Abstract:
Systems and methods are disclosed herein to provide shielding and radio frequency (RF) antenna coupling for communication test systems for the testing of wireless data communication devices and systems, including Multiple Input Multiple Output (MIMO) devices and systems. In accordance with one or more embodiments, a shielding and coupling system containing an array of RF antennas is disclosed that includes a flexible jacket integrated with RF shielding material that simultaneously isolates a device under test (DUT) and couples signals from the antennas of the DUT. Such a system may offer improved capabilities such as a faster and more efficient method of isolating the DUT from external interference, a more repeatable and simplified method of transmitting and receiving MIMO RF signals from DUTs having built-in antennas, and a more portable and lower cost RF test setup.

Description:
TECHNICAL FIELD 
       [0001]    The subject matter described herein relates generally to the test and measurement of wireless data communication systems; and more particularly to systems and methods for testing RF devices and systems with built-in or non-detachable antennas; including, but not limited to, multiple-input multiple-output data communication devices and systems. 
       BACKGROUND 
       [0002]    Sophisticated wireless data communications devices, systems and networks, such as cellular telephones and wireless LAN transceivers, are in widespread use worldwide. There is increasing need for higher data rates and the support of an increased number of users and data traffic, and these networks employ complex signal waveforms and advanced radio frequency capabilities such as multiple-input multiple-output (MIMO) signal coding for achieving higher bandwidths. Further, the rapidly decreasing physical size and power consumption of these devices and systems cause them to become ever more highly integrated, with internal antennas and fully sealed construction. All of these techniques, however, increase the complexity of the wireless devices. Manufacturers, vendors and users therefore have a greater need for better testing of such systems. 
         [0003]    Unfortunately, the complexity of wireless data communication devices and systems makes them particularly problematic to test due to the difficulty of accessing their internally integrated antennas, isolating them from external interference, and controlling the coupling between the wireless device and the test equipment. Actual open-air RF environments contain high levels of uncontrollable noise and interference, and also present time-varying and unpredictable channel statistics. However, external noise and interference have significant impact on device performance. The lack of controllability and repeatability also makes it difficult or impossible to automate the testing of such wireless systems. Therefore, it is very attractive to manufacturers and users to test these devices in a repeatable fashion by excluding the interference and variability of real RF environments and also controlling the degree of coupling between the wireless device and the test equipment. This also enables the tests to be conducted in an automated fashion, or by personnel not highly skilled in RF channel characteristics. 
         [0004]    Traditional methods of isolating and coupling to wireless communications devices include: anechoic and reverberation chambers; shielded enclosures of various sizes; cabled connection to device antenna connectors or antennas; use of antenna ranges; and operation in open air environments. All of these methods exhibit one or more deficiencies when considering the requirements of modern MIMO wireless devices. Anechoic and reverberation chambers are very expensive, bulky and fixed at one location due to their large size and weight. Shielded enclosures offer limited portability but are still relatively expensive and heavy, and suffer from repeatability issues. Further, small shielded enclosures present many problems when dealing with MIMO systems. Cabled connections to the wireless device under test are simple and offer very high repeatability and low cost, but are unfortunately impractical or impossible with modern highly integrated compact devices such as cellular telephones. Outdoor antenna ranges are expensive and difficult to find, due to their real estate requirements, and further have problems when dealing with MIMO transmission. Open air environments are highly variable, nearly impossible to reproduce, and present significant challenges with repeatability and controllability. All of these problems are exacerbated when considering the trend in modern wireless devices of incorporating multiple antennas that are integrated into the device, non-detachable, and with a high degree of impact on device performance. 
         [0005]    The known methods in the field of wireless device testing therefore suffers from serious shortcomings with regard to isolating and coupling to a device under test. There is hence a need for improved wireless data communication test systems and methods. A system that is inexpensive, highly portable, and capable of handling devices with integrated non-detachable antennas is desirable. It is preferable for such a system to provide shielding of the device under test from external interference, as well as coupling of radio frequency signals between the device under test and the test equipment. Further, such a system should allow repeatable coupling to device antennas without special jigs or expensive fittings, even though the device antennas may be located internally and not visible in normal operation. Finally, the system should present simplified use and operation to permit less skilled personnel to conduct testing of advanced wireless devices, and should also accommodate wireless devices of different sizes and shapes without modification. 
       SUMMARY 
       [0006]    A combined shielding and coupling system for isolating and coupling to a wireless device under test is provided. The system includes a flexible jacket including a radio frequency shielding layer for enclosing at least a portion of a device under test, and electromagnetically shielding the device under test. An antenna mounted in or on the jacket resides within an enclosure formed by the jacket and couples with an antenna of the device under test. A connector is provided for connecting the antenna mounted in or on the jacket with a test system. 
         [0007]    The test system described herein may be implemented in hardware, software, firmware, or any combination thereof. As such, the terms “function” “node” or “module” as used herein refer to hardware, which may also include software and/or firmware components, for implementing the feature being described. In one exemplary implementation, the test system described herein may be implemented using a computer readable medium having stored thereon computer executable instructions that when executed by the processor of a computer control the computer to perform steps. Exemplary computer readable media suitable for implementing the test system described herein include non-transitory computer-readable media, such as disk memory devices, chip memory devices, programmable logic devices, and application specific integrated circuits. In addition, a computer readable medium that implements the subject matter described herein may be located on a single device or computing platform or may be distributed across multiple devices or computing platforms. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The subject matter described herein will now be explained with reference to the accompanying drawings of which: 
           [0009]      FIG. 1  is a plan view of a shield jacket with a single antenna cabled to the test equipment and showing placement of DUT according to an embodiment of the subject matter described herein; 
           [0010]      FIG. 2  is a view of shield jacket folded over a DUT and secured according to an embodiment of the subject matter described herein; 
           [0011]      FIG. 3  is a diagram of layers comprising shield jacket according to an embodiment of the subject matter described herein; 
           [0012]      FIG. 4  is an electrical circuit diagram of a DUT with an internal antenna and coupling to a jacket antenna, and showing shield as well according to an embodiment of the subject matter described herein; 
           [0013]      FIG. 5  is an outline diagram of jacket with 2 antennas for 2×2 MIMO according to an embodiment of the subject matter described herein; 
           [0014]      FIG. 6  is an outline diagram of jacket with 6 antennas in a regular pattern, plus dividers according to an embodiment of the subject matter described herein; 
           [0015]      FIG. 7  is a mechanical diagram of jacket (top view) according to an embodiment of the subject matter described herein; 
           [0016]      FIG. 8  is a mechanical diagram of jacket (side view) according to an embodiment of the subject matter described herein; 
           [0017]      FIG. 9  is a diagram of waveguide below cutoff side flaps according to an embodiment of the subject matter described herein; and 
           [0018]      FIG. 10  is a flow chart illustrating an exemplary process for testing a device using a shield jacket according to an embodiment of the subject matter described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The subject matter described herein includes a foldable shield jacket for surrounding RF components of a DUT while allowing those components to communicate with a test device.  FIG. 1  shows a plan view of a flat flexible jacket  100  with an integral RF shielding layer that may be folded and secured over a wireless device under test (DUT)  102  to isolate it from external RF interference. Jacket  100  may be secured with temporarily adhesive strips  104 , such as Velcro. DUT  102  may be placed at a predefined location on jacket  100  before jacket  100  is folded over and secured. A wireless antenna  106  is integrated onto the inner surface of shield jacket  102  to couple RF signals to and from the DUT antenna. Jacket antenna  106  may be connected to an RF connector  108  (such as a standard microwave subminiature version A (SMA) connector) by a short length of flexible RF cable  110 . Both connector  108  and cable  110  may be also permanently attached to shield jacket  100 . 
         [0020]    In  FIG. 1 , jacket  100  is represented for exemplary purposes as being rectangular in shape and foldable about a center line of jacket  100 . In an alternate implementation, jacket  100  may be made of other geometric shapes, such as square or circular shapes. Any foldable regular or irregular polygonal shape for jacket  100  is intended to be within the scope of the subject matter described herein. 
         [0021]      FIG. 2  shows an isometric view of flexible jacket  100  after being folded over the DUT  102  and secured with Velcro strips  104 . Antenna  106  integrated into jacket  100  as well as flexible RF cable  110  and connector  108  are also shown. External test equipment  112  may be connected to RF connector  108  mounted on shield jacket  100  via RF cables  113 . Test equipment  112  can exchange RF signals with DUT  102  as shield jacket antenna  106  is electrically coupled to the DUT antenna(s). The close proximity of shield jacket antenna  106  to the DUT antenna(s) may cause the efficiency of coupling to be quite high, while the fact that DUT  102  is fully enclosed within shield jacket  100  may cause a significant amount of reduction in external interference. 
         [0022]      FIG. 3  shows a cross-section of a possible implementation of shield jacket  100 . Shield jacket  100  comprises an outer layer  114  of insulating material such as polyester or any other flexible plastic or cloth. Outer layer  114  should be sufficiently durable to resist normal wear and tear. A metallic or metallized polymer RF shield layer  116  is then attached to outer layer  114 , and on top of shield layer  116  is attached dielectric layer  118 , such as polyester laminated with dielectric foam. Wireless antenna  106  integrated into jacket  100  is mounted on top of dielectric layer  118 ; dielectric layer  118  improves the electrical performance of antenna  106  and separates and isolates antenna  106  from RF shield layer  116  (which acts as an extended ground plane for the antenna). An inner layer  120  of insulating material (again, polyester or other flexible cloth) is mounted above antenna  106  and dielectric layer  118 . Velcro strips  104  are then attached to inner insulating layer  120 . The whole ensemble may be sewn together or otherwise permanently attached so as to form a flat sheet that can be folded along a predefined line. Note that RF connector  108  and flexible RF cable  110  connecting the RF connector  108  to the shield jacket antenna  106  are normally also attached to shield jacket  100  by stitching, and RF shield layer  116  is grounded to the body of connector  108 . RF connector  108  is mounted such that when shield jacket  100  is folded, connector  108  appears on the outside in a position suitable for connecting to the test equipment. 
         [0023]      FIG. 4  depicts an equivalent electrical model of the shield jacket and DUT mechanical arrangement shown in  FIG. 1  and  FIG. 2 . As shown, shield jacket antenna  106  is very close to DUT antenna  122 , so coupling is usually mainly capacitive (or inductive in rare cases). The close proximity of antennas  106  and  122  means that the coupling coefficient is very high, and RF signal transfer is quite efficient. RF shielding layer  116  enclosed within the inner and outer polyester layers  120  and  114  acts as a nearly continuous electromagnetic shield completely surrounding DUT  102 ; as such, this may perform a similar function to a shielded enclosure, but at a significant reduction in weight, size and cost. The shielding effectiveness of shield jacket  100  is necessarily lower than that of a good quality enclosure, but in most cases this is not a significant issue because of the greatly improved coupling efficiency. RF shield layer  116  is electrically bonded to connector  108  and thus forms an extension of the coaxial cable shield of RF cable  113  used to connect to test equipment  112 . 
         [0024]    Some considerations and alternatives of the arrangement shown in  FIG. 1  may be covered here.  FIG. 1  shows the jacket  100  as being a flat sheet that is folded over the DUT  102 ; however, the jacket may also be constructed in the form of a pocket or pouch into which DUT  102  is placed, optionally with a flap that is folded over to complete the RF shield around the DUT. Electrically bonding shield layer  116  to itself at the edges of the pouch or pocket may improve the shielding effectiveness of jacket  100  in this configuration. Jacket  100  may be constructed from layers of flexible non-conductive fabric and metallized or metallic sheet (e.g., metallized Mylar), and additional layers of fabric may be provided to cover the cabling and antennas to provide for a more pleasing appearance. Further, logos or other pictorial representations may be sewn on to the fabric or stenciled or painted on its surface. DUT  102  is generally assumed to be battery powered; however, power cables or non-RF test wires to DUT  102  may be accommodated by leading these wires in through the corners or sides of jacket  100 . Test antenna  106  mounted on shield jacket  100  may be of any compact type, such as a surface-mount chip-style antenna, a small PCB substrate with etched traces, or compact wire/cylinder styles. 
         [0025]    The multiple laminated layers comprising jacket  100  provide for a certain stiffness, even though the overall construction is flexible. As a consequence, after jacket  100  is folded over DUT  102  and held securely with Velcro strips  104 , DUT  102  remains in an approximately fixed position relative to antenna  106  of shield jacket  100 , even with some limited handling. Inner layer  120  may be given a non-slip surface treatment to further prevent DUT  102  from moving about within jacket  100 . As a consequence, the coupling between DUT  102  and shield jacket antenna  106  is held constant and repeatable even without the use of mounting jigs. To further facilitate this, a DUT outline (or key reference points) may be marked on inner layer  120  of the shield jacket  100  to allow repeatable placement of the same or different DUTs  102  within the jacket. 
         [0026]    As previously mentioned, shield jacket antenna  106  is physically close to the DUT antenna(s)  122 , thereby increasing the efficiency of coupling. This is true even with DUTs  102  having integral antenna(s)  122 ; such DUTs  102  are difficult to deal with in shielded enclosures without special mounting jigs or precautions. If DUT  102  is capable of operating on multiple wireless bands, or implements multiple wireless protocols (such as wireless LAN and Bluetooth), a multiband antenna can be used in shield jacket  100  to enable all of the frequency bands and wireless protocols to be tested. 
         [0027]    It may be apparent that this system is very inexpensive and far lighter and more portable than anechoic chambers or shielded enclosures, while still offering the benefits of enhanced RF isolation and consistent and repeatable signal coupling. In particular it may be apparent that this system can be used without special setup or infrastructure requirements, and it will be readily clear to personnel not trained in RF techniques as to how to position and secure the DUT  102  within jacket  100  and connect it to test equipment  112 . 
         [0028]      FIG. 5  shows a shield jacket system that can be used to test MIMO DUTs. Shield jacket  100  illustrated in  FIG. 5  comprises the standard elements of the single-antenna shield jacket system depicted in  FIG. 1 , but incorporates two (or more) antennas  106  rather than a single antenna  106 . Each antenna  106  is connected to a separate RF connector  108  via a separate run of flexible RF cable  110 . The multiple antennas  106  in shield jacket  100  couple to the multiple antennas  122  of DUT  102 . The geometry of the system and the placement of DUT  102  at the center of the shield jacket system ensures that differential coupling exists between different pairs of DUT antennas  106  and shield jacket antennas. The operation of the remainder of the system is identical to that of the single-antenna case. 
         [0029]    It may not be necessary for careful placement of DUT antennas  122  with respect to shield jacket antennas  106 . As noted above, differential coupling is created by physical separation of shield jacket antennas  106 , and this differential coupling effectively sets up a MIMO channel model between shield jacket antennas  106  and DUT antennas  122 . While this MIMO channel model does not resemble the normal MIMO channel in an open-air environment containing scatterers, it is nevertheless sufficient to allow MIMO transmission to occur and multiple parallel streams of data to be exchanged between DUT  102  and the test equipment  112 . 
         [0030]    One benefit of the arrangement in  FIG. 5  is that MIMO DUTs with integral antennas can be simply and easily tested. There may be a substantial reduction in cost and size over standard MIMO enclosures or chambers. Repeatability may be ensured by placing the DUT on the same location in the shield jacket before folding over and securing it. This aligns the DUT antennas in the same position relative to the shield jacket antennas, and sets up substantially the same MIMO channel model each time the system is set up and used. 
         [0031]      FIG. 6  shows an enhancement of the system of  FIG. 5 , where additional antennas are embedded into the shield jacket  100  and combined into a single system using power dividers  124 . Each block of additional antennas  106  acts electrically as a single antenna, as the signals from all of the antennas are additively combined (or signals injected into the power dividers  124  are linearly split among antennas  106 ). As in the case of  FIG. 1  and  FIG. 5 , there may be either one block of additional antennas  106  (for a SISO system) or multiple blocks (for a MIMO system). The number of MIMO spatial streams supported may be determined by the number of separate blocks of antennas  106 . 
         [0032]    The arrangement in  FIG. 6  has the benefit that there is a shield jacket antenna  106  in close proximity to one of the internal antennas  122  in DUT  102 , regardless of where an antenna  122  may actually be physically integrated into the DUT. This enhances coupling to DUT  102  without necessitating the precise placement of the DUT within the shield jacket, or even determining where DUT antennas  122  are located with respect to the DUT geometry. The use of power dividers  124  ensures that the overall system impedance is maintained regardless of the number of additional antennas employed; the power split among the shield jacket antennas  106  results in a small loss of efficiency, but this is compensated for by the increase in coupling efficiency by having at least one shield jacket antenna  106  in closer proximity to a DUT antenna  122 . SMA connectors  108  for connecting to test equipment  112  may be rigidly mounted on power dividers  124 , or may be separately mounted on jacket  100  and one or more flexible cables  110  used to connect connectors  108  to power dividers  124 . 
         [0033]    The benefits of the arrangement of  FIG. 6  are readily observed. Larger DUTs  102  may be accommodated by enlarging jacket  100  and spreading out the additional antennas across the inner surface of jacket  100 , without losing efficiency due to an increased distance between DUT  102  and shield jacket antennas  106 . The need for precise placement of DUT  102  within shield jacket  100  may be obviated. Any number of antennas  106  may be included in shield jacket  100 , organized as any number of groups/blocks; the number of antennas within each group improves the coupling to the DUT, while the number of groups/blocks increases the number of MIMO spatial streams that can be handled. 
         [0034]      FIG. 7  shows the top view of a typical mechanical drawing for shield jacket  100  and antenna array  106 . The shield jacket fabric may have antennas  106  sewn between the outer and inner layers of fabric (as depicted in  FIG. 3 ). A dual power divider  124  may also be sewn to the fabric; this power divider  124  integrates the two separate power dividers shown in  FIG. 6  into a single housing, but is otherwise electrically similar. C 1 , C 2 , C 3  are flexible SMA cables  110  connecting the antennas  106  to power divider  124 , and may be secured to the jacket fabric by stitching. The test equipment is connected to SMA connectors  108  on the right. 
         [0035]      FIG. 8  is a mechanical drawing of shield jacket fabric layers made of polyester, with Velcro strips  104  used to secure the jacket around the DUT. Polyester layers  118  and  120  sandwich antennas  106  (which may be small ‘chip’ style or ‘PCB’ style multiband antennas), which are mounted on a polyester backing layer  118  with laminated foam. RF shield layer  116  is placed between backing layer  118  and outside polyester fabric layer  118 , so that it is separated from antennas  106  with a dielectric medium. The whole arrangement may be sewn together to create a durable system that facilitates repeatable DUT placement and removal, and can be folded a number of times without losing mechanical or electrical integrity. 
         [0036]      FIG. 9  shows an arrangement for further isolating DUT  102  and reducing the impact of external RF interference, employing the concept of a ‘waveguide below cutoff’. This arrangement makes use of the fact that a slot or hole in an otherwise continuous metallic layer is opaque to RF radiation if the width of the slot or radius of the hole is substantially less than one wavelength. Thus the isolating effect is that of an unbroken metallic sheet. The effect of the waveguide below cutoff is created by providing the shield jacket with a set of flaps  126  located on one half of the jacket. After the jacket is folded in half over the DUT along the main fold, flaps  126  are in turn folded over the other half. By extending the RF shield into the flaps as an electrically continuous conductive layer, RF shield layer  116  is caused to overlap with itself for at least a half wavelength. The effect caused thereby resembles a waveguide below cutoff, and excludes external RF radiation from entering the inside of folded shield jacket  100  and affecting DUT  102 . In order for this to function, RF shield layer  116  must be electrically continuous into folded flaps  126 , and the polyester and foam insulating layers must be sufficiently thin. 
         [0037]    Many other embodiments and applications of this arrangement may be apparent to persons skilled in the art. Jacket  100  may be unfolded and placed within a conventional shielded enclosure or anechoic chamber, potentially being attached to the wall of the chamber with the antennas pointing inwards, to serve as an antenna array. In another embodiment, small holes may be created in the polyester fabric and RF shield layer  116  for power dissipation, in order to deal with DUTs that need cooling airflow for normal operation; if each individual hole is well below 1 wavelength, the RF shielding properties will not be impaired. In yet another embodiment, a power cord and filter may be sewn into the shield jacket to supply operating power to DUTs if required; for example, if the battery capacity of the DUT is insufficient, or the DUT is not battery powered at all. In still another embodiment, the shield jacket may be cut and formed into different shapes (e.g., pouches, bags, wrappings) to accommodate the requirements of thick or oddly shaped DUTs. Another embodiment may include shield jacket antennas that are oriented in different directions to accommodate different polarizations of DUT antennas. 
         [0038]      FIG. 10  is a flow chart illustrating an exemplary process for testing a DUT using jacket  100  according to an embodiment of the subject matter described herein. Referring to  FIG. 10 , at step  1000 , test system  112  is connected to RF connector  108  of jacket  100 . The connection would typically be via an RF cable  113 . At step  1002  the DUT is enclosed within shield jacket  100 . As stated above, the enclosing may be achieved through folding or wrapping of jacket  100  around DUT  102  or placing DUT  102  in a pocket formed by jacket  100 . At step  1004 , test system  112  transmits RF data to and receives RF data from DUT  102  while DUT  102  is shielded by jacket  100 . 
         [0039]    It will be understood that various details of the presently disclosed subject matter may be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.