EA034867B1 - Method of measuring s-parameters - Google Patents

Abstract

The invention can be used for measuring the scattering parameters of two-port UHF devices in large-signal mode. Measurements are carried out preferably with vector network analyzers (VNA) (3). An enhanced signal is fed from a first port of a VNA (3) to an input of the object under test (1). A reflected signal and a transmitted signal from the object under test (1) are fed to a second port of the VNA (3). The reflection coefficients and the transmission coefficients of the object under test (1) are measured while a spatially remote load (7) with two different impedance values is connected to an output of the object under test (1). On the basis of the measured coefficients, a complete S-parameter matrix is constructed.

Description

Technical field

The invention relates to methods for measuring electrical characteristics, namely, to methods for measuring the parameters of microwave devices, and can be used to measure the scattering parameters (S-parameters) of two-port microwave devices in large signal mode.

State of the art

Measuring devices for measuring S-parameters are widely known, the most common of which are vector circuit analyzers (VACs). The design of the standard VAC implements a method for measuring S-parameters, based on the excitation of the studied objects by microwave signals (incident waves), the selection of signals transmitted (transmitted and reflected waves) transmitted through the studied object and reflected from the studied object, and measuring the ratio of amplitudes of the selected waves for calculating the S-parameters of the object under study [Understanding the Fundamental Principles of Vector Network Analysis. ApplicationNote / Agilent Technologies, Inc. 2012]. The most advanced of the VACs provide the measurement of the full matrix of S-parameters of two-port devices, have high sensitivity and high measurement accuracy, and also operate in the widest frequency range.

A disadvantage of the known method for measuring S-parameters implemented in known measuring devices is the impossibility of its application in the large signal mode. The maximum achievable for the described methods, the signal level applied to the object under study is +20 ... + 23dBm [http://literature.cdn.keysight.com/litweb/pdf/5989-7603EN.pdf].

A known method of measuring the scattering parameters of microwave devices in large signal mode based on the polyharmonic distortion method described, for example, in [David E. Root, JanVerspecht, DavidSharrit, JohnWood, Alex Cognata. Broad-Band Poly-Harmonic Distortion (PHD) Behavioral Models From Fast Automated Simulations and Large-Signal Vectorial Network Measurements / IEEE Transactions on microwave theory and techniques, Vol. 53, No. November 11, 2005, p. 3656-3664]. This method is based on measuring the set of parameters of the investigated object, describing linear and nonlinear behavior, building a model of the behavior of the studied object and restoring from this model S-parameters of the studied object. This method allows you to create measuring systems for the analysis of both linear and nonlinear microwave devices in large signal mode. This method is the basis of many modern measuring systems. In particular, the specified measurement method is implemented when measuring X-parameters [D. E. Root, J. Horn, L. Betts, C. Gillease, J. Verspecht, X-parameters: Thenew paradigm for measurement, modeling, and design of nonlinear RF and microwave components, Microwave Engineering Europe, December 2008 pp 16-21 .], which in the case of analysis of linear microwave devices in the large-signal mode degenerate into the desired S-parameters.

The disadvantage of this method is its complexity due to the extreme complexity and redundancy of the polyharmonic distortion method for measuring S-parameters in the large signal mode. In particular, to implement the known method, a VAC with at least two built-in generators and with access to receivers is required.

A known group of methods for measuring hot S-parameters, one of which is described, for example, in [Hot S22 and Hot K-factor measurements. Application note / Anritsu, 2002. downloadfile.anritsu.com/Files/enUS/Application-Notes/Application-Note/11410-00295.pdf]. In particular, the method of measuring the hot S ₂₂ parameter is that a large level signal at a frequency f that sets the operation mode of the device under study is supplied to the input of the object under study, and a low level signal at the tuned frequency (f + Af) is output to the object under investigation, then measure the parameter S ₂₂ at the tuned frequency (f + Af).

The disadvantages of this group of methods, selected as the closest analogue, are the incorrectness (approximation) of the measurement due to the difference in the excitation frequency of the investigated object and the frequency at which the measurements are carried out, as well as the complexity of the implementation associated with the need to use at least two signal generators to generate signals at frequencies f and (f + Af).

Disclosure of invention

The present invention is to simplify the method of measuring S-parameters in the large signal mode.

The technical result consists in the possibility of measuring S-parameters by measuring devices with one signal generator for one connection of the object under study, and also in the possibility of using simple vector network analyzers as direct measuring devices without direct access to the measuring receivers.

The claimed technical result is achieved due to the fact that in the method of measuring S-parameters in the large signal mode, in which the measurements are carried out using a measuring device with at least two measuring ports, including at least one signal generator, and the input to the object under investigation is fed amplified signal from the first port of the measuring device, in accordance with the invention:

- 1 034867 reflected from the studied object and passed through it, the signals are sequentially fed to the second port of the measuring device, while the following sequence of actions is carried out:

measuring the reflection coefficient G and the transmission coefficient K _{1 of the} test object when a spatially remote load with an impedance Z _load1 connected to the output of the test object;

measuring the reflection coefficient G ₂ and the transmission coefficient K _{2 of the} test object when a spatially remote load with an impedance Z _load2 connected to the output of the test object;

restore the full matrix of S-parameters from the measured coefficients.

As a measuring device, it is preferable to use a vector network analyzer (VAC) or a measuring system based on multipolar reflectometers (described, for example, in [Kudryavtsev, AM Intelligent analyzer of microwave circuits and antennas / A.M. Kudryavtsev, SM. Nikulin.N. Novgorod: Nizhny Novgorod State Technical University, 2005. 121 pp. ISBN 5-93272-312-2]), and as a spatially remote load - a spatially remote load (PUN) with a variable impedance.

Brief Description of the Drawings

The accompanying drawing shows a block diagram of an example of a hardware implementation of the proposed method.

The implementation of the invention

The claimed method is generally implemented as follows. To measure the S-parameters of the test object, a two-port vector circuit analyzer is used, including one signal generator. The input of the object under study is connected to the first (output) port of the VAC, and its output to the second (input) port of the VAC, using additional devices widely known in radio engineering that provide the following functions:

providing the required signal level at the input of the investigated object;

selection of a part of the signal reflected from the studied object and its supply to the second VAC port; selection of a part of the signal passed through the studied object and its supply to the second ACV port.

To the output of the test object through a long line connect a coordinated or inconsistent PUN with variable impedance.

To obtain a complete matrix of S-parameters, the VAC is pre-calibrated together with additional hardware in the plane of connection of the measured object by any known method. After that, preliminary measurements are carried out, for which the following actions are performed:

1. A jumper is installed in the place of connection of the object under study.

2. At PUN set the first value of the impedance Z _load1 .

3. They send a signal from the first VAC port to the VAC, select a part of the signal reflected from the VAC to the second VAC port and measure the reflection coefficient Г _1п from the VAC with the impedance value Z _load1 .

4. They send a signal from the first VAC port to the VAC, select a part of the signal passed through the VAC to the second VAC port and measure the transfer coefficient K _1p .

5. At PUN set the second value of the impedance Z _load2 , such that Z _load1 + Z _load2 .

6. Similarly to the above, the coefficients Г _2п and К _2п are measured, respectively, and the jumper is removed.

These preliminary measurements can be performed once for specific VCO or specific impedance values of VCO, since their result does not depend on the characteristics of the studied objects. The obtained values of Г _1п , К _1п , Г _2п and К _2п can be repeatedly used in calculating the matrix of high-signal S-parameters of the studied objects according to the method described below. In the case of replacing the PUN or changing the impedance values Zload1 and Zload2 For PUN with a variable impedance, the above preliminary measurements are carried out again and determine new indicators G1p and K1p.

The characteristics of the test object are measured as follows.

An impedance value Zload1 is set for the object under investigation connected to the output through a long line of PUN. In this case, the line length is chosen equal to at least one, for example two, wavelengths of the signal used in the measurements. Amplified to the level required by the object under study, the signal from the first VAC port is fed to the input of the object under study. A part of the signal reflected from the object under study is taken to the second VAC port with attenuation sufficient for the normal functioning of the VAC and the reflection coefficient from the object under study is measured Г ₁ Then, with the same signal supplied to the input of the studied object, part of the signal passed through the studied object from the output of the studied object selected on the second port of the VAC and measure the transmission coefficient of the investigated object To ₁ . Change the impedance value of the PUN from Z _load1 to Z _load2 . By analogy with the measurement of the coefficients G1 and K1, respectively, the coefficients G2 and K2 are measured.

After this, according to well-known formulas described, for example, in [S. Nikulin, A. Torgovanov. Design of microwave power amplifiers. The effectiveness of the method of remote variable load / Electronics NTB, No. 3 (00143) 2015], hereinafter - (A), the matrix of S-parameters of the object under study is restored by the coefficients Г _1п , К _1п,, Г _2п К _2п , Г ₁ , К ₁ , G ₂ , K ₂ .

- 2 034867

In the case of measurements in a pulsed mode, the signal from the first port of the measuring device supplied to the input of the test object is additionally modulated, and further measurements are made in a manner similar to that described above.

The following example shows one possible embodiment of the invention.

Example.

As a test object (1) for measurements, a device in a coaxial path was chosen.

To measure the S-parameters of the studied object (1), a hardware device (2), which was developed by the applicant, was used that implements the inventive method and is connected to a measuring device. The block diagram of the hardware device (2) is shown in the drawing. Also shown in the drawing:

(3) - measuring device - VAC;

(4) - amplification unit based on a low-noise power amplifier (LNA);

(5), (6) - directional couplers; - (7) -PUN;

(8) - electronic switch;

(9) - a long line (a piece of coaxial cable with a length equal to two wavelengths of the signal supplied from the first port of the WAC);

(10) - plug-in jumper - a piece of coaxial cable 0.1 m long;

(I), (II) - ports for connecting a hardware device to the VAC;

(III), (IV) - ports connecting the hardware device to the device under study.

The VAC Obzor-304/1 with two ports was used as a measuring device, the first of which was used as the output port of the VAC (3), the second as the input port. The signal from the first port of the WAC (3) was fed to the input of the hardware device (2), the signal from the output of the hardware device (2) was sent to the second port of the WAC (3).

An electronically tunable complex load, an impedance tuner, manufactured by FocusMicrowaves of the MMT-N series [http://www.focus-microwaves.com/products] was used as a PUN (7).

We connected the hardware device (2) to the VAC (3) and calibrated the pair of the VAC - the hardware device. After that, a jumper (10) was connected to ports (III) and (IV) of the hardware device (2) and preliminary measurements were carried out in accordance with the claimed method. In this case, two arbitrary positions of the impedance tuner were selected, corresponding to the values of the impedances Z _load1 and Z _load2 . When measuring part of the transmitted and reflected signals, selected with attenuation to the second VAC port (3) using directional couplers (5) and (6), they sequentially switched to the second VAC port (3) using an electronic switch (8). According to the results of preliminary measurements, Г1п, К1п, Гп and К2п were measured.

After that, the jumper (10) was disconnected from the hardware device (2), the object under study (1) was connected to it, and in accordance with the claimed method, the coefficients G ₁ , K ₁ , G ₂ , K _{2 were} measured.

After that, using the formulas (A) indicated in the present description, the matrix of S parameters was reconstructed from the measured coefficients.

To carry out measurements in a pulsed mode when developing a system that implements the proposed method, a measuring device with an integrated pulse modulator is used, or an additional pulse modulator is used in the signal supply path from the first port of the measuring device to the input of the object under study. In this case, the measuring device must be able to analyze in a pulsed mode (for example, this condition is met by the VAC manufactured by Keysight Technologies PNA series [http://literature.cdn.keysight.com/litweb/pdC59897603EN.pdf]).

Industrial applicability

The practical implementation of the claimed method, as was shown in the example described above, is an obvious task for the average specialist, and does not require the construction of complex radio circuits.

If necessary, when developing a system that implements the proposed method, to better ensure the declared functionality, it is possible to use additional units that do not change the functionality of the system being developed, for example, additional decoupling devices - valves, circulators, etc. In addition, to ensure coordination with the measuring device used high power levels when developing a system that implements the proposed method, control devices can be additionally used level of reflected and transmitted signals, for example, attenuators.

Thus, a simplified method for measuring S-parameters in the large-signal mode is proposed, which makes it possible to measure S-parameters by measuring devices with one signal generator for one connection of the object under study, as well as the possibility of using simple vector circuit analyzers as direct measuring devices without direct access to measuring receivers.

Claims (5)

CLAIM 1. The method of measuring S-parameters in the large signal mode, which consists in the fact that the measurements are carried out using a measuring device with at least two measuring ports, including at least one signal generator, and an amplified signal from the first port of the measuring device, characterized in that the signals reflected from the test object and passing through it are sequentially fed to the second port of the measuring device, while the following last consistency of actions: measuring the reflection coefficient G ₁ and the transmission coefficient K _{1 of the} test object when a spatially remote load with an impedance Z _ioad1 connected to the output of the test object; measuring the reflection coefficient G ₂ and the transmission coefficient K _{2 of the} test object when a spatially remote load with an impedance Z _ioad2 connected to the output of the test object; restore the full matrix of S-parameters from the measured coefficients. 2. The method according to claim 1, characterized in that as a measuring device using a vector network analyzer. 3. The method according to claim 1, characterized in that as a measuring device using a measuring system based on multipolar reflectometers. 4. The method according to claim 1, characterized in that as a spatially remote load using a spatially remote load with a variable impedance. 5. The method according to claim 1, characterized in that the signal supplied to the input of the test object from the first port of the measuring device is additionally modulated.