Abstract:
A method for measuring a frequency translation device under test by using a vector network analyzer and a reference frequency translation device comprises: measuring the network characteristics of the abovementioned reference frequency translation device by using the abovementioned vector network analyzer, measuring the network characteristics of a circuit comprised of the abovementioned reference frequency translation device and the abovementioned frequency translation device under test using the abovementioned vector network analyzer, wherein the abovementioned reference frequency translation device has an operation complementary to the abovementioned frequency translation device under test, and removing the network characteristics of the abovementioned reference frequency translation device from the measured network characteristics of the abovementioned circuit.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method for measuring the network characteristics of a frequency translation device by using a vector network analyzer.  
       DISCUSSION OF THE BACKGROUND ART  
       [0002]     One important structural element in communication equipment or communication systems is a frequency translation device. A frequency translation device translates the frequency of some signal to another frequency as in a mixer or a sampler. If the network characteristics of a frequency translation device can be accurately measured, the communication equipment or communication system can be optimized. Until now, several methods for measuring the network characteristics of a frequency translation device have been proposed. These methods measure the network characteristics of a frequency translation device by using a vector network analyzer. Some methods require S 21 =S 12  to be satisfied in the network characteristics of the frequency translation device, which is the device under test (see Unexamined Japanese Patent Publication No. 2002-57530 (pages 2-3, FIG. 1). Other methods require a special structure for the vector network analyzer (see Unexamined Japanese Patent Publication No. 2002-202, 331 (pages 3-4, FIG. 1, FIG. 2). The special structure is a structure for measuring in the state with different source and receiver frequencies.  
         [0003]     In the past few years, balanced input/balanced output frequency translation devices have become widely used. The network characteristics of a balanced input/balanced output frequency translation device can be measured by connecting a balun. However, in this measurement method, the network characteristics of the balun are included in the network characteristics of the frequency translation device. In addition, this measurement method cannot perform measurements related to the in-phase signal component.  
         [0004]     The present invention is to provide a method for measuring the network characteristics of all frequency translation devices by using an ordinary vector network analyzer. In addition, the present invention will provide a method for accurately measuring the network characteristics of a balanced input/balanced output frequency translation device.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention was developed to solve the abovementioned problem. A method for measuring a frequency translation device under test by using a vector network analyzer and a reference frequency translation device, and comprises:  
         [0006]     measuring the network characteristics of the abovementioned reference frequency translation device by using the abovementioned vector network analyzer, using the above-mentioned vector network analyzer to measure the network characteristics of a circuit comprised of the above-mentioned reference frequency translation device and the above-mentioned frequency translation device under test wherein the above-mentioned reference frequency translation device has an operation complementary to the above-mentioned frequency translation device under test, and  
         [0007]     removing the network characteristics of the abovementioned reference frequency translation device from the measured network characteristics of the abovementioned circuit.  
         [0008]     Moreover, the present invention generates a local signal input from the same signal source to the abovementioned reference frequency translation device and the abovementioned frequency translation device under test.  
         [0009]     An additional embodiment according to the present invention pertains to a method for measuring a balanced input/balanced output frequency translation device under test by using a vector network analyzer, a first reference frequency translation device and a second reference frequency translation device that have unbalanced input/unbalanced output configurations, and comprises:  
         [0010]     measuring the network characteristics of the abovementioned first reference frequency translation device by using the abovementioned vector network analyzer;  
         [0011]     measuring the network characteristics of the abovementioned second reference frequency translation device by using the abovementioned vector network analyzer;  
         [0012]     determining the phase difference between a first local signal in the abovementioned first reference frequency translation device and a second local signal in the abovementioned second reference frequency translation device;  
         [0013]     synthesizing the network characteristics representing the abovementioned phase difference that was determined in the measured network characteristics of the abovementioned second reference frequency translation device;  
         [0014]     measuring the network characteristics of a circuit comprised of the abovementioned first reference frequency translation device, the abovementioned second reference frequency translation device, and the abovementioned frequency translation device under test using the above-mentioned vector analyzer, wherein the abovementioned first reference frequency translation device and the abovementioned second reference frequency translation device have an operation complementary to the abovementioned frequency translation device under test; and  
         [0015]     removing the network characteristics of the abovementioned first reference frequency translation device and the synthesized network characteristics of the abovementioned second reference frequency translation device from the measured network characteristics of the abovementioned circuit.  
         [0016]     The present invention also pertains to a circuit comprised of the abovementioned first reference frequency translation device and the abovementioned second reference frequency translation device as the abovementioned step for determining the phase difference, and includes a step that uses the abovementioned vector network analyzer to measure a circuit wherein the abovementioned first reference frequency translation device has an operation complementary to the abovementioned second reference frequency translation device.  
         [0017]     A circuit comprised of the abovementioned first reference frequency translation device, the abovementioned second reference frequency translation device, and an added unbalanced input/unbalanced output frequency translation device as the abovementioned step for determining the phase, and comprises a step that uses the abovementioned vector network analyzer to measure the circuit wherein the abovementioned first reference frequency translation device and the abovementioned second reference frequency translation device have an operation complementary to the abovementioned added frequency translation device.  
         [0018]     Furthermore, the present invention generates a local signal from the same signal source for input to the abovementioned first reference frequency translation device, the abovementioned second reference frequency translation device, and the abovementioned frequency translation device under test in the method of any one of the aforementioned.  
         [0019]     The present invention also includes a program for executing the method of any one of the aforementioned embodiments in a computer for externally controlling a vector network analyzer or a vector network analyzer providing a computation means.  
         [0020]     Another embodiment is a system for measuring a frequency translation device by performing the method of any one of the aforementioned embodiments.  
         [0021]     According to the present invention, the network characteristics of all frequency translation devices can be measured by using an ordinary vector network analyzer. Compared to the prior art, according to the present invention, the number of reference frequency translation devices required for measuring is decreased. Furthermore, according to the present invention, the network characteristics of a balanced input/balanced output frequency translation device can be accurately measured. Furthermore, according to the present invention, a program is provided for measuring and storing the measurement results, such as the network characteristics of the reference frequency translation devices, in advance, for use in extracting the network characteristics of the frequency translation device under test. Consequently, the inconveniences to the tester, such as saving the parameters, are lessened, and measuring the network characteristics of the frequency translation device under test can be easily performed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  illustrates the vector network analyzer  100  of the first embodiment.  
         [0023]      FIG. 2  is a flow chart illustrating the measurement procedure in the first embodiment.  
         [0024]      FIG. 3  illustrates the vector network analyzer  500  of the second embodiment.  
         [0025]      FIG. 4  is a flow chart illustrating the measurement procedure of the second embodiment.  
         [0026]      FIG. 5  illustrates the configuration for measuring the phase difference between the local signals.  
         [0027]      FIG. 6  illustrates the configuration for measuring the phase difference between the local signals. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     Preferred embodiments of the present invention are explained below with reference to the attached drawings. The first embodiment of the present invention is a vector network analyzer  100  for measuring an unbalanced input/unbalanced output frequency translation device.  
         [0029]     Here, refer to  FIG. 1 .  FIG. 1  illustrates the internal configuration of vector network analyzer  100 . In  FIG. 1 , the vector network analyzer  100  is comprised of a measuring device  110 , a central processing unit (CPU)  120 , a memory device  130 , a drive device  140 , and an interface device  150 . In this specification, the interface device is abbreviated as the I/F device and shown.  
         [0030]     The measuring device  110  measures the network characteristics of the device under test connected through a port  111  or a port  112 . The CPU  120  controls each structural element of the vector network analyzer  100  such as the measuring device  110 . The memory device  130  stores data and programs. The drive device  140  can be read by a vector network analyzer  100  or an external computer and operates a removable recording medium. Data and programs are stored on the abovementioned recording medium. The interface device  150  outputs to the user, receives input from the user, and communicates with the external computer. For example, the interface device  150  includes a display and a keyboard, or a local area network (LAN) interface.  
         [0031]     Next, the procedure for measuring the network characteristics of a frequency translation device  200 , which is the device under test, in the vector network analyzer  100  is explained.  FIG. 2  is a flow chart illustrating the measurement procedure of the frequency translation device  200 . The network characteristics of the frequency translation device  200  are measured by executing a program stored in the memory medium in the memory device  130  or the drive device  140 , or under the control of an external computer (not shown) through the interface device  150 . In this specification, the vector network analyzer is abbreviated as VNA and shown. Similarly, the frequency translation device is abbreviated as FTD and shown. Below, refer to  FIGS. 1 and 2 .  
         [0032]     In step S 11 , the vector network analyzer  100  is calibrated. Since the number of ports used when measuring the network characteristics of the frequency translation device  200  is two, a full 2-port calibration is performed.  
         [0033]     In step S 12 , the vector network analyzer  100  is used to measure the network characteristics of an unbalanced input/unbalanced output reference frequency translation device  300 . The method for measuring the network characteristics of the reference frequency translation device is disclosed in Unexamined Japanese Patent Publication No. 2002-57530. The network characteristics of the reference frequency translation device  300  measured in this step are stored in memory device  130 .  
         [0034]     In step S 13 , as shown in  FIG. 1 , circuit A having reference frequency translation device  300  serially connected to frequency translation device  200  connects to the vector network analyzer  100 . The vector network analyzer  100  is used to measure the network characteristics of series circuit A. Then the output signal of a signal source  400  is applied to frequency translation device  200  and reference frequency translation device  300  as the local signal. The local signal is the signal for manipulating the signal input to the frequency translation devices. For example, when the frequency translation device is a mixer, the local signal is input to the local terminal (LO terminal) of the mixer. When the frequency translation device is a sampler, the local signal is input to the control terminal (CTRL terminal) of the sampler. Then the frequency translation device  200  and the reference frequency translation device  300  have complementary operation in series circuit A. That is, if the frequency translation device  200  upconverts the signal passing through circuit A, reference frequency translation device  300  downconverts. Conversely, if frequency translation device  200  downconverts the signal passing through circuit A, reference frequency translation device  300  upconverts. Consequently, since series circuit A outputs a signal having the same frequency as the input signal, the vector network analyzer  100  is not provided with a special structure and can measure series circuit A.  
         [0035]     In step S 14 , the network characteristics of reference frequency translation device  300  measured beforehand are read out of the memory device  130 . Then the network characteristics of reference frequency translation device  300  are removed (de-embedded) from the network characteristics of series circuit A measured in step S 13 . The resulting network characteristics are output to the interface device  150  as the network characteristics of frequency translation device  200 .  
         [0036]     Next, a second embodiment of the present invention is explained. The second embodiment of the present invention is a vector network analyzer for measuring a balanced input/balanced output frequency translation device.  
         [0037]     Here, refer to  FIG. 3 .  FIG. 3  illustrates the internal structure of a vector network analyzer  500 . In  FIG. 3 , the vector network analyzer  500  is comprised of a measuring device  510 , a CPU  520 , a memory device  530 , a drive device  540 , and an interface device  550 .  
         [0038]     The measuring device  510  measures the network characteristics of the device under test connected through a port  511 , a port  512 , a port  513 , or a port  514 . CPU  520  controls each structural element of the vector network analyzer  500 , such as the measuring device  510 . The memory device  530  stores data and programs. The drive device  540  can be read by an external computer and vector network analyzer  500  and operates a removable recording medium. Data and programs are stored on the abovementioned recording medium. The interface device  550  outputs to the user, receives input from the user, and communicates with the external computer. For example, the interface device  550  includes a display and a keyboard, or a LAN interface.  
         [0039]     Next, the procedure in the vector network analyzer  500  for measuring the network characteristics of a frequency translation device  600 , which is the device under test, is explained.  FIG. 4  is a flow chart illustrating the measurement procedure of the frequency translation device  600 . The network characteristics of frequency translation device  600  are measured by executing a program stored in the recording medium in the memory device  530  or the drive device  540 , or by control from the external computer (not shown) through the interface device  550 . Below, refer to  FIGS. 3 and 4 .  
         [0040]     In step S 21 , vector network analyzer  500  is calibrated. Since the number of ports used in the measurement of the network characteristics of frequency translation device  600  is four, a full 4-port calibration is performed.  
         [0041]     In step S 22 , the vector network analyzer  500  is used to measure the network characteristics of an unbalanced input/unbalanced output reference frequency translation device  710 . The method for measuring the network characteristics of the reference frequency translation device is disclosed in Unexamined Japanese Patent Publication No. 2002-57530. The network characteristics of reference frequency translation device  710  measured in this step are stored in memory device  530 .  
         [0042]     Similar to step S 22 , step S 23  uses vector network analyzer  500  to measure the network characteristics of an unbalanced input/unbalanced output reference frequency translation device  720 . The network characteristics of the reference frequency translation device  720  measured in this step are stored in memory device  530 .  
         [0043]     In step S 24 , vector network analyzer  500  is used to measure the phase difference between a local signal  711  applied to reference frequency translation device  710  and a local signal  721  applied to reference frequency translation device  720 . The measured phase difference is stored in the memory device  530 .  
         [0044]     As shown in  FIG. 3 , when frequency translation device  600  is measured, reference frequency translation device  710  and reference frequency translation device  720  are connected to the balanced output of frequency translation device  600 . At this time, if there is a phase difference between local signal  711  and local signal  721 , a phase difference is produced between the output signal of reference frequency translation device  710  and the output signal of reference frequency translation device  720 . Therefore, the network characteristics of frequency translation device  600  cannot be correctly determined. To correct this, the phase difference between local signal  711  and local signal  721  is measured beforehand.  
         [0045]     For example, the phase difference between local signal  711  and local signal  721  is measured by the configurations as shown in  FIGS. 5 and 6 . In  FIGS. 5 and 6 , the same reference numbers are assigned to the same elements as in  FIG. 3  and their descriptions are omitted.  
         [0046]     Here, refer to  FIG. 5 . In the figure, reference frequency translation device  710  and reference frequency translation device  720  are serially connected to have complementary operation. In addition, the local terminals of reference frequency translation device  710  and reference frequency translation device  720  are connected to a signal source  800  to be in the same state as in  FIG. 3 . If reference frequency translation device  710  upconverts the signal passing through series circuit C comprised of reference frequency translation device  710  and reference frequency translation device  720 , reference frequency translation device  720  downconverts. Conversely, if reference frequency translation device  710  downconverts the signal passing in series circuit C, reference frequency translation device  720  upconverts. Then bidirectional measurements (forward direction and reverse direction) are performed on series circuit C. At this time, the phase difference of the measured signal corresponds to twice the phase difference between local signal  711  and local signal  721 . Let the phase difference between local signal  711  and local signal  721  be set to θ, and the S-parameters representing phase difference θ are represented by the following equation. The following equation can be converted to another parametric formula.  
             [         0         ⅇ   jθ               ⅇ     -   jθ           0         ]           Equation   ⁢           ⁢   1             
 
         [0047]     Here, refer to  FIG. 6 . In this figure, reference frequency translation device  710  and reference frequency translation device  720  are connected to an added unbalanced input/unbalanced output frequency translation device  900  to have complementary operation. The network characteristics of frequency translation device  900  do not have to be known. The output signal of signal source  800  is applied to frequency translation device  900  as the local signal. Reference frequency translation device  710  and reference frequency translation device  720  are connected to signal source  800  to be in the same state as in  FIG. 3 , and the output signal of signal source  800  is applied as the local signal. In other words, if frequency translation device  900  upconverts the signal passing through circuit D comprised of reference frequency translation device  710 , reference frequency translation device  720 , and frequency translation device  900 , reference frequency translation device  710  and reference frequency translation device  720  downconvert. Conversely, if frequency translation device  900  downconverts the signal passing through circuit D, reference frequency translation device  710  and reference frequency translation device  720  upconvert. Then the measurement signal is applied to frequency translation device  900 , and circuit D is measured. The result is that the phase difference θ between the output signal of reference frequency translation device  710  and the output signal of reference frequency translation device  720  is measured. The S-parameters representing the phase difference θ are expressed by the above equation.  
         [0048]     Again referring to  FIGS. 3 and 4 , in step S 25 , the network characteristics representing the phase difference obtained in step S 24  (for example, the S-parameters in the above equation) are synthesized in the network characteristics of reference frequency translation device  720  obtained in step S 23 . The synthesized network characteristics of reference frequency translation device  720  are stored in memory device  530 .  
         [0049]     As shown in  FIG. 3 , in step S 26 , circuit B comprised of reference frequency translation device  710 , reference frequency translation device  720 , and frequency translation device  600  are connected to vector network analyzer  500 . Then vector network analyzer  500  is used to measure the network characteristics of circuit B. The output signal of signal source  800  is applied to reference frequency translation device  710 , reference frequency translation device  720 , and frequency translation device  600  as the local signal. In circuit B, reference frequency translation device  710  and reference frequency translation device  720  have an operation complementary to frequency translation device  600 . In other words, if frequency translation device  600  upconverts the signal passing through circuit B, reference frequency translation device  710  and reference frequency translation device  720  downconvert. Conversely, if frequency translation device  600  downconverts the signal passing through circuit B, reference frequency translation device  710  and reference frequency translation device  720  upconvert. Consequently, circuit B outputs a signal having the same frequency as the input signal, and vector network analyzer  500  is not provided with a special configuration and can measure circuit B.  
         [0050]     In step S 27 , the network characteristics of reference frequency translation device  710  measured in advance and of reference frequency translation device  720  synthesized in step S 25  are read out of memory device  530 . Then the network characteristics of reference frequency translation device  710  and the synthesized network characteristics of reference frequency translation device  720  are removed (de-embedded) from the network characteristics of circuit B measured in step S 26 . The resulting network characteristics are output to interface device  550  as the network characteristics of frequency translation device  600 .  
         [0051]     In the above embodiments, the following modifications are possible. In the above embodiments, the vector network analyzer can provide at least several ports required in the measurements. Consequently, vector network analyzer  100  can have at least three ports. Vector network analyzer  500  can have at least five ports.  
         [0052]     In the first and second embodiments, the local signals applied to the frequency translation device do not have to be generated by the same source signal. If the local signals applied to the frequency translation devices have the same frequencies, they may be generated by different signal sources.  
         [0053]     In the above embodiments, the measurements of the network characteristics and the measurement of the phase difference between the local signals of the reference frequency translation devices can be stored in locations other the memory device in the vector network analyzer. For example, the measurements can be stored in the memory of the computer connected externally to the vector network analyzer.