SU1781638A1 - Meter of s-parameters of line four-terminal network - Google Patents

Description

The invention relates to a measurement technique at microwave frequencies and can be used to measure the complex parameters (S-parameters) of linear microwave four-terminal devices (microwave devices of the passage type).

The purpose of the invention is the expansion of the range of operating frequencies and limits of measurement, improving accuracy.

In FIG. 1 is a structural electrical diagram of the S-parameter meter of a linear four-terminal network, which contains a microwave generator 1, tee 2, first and second common-mode dividers 3, 4 of the signals, directional couplers 11,12, 13 and 14, matched loads 15, 16, 17 and 18, the measured four-terminal 19, the waveguide compensator 20 phases, the binary phase shifter 2 ^ measuring heads 22 and 23 and the control unit and the calculation 24. The extension of the measurement limits of the modules S-parameters is achieved by amplitude modulation of the microwave signal in the reference and measuring channel x at different frequencies of the modulating voltages, which is equivalent to a linear phase microwave detector. In this case, the extension of the operating frequency range of the meter is made in the short-wave part of the millimeter wave range. The tasks of the transition from measuring transmission parameters to measuring reflection parameters of quadrupoles having a large electric length are solved using an additional microwave switch introduced into the reference channel. 1 C.p. f-ls, 2 ill.

power, the first, second and third amplitude modulators 5, 6, 7, the first, second and third modulating signal generators 8, 9, 10, the first, second, third and fourth directional couplers 11, 12, 13, 14, the first, second, the third and fourth matched loads 15, 16, 17,18, the measured four-terminal 19, the waveguide compensator 20 phases. binary phase shifter 21, the first and second measuring. heads 22. 23, control and calculation unit 24.

In FIG. 2 shows the connection diagram of an additional microwave switch 25.

SUnn 1781638 A1

The meter S-parameters of the linear four-port network operates as follows.

The output microwave signal of the microwave generator 1 is divided by tee 2 into two parts, one of which is a reference signal, and the second enters through the first in-phase divider 3 into the ring measuring path. The reference signal is first modulated in phase using a binary phase shifter 21 (the initial phase of the signal takes two values at the output of the phase shifter: 0 ° in the absence of a control signal and 90 ° in its presence). Further, this signal is modulated in amplitude by the frequency voltage Oz using a third amplitude modulator 7, controlled from the third generator 10, and fed through the second in-phase divider 4 to the first inputs of the first and second directional couplers 11, 12 and then to the first and second measuring heads 22 . 23.

In turn, the measuring signals received through the first in-phase divider 3 into the arms of the ring measuring path are modulated in amplitude by the frequency voltages Ωι (using the first amplitude modulator 5) and (using the second amplitude modulator 6). They propagate through the measured quadrupole 19 in opposite directions. The third and fourth directional couplers 13, 14 are oriented simultaneously to the waves reflected from the inputs of the measured four-terminal network 19 and passing through it from opposite directions. Branched into the secondary paths of the directional couplers 13 and 14 • the measuring signals thus carry information about the values of all measured S-parameters and are fed to the second inputs of the directional couplers 11 and 12 and then to the measuring heads 22 and 23. Moreover, to each measuring the head 22, 23 actually receives two measurement signals. Let, for example, the first signal supplied to the measuring head 22, contains information about the value of Sn. Then the second signal at the input of the same measuring head 22 will contain information about the value of Si ₂ . The measurement signals at the input of the measuring head 23 contain information on the values of S22 and S21. Each of these signals has its own frequency of amplitude modulation: either Ωι or ^. Let us analyze the spectral composition of the output voltages of the measuring heads, taking into account the fact that the reference signal is also modulated in amplitude by the frequency voltage Oz. ,

In the absence of amplitude modulators 5.6, 7, the output voltages, for example, of the measuring head 22, would be described for the first and second positions of the binary phase shifter 21 with the following expressions:

Ui = α> Εο ² [Κι ² + 2KvK3 | Sik | cos (<£> n <+ 0) nX K3 ² ISikl ² ], _Ό

U ₂ == a-Eo ² [K ₂ ² + 2K2-K3 | Sik | sin (9¾ + 0¾) + Кз ² ISik I ² ).

where ία is the transmission coefficient of the measuring head 2:

Eo is the field amplitude at the branching point of the reference and measuring channels:

Κι, K ₂ - modules of the total transmission coefficients (loss) of the reference channel at the first and second positions of the binary phase shifter 21;

KZ - the loss of the measuring channel: gdn-phase shift, taking into account the non-identity of the phase-frequency characteristics of the reference and measuring channels;

ISikl ^ k - module and phase of the measured S-parameter.

Let, for example, Ui and U2 correspond to the dimension S11. An analysis of the spectral composition of them with a quadratic characteristic of the detector of the head 22 testifies to the presence of:

- DC voltage

Ui = "[K ^ + 2 KrK IS11I cos (9011 + 0> n) + К§ IS11I ² ]:,

- frequency voltages Ωι υ'ί = α · Mi E ² [2 Ki · K3IS11I cos (<pii + 0¾) + K§ IS-hI ² ] cos Ωι t;

- voltage frequency Oz

Ui '= cr Mz Eo [K ^ + 2 Ki Kz ISnl cos (0) 11 + 0¾)] cos Oz t;

where Μι and Мз are the coefficients of amplitude modulation of the measuring and reference signals;

- voltages' ΐί \ = а IS11I ² Ео cos ² Ωι t =.

= kV IS11I ² Eo +

K3IS11IE ² cos2 Ω11)

- voltage

Ui = 0: к7е ² cos ² He = | αΜ§Κ ^ Ε? + '+ | amY Eo cos 2 Ozg;

- voltage

U? = 2aMi M ₃ Ki K3IS11I B ²

COS (/> 11 + £> n) · cos Οι1 cos 6¾ t = = α Μι M3 Κι Ks IS11I Eo cos (ipii + ^) cos ( Ω1 + Oz) ΐ + αΜι Μ ₃ Κι Ks IS11I Ε ² cos ( / η + φ ") cos (Οι - Оз) t.

It can be seen from the above expressions that, if the frequency voltage is selected as the signal of the measuring information

Y (V + O) _t defined by the first term in the expression for Ui ^vl , it will be free of nonlinear terms proportional to IS11I ² and К?, Similar to the output signal in S-parameter meters with frequency transfer. This means expanding the measurement limits of the S-parameter modules. Voltages Ui ^vl and i) 2 ^V frequencies (Οι + Оз) are easily selected in block 24, forming the first autonomous channel for processing measurement information. The second channel has an operating frequency (6¾ + Oz) and corresponds to the output voltages of the measuring head 22, containing information about the value of S12. The same frequencies have measurement channels. information on the values of S22 and S21 contained in the output voltages of the measuring squirrel. 23. This can be either autonomous channels, or in block 24, an alternate measurement of the output voltages of the measuring heads 22 and 23 can be arranged using, for example, an electronic switch.

On the other hand, the variable voltage component Ui ^v can be used as an input signal to the system for automatically adjusting the output power of the microwave generator 1, since it contains information on the change in E _about when its frequency is swinging. Therefore, it is also distinguished by a selective amplifier of the control-computing unit tuned to a frequency of 26¾. It would also be possible to use the frequency voltages (Οι - Оз) and (6¾ - 6¾) as measuring signals. defined by the second terms in the expressions for Ui ^vi and other output voltages of the measuring heads 22 and 23. However, this would degrade the dynamic characteristics (speed).

Frequency channel selection is carried out in block 24 by well-known methods (for example, using band-pass filters). The control and computing part of block 24 is also typical and is based either on the built-in microprocessor or on a personal

A computer interfaced with the analog-digital part of the block.

Frequency selection of measurement information processing channels also allows you to automate the process of measuring nonreciprocal parameters of four-terminal devices. To do this, it is sufficient to carry out additional computational operations using the algorithms following from the definitions of the corresponding nonreciprocal parameters over the output signals of the channels containing information on the values of S21 and S12. In particular, the nonreciprocal phase shift is determined on the basis of information on the initial phases of the channel output signals as Δζ arg = arg S2i ~ argSi2, and the gate ratio is determined on the basis of information on the amplitudes of these signal Рв as В = IS12 I / IS21I.

The introduction of 5.6 different frequencies Οι and 6¾ into the shoulders of the ring path of amplitude modulators ¾ι and 6¾ not only ensures the autonomy of the measuring information processing channels, but also minimizes the number of error sources for each channel. For example, spurious signals due to the finite directivity of the third and fourth directional couplers 13. 14 will no longer affect the measurement results of S12 and S21. Spurious signals due to the final decoupling of the shoulders of the first common-mode divider 3 are additionally modulated in the respective modulators, which is equivalent to the frequency shift of the modulating voltages after detection in the measuring heads 22 and 23 and their removal beyond the bandwidths of the corresponding channels. The situation is similar with most spurious signals arising from multiple reflections. As a result of these measures, the measurement accuracy of all S-parameters reaches its limit values. '

In the transition from measuring transmission parameters to measuring reflection parameters of four-terminal devices having a large electric length, it is solved by using an additional microwave switch inserted into the reference channel. The need for this is due to the fact that the electrical length of the reference channel when measuring Sn and S22 must take into account in such cases not the length of the measuring channel to section 1-1 (Fig. 1), but only the length to section 2-2 (when measuring S11) or '3-3 (when measuring S22). Specifically, a change in the length of the reference channel is necessary if the four-terminal network has a length equal to

1781G38 standing from section 2-2 to section 3-3 (base distance) or close to it.

To ensure this, a microwave switch 2Y is included in the reference channel, as shown in FIG. 2. In the first position of the switch, the initial circuit of FIG. 1 is implemented with a waveguide compensator 20 included in the reference channel, the length of which is equal to the base distance. This corresponds to the measurement mode S21 and S12, as well as S11 and S22, if the four-terminal device has a small electric length (for example, a transistor or a microwave circuit), and section 1-1 should be considered as the reference plane when measuring S and S22. If the four-terminal has a large electric length, the microwave switch 25 when measuring S11 and S22 is moved to the second position, and the signal from the output of the tee 2 (Fig. 2) is fed to the input of the binary phase shifter 21 through the channel 1-2 microwave switch, bypassing the waveguide compensator 20.

The advantages of the S-parameter meter of a linear four-terminal device are as follows:

Significant expansion of the measurement limits of S-parameter modules due to amplitude modulation of the microwave signal in the reference and measuring channels at different frequencies of the modulating voltages, which is equivalent to a linear phase microwave detector.

Extension of the operating frequency range of the meter into the short-wave part of the millimeter wave range.

Providing automation of measurement of the entire set of S-parameters of reciprocal and non-reciprocal microwave four-polar. .

Ensuring high accuracy of measuring S-parameters, which allows you to create not only working, but also exemplary devices.

Claims (2)

Claim 1. An S-parameter meter of a linear four-terminal network, comprising a microwave generator connected to the input of a tee, the first output of which is connected to the input of the first common-mode divider, a second common-mode divider, the outputs of which are connected to the inputs of the primary channels of the first and second directional couplers, the outputs of their secondary channels loaded on the first and second measuring heads connected to the measuring inputs of the control and calculation unit, the first control output of which is connected to the control input of the microwave generator, third and fourth directional couplers, to the outputs of the secondary channels of which the first and second matched loads are connected, and between the outputs of the primary channels, a measured linear four-terminal device is switched on, characterized in that, in order to expand the operating frequency range and measurement limits, the first and second amplitude moduli are introduced, the modulating inputs of which are connected to the outputs of the introduced first and second modulating voltage generators of various frequencies, the inputs of the first and second amplitude modulators soy are dined with the outputs of the first in-phase divider, and the outputs are with the inputs of the primary channels of the third and fourth directional couplers, the second output of the tee is connected through the input of a series-connected waveguide phase compensator, the binary phase shifter and the third amplitude modulator to the input of the second in-phase divider, the modulating input of the third amplitude modulator is connected with the output of the third modulating voltage generator, the frequency of which is different from the frequencies of the first and second modulating voltage generators the outputs of the primary channels of the first and second directional couplers are loaded on the entered third and fourth matched loads, and the outputs of the secondary channels of the first and second directional couplers are connected to the inputs of the secondary channels of the third and fourth directional couplers, and the control input of the binary phase shifter is connected to the second control output of the unit control and computing, the information inputs of which are connected to the information outputs of the first, second and third generators modulate its voltage. 2. The meter according to claim 1, characterized in that, in order to improve the accuracy of measuring the reflection coefficient of an extended linear four-port network, a microwave switch is introduced, the first input of which is connected to the second output of the tee, the first output and second input, respectively, with the input and output waveguide phase compensator, and the second output with the input of the binary phase shifter.