Abstract:
A hand-carriable, single port measurement module of a virtual vector network analyzer is sized and configured so as to be directly connectable to devices typically located within confined spaces normally requiring the use of an intervening test cable and which may be closely spaced to other devices that may need to be tested by other measurement modules. The measurement module includes a single test port extending from a housing wherein the housing is elongated along the axis of insertion of the test port and has a length substantially less than 12 inches. A circuit disposed within the housing is configured to transmit and receive test signals through the test port for measurement of a device under test and to transmit digitized signals representing the test signals through a communication interface of the module to a user interface separate from the housing for presentation to a user.

Description:
RELATED APPLICATION DATA 
       [0001]    This application is a continuation of U.S. application Ser. No. 13/591,124 filed Aug. 21, 2012, now U.S. Pat. No. 9,291,657, the contents of which are incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    Embodiments relate to vector network analyzers and, in particular, hand-held virtual vector network analyzer measurement modules. 
         [0003]    Current vector network analyzers (VNA) exist in either desktop or portable implementations. Desktop VNAs can have built-in user interfaces including displays, keyboards, or the like. The large size of these devices, even in the portable implementation, makes it difficult or impossible to perform measurements immediately on the connectors of the devices-under-test (DUTs) without the use of RF test cables. 
         [0004]    In addition, even with precision test cables, a DUT may be located in a relatively confined location such that the VNA cannot be calibrated with the test cables in their final positions, potentially introducing errors into the measurements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a diagram of a vector network analyzer according to an embodiment. 
           [0006]      FIGS. 2-4  illustrate a vector network analyzer measurement module according to another embodiment. 
           [0007]      FIG. 5  illustrates a test cable attached to a device-under-test in an enclosure. 
           [0008]      FIG. 6  illustrates a vector network analyzer attached to a device-under-test in an enclosure according to an embodiment. 
           [0009]      FIG. 7  is a block diagram of a vector network analyzer measurement module according to an embodiment. 
           [0010]      FIG. 8  is a block diagram of a vector network analyzer measurement module according to another embodiment. 
           [0011]      FIG. 9  is a diagram of a vector network analyzer according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    In an embodiment, a virtual vector network analyzer measurement module&#39;s portability, virtual format, and power draw from a computer interface allows a user to conduct tests directly linking the analyzer test ports and a DUT. The resulting benefit is a considerable enhancement in accuracy; meanwhile, the vector network analyzer (VNA) operation becomes easier and more cost-effective. 
         [0013]      FIG. 1  is a diagram of a VNA according to an embodiment. In this embodiment, a VNA  1  includes a portable measurement module  6  coupled to a computer  2  by a cable  4 . The measurement module  6  is configured to generate and receive test signals. The measurement module  6  includes higher-frequency components, such as oscillators, synthesizers, couplers, splitters, bridges, mixers, amplifiers, filters, transmission lines, or the like. These components are configured to generate and measure test signals of the incident wave for transmission out of a test port of measurement module  6  to the DUT and receive test signals of the reflected wave from the DUT through the aforementioned port. As will be described in further detail below, other components of measurement module  6  process the test signals into a format suitable for transmission over cable  4  to personal computer  2 . 
         [0014]    For example, a synthesizer in the measurement module  6  generates a single frequency incident test signal. That test signal is mixed with a local oscillator signal generated by a second synthesizer, and together they form the IF signal corresponding to the test signal of the incident wave. The incident test signal is also transmitted out of a test port of the measurement module  6 . The measurement module  6  receives the incident test signal, reflected off of a DUT, if present, as a reflected test signal. The reflected test signal is mixed with the local oscillator signal, and together they form the IF signal corresponding to the test signal of the reflected wave. These IF incident and reflected test signals are digitized in the measurement module  6 . The measurement module  6  is configured to generate a phasor representation of a ratio of the IF incident and reflected test signals. The phasor representation for one or more test signal frequencies are digitized test signals that are transmitted to the computer  2  over the cable  4 . Accordingly, a position, movement, deterioration, or the like of components between the measurement module  6  and the computer  2  will not have any effect on the measurement accuracy. 
         [0015]    The cable  4  is associated with a power and communication interface. In this embodiment, the cable  4  is a universal serial bus (USB) cable. A corresponding USB port of the computer  2  provides both communications and power to the measurement module  6 . 
         [0016]    The digitized signals are transmitted to the computer  2  through the cable  4 . Accordingly, the user interface of the VNA  1 , such as a display, keyboard, buttons, knobs, other processing circuitry, or the like, is separate from a housing including a test port of the measurement module  6 . As a result, the measurement module  6  is smaller than a conventional device integrated with the user interface. 
         [0017]    The computer  2  is configured to present a user interface for manipulating the magnitude and phase signals and/or any derived information. For example, the computer  2  is configured to present a display of phase, magnitude, delay, or the like of the received signals in response to user input. The computer  2  is configured to present the information in Cartesian graphs, Smith charts, or the like. 
         [0018]    Since the user interface is located at the computer  2 , user interface components are not present at the measurement module  6 , thus reducing a size and power consumption of the measurement module  6 . The smaller size allows the measurement module  6  to be directly connected to a device under test (DUT). That is, no test cables are needed. In contrast, if the measurement module  6  was integrated with the user interface, test cables would be required to couple to a DUT. 
         [0019]    By eliminating the need for a test cable, any variation in measurement due to the test cables, such as variations due to environmental changes, movement of the test setup, or the like is eliminated. For example, when the VNA  1  is calibrated, the calibration is performed at the test port mounted to the measurement module  6 . Since any circuitry, cables, transmission lines, or the like between the connector of the measurement module  6  and any sensing circuitry is contained within a housing of the measurement module  6 , movement of the measurement module  6  will have a substantially reduced, if not negligible effect on the calibration of the VNA  1 . 
         [0020]    The cable  4  allows for flexibility in positioning the measurement module  6  that both accommodates positions available by using a test cable and positions prohibited by a test cable. For example, a DUT is located in a physically constrained location, such as within a cabinet, a vehicle chassis, or the like. Routing and manipulation of the cable  4  when attaching the measurement module  6  does not substantially affect a calibration of the VNA  1  since the interface cable  4  need not be a precision test cable. Accordingly, costs to locate the test port of the VNA  1  at a desired location are reduced. 
         [0021]    Although a computer  2  has been given as an example, other types of devices can be used. For example, a laptop computer, desktop computer, test and measurement instrument, tablet computer, smartphone, or the like can be used. Any device with a suitable communication interface through which power is provided may be used. 
         [0022]    Although a USB cable has been given as an example of the cable  4 , other cables and interface systems can be used to enable communication and supply power. In another embodiment, the computer  2  is configured to provide a power-over-Ethernet connection. The power and communication interface is any communication interface that supplies power, whether through separate connections of the cable  4  or multiplexed with the communication signals. 
         [0023]      FIGS. 2-4  illustrate a vector network analyzer measurement module  10  according to another embodiment. The measurement module  10  includes a housing  12  with a test port  14  mounted on the housing. A power and communication interface  22  is disposed opposite the test port  14 . In another embodiment, the interface  22  is disposed in other locations where the interface  22  and any connecting cable do not interfere with the test port  14  and mounting the test port  14  to a DUT. 
         [0024]    The housing  12  defines a first dimension  20  that is preferably less than about 2 inches. In an embodiment, the first dimension is less than about 1 inch. The housing  12  has a second dimension  24  that is preferably less than about 1.5 inches. In the illustrated embodiment, the first dimension  20  and second dimension  24  are the smallest major dimensions of the housing  12 . 
         [0025]    The dimensions  20  and  24  are dimensions of the measurement module  10  allow a user to grip the measurement module  10  substantially within the user&#39;s hand. In an embodiment, the length of a perimeter substantially formed by dimensions  20  and  24  is less than about 12 inches, and preferably less than about 5 inches. 
         [0026]    In an embodiment, dimensions  20  and  24  are substantially perpendicular with the insertion axis defined by the test port  14 . Accordingly, a cross-section of the housing  12  is smaller, allowing the measurement module to be attached to a DUT within a confined space. When DUTs are closely spaced, movement in a plane substantially perpendicular with an insertion axis of a port of the DUT is limited. Accordingly, the reduced cross-sectional size of the housing allows the measurement module  10  to be directly connected to a DUT in such an environment. 
         [0027]    In an embodiment, a third dimension  18  of the housing is less than about 5 inches. Accordingly, the housing  12  fits comfortably in a user&#39;s hand. When a user holds the housing  12  in one hand, the user attaches the test port  14  to a DUT using the other hand, for example, with an appropriate torque wrench. The dimensions described above result from separating the user interface device from high frequency circuitry within the measurement module  10 . 
         [0028]      FIG. 5  illustrates a test cable attached to a device-under-test in an enclosure. In an embodiment, a DUT  42  is mounted in an enclosure  40 . The enclosure  40  has a surface  41 , such as a wall, shelf, panel, or the like, that least partially obstruct access to a connector  44  of the DUT  42 . 
         [0029]    As illustrated, a test cable  46  with connector  48  is coupled to the connector  44  of the DUT  42 . Test cables  46  have a specified minimum bend radius below which performance of the cable  46  is undefined. Accordingly, when coupling the test cable  46  to the DUT  42 , the bend radius  50  may approach the test cable&#39;s  46  minimum bend radius due to the confines of the space. 
         [0030]    In addition, a calibration must be performed at the connector  48  to substantially eliminate effects of the cable. However, it is impractical to calibrate the VNA at the connector  48  inside of the enclosure  40 , particularly with the cable  46  in substantially the same position as when coupled to the DUT  42 . Thus, the calibration must be performed outside of the enclosure  40 . As a result, the test cable  46  will not have the same physical characteristics such as position, bend radius, or the like between when the VNA is calibrated and when the test cable  46  is coupled to the DUT  42 . Thus, errors in measurements are introduced. 
         [0031]      FIG. 6  illustrates a vector network analyzer attached to a device-under-test in an enclosure according to an embodiment. In this embodiment, a measurement module  60  is directly coupled to the DUT  42 . Connector  62  of the measurement module  60  is directly connected to the connector  44  of the DUT  42 . 
         [0032]    In this embodiment, a dimension  66  of the housing of the measurement module  60  along an axis of insertion of the DUT connector  44  is less than a minimum bend radius of cable operable over a frequency range including a frequency range of the vector network analyzer. That is, the position of the DUT  42  accommodates a test cable with a bend approaching the minimum bend radius. Since the size of the measurement module  60  is smaller than the minimum bend radius, the measurement module can be inserted into the same space and coupled to the DUT  42 . 
         [0033]    Moreover, the measurement module  60  is calibrated outside of the enclosure  40 . In contrast to the test cable  46 , moving the measurement module  60  into the enclosure  40  will not substantially change the conditions under which the measurement module  60  was calibrated. That is, the calibration was performed at the connector  62 . The connector  62  is substantially rigidly mounted to the housing of the measurement module  60 . Thus, substantially no relative motion will occur between the calibrated port and the sensing circuitry. Any movement, change in position, or the like of cable  64  will not affect the calibration since only digitized signals are transmitted over the cable  64 . 
         [0034]    In an embodiment, locating the user interface external to the housing  12  results in a measurement module  10  that is lighter than a conventional VNA. The absence of components like the display, power supply, keyboard, and the housing necessary for their containment, eliminates additional weight to the measurement module  10 . In an embodiment, the VNA-measurement module  10  weighs less than about 250 g. 
         [0035]      FIG. 7  is a block diagram of a vector network analyzer measurement module according to an embodiment. In this embodiment, the measurement module  80  includes a housing  82 . A power and communication interface  84  and a test port  86  are mounted on the housing. The measurement module  80  also includes a controller  88  and microwave electronics  90 . 
         [0036]    The microwave electronics  90  are configured to generate an incident signal to transmit through the test port  86  and receive a reflected signal through the test port  86 . The microwave electronics  90  include synthesizers, mixers, couplers, splitters, resistive bridges, or the like for generating and processing incident test signals and received test signals, whether reflected off of another device or transmitted from another measurement module. In an embodiment, the microwave electronics  90  include the circuitry to generate test signals and convert both transmitted and received test signals into lower frequency intermediate frequency (IF) signals and/or phasor representations. That is, high frequency circuitry and connections for signals needing a signal path that is affected by geometry, position, motion, or the like is contained within the measurement module  82 . 
         [0037]    The controller  88  is configured to receive such IF signals or similar signals and generate digitized signals for transmission through the power and communication interface  84 . In an embodiment, the controller  88  includes a general purpose processor, an application specific integrated circuit, a digital signal processor, a programmable logic device, a combination of such circuits, or the like. In an embodiment the controller  88  includes integrated analog to digital converters, data ports for external analog to digital converters, or the like. In addition, the controller  88  includes integrated communication interfaces such as USB ports, Ethernet ports, external implementations of such ports, or the like. 
         [0038]    The measurement module  80  is configured to obtain power from the power and communication interface  84 . That is, the power for the controller  88  and microwave electronics  90  is obtained through the power and communication interface. In this embodiment, no other power supply is present. 
         [0039]      FIG. 8  is a block diagram of a vector network analyzer measurement module according to another embodiment. The measurement module  110  includes a test port  116  and a power and communication interface  114  mounted on a housing  112  similar to a measurement module described above. In this embodiment, the measurement module  110  includes a first synthesizer  128  and a second synthesizer  122 . 
         [0040]    The first synthesizer  128  is formed in an integrated circuit  120 . The first synthesizer  128  includes one or more oscillators, frequency dividers, frequency multipliers, attenuators, amplifiers, filters, or the like to generate a desired signal. In particular, the first synthesizer  128  is used to generate an incident signal for the measurement module  110 . 
         [0041]    The first synthesizer  128  is coupled to the controller  152 . The controller  152  is configured to set various parameters of the incident signal, such as frequency power, dividing/multiplying ratio, or the like. 
         [0042]    The incident signal is provided to a resistive bridge or splitter  132 . In an embodiment a resistive bridge couples the incident signal to the resistive bridge  136  and a mixer  126 . Accordingly, the incident signal is transmitted out of the test port  116  and downconverted through the mixer  126  for measurement. 
         [0043]    The measurement module  110  includes a second synthesizer  122 . The second synthesizer  122  is formed in an integrated circuit  118 . The second synthesizer  122  includes one or more oscillators, frequency dividers, frequency multipliers, attenuators, amplifiers, filters, or the like to generate a desired signal. In addition, the integrated circuit  118  including the second synthesizer  122  includes mixers  124  and  126 . In particular, the second synthesizer  122  is configured to generate a local oscillator signal for mixers  124  and  126 . 
         [0044]    The second synthesizer  122  is coupled to the controller  152 . The controller  152  is configured to set various parameters of the incident signal, such as frequency power, dividing/multiplying ratio, or the like. Accordingly, the controller  152  is configured to set parameters of the incident signal from the first synthesizer  128  and the local oscillator signal from the second synthesizer  122  such that the incident signal and a reflected signal are downconverted to a desired IF signal frequency range. That is, the incident signal is downconverted in the mixer  126  and the reflected signal received through the test port  116  is coupled to the mixer  124  through the resistive bridge  136  and downconverted to the desired IF signal frequency range. The controller  152  is configured to sweep frequencies of the first synthesizer and the second synthesizer and substantially maintain a frequency offset between the incident signal and the local oscillator signal. In another embodiment, the controller  152  is configured to receive commands through the power and communication interface  114  to control a sweep of test signals. 
         [0045]    Although a splitter and resistive bridge have been used as examples, in an embodiment, other components and structures are used to isolate signals. For example, circulators, couplers, a combination of such components, or the like are used to route the incident and reflected signals. 
         [0046]    In an embodiment, an IF incident signal  146  and an IF reflected signal  148  are digitized in digitizers  150 . The controller  152  is configured to further process the digitized signals  156  and  158  for storage in the memory  154 , transmission through the power and communication interface  114 , or the like. In an embodiment, the controller  152  is configured to convert the IF signals into a phasor representation of the reflected signal using the incident signal as a reference. Coefficients from a calibration are applied by the controller  152  or at a later time after transmission. In another example, the digitized IF signals are transmitted through the power and communication interface  114 . A user interface is configured to apply a correction for a calibration. That is, once the high frequency signals are converted into lower frequency and/or digital signals, any amount of processing of the signals are distributed between the measurement module  110  and a user interface from complete processing of the signals at the user interface to complete processing of the signals at the measurement module. However, the presentation of any resulting measurements occurs at the user interface, separate from the measurement module. 
         [0047]    In an embodiment, the digitizers  150  are integrated with the controller  152 . For example, a microcontroller, application specific integrated circuit, or the like includes integrated analog to digital converters. In addition, at least a part of the power and communication interface  114  is included in the controller. In an embodiment, the controller  152  includes a communication portion of a USB interface. Accordingly, size, weight, power consumption, or the like is reduced by using such integrated components described above. 
         [0048]    In an embodiment, the memory  154  is any variety of memory. For example, the memory  154  includes static memory, dynamic memory, flash memory, an electrically erasable programmable read only memory (EEPROM), a combination of such memories, or the like. In an embodiment. the memory  154  is configured to store factory correction coefficients, user calibration coefficients and the software for installation onto an external user interface to control the measurement module  110 . In an embodiment, the memory  154  is separate from the controller  152 , integrated with the controller  152 , a combination of external and internal memory, or the like. 
         [0049]    Although a single synthesizer  128  has been described for generating an incident signal, in an embodiment, multiple synthesizers, oscillators, or the like are present. For example, an additional synthesizer is present to increase the measurement range of the measurement module. Additional test signal amplifiers, frequency multipliers, frequency dividers, attenuators, filters, switches, or the like are present. 
         [0050]    In an embodiment, the measurement module  110  includes a reference frequency generator, a programmable automatic frequency control, a reference frequency input, or the like. The synthesizers  122  and  128  are configured to be phase locked to such a reference frequency signal. 
         [0051]    In an embodiment, a measurement range of the measurement module  128  is extended. The mixers  124  and  126  are driven with a local oscillator signal having a frequency that is one third of a sum or difference of a frequency of the incident signal and an intermediate frequency signal. A third harmonic of such a local oscillator signal, generated in the mixer, downconverts the higher frequency incident signal. Accordingly, smaller, lower frequency components are used for a higher operating frequency range. As a result, the size, weight, power consumption, or the like of the measurement module  110  can be reduced. 
         [0052]    In an embodiment, integrating the higher frequency components allows for a smaller footprint, yet a higher frequency range. For example, with the integrated circuits  118  and  120  described above, the frequency range of the measurement module can be extended up to about 5 GHz or greater, for example up to at least 5.4 GHz. In another example, the upper frequency limit can be about 13 GHz or greater, for example, at least about 13.5 GHz. 
         [0053]      FIG. 9  is a block diagram of a vector network analyzer according to another embodiment. As described above, the measurement module  6  is used as a vector reflectometer. That is, measurement module  6  is used as part of a single port vector network analyzer. In another embodiment, multiple measurement modules are used to create a multi-port VNA. 
         [0054]    In this embodiment, a VNA  170  is configured similar to the VNA  1  of  FIG. 1 . However, an additional measurement module  174  is coupled to the computer  2  with a cable  172  similar to the cable  4 . Accordingly, test signals are generated from either measurement modules  6  and  174 . Using the measurement module  6  as an example for generating an incident signal, the incident signal is transmitted through a DUT (not shown) to the measurement module  174 . 
         [0055]    Accordingly, the measurement module  174  measures the transmitted, incident signal. For example, the measurement module  174  measures a magnitude of the transmitted incident signal. That is, the measurement module  174  operates as a scalar test analyzer. 
         [0056]    In another example, the measurement module  174  is configured to receive the transmitted incident signal and generate an internal reference signal. For example, a reference signal, such as a 10 MHz reference signal, can be used to synchronize the measurement modules  6  and  174  to phase lock the internal reference signal to the incident signal. Accordingly, a phase locked local oscillator signal within the measurement module  174  is generated to downconvert a received incident signal to an IF frequency range. In another example, the synchronization can be implemented with a programmable automatic frequency control. 
         [0057]    In an embodiment, the user interface is provided by the computer  2 . Accordingly, the VNA  170  operates as a conventional two-port VNA, albeit without various constraints as described above. However, the computer  2  need not be the interface for the measurement modules. In an embodiment, in a manufacturing setup, a test instrument has several measurement modules. Each of the measurement modules operate substantially independently as reflectometers, or in conjunction as multi-port test setups. To transition from a single-port or two-port setup to a multi-port setup of multiple single or two port setups, a user need only acquire additional measurement modules, rather than purchasing an entire new instrument or an entire new multi-port test set. 
         [0058]    In an embodiment, multiple reflectometers, two-port setups, and multi-port setups, are coupled to the same user interface. In an embodiment, a computer has multiple USB ports, each of which is coupled to a USB hub with multiple ports. Each terminal USB port is coupled to an associated measurement module. Although a USB hub has been used as an example, any switch, router, computer, or other communication device is used to distribute measurement modules in desired location. 
         [0059]    Although particular embodiments have been described above, the scope of the following claims is not limited to these embodiments. Various modifications, changes, combinations, substitution of equivalents, or the like is made within the scope of the following claims.