JP7140793B2 - Cable evaluation system and cable evaluation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cable evaluation system and cable evaluation method, and more particularly to a cable evaluation system and cable evaluation method for evaluating the performance of high-frequency coaxial cables for millimeter wave bands.

In recent years, 5G services that operate millimeter waveband frequencies have started in various countries, and the production of 5G wireless devices such as 5G smartphones and local 5G devices is in full swing. Design and development companies for 5G radio equipment or their manufacturing factories measure the output level and reception sensitivity of the transmission radio waves for the radio communication antennas of the 5G radio equipment, and determine whether or not they meet the prescribed standards. A performance test is performed to determine For example, the 5G wireless device to be tested is housed in an anechoic box that is not affected by the surrounding radio wave environment together with the test antenna, and the test signal is transmitted from the test antenna to the 5G wireless device and the test signal is received. A so-called OTA test, in which a signal under test from a 5G wireless device is received by a test antenna through wireless communication, is being performed.

As shown in FIG. 6, a measurement system 200 for performing an OTA test on a 5G wireless device 110 includes a 5G tester 210, a frequency converter 220 having an upconverter and a downconverter, and an OTA chamber 230. there is The OTA chamber 230 has a 5G wireless device 110 and a test antenna 240 facing the wireless communication antenna of the 5G wireless device 110 in its internal space. housed in such a condition. As the test antenna 240, for example, a directional millimeter wave antenna such as a horn antenna can be used. The test antenna 240 transmits or receives a test signal for measuring transmission characteristics or reception characteristics of the 5G wireless device 110 to or from the wireless communication antenna of the 5G wireless device 110 .

The frequency converter 220 and the test antenna 240 are connected by a high-frequency coaxial cable with a 2.92 mm connector (K connector), a 2.4 mm connector, or a 1.85 mm connector compatible with the millimeter wave band (hereinafter simply referred to as "RF cable"). ) 100 are electrically connected.

The 5G tester 210 is adapted to transmit test signals to the test antenna 240 via the upconverter of the frequency converter 220 and the RF cable 100 . In addition, the 5G tester 210 receives the signal under test from the 5G wireless device 110 from the test antenna 240 via the RF cable 100 and the down converter of the frequency converter 220 .

The frequency converter 220 and the test antenna 240 used in the millimeter-wave band measurement system 200 as described above often have a Voltage Standing Wave Ratio (VSWR) of 2.5 or more. In the RF cable 100 connected to the frequency converter 220 and the test antenna 240 having a VSWR of 2.5 or higher, reflected waves caused by impedance mismatch at both ends of the RF cable 100 cause, for example, Standing waves with amplitudes of 3 dB or more can occur.

FIG. 7 is a diagram for explaining signal level ripple caused by a standing wave generated between the test antenna 240 and the frequency converter 220 connected by the RF cable 100 . Here, let the insertion loss of the RF cable 100 be L (<1), the reflection coefficient of the test antenna 240 be γ ₁ , and the reflection coefficient of the frequency converter 220 be γ ₂ .

First, the test antenna 240 receives a signal under test of level _a0 . By propagating the signal under measurement through the RF cable 100, the signal under test becomes _a signal of level a1 ₌ a0L. A signal of level a ₁ reaching the frequency converter 220 is received by the frequency converter 220 as a _1t =a ₁ (1−γ ₂ ) and reflected as a _1r =a ₁ γ ₂ . The level a _1r signal reflected by the frequency converter 220 propagates through the RF cable 100 and becomes a level a ₂ =a _1r L=a ₁ γ ₂ L signal.

Further, the signal at level a2 is reflected by the test antenna ₂₄₀ to become _a signal at level _{a2r = a2γ1 = a1γ1γ2L} . A signal of level _a2r propagates through the RF cable ₁₀₀ to become _a signal of level a3 ⁼ _{a2rL = a1γ1γ2L2} . A signal of level a ₃ arriving at the frequency converter 220 is received by the frequency converter 220 as a _3t =a ₃ (1−γ ₂ )=a _1t γ ₁ γ ₂ L ² and a _3r =a ₃ γ ₂ = a ₁ γ ₁ γ ₂ ² L ² is reflected. Thereafter, such reflections are repeated between the test antenna 240 and the frequency converter 220 so that the frequency converter 220 receives signals at levels a _1t , a _3t , a _5t , a _7t , . . . It will be.

Assuming that level a _5t and beyond is attenuated to a negligible level, the maximum possible level of the signal received by frequency converter 220 is a _1t +a _3t =a _1t (1+γ ₁ γ ₂ L ² ). Therefore, if the level _a1t of the signal that reaches the frequency converter 220 from the test antenna 240 without being reflected is taken as the reference level, the ripple of the signal received by the frequency converter 220 is at most the following formula (1 )become that way.

Ripple magnitude=±20×log ₁₀ (1+γ ₁ γ ₂ L ² ) (1)
For example, when L=0.944, γ ₁ =2.5, and γ ₂ =2.9, the magnitude of the ripple is ±1.5 dB according to Equation (1).

In general, when an RF cable is bent, the phase of a signal propagating inside it changes (see Patent Documents 1 and 2, for example). Note that the reproducibility of the phase change due to bending greatly differs depending on the performance of the RF cable, and the phase does not return to the original state even if the RF cable with low performance is bent back. Therefore, even if the RF cable 100 in which the ripple due to the standing wave as described above is generated is slightly bent back, the amplitude characteristic of the signal propagating in the RF cable 100 changes greatly according to the phase change. There is Bending back of the RF cable 100 occurs, for example, when installing the RF cable 100 in the OTA chamber 230 after attaching the RF cable 100 to the test antenna 240 .

Conventionally, as shown in FIG. 8, the performance of an RF cable is measured by connecting both ends 100a and 100b of an RF cable 100 to an input port 250a and an output port 250b of a vector network analyzer (VNA) 250, and measuring phase and insertion loss. (insertion loss), reflection loss (return loss), etc.

JP 2019-146113 A

Nobuyuki Kono, Seisuke Kuji, Katsuhisa Sato, Tadanori Hara, and Risao Hayashi, "Changes in delay due to twisting of coaxial cable in VLBI", Journal of the Geodetic Society of Japan, Vol. 40, No. 2 (1994), pp. 137-143

However, even if the frequency characteristics of the RF cable 100 before bending and after being bent back are measured using the measurement system shown in FIG. No more standing waves are generated. For this reason, conventionally, even if phase changes occur, there has been a problem that changes in amplitude characteristics that are expected in actual operation cannot be observed.

SUMMARY OF THE INVENTION The present invention has been made to solve such conventional problems. The purpose is to provide a method.

In order to solve the above problems, a cable evaluation system according to the present invention includes a signal analyzer having an input port and an output port, and a distributor having a first input/output terminal, a second input/output terminal, and a third input/output terminal. wherein the input port and the output port of the signal analyzer are connected to the first input/output terminal and the second input/output terminal, respectively, and one end of the high-frequency coaxial cable to be tested and the second and a standing wave generator to which three input/output terminals are connected, wherein the standing wave generator is input from the output port to the second input/output terminal to generate the high-frequency coaxial cable. and a reflected signal of the test signal reflected at the other end of the high-frequency coaxial cable and propagating in the opposite direction through the high-frequency coaxial cable. A signal output from an output terminal is input to the input port as a signal under measurement, and the signal analysis apparatus analyzes the amplitude characteristics of the signal under measurement before bending the predetermined length of the high frequency coaxial cable, and the high frequency coaxial cable. The configuration includes a cable evaluation unit that calculates a difference from the amplitude characteristic of the signal under measurement after bending back the predetermined length of the cable, and displays the calculated difference on a display device.

With this configuration, in the cable evaluation system according to the present invention, one end of the RF cable to be tested is connected to the third input/output terminal of the three-resistor splitter, and the test signal and the reflected signal are reflected in the splitter and the RF cable. A standing wave is generated by the signal. As a result, the cable evaluation system according to the present invention can observe changes in amplitude characteristics reflecting phase changes caused by bending of the RF cable, which cannot be obtained by conventional measurements using only a VNA. The change in amplitude characteristic is smaller for a higher-performance RF cable and larger for a lower-performance RF cable. Since the cable evaluation system according to the present invention displays changes in the obtained amplitude characteristics on the display device, it is possible to visualize the performance of the RF cable to be tested.

Moreover, in the cable evaluation system according to the present invention, the other end of the high-frequency coaxial cable may be open or short-circuited. Alternatively, in the cable evaluation system according to the present invention, a reflector having a desired reflection coefficient may be connected to the other end of the high frequency coaxial cable.

With this configuration, the cable evaluation system according to the present invention can measure changes in amplitude characteristics according to the environment in which the RF cable is actually used, such as a measurement system for conducting an OTA test.

In addition, the cable evaluation system according to the present invention bends a predetermined length of the straight high-frequency coaxial cable with a predetermined curvature, and then restores the straight high-frequency coaxial cable to the original straight shape. The configuration may be further provided with a bending and stretching jig.

With this configuration, the cable evaluation system according to the present invention can, for example, unify the lengths of various RF cables to be tested in advance, and bend these cables in the same manner using a bending and stretching jig. A return can be made. In addition, this enables the cable evaluation system according to the present invention to measure changes in amplitude characteristics under equal conditions for various types of RF cables.

In the cable evaluation system according to the present invention, the standing wave generator may further include an attenuator inserted between the third input/output terminal and one end of the high-frequency coaxial cable. .

With this configuration, the cable evaluation system according to the present invention can detect the signal under measurement from the input port and output port of the signal analysis device even when the amplitude of the standing wave generated in the splitter and the RF cable is relatively large. can be attenuated to an amplitude suitable for

Also, a cable evaluation method according to the present invention includes a signal analyzer having an input port and an output port, and a distributor having a first input/output terminal, a second input/output terminal, and a third input/output terminal. A cable evaluation method using a generator, wherein the input port and the output port of the signal analysis device are connected to the first input/output terminal and the second input/output terminal, respectively, and the a connecting step of connecting one end of a high-frequency coaxial cable and the third input/output terminal; a test signal input from the output port to the second input/output terminal and propagating through the high-frequency coaxial cable; A signal output from the first input/output terminal is used as a signal to be measured in a state in which a standing wave is generated by the reflected signal of the test signal that is reflected at the other end and propagates in the opposite direction through the high-frequency coaxial cable. a step of generating a standing wave for input to the input port; a first measuring step of measuring amplitude characteristics of the signal under test before bending the predetermined length of the high-frequency coaxial cable; and the predetermined length of the high-frequency coaxial cable. A second measuring step of measuring the amplitude characteristics of the signal under measurement after bending back the portion, the amplitude characteristics measured in the first measuring step, and the amplitude characteristics measured in the second measuring step. a cable evaluation step of calculating the difference and displaying the calculated difference on a display device.

With this configuration, in the cable evaluation method according to the present invention, one end of the RF cable to be tested is connected to the third input/output terminal of the three-resistor splitter, and the test signal and the reflected signal are reflected in the splitter and the RF cable. A standing wave is generated by the signal. As a result, the cable evaluation method according to the present invention can observe changes in amplitude characteristics reflecting phase changes caused by bending of the RF cable, which cannot be obtained by conventional measurements using only a VNA. The change in amplitude characteristic is smaller for a higher-performance RF cable and larger for a lower-performance RF cable. Since the cable evaluation method according to the present invention displays changes in the obtained amplitude characteristics on the display device, it is possible to visualize the performance of the RF cable to be tested.

SUMMARY OF THE INVENTION The present invention provides a cable evaluation system and cable evaluation method capable of observing changes in amplitude characteristics reflecting phase changes caused by bending of a high-frequency coaxial cable.

1 is a configuration diagram showing the configuration of a cable evaluation system according to an embodiment of the present invention; FIG. It is a top view which shows the structure of the bending-stretching jig|tool with which the cable evaluation system which concerns on embodiment of this invention is provided. 1 is a plan view showing a procedure for bending and stretching an RF cable using a bending and stretching jig provided in a cable evaluation system according to an embodiment of the present invention, in which (a) shows a state in which the RF cable is stretched straight; (b) shows the RF cable bent, and (c) shows the RF cable straightened again. 1 is a graph schematically showing measurement results of a signal analysis device provided in a cable evaluation system according to an embodiment of the present invention, where (a) shows measurement results of an ultra-high-performance and expensive RF cable, and (b) ) shows measurement results for a high-performance, relatively inexpensive RF cable, and (c) shows measurement results for a relatively low-performance, very inexpensive RF cable. 4 is a flowchart for explaining processing of a cable evaluation method using the cable evaluation system according to the embodiment of the present invention; 1 is a configuration diagram showing the configuration of a conventional measurement system for performing OTA tests on 5G wireless devices; FIG. 7 is a diagram for explaining signal level ripple caused by a standing wave generated between a test antenna and a frequency converter connected by an RF cable in the measurement system of FIG. 6; FIG. 1 is a configuration diagram showing the configuration of a conventional measurement system for measuring frequency characteristics of an RF cable using a VNA; FIG.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of the cable evaluation system which concerns on this invention, and a cable evaluation method is described using drawing. Note that the dimensional ratio of each component on each drawing does not necessarily match the actual dimensional ratio.

As shown in FIG. 1, a cable evaluation system 1 according to an embodiment of the present invention evaluates the performance of an RF cable 100 to be tested. A bending and stretching jig 40 , a display device 51 , an operation device 52 and a control device 53 are provided.

The RF cable 100 to be tested is, for example, a 3.5 mm connector, a 2.92 mm connector (K connector), a 2.4 mm connector, a 1.85 mm, 1.35 mm, 1.0 mm, or 0 mm connector corresponding to the millimeter wave band. High frequency coaxial cable with .8mm connector.

The signal analysis device 10 is, for example, a two-port VNA including a signal generator 11, an input/output unit 12, an input port 13 and an output port 14, an amplitude characteristic measurement unit 15, and a cable evaluation unit 16. . One end 100 a of the RF cable 100 to be tested is connected between the input port 13 and the output port 14 via the standing wave generator 20 .

The signal generating section 11 generates a test signal with an arbitrary frequency, for example, from several MHz to several tens of GHz, an arbitrary signal level, and an arbitrary modulation method.

The input/output section 12 outputs the test signal output from the signal generating section 11 to the output port 14 . The input/output unit 12 also outputs the signal under measurement input from the input port 13 to the amplitude characteristic measuring unit 15 .

The amplitude characteristic measuring section 15 measures the amplitude characteristic (insertion loss S ₂₁ ) of the signal under measurement input from the input/output section 12 .

The standing wave generator 20 has three resistors of 16+2/3Ω and a first input/output terminal 31, a second input/output terminal 32, and a third input/output terminal 33 connected to the ends of each resistor. A 3-resistor divider 30 is included. The first input/output terminal 31 and the second input/output terminal 32 are connected to the input port 13 and the output port 14 of the signal analysis device 10, respectively.

One end 100 a of an RF cable 100 to be tested is connected to the third input/output terminal 33 . The standing wave generator 20 may further include an attenuator 34 with a characteristic impedance of 50Ω. The attenuator 34 is inserted between the third input/output terminal 33 of the distributor 30 and one end 100a of the RF cable 100 in order to attenuate the signal input/output to/from the signal analyzer 10 to an appropriate amplitude. In this case, one end 100 a of the RF cable 100 is connected to the third input/output terminal 33 via the attenuator 34 .

The standing wave generator 20 generates a test signal that is input from the output port 14 of the signal analyzer 10 to the second input/output terminal 32 and propagates through the RF cable 100, A standing wave is generated by the reflected signal of the test signal counter-propagating 100 . As a result, the signal under measurement obtained by adding the reflected signal to the test signal input to the second input/output terminal 32 is input to the input port 13 of the signal analyzer 10 from the first input/output terminal 31 .

When the frequency band used for the distributor 30 is, for example, about DC to 100 GHz, and all terminals of the first input/output terminal 31, the second input/output terminal 32, and the third input/output terminal 33 are terminated with 50Ω. In addition, it is designed so that the amplitude balance between the terminals is even. On the other hand, if any one of the first input/output terminal 31, the second input/output terminal 32, and the third input/output terminal 33 has a terminal that is not terminated with 50Ω, the amplitude balance between the terminals is It will collapse. In the present invention, a standing wave is generated in the distributor 30 and the RF cable 100 by using the distributor 30 with the amplitude balance between terminals intentionally disturbed. Specifically, by opening the other end 100b of the RF cable 100, it is possible to create a situation in which the generated standing wave has the largest amplitude. Alternatively, the other end 100b of the RF cable 100 may be short-circuited. Alternatively, a circuit that does not cause total reflection, such as a reflector having a desired reflection coefficient according to the actual usage environment of the RF cable 100, may be connected to the other end 100b of the RF cable 100. FIG.

As shown in FIG. 2, the bending/stretching jig 40 is a plate-like member having a predetermined thickness in a direction perpendicular to the plane of the paper, and is used to bend a straight RF cable 100 to a predetermined length. A groove-like bending portion 41 for bending with a curvature (1/R) and a groove-like stretching portion 42 for straightening the RF cable 100 are formed. For example, the width of the bent portion 41 and the stretched portion 42 is 20 mm. The bent portion 41 is composed of two straight portions each having a length of 50 mm and a curved portion connecting the two straight portions and having an inner radius of curvature R of 120 mm. In this case, the predetermined length of the RF cable 100 bent by the bending portion 41 is approximately 380 mm. Further, the stretched portion 42 consists of a straight portion with a length of 500 mm and includes one of the two straight portions of the bent portion 41 . The bending portion 41 and the extending portion 42 are arranged such that the RF cable 100 can be arranged from the direction perpendicular to the plane of FIG. 2 from the front side to the back side.

FIG. 3 is a diagram showing a procedure for bending and stretching the RF cable 100 using the bending and stretching jig 40. As shown in FIG. First, as shown in FIG. 3(a), the RF cable 100 is arranged in the extension part 42, and the RF cable 100 is straightened. At this time, the reference insertion loss S ₂₁ (hereinafter also referred to as “reference amplitude characteristic”) is measured by the amplitude characteristic measurement unit 15 of the signal analysis device 10 .

Next, as shown in FIG. 3(b), while a portion of the RF cable 100 on the one end 100a side is arranged in a straight portion common to the stretching portion 42 and the bending portion 41 of the bending and stretching jig 40, By arranging the predetermined length portion of the RF cable 100 on the bending portion 41 of the bending and straightening jig 40, the straight RF cable 100 having a predetermined length portion is bent with a predetermined curvature. Next, as shown in FIG. 3(c), while a part of the RF cable 100 on the side of the one end 100a is arranged in a straight portion common to the stretching portion 42 and the bending portion 41 of the bending and stretching jig 40, , the RF cable 100 is again placed on the stretched portion 42 to return the RF cable 100 to its original straightened shape. At this time, the amplitude characteristic measurement unit 15 of the signal analysis device 10 again measures the insertion loss S ₂₁ (hereinafter, also referred to as "amplitude characteristic after bending back").

That is, the amplitude characteristic measuring unit 15 of the signal analysis apparatus 10 measures the reference amplitude characteristic of the signal under measurement before bending the predetermined length of the RF cable 100 and the measured signal after bending back the predetermined length of the RF cable 100. Amplitude characteristics after bending back of the measurement signal are measured.

The cable evaluation unit 16 of the signal analysis device 10 calculates the difference between the reference amplitude characteristic measured by the amplitude characteristic measurement unit 15 and the amplitude characteristic after unbending, that is, the change in the amplitude characteristic due to unbending of the RF cable 100 . Furthermore, the cable evaluation unit 16 causes the display device 51 to display the calculated change in the amplitude characteristic. This change in amplitude characteristic is, so to speak, a change in phase of the RF cable 100 converted into a change in amplitude. If the other end 100b of the RF cable 100 is terminated with 50Ω, the reflection at the other end 100b is suppressed, so that substantially the same amplitude characteristics can be obtained before and after bending the RF cable 100. , and changes in the amplitude characteristic become unobservable.

The graph of FIG. 4 schematically shows the frequency characteristics of the difference between the reference amplitude characteristics and the amplitude characteristics after bending back for three types of RF cables having different performances. Figure 4(a) is a high performance and expensive RF cable (product A), Figure 4(b) is a high performance and relatively inexpensive RF cable (product B), and Figure 4(c) is a relatively low performance cable. Results are shown for a very inexpensive RF cable (Product C). The ultra-high-performance RF cable (product A) is designed to suppress phase changes due to bending, so changes in amplitude characteristics are extremely small. Conversely, it was found that the lower the performance of the RF cable, the greater the change in amplitude characteristics.

The display device 51 is composed of a display device such as an LCD or a CRT, for example, and displays the reference amplitude characteristics, the post-bending amplitude characteristics, and the reference amplitude measured by the signal analysis device 10 according to the control signal output from the control device 53. Various display contents such as the difference between the characteristics and the amplitude characteristics after bending back are displayed. Further, the display device 51 displays operation objects such as buttons, soft keys, pull-down menus, and text boxes for setting measurement conditions according to control signals output from the control device 53. there is

The operation device 52 is for receiving an operation input by a user, and is configured by, for example, a touch panel provided on the surface of the display screen of the display device 51 . Alternatively, the operating device 52 may include an input device such as a keyboard or mouse. An operation input to the operation device 52 is detected by the control device 53 . For example, the operation device 52 allows the user to arbitrarily specify the timing of starting measurement by the amplitude characteristic measuring section 15 .

The control device 53 is composed of, for example, a microcomputer or a personal computer including a CPU, ROM, RAM, HDD, etc., and controls the operations of the above-described sections that constitute the cable evaluation system 1 . Further, the control device 53 can configure at least a part of the amplitude characteristic measuring section 15 and the cable evaluating section 16 by software by transferring a predetermined program stored in ROM or the like to RAM and executing it. be. At least part of the amplitude characteristic measurement unit 15 and the cable evaluation unit 16 can also be configured by a digital circuit such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit). Alternatively, at least part of the amplitude characteristic measurement unit 15 and the cable evaluation unit 16 can be configured by appropriately combining hardware processing by a digital circuit and software processing by a predetermined program.

The display device 51 , the operation device 52 and the control device 53 may be configured within the signal analysis device 10 .

An example of processing of a cable evaluation method using the cable evaluation system 1 of the present embodiment will be described below with reference to the flowchart of FIG.

First, as shown in FIG. 3A, the user arranges the RF cable 100 on the stretching portion 42 of the bending and stretching jig 40 to straighten the RF cable 100 (step S1).

Next, the user connects the input port 13 and the output port 14 of the signal analysis device 10 to the first input/output terminal 31 and the second input/output terminal 32 of the standing wave generator 20, respectively. Further, the user connects the end 100a of the RF cable 100 to be tested to the third input/output terminal 33 of the standing wave generator 20 via the attenuator 34 (connection step S2).

Next, the signal generator 11 of the signal analyzer 10 outputs the test signal from the output port 14 to the second input/output terminal 32 via the input/output unit 12 . As a result, a standing wave is generated by the test signal propagating through the RF cable 100 and the reflected signal of the test signal that is reflected by the other end 100b of the RF cable 100 and propagating through the RF cable 100 in the opposite direction. In this state, the signal under measurement obtained by adding the reflected signal to the test signal input to the second input/output terminal 32 is input from the first input/output terminal 31 to the input port 13 (standing wave generating step S3). .

Next, the amplitude characteristic measurement unit 15 of the signal analysis device 10 receives the RF cable 100 input from the input port 13 via the input/output unit 12 in response to the measurement start instruction from the operation device 52 by the user's operation input. A reference amplitude characteristic of the signal under measurement is measured before bending a predetermined length of the signal. Further, the display device 51 displays the reference amplitude characteristic measured by the amplitude characteristic measuring section 15 (first measurement step S4).

Next, as shown in FIG. 3(b), the user places part of the RF cable 100 on the side of the one end 100a of the bending/stretching jig 40 in a straight line common to the extending portion 42 and the bending portion 41. By arranging the predetermined length portion of the RF cable 100 on the bending portion 41 of the bending and stretching jig 40 in the state of , the work of bending the predetermined length portion of the straightly extended RF cable 100 with a predetermined curvature can be performed. done. Furthermore, as shown in FIG. 3(c), a part of the RF cable 100 on the side of the one end 100a of the bending/stretching jig 40 is arranged in a common straight portion between the stretching portion 42 and the bending portion 41 by the user. In this state, the RF cable 100 is placed on the stretched portion 42 again to return the RF cable 100 to its original straight shape (step S5).

Next, the amplitude characteristic measurement unit 15 of the signal analysis device 10 receives the RF cable 100 input from the input port 13 via the input/output unit 12 in response to the measurement start instruction from the operation device 52 by the user's operation input. After bending back a predetermined length of the signal under measurement, the amplitude characteristics after bending back are measured. Further, the display device 51 displays the post-bending amplitude characteristics measured by the amplitude characteristics measuring unit 15 (second measurement step S6).

Next, the cable evaluation unit 16 of the signal analysis device 10 determines the difference between the reference amplitude characteristic measured in the first measurement step S4 and the amplitude after bending back measured in the second measurement step S6, that is, the RF cable 100 Calculate the change in the amplitude characteristic due to the bending back. Further, the display device 51 displays changes in amplitude characteristics calculated by the cable evaluation unit 16 (cable evaluation step S7).

As described above, the cable evaluation system 1 according to the present embodiment connects one end 100a of the RF cable 100 to be tested to the third input/output terminal 33 of the three-resistor type distributor 30, and the distributor 30 and generate a standing wave in the RF cable 100 by the test signal and the reflected signal. As a result, the cable evaluation system 1 according to the present embodiment can observe changes in amplitude characteristics reflecting phase changes caused by bending of the RF cable 100, which cannot be obtained by conventional measurement using only a VNA. The change in amplitude characteristic is smaller for a higher-performance RF cable and larger for a lower-performance RF cable. Since the cable evaluation system 1 according to the present embodiment displays the obtained change in the amplitude characteristic on the display device 51, it is possible to visualize the performance of the RF cable 100 to be tested.

Further, in the cable evaluation system 1 according to this embodiment, the other end 100b of the RF cable 100 to be tested may be open or short-circuited. Alternatively, a reflector having a desired reflection coefficient may be connected to the other end 100b of the RF cable 100 to be tested. As a result, the cable evaluation system 1 according to the present embodiment can measure changes in amplitude characteristics according to the environment in which the RF cable 100 is actually used, such as a measurement system for performing an OTA test.

The cable evaluation system 1 according to the present embodiment also includes a bending and straightening jig 40 for bending back a predetermined length portion of the RF cable 100 with a predetermined curvature. For example, if the lengths of various RF cables to be tested are unified in advance, these cables can be similarly bent back by the bending and stretching jig 40 . In addition, the cable evaluation system 1 according to the present embodiment can thereby measure changes in amplitude characteristics of various RF cables under equal conditions.

Further, in the cable evaluation system 1 according to this embodiment, the attenuator 34 is inserted between the third input/output terminal 33 of the distributor 30 and the one end 100a of the RF cable 100 . As a result, the cable evaluation system 1 according to the present embodiment can input the signal under measurement to the signal analyzer 10 even when the amplitude of the standing wave generated in the distributor 30 and the RF cable 100 is relatively large. It can be attenuated to an amplitude suitable for port 13 and output port 14 .

Further, in the embodiment described above, the signal analysis apparatus 10 outputs a test signal from the output port 14 and measures the amplitude characteristic of the signal input from the input port 13 by the amplitude characteristic measuring unit 15, which performs two-port measurement. However, the present invention is not limited to this. For example, the signal analysis apparatus 10 outputs a test signal from the output port 14, and measures the amplitude characteristic (reflection coefficient S ₁₁ ) of the signal of the reflected wave input from the output port 14 again by the amplitude characteristic measuring unit 151. It may be one that performs port measurements. At this time, the unused first input/output terminal 31 of the distributor 30 must be terminated with 50Ω. Alternatively, the signal analysis apparatus 10 outputs a test signal from the input port 13, and measures the amplitude characteristic (reflection coefficient S ₁₁ ) of the signal of the reflected wave input from the input port 13 again by the amplitude characteristic measuring unit 151. It may be one that performs port measurements. At this time, the unused second input/output terminal 32 of the distributor 30 must be terminated with 50Ω.

1 cable evaluation system 10 signal analyzer 11 signal generator 12 input/output unit 13 input port 14 output port 15 amplitude characteristic measurement unit 16 cable evaluation unit 20 standing wave generator 30 distributor 31 first input/output terminal 32 second input Output terminal 33 Third input/output terminal 34 Attenuator 40 Bending and stretching jig 41 Bending part 42 Stretching part 51 Display device 52 Operating device 53 Control device 100 RF cable 100a One end 100b Other end

Claims (7)

a signal analyzer (10) having an input port (13) and an output port (14);
comprising a distributor (30) having a first input/output terminal (31), a second input/output terminal (32) and a third input/output terminal (33), with the input port and the output port of the signal analysis device; A standing wave in which the first input/output terminal and the second input/output terminal are connected, respectively, and one end (100a) of a high-frequency coaxial cable (100) to be tested is connected to the third input/output terminal. A cable evaluation system (1) comprising a generator (20),
The standing wave generator generates a test signal that is input from the output port to the second input/output terminal and propagates through the high-frequency coaxial cable, and a test signal that is reflected at the other end (100b) of the high-frequency coaxial cable and generates inputting the signal output from the first input/output terminal to the input port as a signal under measurement in a state in which a standing wave is generated by the reflected signal of the test signal propagating in the opposite direction through the cable;
The signal analyzer measures the amplitude characteristics of the signal under measurement before bending the predetermined length of the high frequency coaxial cable and the amplitude of the signal under measurement after bending back the predetermined length of the high frequency coaxial cable. A cable evaluation system, comprising: a cable evaluation unit (16) that calculates a difference from a characteristic and displays the calculated difference on a display device (51). 2. The cable evaluation system according to claim 1, wherein said other end of said high frequency coaxial cable is open. 2. The cable evaluation system of claim 1, wherein said other end of said high frequency coaxial cable is shorted. 2. The cable evaluation system according to claim 1, wherein a reflector having a desired reflection coefficient is connected to said other end of said high frequency coaxial cable. A bending and straightening jig (40) is further provided for returning the straight high-frequency coaxial cable to its original straight shape after bending a predetermined length portion of the straight high-frequency coaxial cable with a predetermined curvature. The cable evaluation system according to any one of claims 1 to 4, characterized in that: 6. The standing wave generator further includes an attenuator (34) inserted between the third input/output terminal and one end of the high frequency coaxial cable. The cable rating system described in . a signal analyzer (10) having an input port (13) and an output port (14);
a standing wave generator (20) comprising a divider (30) having a first input/output terminal (31), a second input/output terminal (32) and a third input/output terminal (33) a method,
The input port and the output port of the signal analysis device are connected to the first input/output terminal and the second input/output terminal, respectively, and one end (100a) of a high-frequency coaxial cable (100) to be tested and the A connection step (S2) of connecting with the third input/output terminal;
The test signal that is input from the output port to the second input/output terminal and propagates through the high-frequency coaxial cable and the test signal that is reflected by the other end (100b) of the high-frequency coaxial cable and propagates through the high-frequency coaxial cable in the opposite direction a standing wave generating step (S3) of inputting the signal output from the first input/output terminal to the input port as the signal under measurement in a state where the standing wave is generated by the reflected signal of the test signal;
a first measuring step (S4) of measuring amplitude characteristics of the signal under measurement before bending the predetermined length of the high-frequency coaxial cable;
a second measuring step (S6) of measuring amplitude characteristics of the signal under measurement after bending back the predetermined length portion of the high-frequency coaxial cable;
A cable evaluation step (S7) of calculating a difference between the amplitude characteristic measured in the first measuring step and the amplitude characteristic measured in the second measuring step and displaying the calculated difference on a display device (51) A cable evaluation method comprising:

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