Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/0082—Monitoring; Testing using service channels; using auxiliary channels
  • H04B17/0085—Monitoring; Testing using service channels; using auxiliary channels using test signal generators
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
  • G01R29/08—Measuring electromagnetic field characteristics
  • G01R29/10—Radiation diagrams of antennas

Definitions

• the present invention relates to testing of radio frequency (RF) wireless signal transceivers, and in particular, to testing such devices without a need for RF signal cables for conveyance of RF test signals.
• RF radio frequency
• testers For testing these devices following their manufacture and assembly, current wireless device test systems (“testers”) employ a subsystem for analyzing signals received from each device. Such subsystems typically include at least a vector signal generator (VSG) for providing the source signals to be transmitted to the device, and a vector signal analyzer (VSA) for analyzing signals produced by the device.
• VSG vector signal generator
• VSA vector signal analyzer
• the production of test signals by the VSG and signal analyses performed by the VSA are generally programmable so as to allow each to be used for testing a variety of devices for adherence to a variety of wireless technology standards with differing frequency ranges, bandwidths and signal modulation characteristics.
• Calibration and performance verification testing of a device under test are typically done using electrically conductive signal paths, such as RF cables, rather than wireless signal paths, by which a DUT and tester communicate via electromagnetic radiation. Accordingly, the signals between the tester and DUT are conveyed via the conductive signal path rather than being radiated through ambient space. Using such conductive signal paths helps to ensure repeatability and consistency of measurements, and eliminates positioning and orientation of the DUT as a factor in signal conveyance (transmission and reception).
• a signal path In the case of a multiple input, multiple output (MIMO) DUT, a signal path must be provided, in some form, for each input/output connection of the DUT. For example, for a MIMO device intended to operate with three antennas, three conductive signal paths, e.g., cables and connections, must be provided for testing.
• MIMO multiple input, multiple output
• testing could be done using test signals conveyed via electromagnetic radiation rather than electrical conduction via cables. This would have the benefit of requiring no connecting and disconnecting of test cables, thereby reducing the test time associated with such connections and disconnections.
• the "channel" in which the radiated signals and receiver antennas exist i.e., the ambient space through which the test signals are radiated and received, is inherently prone to signal interference and errors due to other electromagnetic signals originating elsewhere and permeating the ambient space.
• Such signals will be received by the DUT antennas and can include multipath signals from each interfering signal source due to signal reflections. Accordingly, the "condition" of the "channel” will typically be poor compared to using individual conductive signal paths, e.g., cables, for each antenna connection.
• One way to prevent, or at least significantly reduce, interference from such extraneous signals is to isolate the radiated signal interface for the DUT and tester using a shielded enclosure.
• enclosures have typically not produced comparable measurement accuracy and repeatability. This is particularly true for enclosures that are smaller than the smallest anechoic chambers. Additionally, such enclosures tend to be sensitive to the positioning and orientation of the DUT, as well as to constructive and destructive interference of multipath signals produced within such enclosures.
• a method provides for facilitating wireless testing of multiple radio frequency (RF) signal transceiver devices under test (DUTs).
• DUTs radio frequency
• RF test signals radiated to the DUTs can have their respective signal phases controlled to maximize the direct-coupled signals to their respective intended DUTs while minimizing the cross-coupled signals.
• the wireless RF test signals radiated to the DUTs can have their respective signal magnitudes controlled to normalize the direct-coupled signals to their respective intended DUTs while still sufficiently reducing the cross-coupled signals.
• compensation is provided for the multipath signal environment within the shielded enclosure, thereby simulating wired test signal paths during wireless testing of the DUTs.
• a method of facilitating wireless testing of a plurality of radio frequency (RF) signal transceiver devices under test (DUTs) includes:
• a method of facilitating wireless testing of a plurality of radio frequency (RF) signal transceiver devices under test (DUTs) includes:
• the structure defines the interior region and an exterior region, and is configured to substantially isolate the interior region from electromagnetic radiation originating from the exterior region, and
• the plurality of antennas and at least a portion of the interior region together define at least a portion of a wireless communication channel via which at least first and second pluralities of controlled RF signal components related to the at least first and second controlled RF signals, respectively, propagate for reception by the at least first and second DUTs, respectively;
• a method of facilitating wireless testing of a plurality of radio frequency (RF) signal transceiver devices under test (DUTs) includes:
• the structure defines the interior region and an exterior region, and is configured to substantially isolate the interior region from electromagnetic radiation originating from the exterior region, and
• Figure 1 depicts a typical operating and possible testing environment for a wireless signal transceiver.
• Figure 2 depicts a testing environment for a wireless signal transceiver using a conductive test signal path.
• Figure 3 depicts a testing environment for a MIMO wireless signal transceiver using conductive signal paths and a channel model for such testing environment.
• Figure 4 depicts a testing environment for a MIMO wireless signal transceiver using radiated electromagnetic signals a channel model for such testing environment.
• Figure 5 depicts a testing environment in accordance with exemplary embodiments in which a MIMO DUT can be tested using radiated electromagnetic test signals.
• Figure 6 depicts a testing environment in which a DUT is tested using radiated electromagnetic test signals within a shielded enclosure.
• Figures 7 and 8 depict exemplary embodiments of testing environments in which a wireless DUT is tested using radiated electromagnetic test signals in a shielded enclosure with reduced multipath signal effects.
• Figure 9 depicts a physical representation of a shielded enclosure in accordance with an exemplary embodiment for use in the testing environments of Figures 7 and 8.
• Figure 10 depicts a testing environment in accordance with exemplary embodiments in which a DUT can be tested using radiated electromagnetic test signals.
• Figure 11 depicts another testing environment in accordance with exemplary embodiments in which a DUT can be tested using radiated electromagnetic test signals.
• Figure 12 depicts an exemplary algorithm for testing a DUT using the testing environment of Figure 11.
• Figure 13 depicts another testing environment in accordance with exemplary embodiments in which a DUT can be tested using radiated electromagnetic test signals.
• Figure 14 depicts an exemplary algorithm for testing a DUT using the testing environment of Figure 13.
• Figure 15 depicts another testing environment in accordance with exemplary embodiments in which a DUT can be tested using radiated electromagnetic test signals.
• Figure 16 depicts an exemplary algorithm for testing a DUT using the testing environment of Figure 15.
• Figure 17 depicts a test signal transmitted by a DUT over a defined frequency range prior to compensation in accordance with exemplary embodiments.
• Figure 18 depicts the swept test signal of Figure 17 prior to and following compensation in accordance with exemplary embodiments, along with exemplary phase shift values for the testing environments of Figures 10, 11, 13 and 15.
• Figure 19 depicts an exemplary algorithm for performing compensation as depicted in Figure 18.
• Figure 20 depicts another testing environment for testing a wireless DUT with compensation using multiple test signal phase shifts in accordance with exemplary embodiments.
• Figure 21 depicts the testing environment of Figure 20 with the addition of test signal gain adjustments for compensating in accordance with additional exemplary embodiments.
• signal may refer to one or more currents, one or more voltages, or a data signal.
• test controller 10 e.g., a personal computer
• the tester 100 and DUT 200 each have one (or more for MIMO devices) respective antennas 102, 202, which connect by way of conductive signal connectors 104, 204 (e.g., coaxial cable connections, many types of which are well known in the art).
• Test signals are conveyed wirelessly between the tester 100 and DUT 200 via the antennas 102, 202.
• electromagnetic signals 203 are radiated from the DUT antenna 202.
• this signal 203 will radiate in numerous directions, resulting in an incident signal component 203i and reflected signal components 203r being received by the tester antenna 102.
• these reflected signal components 203r often the products of multipath signal effects as well as other electromagnetic signals originating elsewhere (not shown), result in constructive and destructive signal interference, thereby preventing reliable and repeatable signal reception and testing results.
• a conductive signal path such as a RF coaxial cable 106, is used to connect the antenna connectors 104, 204 of the tester 100 and DUT 200 to provide a consistent, reliable and repeatable electrically conductive signal path for conveyance of the test signals between the tester 100 and DUT 200.
• this increases the overall test time due to the time needed for connecting and disconnecting the cable 106 before and after testing.
• the additional test time for connecting and disconnecting test cabling becomes even longer when testing a MIMO DUT 200a.
• multiple test cables 106 are needed to connect corresponding tester 104 and DUT 204 connectors to enable conveyance of the RF test signals from the RF signal sources 110 (e.g., VSGs) within the tester 100a for reception by the RF signal receivers 210 within the DUT 200a.
• the tester for testing MIMO devices will have one or more VSGs 110a, 110b, ..., 110 ⁇ providing corresponding one or more RF test signals 111a, 11 lb, ..., 11 In (e.g., packet data signals having variable signal power, packet contents and data rates).
• test cables 106a, 106b, 106n connected via respective tester 104a, 104b, 104n and DUT 204a, 204b, ..., 204n connectors, convey these signals to provide the received RF test signals 21 la, 21 lb, ..., 21 In for the corresponding RF signal receivers 210a, 210b, ..., 21 On within the DUT 200a. Accordingly, the additional test time required for connecting and disconnecting these test cables 106 can be increased by a factor n corresponding to the number of test cables 106.
• the conductive, or wired, channel 107 ( Figure 3) is replaced by a wireless channel 107a corresponding to a wireless signal interface 106a between the tester 100a and DUT 200a.
• the tester 100a and DUT 200a communicate test signals 111, 211 via respective arrays of antennas 102, 202.
• the signal channel 107a is no longer represented by a diagonal matrix 20, but is instead represented by a matrix 20a having one or more non-zero cross-coupled coefficients 24a, 24b (hy , where i ⁇ j) off of the diagonal 22.
• the first DUT antenna 202a receives test signals radiated by all of the tester antennas 102a, 102b, 102n, e.g., corresponding to channel H matrix coefficients hn, hi 2 , ..., and hi n .
• the coefficients h of the channel matrix H correspond to characteristics of the channel 107a affecting transmission and reception of the RF test signals.
• the factors affecting these coefficients can alter the channel condition number in ways that can create measurement errors. For example, in a poorly conditioned channel, small errors can cause large errors in the testing results. Where the channel number is low, small errors in the channel can produce small measurements at the receive (RX) antenna. However, where the channel number is high, small errors in the channel can cause large measurement errors at the receive antenna.
• This channel condition number k(H) is also sensitive to the physical positioning and orientation of the DUT within its testing environment (e.g., a shielded enclosure) and the orientation of its various antennas 204. Accordingly, even if with no extraneous interfering signals originating elsewhere or arriving via reflections and impinging on the receive antennas 204, the likelihood of repeatable accurate test results will be low.
• the test signal interface between the tester 100a and DUT 200a can be wireless.
• the DUT 200a is placed within the interior 301 of a shielded enclosure 300.
• Such shielded enclosure 300 can be implemented as a metallic enclosure, e.g., similar in construction or at least in effect to a Faraday cage. This isolates the DUT 200a from radiated signals originating from the exterior region 302 of the enclosure 300.
• the geometry of the enclosure 300 is such that it functions as a closed-ended waveguide.
• each antenna array includes multiple (M) antenna elements.
• the first antenna array 102a includes m antenna elements 102aa, 102ab, ... 102am.
• Each of these antenna elements 102aa, 102ab, 102am is driven by a respective phase-controlled RF test signal 131aa, 13 lab, 131am provided by respective RF signal control circuitry 130a.
• the RF test signal 111a from the first RF test signal source 110a has its magnitude increased (e.g., amplified) or decreased (e.g., attenuated) by signal magnitude control circuitry 132.
• the resulting magnitude-controlled test signal 133 is replicated by signal replication circuitry 134 (e.g., a signal divider).
• the resulting magnitude-controlled, replicated RF test signals 135a, 135b, 135m have their respective signal phases controlled (e.g., shifted) by respective phase control circuits 136a, 136b, 136m to produce magnitude- and phase-controlled signals 131aa, 13 lab, ...
• antenna elements 102aa, 102ab, ... , 102am of the antenna array 102a are driven in a similar manner by corresponding RF signal control circuits 130b, ..., 130m. This produces corresponding numbers of composite radiated signals 103a, 103b, 103n for conveyance to and reception by the antennas 202a, 202b, 202n of the DUT 200a in accordance with the channel H matrix, as discussed above.
• the DUT 200a processes its corresponding received test signals 211a, 211b, 211m and provides one or more feedback signals 201a indicative of the characteristics (e.g., magnitudes, relative phases, etc.) of these received signals.
• These feedback signals 201a are provided to control circuitry 138 within the RF signal control circuits 130.
• This control circuitry 138 provides control signals 137, 139a, 139b, 139m for the magnitude control circuitry 132 and phase control circuitry 136. Accordingly, a closed loop control path is provided, thereby enabling gain and phase control of the individual radiated signals from the tester 100a for reception by the DUT 200a. (Alternatively, this control circuitry 130 can be included as part of the tester 100a.)
• the control circuitry 138 uses this feedback data 201a from the DUT 200a to achieve optimal channel conditions by altering the magnitudes and phases of the radiated signals in such a manner as to minimize the channel condition number k(H), and produce received signals, as measured at each DUT antenna 202, having approximately equal magnitudes. This will create a communication channel through which the radiated signals produce test results substantially comparable to those produced using conductive signal paths (e.g., RF signal cables).
• conductive signal paths e.g., RF signal cables
• a reference DUT can be placed in a test fixture within the shielded enclosure 300 for use in optimizing the channel conditions through the iterative process discussed above. Thereafter, further DUTs of the same design can be successively tested without having to execute channel optimization in every instance, since differences in path loss experienced in the controlled channel environment of the enclosure 300 should be well within normal testing tolerances.
• the channel condition number k(H) was reduced to 2.27db, and the amplitudes of the hn and h 22 coefficients were -0.12db and -0.18db, respectively, producing a channel magnitude matrix as follows:
• RF absorbent materials 320a, 320b are disposed at the reflective surfaces 304, 306.
• the reflected signal components 203br, 203 cr are attenuated significantly, thereby producing less interference, either constructively or destructively, with the incident primary signal component 203ai.
• Additional RF signal control circuitry 150 can be included for use between the antenna array 102a mounted within the interior 301 or on the interior surface 302 of the enclosure 300a and the tester 100a. (Alternatively, this additional control circuitry 150 can be included as part of the tester 100a.)
• the radiated signals impinging upon the antenna elements 102aa, 102ab, 102am produce received signals 103aa, 103ab, 103am with respective signal phases controlled (e.g., shifted) by phase control circuitry 152 having phase control elements 152a, 152b, 152m controlled in accordance with one or more phase control signals 157a, 157b, 157m provided by a control system 156.
• the resulting phase-controlled signals 153 are combined in a signal combiner 154 to provide the received signal 155a for the tester 100a and a feedback signal 155b for the control system 156.
• the control system 156 processes this feedback signal 155b, as part of a closed loop control network, to adjust, as needed, the respective phases of the composite receive signals 103aa, 103ab, 103am to minimize the apparent signal path loss associated with the interior region 301 of the enclosure 300a.
• This closed loop control network also allows the system to reconfigure the phased array enabled by these antennas 102a and phase control circuitry 152 in the event that the positioning or orientation of the DUT 200a changes within the enclosure 300a. As a result, following minimization of the path loss using this feedback loop, accurate and repeatable conveyance of the DUT signal 203a to the tester 100a using the radiated signal environment within the enclosure 300a can be achieved.
• test signal 111a provided by the tester 100a is replicated by the signal combiner/sp litter 154, and the respective phases of the replicated test signals 153 are adjusted as necessary by the phase control circuitry 152 before being radiated by the antenna elements 102aa, 102ab, 102am.
• the reflected signal components 103br, 103cr are significantly attenuated and result in reduced constructive and destructive interference with the primary incident signal component 103ai.
• One or more feedback signals 203a from the DUT 200a provide the control system 156 with the information necessary for controlling the phases of the replicated test signals 153 to minimize the apparent signal path loss associated with the interior 301 of the enclosure 300a, thereby establishing consistent and repeatable signal path loss conditions.
• the shielded enclosure 300b can be implemented substantially as shown.
• the DUT can be positioned at one end 30 Id of the interior 301 of the enclosure 300b, opposite of the interior region 301b containing or facing the interior surface 302 on which the tester antenna arrays 102a, 102b, 102n ( Figure 5) are located. In between is an interior region 301a forming a waveguide cavity surrounded by the RF absorbent materials 320.
• exemplary embodiments of systems and methods enable cable-free testing of wireless DUTs while compensating for multipath effects and optimizing control of signal path losses.
• Multiple antennas, as well as antenna arrays, used in conjunction with control systems allow for adjustment of the phases of the test signals provided to the antenna elements in such a manner as to emulate the stable and repeatable signal path loss environment normally associated with a conductive signal path environment, while using a radiated signal environment within a shielded enclosure. While the time needed for adjusting the phase shifters is part of the overall test time, such adjustment time is significantly less than that needed for connecting and disconnecting test cables and provides the added benefit of real world testing that includes the antenna elements.
• exemplary embodiments provide for cable-free testing of wireless DUTs while achieving testing accuracies and repeatable measurements commensurate with testing using conductive signal paths, e.g., test cables, for signals having a wide bandwidth, such as the 160 megahertz (MHz) wide signal as prescribed by the Institute of Electrical and Electronic Engineers (IEEE) standard 802.1 lac.
• a substantially flat signal response can be created for the wideband signal being received within the shielded test enclosure.
• the testing using the wideband signal may proceed without further adjustment, just as though it were in a cabled test environment. While positioning of the DUT within the shielded enclosure can affect the flatness of the channel response, such positioning sensitivity has been found to be well within the tolerance of measurements prescribed by underlying signal standards (e.g., IEEE 802.1 lac).
• such cable-free testing can be performed upon multiple DUTs simultaneously within the same shielded enclosure.
• the low crosstalk signal environment of conductive signal paths can be emulated using a radiated test signal environment within a shielded enclosure.
• the signals received at the antennas of the multiple DUTs will be commensurate with signals received using cabled signal paths. For example, this can be achieved by maximizing the direct-coupled coefficients while minimizing the cross-coupled coefficients of the channel matrix (e.g., producing differences of at least 10 decibels between the direct- and cross-coupled coefficients).
• a DUT 200a is positioned within the shielded enclosure 300 for transmit signal testing.
• the DUT test signal 203a transmitted via its antenna 202a, is received by the multiple antenna elements 102a, 102b, ..., 102n.
• the resulting received signals 105a, 105b, ..., 105n have their respective signal phases controlled and adjusted by respective phase control circuits 236a, 236b, ..., 236n.
• the resulting phase-controlled test signals 237a, 237b, 237n are conveyed to a control system 242 (discussed in more detail below) and signal combining circuitry 234.
• the control system 242 provides phase control signals 243a, 243b, 243n for the phase control circuits 236a, 236b, 236n.
• the combined (e.g., summed) phase-controlled test signals 237a, 237b, 237n produce a composite test signal 235 for downstream analysis, e.g., by a VSA (not shown).
• phase-controlled test signals 237a, 237b, ..., 237n are combined in the signal combiner 234 to produce the composite test signal 235.
• the composite test signal 235 is conveyed to an alternative control system 244 (discussed in more detail below), which, in turn, provides the phase control signals 245a, 245b, 245n for the phase control circuits 236a, 236b, ..., 236n.
• the in-line control system 242 includes power measurement circuits 242aa, 242ab, 242an for measuring respective power levels of the phase-controlled test signals 237a, 237b, 237n.
• the resulting power measurement signals 243aa, 243ab, 243an, indicative of the respective test signal power levels, are provided to control circuitry 242b, e.g., in the form of a digital signal processor (DSP), which, in turn, provides appropriate phase control signals 243ba, 243bb, 243bn for the phase control circuits 236a, 236b, ..., 236n.
• DSP digital signal processor
• operation 410 of the testing environment of Figure 11 can proceed as shown.
• the phase shifters 236a, 236b, ..., 236n are initialized 411, e.g. where all phase shift values are set to a common reference phase value or individual reference phase values.
• the power levels of the phase-controlled signals, 237a, 237b, 237n are measured 412.
• the measured power values are summed 413 and the cumulative measured signal power is compared 414 to a previous cumulative measured signal power.
• the current phase shift values and cumulative measured power are stored 415, following which, these stored values are compared 416 against the desired criteria (e.g., a maximized cumulative measured power). If such criteria are met, adjustments of the test signal phases are terminated 417. If not, adjustments of the test signal phases continue.
• phase shifters 236a, 236b, 236n are adjusted 418 to impart another combination or permutation of phase shift values upon the received test signals 105a, 105b, ..., 105n, e.g., in accordance with a genetic algorithm (GA) or a particle swarm algorithm (PSA). Following this, the measuring 412, summing 413 and comparing 414 of powers are repeated until the desired criteria have been met.
• GA genetic algorithm
• PSA particle swarm algorithm
• the alternative downstream control system 244 ( Figure 10) includes power measurement circuitry 244a (e.g., a VSA) and control circuitry 244b (e.g., a DSP).
• a power level of the composite signal 235 is measured by the power measurement circuitry 244a, which provides power measurement data 245a to the control circuitry 244b.
• the control circuitry 244b provides appropriate phase control signals 245ba, 245bb, 245bn to the phase shifters 236a, 236b, 236n.
• phase shifters 236a, 236b, 236n are initialized 421, by being preset to one or more respective phase shift values.
• the power level of the composite signal 235 is measured 422, following which, the current measured power is compared 423 to a previous measured power level. If the current measured power level is greater than the previous measured power level, the current phase shift values and measured power are stored 424 and used for determining 425 whether the desired criteria (e.g., a maximized measured power level) have been met. If so, phase adjustments are terminated 426. If not, phase adjustments continue.
• phase shifters 236a, 236b, 236n are adjusted to impart another set of phase shift values upon the received test signals 105a, 105b, ..., 105n in accordance with an optimization algorithm (e.g., a GA or PSA).
• an optimization algorithm e.g., a GA or PSA
• the inline control system 242 ( Figure 10) includes phase detection circuits 242ca, 242cb, 242cn and control circuitry 242d (e.g., a DSP).
• the phase detectors 242ca, 242cb, ..., 242cn detect the respective signal phases of the phase-controlled signals 237a, 237b, 237n, and provide corresponding phase data 243ca, 243cb, ..., 243cn to the control circuitry 242d.
• the control circuitry 242d provides appropriate phase control signals 243da, 243db, 243dn for the phase shifters 236a, 236b, ..., 236n.
• phase shifters 236a, 236b 236n are initialized 431 by being present to one or more respective phase shift values.
• the respective phases of the phase-controlled signals 237a, 237b, ... 237n are measured 432 (e.g., relative to a common or reference signal phase).
• phase adjustments of the phase shifters 236a, 236b ..., 236n are configured 433 in accordance with optimized phase shift values.
• the power level of the composite signal 235 is measured 434 to confirm its attainment of the desired composite signal power level, following which phase adjustments are terminated 435.
• an exemplary received signal 203 radiated from a DUT 200a with constant power from a wideband antenna 202a with good response for frequencies ranging from 700 through 6000 MHz within a shielded enclosure 300 would appear substantially as shown.
• its power profile will not be flat due to the rich multipath signal environment existing within the shielded enclosure 300.
• the 160 MHz wide frequency band from 5000 through 5160 MHz.
• the received signal displays a power variation of approximately 25 decibels (dB).
• this profile can be compensated so as to become substantially flat over the frequency band 511 of interest.
• this can be achieved using multiple (e.g., 16) antenna elements 102 and corresponding phase shifters 236.
• multiple e.g., 16
• an optimization algorithm discussed in more detail below
• quadrature phase adjustments of 0, 90, 180 and 270 degrees
• the response profile 522 varies more than 5 dB over the 160 MHz bandwidth 511 of this exemplary test signal.
• received signal variation is still approximately 5 dB.
• the multiple phase adjusters 236a, 236b, 236p are appropriately adjusted, even though confined to quadrature phase adjustments only, it is possible to achieve a response profile 523 that varies no more than 0.5 dB.
• the compensation has depicted in Figure 18 can be achieved using a process 440 as shown.
• a number of frequencies within the desired signal bandwidth are defined 441, following which an initial set of phase shift values for the phase shifters is defined 442.
• the phase shifters are then set 443 with such defined phase values and the power is measured 444 at each frequency.
• differences between measured powers at multiple pairs of the defined frequencies are computed 445 and summed for evaluation of 446 a function F equal to a difference between a defined maximum power difference and the summed differences of computed powers.
• phase shifter values are retained 448 and it is determined 449 whether a desired condition has been met (e.g., a maximized computed function F has been attained). If so, phase adjustments are terminated 450. If not, phase adjustments continue. Similarly, if the current computed function F curren t is not greater than a former computed function F ol d, phase adjustments continue. These phase adjustments continue by defining another set of phase shifter values 451 and repeating the steps of adjusting the phases 443, measuring power 444, computing power differences 445 and evaluating the computed function F 446. This process is repeated until the condition has been met 449.
• signal sources 110 provide test signals 111 which are replicated using signal splitters 234 to provide replica test signals 235 for phase shifting using multiple phase shifters 231 for driving the antenna elements 102 of the antenna arrays 235.
• These antenna arrays 235 a, 235b provide radiated signal components 103aa, 103ab, 103ba, 103bb corresponding to the direct-coupled and cross-coupled coefficients of the channel matrix H (e.g., as discussed above).
• Received signal data 201a, 201b are provided by the DUTs 200a, 200b to a control system 206 (e.g., a DSP), which, in turn, provides appropriate phase control signals 207ap, 207bp for the phase shifters 236aa, 236am, 236ba, 236bm for controlling the phases of the signals to be radiated from the antenna elements 102aa, 102am, 102ba, ...102bm of the antenna arrays 235 a, 235b.
• a control system 206 e.g., a DSP
• the direct-coupled channel matrix H coefficients 103aa, 103ba can be maximized and the cross- coupled coefficients 103ab, 103bb minimized (e.g., with the final cross-coupled coefficients ideally becoming more than 10 dB less than the direct-coupled coefficients).
• control system 206 can be further configured to provide gain control signals 207ag, 207bg for controlling the magnitudes of the test signals 111a, 11 1b being replicated for transmission to the DUTs 200a, 200b.
• These signal magnitudes can be controlled by controlling signal gain stages (e.g., variable gain amplifiers or signal attenuators) 232a, 232b. This can beneficially provide for further optimizing the relative magnitudes of the direct-coupled coefficients 103aa, 103ba and cross-coupled coefficients 103ab, 103bb of the channel matrix H.
• the magnitudes of the direct-coupled coefficients 103aa, 103ba can be normalized, while still maintaining sufficient attenuation of the cross-coupled coefficients 103ab, 103bb (e.g., 10 dB or more).

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• 2014
  • 2014-05-16 WO PCT/US2014/038351 patent/WO2014197186A1/en active Application Filing
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