JP2000329808A - S parameter test set and signal separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen a dynamic range when a transmission coefficient is measured. SOLUTION: This S parameter test set 20 includes five selector switches 21, 22, 23, 24, 25, three signal separators 26, 27, 28, and two test ports 30, 32. When a transmission coefficient S21 is measured, each connection condition of the switches 21 to 23 is set on the contact (a) side, and each connection condition of the switches 24, 25 is set on the contact (b) side. A signal outputted from a signal source 12 is inputted into a port 1 on one side of a measured device 40 through the test port 30 and the signal separator 26, and a signal outputted from a port 2 on the other side is led to a receiving circuit 14 through the changeover switch 24, a signal wire 36, and the changeover switch 25, and detected to measure the transmission coefficient S21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an S-parameter test set and a signal separator used when measuring S-parameters using a network analyzer or the like.

[0002]

2. Description of the Related Art Conventionally, a network analyzer has been used as a measuring instrument for measuring various parameters of a linear circuit network by inputting a predetermined sine wave signal. When actually measuring various parameters, a test set suitable for the parameters to be measured is prepared, and by attaching this to the network analyzer, signals are input and output between the device under test and the network analyzer. Thus, various parameters can be measured. Items that can be measured include, for example, S-parameters, phase characteristics, and voltage standing wave ratio (VSWR). In addition,
Although the above-described test set may be built in the network analyzer, it is assumed in this specification that the test set is prepared separately from the network analyzer.

When measuring the S-parameters of a device under test using the above-described network analyzer,
An S-parameter test set prepared for parameter measurement is used. FIG. 9 is a diagram showing a configuration of a conventional S-parameter test set, and shows a connection state between each component included in the S-parameter test set, a network analyzer, and a device under test.

The network analyzer 90 includes one signal source 92 and three receiving circuits 94, 96, 98, which are connected to a device under test (DUT) 10.
By switching the connection state to 0 by the S-parameter test set 80, two transmission coefficients S ₂₁ and S ₁₂ and two reflection coefficients S ₁₁ and S regarding the device under test 100 are changed.
₂₂ measurements are made.

[0005] The S-parameter test set 80 includes a switch 82 for switching a connection destination of a signal source 92 and two signal separators 84 and 86 for separating signals input and output through two ports 102 and 104, respectively. It is comprised including. For example, when measuring the transmission coefficient S ₂₁ , the switch 82 is switched to the contact “a” and the signal source 92 is switched.
The signal output from port 1 of the device under test 100
And a signal output from the port 2 is received by the receiving circuit 94 and detected. The signal output from the signal source 92 is always input to the receiving circuit 98 and detected, and the ratio between the powers of the signals detected by the two receiving circuits 94 and 98 is calculated to obtain the transmission coefficient S ₂₁ . A measurement is taken. Similarly, when measuring the transmission coefficient S ₁₂ , the switch 82 is switched to the contact “b” and the signal source 9 is turned on.
The signal output from port 2 is input to port 2 of device under test 100, and the signal output from port 1 is received by reception circuit 96 for detection. Then, by obtaining the ratio of the power of the signal detected by the receiving circuit 98 connected to the power and signal source 92 of the signal detected by the receiving circuit 96, the measurement of the transmission coefficient S ₁₂ is performed.

[0006]

As described above, when the two transmission coefficients S ₂₁ and S ₁₂ of the device under test 100 are measured using the conventional S-parameter test set 80, the output from the signal source 92 is measured. Since the two signal separators 84 and 86 are included in the transmission path of the signal to be transmitted, and a loss occurs, there is a problem that the dynamic range is narrowed accordingly. For example, one signal separator 84
The path between the signal source 92 and the device under test 100 is set so as to reduce the loss of the path for connection, and the path between the device under test 100 and the receiving circuit 96 is set so as to increase the loss. It is assumed that
Further, the other signal separator 86 is set so that the loss of a path for connecting between the signal source 92 and the device under test 100 is reduced, and the device under test 10
It is assumed that the setting is made such that the loss of the path between 0 and the receiving circuit 94 increases. When the transmission coefficient S ₂₁ is measured using the two signal separators 84 and 86, when the signal output from the port 2 of the device under test 100 is guided to the receiving circuit 94 side, the signal separator Since a large attenuation occurs at 86, the level of the signal input to the receiving circuit 94 decreases, and the dynamic range deteriorates.
Similarly, when measuring the transmission coefficient S ₁₂ , the signal output from the port 1 of the device under test 100 is
In leading to 6, the signal separator 84 undergoes a large attenuation, so that the level of the signal input to the receiving circuit 96 decreases and the dynamic range deteriorates.

[0007] The present invention has been made in view of the above points, and an object of the present invention is to provide an S-parameter test set and a signal separator capable of expanding a dynamic range when measuring a transmission coefficient. It is in.

[0008]

In order to solve the above-mentioned problems, an S-parameter test set of the present invention has a plurality of signal separators for connecting each port of a device under test to a signal source and a receiving circuit. In addition, a bypass path is provided that bypasses at least one of the plurality of signal separators existing on the signal transmission path when measuring the transmission coefficient of the device under test. Therefore, the signal can be transmitted without passing through the signal separator in which the loss of the transmitted signal is large, and the dynamic range at the time of measuring the transmission coefficient can be set wide.

Further, the above-mentioned detour path is constituted by a switch and a signal line, and by switching the switch, connects between the receiving circuit, at least one of the signal sources, and the device under test without a signal separator. It is desirable to use a signal line as a bypass route. By simply operating the switch, a detour path that does not pass through the signal separator can be set, so that the detour path switching control is facilitated.

Further, the above-mentioned signal separator has a through port having a small loss and a coupling port having a large loss, and the signal separation through which the signal is transmitted through the coupling port when measuring the transmission coefficient. It is desirable to perform signal transmission using a detour path instead of a device. Since a large loss occurs when transmitting a signal through the coupling port, if a bypass path is used in such a case, the loss of the transmitted signal can be reduced, and a wide dynamic range can be obtained. Can be secured.

Further, the signal separator of the present invention connects each port of the device under test to a signal source and a receiving circuit, and exists on a signal transmission path when measuring a transmission coefficient of the device under test. A low loss path bypassing the high loss path is provided. Therefore, by using a low-loss path formed inside when transmitting a signal through this signal separator, a dynamic range for measuring a transmission coefficient can be set wide.

Further, a signal separator is constituted by a bridge circuit having a plurality of resistors and a plurality of switches, and by switching these switches, the magnitude relationship between the resistance values of the two opposing resistors is inverted, thereby achieving high loss. It is desirable to switch between the path and the low-loss path. Alternatively, a signal separator is constituted by a bridge circuit having a plurality of resistors and a plurality of switches, and by switching these switches, a low-loss path and a high-loss path as short-circuit paths for transmitting signals without using a resistor. It is desirable to perform switching. Signals can be transmitted through the low-loss path only by operating the switch, and control of switching between the low-loss path and the high-loss path is facilitated.

Further, a signal separator is constituted by a coupler having a plurality of transmission conductors and a switch partially approached to each other, and by switching this switch,
Switching may be performed between a high-loss path formed including the approaching portions of the plurality of transmission conductors and a low-loss path as a short-circuit path formed by the switch. Also in this case, the switching control between the short-circuit path as the low-loss path formed in the coupler and the high-loss path becomes easy as in the case where the signal separator is configured using the bridge circuit.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An S-parameter test set and a signal separator according to an embodiment of the present invention will be described below with reference to the drawings. For example, a network analyzer that performs S-parameter measurement of a two-port device is considered as a measuring instrument according to an embodiment to which the present invention is applied.

[First Embodiment] FIG. 1 is a diagram showing a configuration of a measuring instrument according to a first embodiment, showing a state in which an S-parameter test set for a two-port device is connected to a network analyzer. ing.

The measuring instrument shown in FIG. 1 includes a network analyzer 10 including a signal source and a plurality of receiving circuits for measuring S parameters, and an S parameter for switching a connection state of a device under test (DUT) 40 to the network analyzer 10. And a test set 20.

The network analyzer 10 includes a signal source 1
It is configured to include a few receiving circuits 14, 16 and 18. The signal source 12 generates a sine wave signal having a predetermined frequency. The receiving circuits 14, 16, and 18 perform vector detection on the sine wave signal transmitted via the S-parameter test set 20. For example, each receiving circuit 14 or the like converts a high frequency input signal into a low frequency signal which is a difference component by mixing a predetermined local oscillation signal with the high frequency input signal, and converts the low frequency signal into a predetermined resistance value. (For example, 50Ω) is converted into a voltage by passing through a resistor.

The S-parameter test set 20 is
Five changeover switches 21, 22, 23, 24, 25, 3
It comprises two signal separators 26, 27, 28 and two test ports 30, 32. The two test ports 30 and 32 are connection terminals to which the device under test 40 as a two-port device is connected via a cable. The changeover switch 21 is connected to the network analyzer 10.
This is for switching the output destination of the signal generated by the signal source 12 in one of the two test ports 30 and 32. Further, the two changeover switches 22 and 23 are for bypassing the signal separator 26, and by switching each of them to the contact b side, the signal line 34 with little loss is connected to the detour path of the signal separator 26. Is set as Similarly, the two changeover switches 24 and 25 are for bypassing the signal separator 27, and by switching each of them to the contact b side, the signal line 36 with almost no loss is connected to the bypass path of the signal separator 27. Is set as

Each of the two signal separators 26 and 27 is for separating a signal input / output through the corresponding test port 30 or 32. For example, a bridge type or coupler type signal separator is used. In the signal separator 26, the path on the side connecting the test port 30 and the signal source 12 corresponds to the through port with a small loss, and the path on the side connecting the test port 30 with the reception circuit 16 has a coupler port with a large loss. Corresponding to Similarly, in the signal separator 27, the path on the side connecting the test port 32 and the signal source 12 corresponds to the through port having a small loss, and the path on the side connecting the test port 30 and the receiving circuit 14 has a loss. It corresponds to a large coupler port. The signal separator 28 sends a part of the signal transmitted through the transmission line extending from the signal source 12 to the receiving circuit 18.

S-parameter test set 2 of this embodiment
0 has such a configuration, and its operation will be described next. FIG. 2 shows a switch (SW) for S-parameter measurement.
It is a figure which shows the connection state of 21-25. As shown in FIG. 2, when measuring the transmission coefficients S ₂₁ and the reflection coefficient S _11, each connection state of the three switches 21 to 23 are set to the contact a side, the remaining two switches 24 and 25
Are set to the contact b side. Therefore, the signal output from the signal source 12 is
6 and the device under test 40 via the test port 30
Is input to one of the ports 1. Then, signals reflected from a port 1 of the one is led to the receiving circuit 16 through the switch 23 through the signal separator 26 again, the measurement of the reflection coefficient S ₁₁ is performed is detected. The other signal changeover switch 24 to be output from the port 2 of the DUT 40, the signal line 36, is led to the receiving circuit 14 through the switch 25, the measurement of the transmission coefficient S ₂₁ is performed is detected .

The transmission coefficient S₁₂And reflection coefficient S_{twenty two}To
When measuring, each of the three switches 21 to 23
The connection state is set to the contact b side, and the remaining two switches
Switches 24 and 25 are set to contact a side
Is done. Therefore, the signal output from the signal source 12
Is connected via the signal separator 27 and the test port 32.
It is input to the other port 2 of the measuring device 40. Soshi
The signal reflected from the other port 2 again
A receiving circuit through a changeover switch 25 through a separator 27
14 and is detected and reflected by the reflection coefficient S._{twenty two}Is measured
You. In addition, output from one port 1 of the device under test 40 is performed.
The signal to be input is the changeover switch 22, the signal line 34, the changeover switch.
The signal is guided to the receiving circuit 16 via the switch 23 and detected.
Transmission coefficient S ₁₂Is measured.

As described above, when the transmission coefficients S ₂₁ and S ₁₂ are measured, when the signals output from the device under test 40 are guided to the receiving circuits 14 and 16, the signal separators 27 and 26 are used.
The signal lines 36 and 34 are used as detour paths without passing through. Therefore, each signal separator 27, 2
The signal is not transmitted via the coupling port 6 and the signal is transmitted via the low-loss signal lines 36 and 34 instead. For this reason, the level of the signal input to the receiving circuits 14 and 16 can be increased, and the dynamic range when measuring the transmission coefficients S ₂₁ and S ₁₂ can be expanded.

[Second Embodiment] By the way, in the first embodiment described above, when measuring the transmission coefficient, the signal is not passed through a signal separator that causes a large loss of a signal, but is instead passed through a bypass path. Although the signal is transmitted, the function of switching the detour path as necessary may be built in the signal separator.

FIG. 3 is a diagram showing a detailed configuration of the signal separator of the second embodiment. FIG. 4 is a diagram showing the correspondence of each port of the signal separator 50 shown in FIG. As shown in FIG. 3, the signal separator 50 is realized by a bridge circuit and includes five resistors 51 to 55 and four changeover switches 56 to 59.

The two resistors 52, 54 sandwiched between the two changeover switches 56, 57 are selected alternatively. For example,
By switching each of the switches 56 and 57 to the contact a side, the resistor 52 having the resistance value R ₁ is selected, and conversely, by switching to the contact b side, the resistor 54 having the resistance value R ₁ ′ is selected.

Similarly, the two resistors 53 and 55 sandwiched between the two changeover switches 58 and 59 are alternatively selected.
For example, the resistance 53 having a resistance value R ₂ by switching the respective switches 58 and 59 to the contact a side is selected, the resistance value R by switching to the contact point b side opposite
_The resistor 55 having ₂ 'is selected.

In the signal separator 50 described above, each of the four changeover switches 56 to 59 is connected to the contact a.
The two resistors 52 and 53 selected when switching to the side
Have a relationship of R ₁ <R ₂ between the resistance values R ₁ and R ₂ . In such a connection state, a signal loss that occurs when a signal passes through a path from port BB 'formed by terminals B and B' to port AA 'formed by terminals A and A' is generated. Port B-
Port C- composed of terminals C and C 'from B'
The loss of a signal that occurs when the signal passes through the path leading to C 'increases. Therefore, port A is connected to port BB '.
-A 'functions as a through port, and port CC' functions as a coupling port with respect to port BB '.

In the signal separator 50 described above,
R ₁ ′> R ₂ ′ between the resistance values R ₁ ′ and R ₂ ′ of the _two resistors 54 and 55 selected when each of the four changeover switches 56 to 59 is switched to the contact b side. There is a relationship. In such a connection state, port B-
A large signal loss occurs when the signal passes through the path from B 'to port AA', and the port C-
The loss of a signal that occurs when the signal passes through the path leading to C 'is reduced. Therefore, port A is connected to port BB '.
-A 'functions as a coupling port and port B-
Port C-C 'functions as a through port for B'.

FIG. 5 is a diagram showing a configuration of an S-parameter test set configured by using the signal separator 50 shown in FIGS. 3 and 4, and shows a configuration between the network analyzer and the device under test (DUT). Is shown. The S-parameter test set 20A shown in FIG. 5 includes a changeover switch 21 and three signal separators 50, 50A. Each of the signal separators 50 and 50A has the detailed configuration shown in FIG.

The signal separators 50 and 50A of the present embodiment and the S-parameter test set 20A using the same have such a configuration, and the operation thereof will be described below. FIG. 6 shows the switches 21, 56 to 59 when measuring the S parameter.
FIG. 4 is a diagram showing a connection state of FIG.

As shown in FIG. 6, when measuring the transmission coefficient S ₂₁ and the reflection coefficient S ₁₁ , the changeover switch 21 included in the S-parameter test set 20A and the four changeover switches 56 included in the signal separator 50 are used. To 59 are set on the contact a side, and the connection states of the four changeover switches 56 to 59 included in the signal separator 50A are set on the contact b side. Therefore, the signal output from the signal source 12 is measured via the test port 30 after passing through the path connecting the ports AA 'and BB' of the signal separator 50 set to low loss. It is input to one port 1 of the device 40. And this one port 1
Signals reflected is guided to the receiving circuit 16 through the signal separator 50 again, the measurement of the reflection coefficient S ₁₁ is performed is detected. The signal output from the other port 2 of the device under test 40 is connected via the test port 32 to the port BB 'and the port CC' of the signal separator 50A set to low loss. Receiving circuit 14 after passing the route
, Is detected, and the transmission coefficient S ₂₁ is measured.

When the transmission coefficient S ₁₂ and the reflection coefficient S ₂₂ are measured, each connection of the changeover switch 21 included in the S-parameter test set 20A and the four changeover switches 56 to 59 included in the signal separator 50 is performed. The state is set to the contact b side, and each connection state of the four changeover switches 56 to 59 included in the signal separator 50A is set to the contact a side. Therefore, the signal output from the signal source 12 is
Ports AA 'of signal separator 50A set to low loss
And the other port 2 of the device under test 40 via the test port 32 after passing through the path connecting
Is input to Then, the signal reflected from the other port 2 passes through the signal separator 50A again, and
Is led to, the measurement of the reflection coefficient S ₂₂ is performed is detected.
Further, the signal output from one port 1 of the device under test 40 is transmitted via the test port 30 to the ports BB ′ and C−B of the signal separator 50 set to low loss.
Is led to the receiving circuit 16 after passing through a path connecting the C ', the measurement of the transmission coefficient S ₁₂ is performed is detected.

As described above, when the transmission coefficients S ₂₁ and S ₁₂ are measured, when the signals output from the device under test 40 are guided to the receiving circuits 14 and 16, the signal separators 50 and 50 are used.
The transmission path in A is set to low loss. Therefore, the level of the signal input to the receiving circuits 14 and 16 increases, and the dynamic range when measuring the transmission coefficients S ₂₁ and S ₁₂ can be expanded.

[Third Embodiment] In the above-described second embodiment, the loss amounts of the two signal transmission paths in the signal separators 50 and 50A are appropriately switched to measure the transmission coefficients S ₂₁ and S _12. Has increased the dynamic range of
Focusing on the signal separator on the side to which the transmission signal is input, since only the transmission path connected to the receiving circuit is used, the loss of this transmission path is further reduced and the port B
-B 'and the port CC' may be directly connected.

FIG. 7 is a diagram showing a detailed configuration of the signal separator of the third embodiment. As shown in FIG. 7, the signal separator 60 is realized by a bridge circuit, and includes three resistors 61, 62, 63 and two switches 64, 65.

When the signal separator 60 is used as a normal bridge circuit, one switch 64 connected in series with the resistor 62 is turned on, and the other switch 65 connected in parallel with the resistor 63 is turned off. State. Between the resistance R ₃ of the resistor 62 and the resistance value R ₄ of the resistors 63 a relationship of R ₃ <R _4. Therefore, port B
The signal loss that occurs when the signal passes through the path from -B 'to port AA' is small,
The loss of the signal that occurs when the signal passes through the path leading to -C 'increases. For this reason, the port A
-A 'functions as a through port, and port CC' functions as a coupling port with respect to port BB '.

When measuring the transmission coefficients S ₂₁ and S ₁₂ , the signal separator 6 is used to guide the transmitted signal to the receiving circuit.
When 0 is used, one switch 64 connected in series with the resistor 62 is turned off, and the other switch 65 connected in parallel with the resistor 63 is turned on.
Therefore, the path from port BB 'to port CC' is cut off, and port BB 'and port C
−C ′, the signals input to the receiving circuits 14 and 16 via the ports CC ′ are separated by the signal separator 60.
Hardly attenuates within Therefore, the receiving circuits 14, 1
6, it is possible to increase the level of the signal input to
It is possible to widen the dynamic range when measuring the transmission coefficients S ₂₁ and S ₁₂ .

[Fourth Embodiment] In the above-described second and third embodiments, the signal separator 50 and the like are realized by a bridge circuit, but may be realized by a coupler. FIG. 8 is a diagram illustrating a detailed configuration of a signal separator according to the fourth embodiment. The signal separator 70 shown in FIG.
This is realized by a coupler using a microstrip line, and includes a dielectric substrate 71 and five conductors 72-1 and 72-2 as transmission conductors formed on the surface thereof.
74, 77-1, 77-2 and three ports AA ',
It is configured to include four switches 73, 75, 76, and 78 for switching the connection state between BB 'and CC'. Each of the switches 73 and the like may be, for example, a case using a micro relay switch or a case using a semiconductor switch such as a pin diode. Note that a grounding conductor is formed on the entire back surface of the dielectric substrate 71, and a terminating resistor 79 having a predetermined resistance value is provided at the fourth port DD ′ so that signal reflection does not occur. Is connected.

A switch 73 is connected between the conductors 72-1 and 72-2 formed between the port BB 'and the port AA', and the switch 73 is turned on. Thereby, a transmission path connecting these two ports is formed. The conductor 77-1 connected to the port CC 'is connected to the conductor 72-1 connected to the port AA'.
Is formed at a predetermined position partially approaching the
When a signal is transmitted through the conductor 72-1, a part of the signal leaks to the conductor 77-1 side. Therefore, when a signal is input to port BB ', part of the signal is output from port AA' via conductors 72-2 and 72-1 and the rest is output from conductor 77-1.
Is output from the port C-C '. Normally, a signal output from port AA 'directly connected to port BB' via conductors 72-1 and 72-2 is output from port C-A.
Since the signal becomes larger than the signal output from C ', the port AA' side becomes a through port and the port CC 'side becomes a coupling port.

When used in such a state, the switch 78 connected between the conductors 77-1 and 77-2 is set to the ON state, so that unnecessary reflection does not occur. It has become. The switch 75 provided between the conductor 72-2 and the conductor 74 and the switch 76 provided between the conductor 77-2 and the conductor 74 are turned off.

When measuring the transmission coefficients S ₂₁ and S ₁₂ , the signal separator 7 is used to guide the transmitted signal to the receiving circuit.
When 0 is used, the switch 73 formed between the conductors 72-1 and 72-2 is set to the off state, and the other three switches 75, 76, and 78 are set to the on state. Therefore, the conductor 72-2 connected to the port BB 'and the conductor 77-1 connected to the port CC'
Are short-circuited via the conductor 74 and the three switches 75, 76, 78, and the loss of this transmission path is reduced. For this reason, the level of the signal input to the receiving circuits 14 and 16 via the ports CC ′ increases, and the dynamic range when measuring the transmission coefficients S ₂₁ and S ₁₂ can be expanded.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the above-described embodiment, the S-parameter test set for the port and the signal separator included therein have been described. However, the S-parameter test set having a different number of ports (for example, for three ports) and the signal separator used for the same are used. The present invention can be applied.

[0043]

As described above, according to the present invention, the transmission of a device under test in an S-parameter test set having a plurality of signal separators for connecting each port of the device under test to a signal source and a receiving circuit. A bypass path is provided to bypass at least one of the plurality of signal separators present on the signal transmission path when measuring the coefficient. Therefore, the signal can be transmitted without passing through the signal separator in which the loss of the transmitted signal is large, and the dynamic range at the time of measuring the transmission coefficient can be set wide.

Further, according to the present invention, in a signal separator for connecting each port of a device under test to a signal source and a receiving circuit, when a transmission coefficient of the device under test is measured, the signal exists on a signal transmission path. A low-loss path bypassing the high-loss path is provided. Therefore, by using a low-loss path formed inside when transmitting a signal through this signal separator, a dynamic range for measuring a transmission coefficient can be set wide.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a measuring instrument according to a first embodiment.

FIG. 2 is a diagram illustrating a connection state of each switch at the time of S parameter measurement.

FIG. 3 is a diagram illustrating a detailed configuration of a signal separator according to a second embodiment.

FIG. 4 is a diagram showing a correspondence relationship of each port of the signal separator shown in FIG.

5 is a diagram illustrating a configuration of an S-parameter test set configured by using the signal separator illustrated in FIGS. 3 and 4. FIG.

FIG. 6 is a diagram illustrating a connection state of each switch at the time of S parameter measurement.

FIG. 7 is a diagram illustrating a detailed configuration of a signal separator according to a third embodiment.

FIG. 8 is a diagram illustrating a detailed configuration of a signal separator according to a fourth embodiment.

FIG. 9 is a diagram showing a configuration of a conventional S-parameter test set.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Network analyzer 12 Signal source 14, 16, 18 Receiving circuit 20 S-parameter test set 21, 22, 23, 24, 25 Changeover switch 26, 27, 28, 50, 50A, 60, 70 Signal separator

Claims (7)

[Claims] An apparatus has a plurality of signal separators for connecting each port of a device under test with a signal source and a receiving circuit, and exists on a signal transmission path when measuring a transmission coefficient of the device under test. An S-parameter test set, wherein a detour path bypassing at least one of the plurality of signal separators is provided. 2. The signal processing device according to claim 1, wherein the detour path includes a switch and a signal line, and by switching the switch, at least one of the receiving circuit and the signal source without passing through the signal separator. An S-parameter test set, wherein the signal line connecting one side and the device under test is used as the bypass route. 3. The signal separator according to claim 1, wherein the signal separator has a through port having a small loss and a coupling port having a large loss, and is connected via the coupling port when measuring a transmission coefficient. An S-parameter test set, wherein a signal is transmitted using the bypass path instead of the signal separator through which a signal is transmitted. 4. A signal separator for connecting each port of a device under test to a signal source and a receiving circuit, wherein a high-loss path existing on a signal transmission path when a transmission coefficient of the device under test is measured. A signal separator comprising a low-loss path to bypass. 5. The bridge circuit according to claim 4, wherein the bridge circuit has a plurality of resistors and a plurality of switches, and switches the switches to invert a magnitude relationship between two opposed resistors. A signal separator for switching between the high-loss path and the low-loss path. 6. The bridge circuit according to claim 4, wherein the bridge circuit includes a plurality of resistors and a plurality of switches, wherein the switch is switched so that the short circuit as a short-circuit path for transmitting a signal without passing through the resistor. A signal separator for switching between a loss path and the high loss path. 7. The coupler according to claim 4, wherein the coupler includes a plurality of transmission conductors and a switch partially approached to each other, and includes an approaching portion of the plurality of transmission conductors by switching the switch. Switching between the high-loss path formed by the switch and the low-loss path as a short-circuit path formed by the switch.