RU2487464C2 - Method for linearisation of microwave amplifier characteristics (versions) - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: method for linearisation of characteristics of a microwave amplifier using a signal at envelope curve signals to suppress nonlinear distortions consists in that, in a microwave amplifier based on a travelling-wave tube or a klystron, a low-frequency correction signal of the envelope curve from the output of a modulator or the output of a detector is fed to the focusing electrode or the first anode of the travelling-wave tube or a klystron, and in a transistor microwave amplifier, a low-frequency correction signal of the envelope curve from the output of a modulator or the output of a detector is fed to the input of the transistor through circuits which determine the operating point. Amplifier characteristics consistently vary under the action of the signal, which is the envelope curve of the modulated microwave signal at the input of the amplifier.

EFFECT: high linearity of amplifier characteristics while maintaining efficiency, output power and the operating frequency band.

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Description

The invention relates to microwave (microwave) electronics and can be used to create powerful microwave amplifiers with a high degree of linearity of characteristics and, accordingly, a low level of non-linear distortion of the amplified signal.

A known method of linearizing the characteristics of the amplifier and suppressing non-linear distortions, based on the use of pre-emphasis of the amplified high-frequency signal or high-frequency feedback circuits [1].

Such circuits significantly affect the working frequency band of the amplifier and can lead to its self-excitation, in addition, the gain of the entire path decreases.

Closest to the proposed is a method of linearizing the characteristics and reducing non-linear distortion of the amplifier by creating feedback circuits at the envelope frequencies of the modulated amplified high-frequency signal [2].

The known method consists in the fact that the reduction of high-frequency signals of 3rd order intermodulation distortion in the working frequency band of a microwave amplifier on a field effect transistor can be achieved by applying to the gate of the transistor from its drain low-frequency envelope oscillations generated at the amplifier output as 2nd order intermodulation distortion , through a special low-frequency feedback circuit. A necessary condition of this method is the presence at the output of the amplifier of low-frequency oscillations corresponding to the frequencies of the envelope. Due to the fact that this condition is not always fulfilled, a method based on the construction of low-frequency feedback circuits is not universal and is therefore not applicable to traveling-wave tube amplifiers (TWTs) and a number of microwave amplifiers built on transistors.

The technical problem to which the claimed invention is directed is the linearization of the characteristics of the microwave amplifier and the suppression of non-linear distortion of the microwave amplifier without the use of feedback circuits and pre-emphasis of the amplified high-frequency signal.

The stated technical problem is solved by the fact that according to the proposed invention according to the first embodiment, the method of linearizing the characteristics of the microwave amplifier by using the signal at the envelope frequencies to suppress non-linear distortions is that in the microwave amplifier using a traveling wave lamp or klystron, a low-frequency correction envelope signal is output from the modulator output on a focusing electrode or the first anode of a traveling wave lamp or klystron.

The stated technical problem is also solved by the fact that according to the proposed invention according to the second embodiment, the method of linearizing the characteristics of the microwave amplifier by using the signal at the envelope frequencies to suppress non-linear distortions is that in the microwave amplifier using a traveling wave lamp or klystron, the low-frequency correction envelope signal from the detector output fed to the focusing electrode or the first anode of the traveling wave lamp or klystron.

The stated technical problem is also solved by the fact that according to the proposed invention according to the third embodiment, the method of linearizing the characteristics of the microwave amplifier by using the signal at the envelope frequencies to suppress non-linear distortions consists in the fact that the microwave amplifier on the transistor has a low-frequency correction envelope signal from the output of the modulator or from the output of the detector fed to the input of the transistor through circuits that define the operating point.

The technical result, the achievement of which is ensured by the implementation of the entire claimed combination of essential features, is to increase the linearity of the characteristics of the amplifier while maintaining the efficiency (efficiency), output power and operating frequency band.

This result is achieved by the fact that the characteristics of the amplifier consistently change under the action of a signal representing the envelope of the modulated microwave signal at the input of the amplifier.

The invention is illustrated by drawings, where:

figure 1 presents a diagram of a traveling wave lamp (TWT);

figure 2 presents typical nonlinear characteristics of a traveling wave lamp at different currents of the electron beam,

figure 3 and 4 presents the options for applying the envelope signal to the focusing electrode (figure 3) or the first anode (figure 4).

Figure 1 contains the following positions:

1 - cathode of the electron gun,

2 - focusing electrode,

3 - the first anode,

4 - the second anode,

5 - retarding system

6 - collector.

New in the proposed method for amplifiers on a traveling wave lamp or klystron is that an envelope signal is applied to the focusing electrode (1) or the first anode (2) of the device, which ensures a change in the electron beam current, leading to a change in the amplitude and phase-amplitude characteristics, consistent with envelope signal.

The envelope signal can be applied to the focusing electrode (Fig. 3) or the first anode (Fig. 4) both from the output of the modulator and from the detector (7 - modulator / detector, 8 - input of the modulator / detector, 9 - output of the modulator / detector) , emitting an envelope of modulated oscillation supplied to the microwave input of the amplifier.

The principle of linearization of the characteristics of the amplifier using a low-frequency envelope signal is illustrated in figure 2, which presents typical nonlinear characteristics of a traveling wave lamp at different currents of the electron beam. When a voltage U proportional to A _{in is} applied to the focusing electrode or the first anode, the current of the electron beam will change and each A _in will correspond to a static amplitude characteristic determined by the current value of the electron beam. As a result, upon changing A _in and the current of the electron beam, we obtain a “dynamic amplitude” characteristic, which, with the appropriate choice of the phase of the envelope signal A _I, will be closer to linear than the original static characteristics.

To quantify the level of nonlinear distortions and the degree of their suppression, we apply the quasistationary method for analyzing nonlinear signal transformations [3], which is valid for commonly used modulating signals whose spectrum Δω is small enough in comparison with the carrier frequency ω, Δω << ω.

The complex amplitude of the envelope of the signal can be represented as the sum of N components with frequencies nΩ << ω lying within Δω:

$$A(t)={\displaystyle \sum _{n=\mathrm{one}}^N\left|E_n\right|}{e}^{-i}{}^{\left[({\omega }_n-{\omega }_0)t+{\alpha }_n\right]},\text{(one)}$$

where the amplitudes of the components

$$E_n=\left|E_n\right|e^{-i{\alpha }_n}=\frac{\mathrm{one}}{2\pi }{\displaystyle \underset{0}{\overset{2\pi }{\int }}A(t)e^{in\Omega t}d(\Omega t).\text{(2)}}$$

The amplifier will be described by the complex transfer coefficient, including the amplitude | A _o (| A _o | |) | and phase-amplitude characteristics:

φ (| A _in | |)

$$K(\left|A_{\mathrm{at}x}\right|)=\frac{A_{\mathrm{at}sx}}{{\mathrm{BUT}}_{\mathrm{at}x}}=\frac{\left|{\mathrm{BUT}}_{\mathrm{at}sx}\right|}{\left|{\mathrm{BUT}}_{\mathrm{at}x}\right|}{e}^{-i\Delta \phi }\text{(3)}$$

For the spectral components of the signal at the output of E _{nout of the} amplifier, the following simple expression can be obtained through the spectral components at the input of E _nin [3]:

$$E_{n\mathrm{at}sx}={\displaystyle \sum _{n^{|}=\mathrm{one}}^{\text{N}}{K}_{n-n^{|}}}{E}_{n^{|}\mathrm{at}x}\text{, (four)}$$

Where

$$K_n=\frac{\mathrm{one}}{2\cdot \pi }{\displaystyle \underset{0}{\overset{2\cdot \pi }{\int }}K{e}^{in\Omega t}d(\Omega t)-\text{(5)}}$$

complex Fourier amplitudes of the transmission coefficient K.

When calculating the suppression of nonlinear distortion in amplifiers according to the proposed method, the dependence of the transfer coefficient K on the electron beam current or another parameter J determining the transfer characteristics of the amplifier is also taken into account. In turn, this parameter in accordance with the proposed method under the action of the envelope of the input signal | And _I |. therefore

$$K=K\left[\left|A_{\mathrm{at}x}(t)\right|,J(|A_{\mathrm{at}x}(t)|)\right]\text{(6)}$$

and the magnitude of the Fourier amplitude K _n , which determine the nonlinear distortion, can be reduced by a corresponding choice of the dependence J (| A _in (t) |).

Following the methodology of [4], universal amplitude characteristics can be introduced to estimate the relative level of nonlinear distortions. When approximating the amplitude characteristic of the amplifier by a third-degree polynomial when the amplifier is in two-frequency mode and the test signal is applied to the amplifier input (the amplitudes of the input signals are equal to each other, the initial phases are also equal to each other and equal to zero), the universal amplitude characteristics can be written as:

$${\mathrm{BUT}}_{\mathrm{at}sx}=a_{\mathrm{one}}\cdot {\mathrm{BUT}}_{\mathrm{at}x}-\left|a_3\right|\cdot A_{\mathrm{at}x}{}^3,{\mathrm{BUT}}_{\mathrm{at}sx.\mathrm{to}\mathrm{from}3}=\left|a_3\right|\cdot {\mathrm{BUT}}_{\mathrm{at}x}{}^3,\text{(7)}$$

$$Y=\mathrm{1,5}\cdot X-0.5X^3,Y_{\mathrm{to}\mathrm{<figure-callout\; id="3"\; label="c"\; filenames="00000013.png"\; state="\{\{state\}\}">c</figure-callout>}3}=\frac{\mathrm{one}}{6}\cdot X^3,gde\text{(8)}$$

$$Y=\frac{A_{\mathrm{at}sx}}{{\mathrm{BUT}}_{\mathrm{at}sx.n\mathrm{but}\mathrm{from}}},X=\frac{A_{\mathrm{at}x}}{{\mathrm{BUT}}_{\mathrm{at}x.n\mathrm{but}\mathrm{from}}},Y_{\mathrm{to}\mathrm{from}3}=\frac{A_{\mathrm{at}sx.\mathrm{to}\mathrm{from}3}}{{\mathrm{BUT}}_{\mathrm{at}sx.n\mathrm{but}\mathrm{from}}},$$

$${\mathrm{BUT}}_{\mathrm{at}x.n\mathrm{but}\mathrm{from}}=\sqrt{\frac{\mathrm{one}}{3}\cdot \frac{a_{\mathrm{one}}}{\left|a_3\right|}},{\mathrm{BUT}}_{\mathrm{at}sx.n\mathrm{but}\mathrm{from}}=\frac{2}{3}\cdot a_{\mathrm{one}}\sqrt{\frac{\mathrm{one}}{3}\cdot \frac{a_{\mathrm{one}}}{\left|a_3\right|}},$$

And _output.x is the amplitude of the third-order combination component.

To assess the relative level of combination components in dB, the expression can be used:

$$dB(X)=\mathrm{twenty}\cdot \lg \left|\frac{Y_{\mathrm{to}c3}}{Y}\right|=\mathrm{twenty}\cdot \lg \left|\frac{{\mathrm{<figure-callout\; id="2"\; label="X"\; filenames="00000013.png,00000014.png"\; state="\{\{state\}\}">X</figure-callout>}}^2}{3\cdot X^3-9}\right|.\text{(10)}$$

For a traveling wave lamp having the amplitude characteristics shown in FIG. 2, the calculation according to formula (4) gave for each of the characteristics without the use of non-linear characteristics correction the level of combinational components of the third order (-17) dB. Using correction, the level is (-30) dB.

The proposed method allows to reduce third-order nonlinear distortion by 13 dB and expand the dynamic range by 1.7 times.

The proposed method for linearizing the characteristics of a microwave amplifier can be used for other microwave amplifiers, acting with the help of an envelope on a parameter on which the static amplitude characteristics of the amplifier depend, i.e. moving on to the dynamic amplitude response.

Thus, using a change in the beam current or other parameter, which is consistent with the envelope of the input signal, on which the nonlinear characteristics of the amplifier depend, it is possible to increase the linearity of the characteristics of the amplifier and obtain a low level of nonlinear distortion, while the efficiency of the amplifier, its output power, and the operating frequency range do not change.

Information sources

1. Yu.N. Khlopov, N.N. Kuzovkova. Side Oscillations in Microwave Vacuum Devices, vol. No. 2, 1970.

2. I.N. Dutyshev. “A 100-watt power amplifier with a reduced level of intermodulation distortion and protection of the output transistors against breakdown when operating in two-signal mode,” Electronic Technology, ser. 1, microwave technology, vol. 4 (492), 2007.

3. V.I. Malyshenko, V. A. Solntsev. Nonlinear analysis of multi-frequency TWT operating modes at close frequencies, Electronic Engineering, ser. 1, Microwave Electronics, issue 10, 1972.

4. V.A. Solntsev, T.M. Andreevskaya. “The use of electronic devices and devices. Analysis of the conversion of signals with several carriers in a powerful TWT ", Electronic technology, ser. Microwave Technology, issue 1 (469), 1997.

Claims (3)

1. A method of linearizing the characteristics of a microwave amplifier by using a signal at envelope frequencies to suppress non-linear distortions, namely, that in a microwave amplifier using a traveling wave lamp or klystron, a low-frequency correction envelope signal from the output of the modulator is fed to the focusing electrode or the first anode of the traveling wave lamp or klystron. 2. A method of linearizing the characteristics of a microwave amplifier by using a signal at envelope frequencies to suppress non-linear distortions, namely, that in a microwave amplifier using a traveling wave lamp or klystron, a low-frequency correction envelope signal from the detector output is fed to the focusing electrode or the first anode of the traveling wave lamp or klystron. 3. A method of linearizing the characteristics of a microwave amplifier by using a signal at envelope frequencies to suppress non-linear distortions, namely, that in a microwave amplifier on a transistor, a low-frequency correction envelope signal from the output of the modulator or from the output of the detector is fed to the input of the transistor through circuits defining the operating point.

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