Electronic devices, methods, and computer program products for selecting an antenna element based on a wireless communication performance criterion

A method of operating an electronic device includes providing a plurality of antenna elements, evaluating a wireless communication performance criterion to obtain a performance evaluation, and assigning a first one of the plurality of antenna elements to a main wireless signal reception and transmission path and a second one of the plurality of antenna elements to a diversity wireless signal reception path based on the performance evaluation.

BACKGROUND OF THE INVENTION

Wireless communication devices, such as WIFI 802.11N and LTE compliant communication devices, are increasingly using Multiple Input-Multiple Output (MIMO) antenna technology to provide increased data communication rates with decreased error rates. A MIMO antenna includes at least two antenna elements.

MIMO technology may offer significant increases in data throughput and/or transmission range without the need for additional bandwidth or transmit power. It can achieve this due to the ability of MIMO to obtain higher spectral efficiency (more bits per second per hertz of bandwidth) and/or reduced fading.

MIMO based systems allow the use of a variety of coding techniques that take advantage of the presence of multiple transmit and receive antennas. For example, wireless communications performed over a MIMO channel can use beamforming, spatial multiplexing and/or diversity coding techniques.

The operational performance of a MIMO antenna depends upon obtaining sufficient decoupling and decorrelation between its antenna elements. It is therefore usually desirable to position the antenna elements far apart within a device and/or to use radiofrequency (RF) shielding therebetween while balancing its size and other design constraints.

Correlation between antennas can also be reduced by causing the antennas to have different polarizations, i.e. sending and receiving signals with orthogonal polarizations. Furthermore, antennas for MIMO systems may utilize spatial separation, or physical separation, to reduce correlation between antennas.

Mobile terminals may need to cover multiple-bands in Long Term Evolution (LTE) environments. Antenna systems may, therefore, be required to cover up to seven different frequency bands, for example. In addition, the antenna systems may be required to meet the requirements of Single Input-Single Output (SISO) and Single Input-Multiple Output (SIMO) for 3GPP and 2G bands. The antenna configuration will generally be required to fulfill Specific Absorption Rate (SAR) requirements and other industry standards as well. User effects, such as the way a user holds a mobile terminal relative to the positioning of the antenna elements therein may affect the over the air performance of the device.

SUMMARY

According to some embodiments of the present invention, a method of operating an electronic device includes providing a plurality of antenna elements, evaluating a wireless communication performance criterion to obtain a performance evaluation, and assigning a first one of the plurality of antenna elements to a main wireless signal reception and transmission path and a second one of the plurality of antenna elements to a diversity wireless signal reception path based on the performance evaluation.

In other embodiments, evaluating the wireless communication performance criterion comprises determining transmission power for signals transmitted through each of the plurality of antenna elements and power associated with signals reflected back through each of the plurality of antenna elements.

In still other embodiments, evaluating the wireless communication performance criterion comprises determining Received Signal Strength Indication (RSSI) data for each of the plurality of antenna elements.

In still other embodiments, evaluating the wireless communication performance criterion comprises processing feedback from a wireless basestation, the feedback including signal strength information for signals transmitted from each of the plurality of antenna elements.

In still other embodiments, evaluating the wireless communication performance criterion comprises determining proximity information of structure abutting the mobile terminal via at least one sensor.

In still other embodiments, the method further comprises determining whether first and second communication channels associated with the main wireless signal reception path and the diversity wireless signal reception path, respectively, have changed and updating channel estimation models and/or multipath mitigation modules in a digital baseband signal processing section of the electronic device responsive to a determination that the first and second communication channels associated with the main wireless signal reception path and the diversity wireless signal reception path, respectively, have changed.

In still other embodiments, the method further comprises determining whether first and second communication channels associated with the main wireless signal reception path and the diversity wireless signal reception path, respectively, have changed, routing signals received on the first communication channel through the diversity wireless signal reception path in a radio frequency processing section of the electronic device and through the main wireless signal reception path in a digital baseband signal processing section of the electronic device responsive to a determination that the first and second communication channels associated with the main wireless signal reception path and the diversity wireless signal reception path, respectively, have changed, and routing signals received on the second communication channel through the main wireless signal reception path of the radio frequency processing section of the electronic device and through the diversity wireless signal reception path in the digital baseband signal processing section of the electronic device responsive to the determination that the first and second communication channels associated with the main wireless signal reception path and the diversity wireless signal reception path, respectively, have changed.

In still other embodiments, the electronic device is a mobile terminal.

In still other embodiments, a computer program product comprises a non-transitory computer readable program medium, the computer readable program medium comprises computer readable program code configured to carry out methods as described above.

In further embodiments, a method of operating an electronic device comprises providing a plurality of antenna elements, evaluating a wireless communication performance criterion to obtain a performance evaluation, and selecting a pair of the plurality of antenna elements for use in wireless communication based on the performance evaluation.

In still further embodiments, evaluating the wireless communication performance criterion comprises determining a Multiplexing Efficiency where the Multiplexing Efficiency is given by
Multiplexing Efficiency=√{square root over ((1−ρ∈)η1η2)}

where η1and η2are a total efficiency of a first and a second one of the plurality of antenna elements, respectively and ρ∈is an envelope correlation coefficient between the first and second one of the plurality of antenna elements.

In still further embodiments, evaluating the wireless communication performance criterion comprises determining a Normalized Multiplexing Efficiency where the Normalized Multiplexing Efficiency is given by
Normalized Multiplexing Efficiency=Multiplexing Efficiency in Free Space−Multiplexing Efficiency in a User Application.

In still further embodiments, the electronic device is a mobile terminal.

In still further embodiments, a computer program product comprises a non-transitory computer readable program medium, the computer readable program medium comprises computer readable program code configured to carry out methods as described above.

In other embodiments, an electronic device comprises a plurality of antenna elements and antenna selection control circuitry that is configured to evaluate a wireless communication performance criterion to obtain a performance evaluation and assign a first one of the plurality of antenna elements to a main wireless signal reception and transmission path and a second one of the plurality of antenna elements to a diversity wireless signal reception path based on the performance evaluation.

In still other embodiments, the antenna selection control circuitry is configured to evaluate the wireless communication performance criterion by determining transmission power for signals transmitted through each of the plurality of antenna elements and power associated with signals reflected back through each of the plurality of antenna elements.

In still other embodiments, the antenna selection control circuitry is configured to evaluate the wireless communication performance criterion by determining Received Signal Strength Indication (RSSI) data for each of the plurality of antenna elements.

In still other embodiments, the antenna selection control circuitry is configured to evaluate the wireless communication performance criterion by processing feedback from a wireless basestation, the feedback including signal strength information for signals transmitted from each of the plurality of antenna elements.

In still other embodiments, the antenna selection control circuitry is configured to evaluate the wireless communication performance criterion by determining proximity information of structure abutting the mobile terminal via at least one sensor.

In still other embodiments, the electronic device is a mobile terminal.

In further embodiments of the present invention, an electronic device comprises a plurality of antenna elements and antenna selection control circuitry that is configured to evaluate a wireless communication performance criterion to obtain a performance evaluation and select a pair of the plurality of antenna elements for use in wireless communication based on the performance evaluation.

In still further embodiments, the antenna selection control circuitry is configured to evaluate the wireless communication performance criterion by determining a Multiplexing Efficiency where the Multiplexing Efficiency is given by
Multiplexing Efficiency=√{square root over ((1−ρ∈)η1η2)}

where η1and η2are a total efficiency of a first and a second one of the plurality of antenna elements, respectively and ρ∈is an envelope correlation coefficient between the first and second one of the plurality of antenna elements.

In still further embodiments, the electronic device is a mobile terminal.

DETAILED DESCRIPTION OF EMBODIMENTS

As used herein, the term “signal” may take the form of a continuous waveform and/or discrete value(s), such as digital value(s) in a memory or register. As used herein, the terms “module,” “circuit,” and “controller” may take the form of digital circuitry, such as computer-readable program code executed by an instruction processing device(s) (e.g., general purpose microprocessor and/or digital signal processor), and/or analog circuitry.

It will be understood that embodiments of the invention may be implemented in an electronic device, such as a mobile terminal, that includes a Multiple-Input Multiple-Output (MIMO) antenna that is configured to transmit and receive RF signals in two or more frequency bands. The MIMO antenna may be configured, for example, to transmit/receive RF communication signals in the frequency ranges used for cellular communications (e.g., cellular voice and/or data communications), WLAN communications, and/or TransferJet communications, etc. As used herein, the term “mobile terminal” may include a satellite or cellular radiotelephone with or without a multi-line display; a Personal Communications System (PCS) terminal that may combine a cellular radiotelephone with data processing, facsimile and data communications capabilities; a PDA that can include a radiotelephone, pager, Internet/intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and a conventional laptop and/or palmtop receiver or other appliance that includes a radiotelephone transceiver. Mobile terminals may also be referred to as “pervasive computing” devices.

It will be understood mobile terminals according to various embodiments of the invention may operate in any type of wireless communications network. In some embodiments according to the invention, for example, the network may provide services broadly labeled as PCS (Personal Communications Services) including advanced digital cellular systems conforming to standards such as IS-136 and IS-95, lower-power systems such as DECT (Digital Enhanced Cordless Telephone), data communications services such as CDPD (Cellular Digital Packet Data), and other systems such as CDMA-2000, that are proposed using a format commonly referred to as Wideband Code Division Multiple Access (WCDMA).

Some embodiments of the present invention stem from a realization that Long Term Evolution (LTE) mobile devices may need antenna systems that cover seven frequency bands (760-800 MHz, 824-894 MHz, 880-960 MHz, 1710-1850 MHz, 1820-1990 MHz, 1920-2170 MHz, and 2500-2700 MHz. The antenna systems used in LTE devices may also need to meet the requirements of Single In-Single Output (SISO) and Single In-Multiple Output (SIMO) applications for other 3GPP and 2G bands. The antenna systems may be required to meet Specific Absorption Rate (SAR) requirements and other industry standards. To enhance the performance of such a device, an intelligent control system, according to some embodiments of the present invention, may be used to select particular antenna(s) for transmitting and receiving wireless signals based on various performance factors and criteria. In some embodiments, the antenna selection may be based on various modes of operation of the device, such as particular ways a user holds the device during operation.

FIGS. 1A and 1Billustrate a mobile terminal100including a MIMO antenna that includes at least two radiating elements or antennas152,154. The first and second radiating elements152,154may be formed on a planar substrate, such as on a conventional printed circuit board, which includes a dielectric material, ceramic material, or insulation material. The first and second radiating elements152,154are adjacent to grounding elements160, which couple the first and second radiating elements152,154to a ground plane on the printed circuit board. The first and second radiating elements152,154may be formed by patterning a conductive (e.g., metallization) layer on a printed circuit board. The ground plane160may act as a counterpoise for each of the first and second radiating elements152,154.

RF signals are coupled to the first radiating element152through a first feed element or port162, while RF signals are coupled to the second radiating element154through a second feed element or port164. The first feed element162is coupled to the first radiating element152near an end of the first radiating element152, so that the first radiating element152generally extends away from the first feed element162along an upper end of the mobile terminal100.

Similarly, the second feed element164is coupled to the second radiating element154near an end of the second radiating element154, so that the second radiating element152generally extends away from the second feed element164along the upper end of the mobile terminal100. The two radiating elements152and154are separated via an isolator element166.

Although shown with both radiating elements or antennas152,154at the same end of the mobile terminal100, it will be understood that the radiating elements or antennas152and154may be disposed in a variety of positions in mobile terminal100in accordance with various embodiments of the present invention. Moreover, more than two antennas can be used in other embodiments of the present invention.

In general, the efficiency of a single antenna is increased when the antenna excites the fundamental mode of the antenna's counterpoise. However, if both antennas in a MIMO antenna excite the same mode, they will tend to experience mutual coupling. This coupling causes the signals on the antennas to become correlated, which can reduce the performance of the MIMO antenna system.

An additional complexity arises when the MIMO antennas are used in a dual band system, i.e., a system that is intended to operate over more than one frequency range. For example, in a Long Term Evolution (LTE) handset, the antenna may transmit/receive signals in both a 750 MHz band and an 850 MHz band. Within this general frequency range, the correlation of radiating elements that use the same ground plane may be unacceptably high, such as about 0.8 to 0.9.

FIG. 2is a block diagram that illustrates control circuitry for selecting an antenna in a mobile terminal that includes a MIMO antenna system200according to some embodiments of the present invention. The MIMO antenna system200comprises antennas152and154that are connected to downconvertor circuitry via a multiplexer205. The downconvertor circuitry comprises low noise amplifiers (LNAs)210and215in the main path and diversity path, respectively, along with power amplifiers (PAs)220in the main path. An RF ASIC225is coupled to the amplifier circuits210,215, and220and may be configured to implement the mixer circuits, oscillators, and input/output filters to generate the complex baseband signal from a received RF signal via antennas152and154and to generate the RF signal for transmission on one of the antennas152and154from a complex baseband signal. To enhance the performance of a mobile terminal incorporating the MIMO antenna system200, the multiplexer205is operable in response to various control circuitry and signals to select one the antennas152and154for transmission and to select which of the antennas152and154is to be used for the main path signal and which is to be used for the diversity path signal when processing a received RF signal.

FIG. 3is a block diagram that illustrates control circuitry for selecting an antenna in a mobile terminal that includes a MIMO antenna system300according to some embodiments of the present invention. The MIMO antenna system300is similar to that illustrated inFIG. 2, but includes a coupler305connected in the main path. A detector310and microcontroller315connect the coupler to the multiplexer205. In accordance with various embodiments of the present invention, the coupler305can be a single directional coupler or a bi-directional coupler. The detector310can be implemented in a variety of different ways in accordance with various embodiments of the present invention. For example, the detector310may detect amplitude only or may be a complex detector capable of detecting both amplitude and phase. According to some embodiments, the detector310can measure power associated with transmitted signals sent through the power amplifiers220via each antenna152and154along with the power associated with signals reflected back through the two antennas152and154. Based on these measurements, the microcontroller315can select which of the two antennas152and154to use for transmission. Once an antenna is selected for transmission, the microcontroller315may at certain times, such as on a periodic schedule and/or if performance degrades below some threshold level, switch which antenna is used for transmission to collect additional signal transmission power and signal reflection power data to determine if the current antenna is still the preferred choice. In the embodiments ofFIG. 3, however, the effects of absorption loss may not be considered, which may be dominant for some antenna types and/or conditions.

FIG. 4is a block diagram that illustrates control circuitry for selecting an antenna in a mobile terminal that includes a MIMO antenna system400according to some embodiments of the present invention. The MIMO antenna system400is similar to that illustrated inFIG. 2, but includes a processor405coupled to a memory410that includes a Received Signal Strength Indication (RSSI) antenna selection module415. According to some embodiments, the RF ASIC225provides RSSI data, which is processed using the antenna selection module415. The RSSI data may be collected for both antennas152and154(i.e., both the main and diversity paths) and the RSSI antenna selection module415may determine which antenna provides signals with the higher RSSI power values. The multiplexer205may then be used to assign the antenna with the best RSSI power value to the main path in response to a signal from the processor405. In the embodiments ofFIG. 4, the selection of which antenna to assign to the main path and which to assign to the diversity path is based solely on the performance in the frequency bands involved in signal reception. This may not be a disadvantage, however, in systems where the correlation between the receive and transmit frequency performance is high.

FIG. 5is a block diagram that illustrates control circuitry for selecting an antenna in a mobile terminal that includes a MIMO antenna system500according to some embodiments of the present invention. The MIMO antenna system500is similar to that illustrated inFIG. 2, but includes a processor505coupled to a memory510that includes a base station feedback antenna selection module515. According to some embodiments, the radio frequency signal processing platform525provides feedback information from the base station520with regard to signal strength received from the device, which is processed using the base station feedback antenna selection module515. The radio frequency processing platform525may include such functionality as the main and diversity path amplifiers220,210, and215along with the RF ASIC225described above. The base station signal strength feedback data may be collected for both antennas152and154and the base station feedback antenna selection module515may determine which antenna transmits signals with the higher power values. The multiplexer205may then be used to assign the antenna with the best transmit power values based on the base station feedback to the main path in response to a signal from the processor505. In the embodiments ofFIG. 5, the base station feedback antenna selection module515may at certain times, such as on a periodic schedule or if performance degrades below some threshold level, switch which antenna is used for transmission to collect feedback from the base station520with respect to the transmitted signal strength.

FIG. 6is a block diagram that illustrates control circuitry for selecting an antenna in a mobile terminal that includes a MIMO antenna system600according to some embodiments of the present invention. The MIMO antenna system600is similar to that illustrated inFIG. 2, but includes a processor605coupled to a memory610that includes a proximity sensor antenna selection module615. According to some embodiments, one or more proximity sensors620may detect placement of a user's hand on the device or some other external object that may affect operation of the antennas152and154. The proximity information captured by the proximity sensors620is processed using the proximity sensor antenna selection module515. Based on the proximity of outside structure, such as a user's hand, to the antennas152and154, the proximity sensor antenna selection module615may determine which antenna is preferred for transmission and/or receiving based on the likelihood of reduced interference by the proximity of the antenna to outside structure. The multiplexer205may then be used to assign the antenna with that has the least interference from external structure based on the proximity sensor620data to the main path in response to a signal from the processor605. In other embodiments, orientation circuitry may be used in place of or in addition to the proximity sensors620to determine the particular orientation of the device. Such orientation information may also be processed using the proximity sensor antenna selection module615to determine which antenna is preferred for transmission and/or receiving based on the likelihood of reduced interference as compared to the other antenna based on the orientation of the device.

FIG. 7is a block diagram of digital baseband processing circuitry700for a mobile terminal that includes a MIMO antenna system according to some embodiments of the present invention. As described above with respect to some embodiments of the present invention, to enhance the performance of a mobile terminal, an intelligent control system may be used to select particular antenna(s) for transmitting and receiving wireless signals based on various performance factors and criteria. Such dynamic selection, however, may impact decoding of the received wireless signals in the digital baseband.

A typical signal received by mobile terminal will have been affected by multipath fading. To compensate for the effects of multipath fading and other undesirable effects of the communication medium, such as noise, the receiver circuitry uses channel estimation algorithms to model the channel state information or channel properties of the communication link. The modeling may include an estimation of the transfer function and noise associated with the communication link.

Dynamic antenna selection in accordance with the embodiments described above, however, may affect the signal processing performed in the digital baseband portion of the receiver architecture, however. Referring toFIG. 7, the RF ASIC outputs the complex baseband signals for the main path and the diversity path. The digital baseband processing circuitry700includes channel estimation modules705and710for the main and diversity signal paths, respectively. The channel estimation modules705,710are configured to filter the received main and diversity signals based on a statistical modeling of the main and diversity signal paths. Multipath mitigation modules715and720are used to compensate for the effects of multipath fading, for example. The multipath mitigation modules715and720may implement any multipath mitigation algorithm used and the signals from the main signal path and diversity signal path are coherently combined at the adder725. The output of the adder725is provided to a decoding module730to extract the symbol information from the baseband signal.

As described above, intelligent control systems may dynamically switch which antenna is used for main signal path reception and which antenna is used for diversity signal path reception in a MIMO antenna system. Such switching of antennas, however, changes the communication channel used for the main and diversity signal paths as well. As a result, the channel estimation filters and multipath mitigation algorithms are set up for the wrong communication channels. According to some embodiments of the present invention, an antenna switch control module735is used to update the channel estimation modules705and710so as to reconfigure the filters to model the appropriate communication link. Similarly, the antenna switch control module735updates the multipath mitigation modules715and720to model the appropriate communication link. In the present example where only two antennas are used, the channel estimation models uses in the channel estimation modules705and710are swapped and the multipath mitigation models used in the multipath mitigation modules715and720are swapped.

FIG. 8is a block diagram that illustrates control circuitry for selecting an antenna in a mobile terminal that includes a MIMO antenna system800according to some embodiments of the present invention. The MIMO antenna system800is similar to that illustrated inFIG. 2, but includes a second multiplexer805that is responsive to an antenna control signal for selecting which antennas152,154to use for the main and diversity signal paths. According to some embodiments of the present invention, once the channel estimation modules705,710and/or multipath mitigation modules715,720have been configured for the respective main and diversity communication links when the antennas152,154are swapped in response to an antenna selection signal as described above with respect to theFIGS. 2-6, the multiplexer805switches the signals received from the antennas152and154back to their former paths so that there is no need to change the settings in the digital baseband processing circuitry, i.e., the channel estimation modules705,710and/or multipath mitigation modules715,720. A combiner or duplexer810is shown to handle the two way communication between the multiplexer205and the amplifiers220and210. The embodiments ofFIGS. 7 and 8may allow antenna reassignments between the main and diversity paths to be conducted at any time without any loss in channel estimation and signal demodulation performance.

The embodiments ofFIGS. 2-8have been described with respect to comparing the performance of two antennas and determining which to assign to a main demodulation path and which to assign to a diversity demodulation path. Some mobile terminals, however, may include a quad-element LTE MIMO antenna array. In some applications only the optimal two antenna elements of the four are selected for operation with the other two antenna elements being disabled. As the antenna elements are typically spread out in the mobile terminal, the two antenna elements providing the best performance may vary depending on, for example, user effects or other external obstructions affecting signal reception.

FIG. 9illustrates a mobile terminal900including a quad element MIMO antenna array comprising radiating elements or antennas1-4905,910,915, and920configured as shown. Antenna element1905includes port925and grounding port930; antenna element2910includes port935and grounding port940; antenna element3905includes port945and grounding port950; and antenna element4920includes port955and grounding port960. For ease of description, antenna ij represents antenna i and antenna j operating with the other two antenna elements being operationally disabled via leaving their ports and grounding ports open.

According to some embodiments of the present invention, the performance of a particular antenna pairing in a quad element MIMO antenna array may be represented by a parameter called multiplexing efficiency. Multiplexing efficiency estimates MIMO channel performance through the efficiency and envelope correlation coefficient between the two antenna elements. Multiplexing efficiency is expressed as follows:
Multiplexing Efficiency=√{square root over ((1−ρ∈)η1η2)}
where η1and η2are the total efficiency of the first and the second MIMO antenna element, respectively. ρ∈is the envelope correlation coefficient between two elements.

The s parameters, total efficiency, envelope correlation coefficients, and multiplexing efficiency, of the different dual-element combinations in the adaptive quad-element LTE MIMO antenna array900ofFIG. 9are shown inFIGS. 10A-10D, respectively. It can be observed that each combination can cover the bands of 750-960 MHz and 1700-2700 MHz with a high efficiency and multiplexing efficiency.

FIGS. 11A-11Cshow the comparisons between the simulated and measured s parameters, envelope correlation coefficient, multiplexing efficiency, of antenna12and antenna34in the quad-element array.

Examples of the mobile terminal900placed in various user orientations and the performance of various antenna element pairings of the quad element MIMO antenna array will now be described.FIG. 12illustrates the mobile terminal900held in a user's hand with the speaker pressed up against the user's ear. In this orientation the mobile terminal900may be considered to be in talk mode.

FIG. 13Aillustrates the envelope correlation coefficient for the various antenna pairings with the mobile terminal900in the orientation ofFIG. 12. The correlation of antenna34in low frequency has been reduced much more efficiently than the other combinations. For the antenna34case, it has two characteristics: large human body coverage of the whole dual-element antenna array and human a hand placed approximately symmetrically between two ports. When the dual-element array satisfies these two characteristics the user hand can be viewed as a scatter causing structure. This scatter may efficiently separate the radiation patterns of the two MIMO antenna elements to achieve a low correlation.

The multiplexing efficiency of the different dual-element combinations for the talk mode orientation ofFIG. 12can be calculated and is shown inFIG. 13B. For the talk mode, low band antenna34can be used while in high band antenna12may be used.

To normalize the measured multiplexing efficiency, a parameter of multiplexing efficiency loss (MEL) is used and defined as follows:
MEL=measured multiplexing efficiency in free space−measured multiplexing efficiency in user case
FIGS. 14A and 14Billustrate the simulated and measured envelope correlation coefficient and multiplexing efficiency of antenna12and antenna34, respectively, for talk mode. The measured results are generally consistent with the simulations.

FIG. 15illustrates the mobile terminal900held in a user's hand. When the mobile terminal900is in this orientation it may be considered to be in data mode.FIG. 16Aillustrates the envelope correlation coefficient when the mobile terminal900is in the data mode orientation ofFIG. 15. The correlation of antenna13also has the lowest correlation and its characteristics are the same as those for the talk mode orientation ofFIG. 12. Multiplexing efficiency for the data mode orientation ofFIG. 15is illustrated inFIG. 16B. It can be observed that antenna34(which has the most coverage) is a little better than antenna12in the low band due to the lower correlation, but not so significant because of the high loss of port955. Therefore, for the data mode, antenna12or antenna34can be used in the low band and antenna12can be used in the high band based on the simulations.

The simulated and measured envelope correlation coefficient along with the multiplexing efficiency of antenna12and antenna34when the mobile terminal900is in the data mode orientation are shown inFIGS. 17A and 17B, respectively. As shown inFIG. 17B, antenna12provides similar performance to the simulated results in the low band, but antenna34provides worse performance than the simulated results due to the greater losses of port955. Antenna12may, therefore, be preferred to antenna34for low band applications. The measured losses are higher than the simulations for the high band antenna pairings, but the relative losses between antenna12and antenna34are approximately the same as the simulations. Therefore, when the mobile terminal900is in the data mode orientation, antenna12can be used in low band and in high band applications based on the measurement results.

FIG. 18illustrates the mobile terminal900held in a user's two hands. This orientation of the mobile terminal900may be called the reading mode.FIG. 19Aillustrates the envelope correlation coefficient when the mobile terminal900is in the reading mode orientation ofFIG. 18. As shown inFIG. 19A, antenna14has the greatest amount of coverage due to the user's hands and, therefore, has the lowest envelope correlation. Multiplexing efficiency for the reading mode orientation ofFIG. 18is illustrated inFIG. 19B. Due to the similar efficiency in the low band, the envelope correlation is the dominant factor for the high multiplexing efficiency. As a result, antenna14has the best multiplexing efficiency as shown inFIG. 19B. In the higher bands multiplexing efficiency may be important because of the similar envelope correlations. Therefore, when the mobile terminal900is in reading mode, antenna14may be used for low band applications and antenna23may be used for high band applications.

The simulated and measured envelope correlation coefficient along with the multiplexing efficiency of antenna12when the mobile terminal900is in the reading mode orientation are shown inFIGS. 20A and 20B, respectively. As can be seen inFIGS. 20A and 20B, the measured results generally agree with the simulations.

Based on the simulations and measured results from the embodiments ofFIGS. 12-20, for low band applications, antenna34, antenna12, and antenna14can be used when the mobile terminal900is in talk mode, data mode, and reading mode, respectively. For high band applications, antenna13, antenna12, and antenna23can be used when the mobile terminal900is in talk mode, data mode, and reading mode, respectively.

FIG. 21is a block diagram of a wireless communication terminal2100that includes a MIMO antenna array in accordance with some embodiments of the present invention. Referring toFIG. 21, the mobile terminal2100includes a MIMO antenna array2110, a transceiver2140, a processor2127, and can further include a conventional display2108, keypad2102, speaker2104, mass memory2128, microphone2106, and/or camera2124, one or more of which may be electrically grounded to the same ground plane as the MIMO antenna array2110. The MIMO antenna array2110may be structurally configured as shown for the MIMO antenna arrays ofFIGS. 1B and 9, or may be configured in accordance with various other embodiments of the present invention. Moreover, MIMO antennas in accordance with various embodiments of the present invention may be embodied as, but are not limited to, ground free monopole antennas, planar inverted F-antennas (PIFA) radiating elements and/or on-ground antenna radiating elements as well.

The transceiver2140may include transmit/receive circuitry (TX/RX) that provides separate communication paths for supplying/receiving RF signals to different radiating elements of the MIMO antenna2110via their respective RF feeds. Accordingly, when the MIMO antenna2110includes two radiating antenna elements2152,2154, the transceiver2140may include two transmit/receive circuits2142,2144connected to different ones of the antenna elements via the respective RF feeds.

The transceiver2140in cooperation with the processor2127may be configured to communicate according using at least one radio access technology in two or more frequency ranges. The at least one radio access technology may include, but is not limited to, WLAN (e.g., 802.11), WiMAX (Worldwide Interoperability for Microwave Access), TransferJet, 3GPP LTE (3rd Generation Partnership Project Long Term Evolution), Universal Mobile Telecommunications System (UMTS), Global Standard for Mobile (GSM) communication, General Packet Radio Service (GPRS), enhanced data rates for GSM evolution (EDGE), DCS, PDC, PCS, code division multiple access (CDMA), wideband-CDMA, and/or CDMA2000. Other radio access technologies and/or frequency bands can also be used in embodiments according to the invention.

It will be appreciated that certain characteristics of the components of the MIMO antennas shown in the figures such as, for example, the relative widths, conductive lengths, and/or shapes of the radiating elements, the conductive neutralization lines, and/or other elements of the MIMO antennas may vary within the scope of the present invention.

Many variations and modifications can be made to the exemplary embodiments without substantially departing from the principles of the present invention. All such variations and modifications are intended to be included herein within the scope of the present invention, as set forth in the following claims.