JP7153309B2 - Measurement method of reflection coefficient using vector network analyzer - Google Patents

Description

The present invention relates to a reflection coefficient measurement method using a vector network analyzer (hereinafter referred to as "VNA"). ) relates to a method for measuring the reflection coefficient.

Design, manufacturing and measurement are all indispensable technologies in research and development in the high frequency field. In recent years, techniques for modeling high-frequency devices and circuits based on measurement results have also been used, increasing the demand for accurate measurements. In particular, in the high-frequency field, VNAs are used not only for devices and circuits, but also for characterization of materials, and VNAs have become an important tool in industrial activities in the high-frequency field.

A VNA can measure the reflection coefficient (reflected wave/incident wave) and transmission coefficient (transmitted wave/incident wave) of high frequency devices and circuits. The reflection coefficient and transmission coefficient can be represented by parameters called S-parameters, which represent the input/output characteristics of the DUT. For example, if the ports of a DUT having two ports are port1 and port2, the reflection coefficient on the port1 side is _S11 and the reflection coefficient on the _port2 side is S22. Also, the transmission coefficient from port1 to _port2 is S21, and the transmission coefficient from port2 to _port1 is S12. Note that port1 and port2 can be regarded as two ports of the VNA. Also, the reflection coefficient for a DUT with one port is S ₁₁ or S ₂₂ . Therefore, the S-parameters are called differently depending on the definition of the port.

The VNA consists of high-frequency components and circuits such as power dividers and directional couplers, and the DUT to be measured is connected to the VNA port via a cable or adapter. The characteristics (circuit errors) of these parts are mixed. Therefore, it is customary to calibrate the VNA to obtain and remove the characteristics (circuit errors) of these components before measuring the DUT. For the calibration, calibration using a line called TRL (thru-reflect-line) in the case of 2 ports, open, short, and load terminator such as OSLT (open-short-load-thru) ( In the case of one port, calibration using open, short, and load such as OSL (open-short-load) calibration is performed.

JP 2006-317156 A

G.F.Engen and C.A.Hoer, “Thru-Reflect-Line: An improved Technique for Calibrating the Dual Six-Port Automatic Network Analyzer”, IEEE Transactions on Microwave Theory and Techniques, vol.27, no.12, Dec.1979.

The conventional TRL calibration described above must make several assumptions, such as a 50Ω termination resistor and the use of reflective devices with identical characteristics at the two ports. Although the assumption facilitates the calculation of the S-parameters, there is the problem that the measurement accuracy depends on the assumption.

It is an object of the present invention to provide a one-port VNA calibration method that does not require such assumptions, and more specifically, to calibrate the VNA simultaneously with measurement of the reflection coefficient of the DUT at one port of the VNA. to determine the true reflection coefficient of the DUT.

The present invention provides a method of measuring reflection coefficients using a vector network analyzer (VNA). The measurement method includes the steps of ( a ) measuring the reflection coefficient Γ _dm of an object under test directly connected to one port of the _VNA ; = 1, 2, X = A, B, C) connected via three lines A, B, C of different known lengths, the reflection coefficient Γ _Xm (X = A, B, C ) and (c) using the reflection coefficients Γ _dm , Γ _Xm and the S-parameters S _ij,X to determine the true reflection coefficient Γ _d of the device under test.

According to the present invention, it is possible to measure the reflection coefficient of the DUT at one port of the VNA with all the circuit errors of the VNA removed, that is, the measurement including calibration of the circuit errors. A highly accurate measurement result (true reflection coefficient) can be obtained. In addition, since only three lines with different lengths are used as the standard, it is easy to manufacture and evaluate characteristics based on the length.

FIG. 2 is a conceptual diagram of measuring the reflection coefficient of a conventional VNA; FIG. 2 is a conceptual diagram of measuring the reflection coefficient of a VNA according to one embodiment of the present invention; FIG. 4 is a vector representation of the reflection coefficient of one embodiment of the present invention;

An embodiment of the present invention will be described with reference to the drawings. First, in order to clarify the characteristics of the measurement method of one embodiment of the present invention, the reflection of the DUT at one port (hereinafter referred to as "1 port") of the conventional VNA is shown in FIG. A method for measuring the coefficient will be described. FIG. 1 is a conceptual diagram of measuring the reflection coefficient of a conventional VNA. In FIG. 1, only a signal source 1 and a receiver 2 are shown as internal circuits (components) of the VNA 10. FIG. In practice, VNA 10 also includes signal separators (splitters, couplers), detectors, signal processing units (processors), display units, and the like.

.delta., .mu., and .tau. in the rectangular frame of FIG. 1 mean circuit errors inside the VNA for directivity, matching, and tracking , respectively. A DUT 3 is connected to one port of the VNA 10 to which connectors and cables for connection with the DUT are connected. A dashed line P indicates a detection surface containing circuit errors, and the result of measurement of the reflection coefficient by the receiver 2 with reference to this surface is Γ _dm . The reflection coefficient Γ _dm is a measurement result including circuit errors. A dashed line Q indicates a detection surface that does not include circuit errors, and the reflection coefficient with respect to this surface is the true reflection coefficient Γ _d of DUT 3 .

Measurement of the reflection coefficient of the DUT at one port of the conventional VNA of FIG. 1 requires the following three steps.
(a) VNA and peripheral circuit settings such as setting cables and measurement conditions (b) VNA calibration (c) Measurement of reflection coefficient of DUT by VNA In a necessary step before measuring the DUT to achieve the above, the following equation holds between the reflection coefficient Γ _dm obtained at the receiver 2 and the reflection coefficient Γ _d of the DUT 3 when the DUT 3 is connected to one port of the VNA. This is the task of determining δ, μ, and τ in Equation (1). OSL (open-short-load) described above is a common one-port calibration method for VNAs. OSL calibration determines .delta., .mu., and .tau. in equation (1) using open, short, and load devices (reference devices) with known characteristics. A measurement of the DUT's reflection coefficient is then performed to determine the true reflection coefficient Γ _d of DUT 3 .

FIG. 2 is a conceptual diagram of measuring the reflection coefficient of a DUT at one port of a VNA according to one embodiment of the present invention. As in FIG. 1, only the signal source 11 and the receiver 12 are shown in FIG. 2 as internal circuits (parts) of the VNA 20. FIG. In practice, the VNA 20 also includes signal separators (splitters, couplers), detectors, signal processing units (processors), display units, and the like. .delta., .mu., and .tau. in the rectangular frame of FIG. 2 mean circuit errors inside the VNA for directivity, matching, and tracking , respectively.

One port of VNA 20 has, chronologically (sequentially): (i) DUT 13 alone, (ii) DUT 13 via line A (15) for calibration, (iii) line B (16) for calibration. ) and (iv) the DUT 13 via calibration line C (17). Broken line P means a detection plane containing circuit errors, and the measurement results of the reflection coefficient by the receiver 12 with reference to this plane P are shown in the order of (i) to (iv) above, Γ _dm , Γ _Am , and Γ _Bm . , Γ _Cm . Reflection coefficients Γ _dm , Γ _Am , Γ _Bm and Γ _Cm are measurement results including circuit errors. Broken line Q means a detection surface that does not contain circuit errors, and the reflection coefficients based on this surface Q are the reflection coefficient Γ _d of DUT 3, the reflection coefficients of line A and DUT 3 in the order of (i) to (iv) above. _.GAMMA.'A , the reflection coefficient .GAMMA.'B between line _B and DUT3, and the reflection coefficient .GAMMA.'C between line _C and DUT3.

Measuring the reflection coefficient of the DUT at one port of the VNA of the inventive embodiment of FIG. 2 requires the following two steps.
(A) Setting of VNA and peripheral circuits such as setting of cables and measurement conditions (B) Measurement of reflection coefficient of DUT by VNA including VNA calibration An embodiment of the present invention, unlike the conventional measurement method shown in FIG. One feature of this measurement method is that the VNA is calibrated at the same time as the measurement of the reflection coefficient of the DUT. is.

In the VNA calibration performed at the same time as measuring the reflection coefficient of the DUT in (B), three lines A, B, and C with known characteristics are used to Determine τ. The model equations for calibration are the above equation (1) and the following equations (2) to (4). Equations (2)-(4) are applied in sequence to (ii) DUT 13 via calibration line A (15), (iii) DUT 13 via calibration line B (16), and (iv) calibration is an equation corresponding to the measurement of each reflection coefficient of DUT 13 via line C(17) for . Here, the reflection coefficients Γ _dm , Γ _Am , Γ _Bm , Γ _Cm , Γ _d , Γ' _A , Γ' _B , and Γ' _C in each formula are as described above with reference to FIG. Also, S _ij,X (i, j=1, 2, X=A, B, C) is the S-parameter of line X. Knowing the characteristics of the line X means that the S-parameters S _ij,X are known.

Table 1 summarizes the meaning of each parameter. Since there are four simultaneous equations for four unknown parameters, equations (1) to (4) can be solved to obtain the DUT 3 reflection coefficient Γ _d and circuit errors δ, μ, and τ. Specifically, each value that simultaneously satisfies equations (1) to (4) is obtained by iterative convergence calculation (for example, using the Monte Carlo method).

Lines X (X=A, B, C) are hollow coaxial lines (air lines) or waveguides made of the same material, e.g. copper or copper alloy, or planar circuits (patterned copper wiring on a substrate). ), etc. The lines X (X=A, B, C) have different lengths, and the S-parameters S _ij,X of the lines X are adjusted according to the length of each line. Specifically, as shown in the _vector display diagram (reflection _coefficient surface diagram) of the _{reflection coefficient} of one embodiment of the present invention in FIG. The length of each line is determined to have a phase difference of (π/4). Although it is preferable that the phase difference between the three lines is π/4, it is possible to implement a case where the phase difference is shifted (not matched) from this. Also, the length of each line becomes shorter as the measurement frequency in the VNA increases.

Embodiments of the present invention have been described with reference to the drawings. However, the invention is not limited to these embodiments. Furthermore, the present invention can be implemented with various improvements, modifications, and variations based on the knowledge of those skilled in the art without departing from the scope of the invention.

The method of measuring the reflection coefficient of a DUT at one port of a VNA according to the present invention uses only the simplest line as a reference device, and is applicable to measurement of the reflection coefficients of high-frequency devices of various shapes. Also, application to precise measurement of material constants such as permittivity is possible.

1, 11: signal source 2, 12: receiver 3, 13: device under test (DUT)
10, 20: vector network analyzer (VNA)
15, 16, 17: lines A, B, C

Claims (3)

A method of measuring a reflection coefficient using a vector network analyzer (VNA), comprising:
measuring the reflection coefficient Γ _dm of a device under test directly connected to one port of the VNA;
S-parameters S _ij,X (i, j=1, 2, X=A, B, C) are known to the one port and the DUT through three lines A, B, C with different lengths measuring the reflection coefficient Γ _Xm (X=A, B, C) when connecting
determining a true reflection coefficient Γ _d of the device under test using the reflection coefficients Γ _dm , Γ _Xm and the S-parameters S _ij,X ;
the lengths of the three lines A, B, and C are set such that the phases of the reflection coefficients Γ _dm and Γ _Xm at the measurement frequency are shifted by π/4;
Let δ be the directional circuit error, μ be the matching circuit error, and τ be the tracking circuit error.
The step of determining the true reflection coefficient Γ _d of the object under test includes:

A measuring method comprising the step of determining the true reflection coefficient Γ _d as a system of equations . The step of measuring the reflection coefficient Γ _Xm of the object under test includes:
measuring the reflection coefficient Γ _Am when the device under test is connected to the one port via the line A;
measuring the reflection coefficient Γ _Bm when the device under test is connected to the one port through the line B;
2. The measuring method according to claim 1 , further comprising the step of measuring the reflection coefficient _.GAMMA.Cm when the device under test is connected to the one port via the line C. 3. The measuring method according to claim 1 or 2 , wherein the three lines A, B, C comprise airlines, waveguides or planar circuits.

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