be generated to provide a two antenna receive diversity function. For the twenty eight combinations of patterns some patterns are from single antenna elements and some are generated by combining two antennas together into a two element array. FIG. 6B shows a table of example mode configurations for twenty eight unique radition pattern pairings for a two antenna receive diversity scheme using three modal antennas with two modes for each modal antenna.
FIG. 7A illustrates an M element array of Modal antennas in a wireless device in accordance with a receive diversity configuration. Each of “M” Modal antennas has “N” unique radiation patterns. A plurality of combinations of pairs of radiation patterns can be generated to provide a two antenna receive diversity function. For the plurality of combinations of patterns some patterns are from single antenna elements and some are generated by combining two antennas together into a two element array. FIG. 7B shows a table of possible configurations for a plurality of unique radiation pattern pairings in a two antenna receive diversity scheme using “M” modal antennas with “N” modes each.
FIG. 8A illustrates a three element array of Modal antennas in a wireless device in a three antenna MIMO configuration. Each Modal antenna has two unique radiation patterns. Twenty eight (28) combinations of pairs of radiation patterns can be generated to provide a two antenna Multiple Input Multiple Output (MIMO) function. For the 28 combinations of patterns some patterns are from single antenna elements and some are generated by combining two antennas together into a two element array. FIG. 8B shows a table of configurations for twenty eight unique radiation pattern pairings of a two antenna MIMO scheme using three modal antennas with two modes per modal antenna.
FIG. 9A illustrates an M element array of Modal antennas in a wireless device in accordance with an M antenna MIMO configuration. Each Modal antenna has N unique radiation patterns. A plurality of combinations of radiation patterns can be generated to provide a multi-antenna Multiple Input Multiple Output (MIMO) function. For the plurality of combinations of patterns some patterns are from single antenna elements and some are generated by combining two or more antennas together into a multi-element array. FIG. 9B shows a table illustrating a plurality of unique radiation pattern combinations for A×B antenna MIMO scheme using “M” modal antennas with “N” modes each.
FIG. 10 illustrates a three element array of Modal antennas in a wireless device in accordance with an interferometer configuration. Each Modal antenna has three unique radiation patterns or modes. The amplitude and phase data for each mode for each antenna is stored in a processor and can be retrieved and used to determine the angle of arrival (AOA) of an incoming RF signal. Standard processing of received phase to discern angle of arrival can be performed. The amplitude characteristics of the radiation patterns can be used to improve accuracy of the phase processing.
FIGS. 11(A-B) illustrate two basic combining circuit topologies to connect multiple Modal antennas to a transceiver port. One topology, as shown in FIG. 11A, shows a switch assembly between the antenna elements and the combiner to allow for individual antenna elements to be accessed for a MIMO, receive diversity, or interferometer function. The combining circuit provides single beam antennas for MIMO and Rx diversity. Note the separate array port. A second topology, as shown in FIG. 11B, shows the antenna elements connected to a phase shifter assembly and then connected to a combiner/switch assembly. The combining circuit in this topology provides single beam antennas for MIMO and Rx diversity.
FIG. 12 illustrates a combining circuit configured to allow the four individual antenna elements to be accessed in the transceiver or for two, three, or four of the antenna elements can be combined for use by the transceiver. The combining circuit provides ability to mix single element and combined elements into “N” port transceiver.
FIG. 13A illustrates a practical realization of a two element Modal array. Two IMD antennas along with pairs of parasitics elements for frequency adjustment and mode altering are included. The two IMD antennas are connected to a combining circuit which in turn is connected to the port of a transceiver. FIG. 13B shows the radiation patterns of one antenna only, or a combination radiation pattern of two antennas according to the embodiment of FIG. 13A.
In one embodiment, an antenna system comprises: two or more antennas; and a combining circuit. One or more of the antennas comprises a modal antenna capable of generating two or more unique radiation patterns. The one or more modal antennas comprises an antenna radiator disposed above a ground plane and forming an antenna volume there between, a tuning conductor positioned within the antenna volume, the tuning conductor attached to a first active element for varying a reactance of the antenna; and a steering conductor positioned outside of said antenna volume and adjacent to the antenna radiator, the steering conductor attached to a second active element for varying a current mode thereon. The combining circuit is configured to feed two or more of the antennas in the antenna system simultaneously, providing an array. Multiple antenna beams are formed by selecting combinations of radiation patterns from individual antennas forming the array.
In one embodiment, the combining circuit is capable of selecting two radiation patterns from the antenna array to provide a receive diversity capability. One or both of the radiation patterns can be the resultant pattern from combining two or more antennas in the array.
In another embodiment, the combining circuit is capable of selecting two or more antennas to be used simultaneously for a Multiple Input Multiple Output (MIMO) system. One or more of the radiation patterns can be the resultant pattern from combining two or more antennas in the array.
In another embodiment, a multi-function array is described where several communication system functions are realized using the same antenna architecture. An array of antenna elements where each antenna element can generate multiple radiation patterns is described; the multiple radiation patterns from each antenna element provides increased capability and flexibility in generating a phased array, a MIMO antenna system, a receive diversity antenna system, as well as direction finding feature by way of an interferometer function provided by one or multiple elements. The small volume attributes of the antenna elements populating the array lend this technique to mobile wireless devices as well as access points.
In yet another embodiment, one or more of the antennas is capable of generating two or more unique radiation patterns. The phase of the individual patterns of two or more of the antennas is monitored during reception of an electromagnetic (EM) wave. A look-up table stored in a processor is used to determine the angle of arrival of the incoming EM wave by comparing phase of the received signals from the antennas.
In certain embodiments, a tuning conductor is not required.
The active tuning elements may comprise a switch, FET, MEMS device, or any component that exhibits active capacitive or inductive characteristics such as a tunable capacitor or tunable inductor, or any combination of these components.

## Claims

1. An antenna system, comprising:
a first active modal antenna, the first active modal antenna including: a first antenna radiating element disposed above a circuit board forming an antenna volume therebetween, a first parasitic element positioned adjacent to the first antenna radiating element and outside of said antenna volume, said first parasitic element coupled with a first active tuning element adapted to vary a current mode associated with the first parasitic element;
a second antenna; and
a combining circuit;
said combining circuit configured to feed said first and second antennas simultaneously forming an antenna array;
wherein said antenna system is adapted to form multiple antenna beams by varying antenna patterns of at least one of said first and second antenna.

2. The antenna system of claim 1, wherein said combining circuit is configured to select multiple antenna patterns of the array for providing receive diversity capability.

3. The antenna system of claim 1, wherein said combining circuit is configured to select said first and second antennas for use with multi input multi output (MIMO) functions.

4. The antenna system of claim 1, comprising three or more antennas.

5. The antenna system of claim 4, wherein at least one of said antennas is an active modal antenna adapted to generate two or more independent radiation modes.

6. The antenna system of claim 1, comprising memory containing a lookup table and stored data, wherein phase is monitored for each of said first and second antennas during reception, and the lookup table stored in memory is analyzed to determine an angle of arrival by comparing phase of the received signals.

7. The antenna system of claim 1, wherein said active tuning element is individually selected from the group consisting of: a switch, FET, MEMs device, tunable capacitor, and a tunable inductor.

8. An antenna system, comprising:
a first active modal antenna, the first active modal antenna including: a first antenna radiating element disposed above a circuit board forming an antenna volume therebetween, a first parasitic element positioned adjacent to the first antenna radiating element and outside of said antenna volume, said first parasitic element coupled with a first active tuning element adapted to vary a current mode associated with the first parasitic element, a second parasitic element positioned within the antenna volume and coupled with a second active tuning element adapted to adjust a reactance associated with the second parasitic element, said first active modal antenna being selectable between one of a plurality of possible antenna modes, wherein the first active modal antenna comprises a distinct radiation pattern in each of said plurality of possible modes;
a second antenna; and
a combining circuit;
said combining circuit configured to feed said first and second antennas simultaneously forming an antenna array;
wherein said antenna system is adapted to form multiple antenna beams by varying antenna patterns of at least one of said first and second antenna.

9. The antenna system of claim 8, wherein the combining circuit is configured to feed two or more of the antennas in the antenna system simultaneously, the two or more of the antennas forming an antenna array.

10. The antenna system of claim 9, wherein the antenna system is configured to form one or more antenna beams by selecting combinations of radiation patterns from each of the antennas forming the antenna array.

11. The antenna system of claim 9, wherein the combining circuit is configured to select two radiation patterns from the antenna array to provide a receive diversity capability.

12. The antenna system of claim 11, wherein one or both of the radiation patterns can be the resultant pattern from combining two or more of the antennas in the antenna array.

13. The antenna system of claim 8, where the combining circuit is capable of selecting two or more of the antennas to be used simultaneously for a Multiple Input Multiple Output (MIMO) function.

14. The antenna system of claim 8, wherein one or more of the antennas is capable of generating two or more unique radiation patterns, the antenna system is configured to monitor a phase of each radiation pattern of the antennas during reception of an electromagnetic (EM) wave; a look-up table stored in a processor is used to determine the angle of arrival of the incoming EM wave by comparing phase of the received signals from the antennas.

15. The antenna system of claim 8, wherein said active tuning elements are individually selected from the group consisting of: a switch, FET, MEMs device, tunable capacitor, and a tunable inductor.