RU2804927C1 - Self-oscillator of chaotic pulses - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: used in communication systems for transmission of information messages based on chaotic microwave pulses. To achieve the effect, the self-oscillator of chaotic pulses additionally contains a nonlinear amplifier, the input of which is connected to the output of the linear amplifier, and the output to a directional coupler, while the nonlinear delay line additionally contains a metal conductor placed on the surface of the periodic structure and connected to a direct current source. The nonlinear amplifier is designed to operate in the maximum output power mode, and the linear amplifier is a multi-cavity system, the resonant frequency of which is tuned to the central frequency of the stopband of the periodic structure.

EFFECT: ensuring a change in the level of nonlinear losses of a magnetostatic wave propagating in a dispersive delay line with a magnon crystal using a direct electric current.

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Description

The invention relates to radio engineering and can be used in communication systems for transmitting information messages based on chaotic ultra-high frequency (microwave) pulses of various duty cycles.

A generator of chaotic microwave pulses is known (see RF patent No. 2386204 according to class IPC N03V 29/00, publ. 04/10/2010), which is a series-connected microwave amplifier, a directional coupler and a load, as well as a feedback circuit connected between the other the output of a directional coupler and the input of a microwave amplifier and containing a resonator and a dispersive delay line tunable by a magnetic field with a ferrite film when magnetostatic waves are excited in it, which is at the same time a nonlinear element. The presence of dispersion and nonlinearity in the MSW propagating in the ferrite film, as well as the use of a resonator in the ring capable of changing the law of dispersion and nonlinearity of the entire ring as a whole in a narrow frequency band, leads to the generation of a stationary sequence of chaotic microwave pulses in the ring.

However, in this generator of chaotic microwave pulses it is not possible to control the duty cycle of the generated pulses due to the lack of synchronization of the frequencies of self-modulation of spin waves when the gain of the ring changes.

A self-oscillator of chaotic pulses is also known (see RF patent No. 2740397 according to class IPC N03V 29/00, publ. 01/14/2021), containing linear and nonlinear microwave amplifiers connected in series in a ring, a directional coupler, an attenuator, and an L-shaped magnetic waveguide. A linear amplifier amplifies the microwave signal to a power level at which the nonlinear amplifier operates in output power saturation mode. Thus, the chaotic microwave signal generated in the ring is formed due to three- and four-wave nonlinear spin-wave interactions, and the nonlinear amplifier limits the growth of the amplitude of the chaotic microwave signal. This leads to generation in the time domain against a chaotic amplitude background of relatively wide dips of submicrosecond duration due to three-wave nonlinear processes, the envelope of which, in turn, is modulated by faster oscillations of subnanosecond duration arising due to the generation of a microwave signal on the eigenmodes of the ring self-oscillator in as a result of four-wave nonlinear interactions. The presence of a nonlinear amplifier also contributes to the establishment of partial chaotic synchronization of the self-modulation frequencies of spin waves with the frequencies of the eigenmodes of the ring resonator and to the generation of a stationary sequence of microwave pulses of subnanosecond duration.

However, in this device, the nonlinear dispersive delay line on the MSW contains an irregular (L-shaped) magnon waveguide, on the surface of which there is no dynamic linear defect, i.e. there is no possibility of dynamic control of the duty cycle of the pulse sequence.

The closest to the claimed one is a ring self-oscillator (see RF patent for utility model No. 135202 according to class IPC H03B 29/00, publ. November 27, 2013), containing a microwave power amplifier, a linear resonator and a nonlinear dispersive delay line connected in series in a ring with a magnon crystal (MC), made on the basis of a ferrite film, on one side of which a periodic structure is formed in the form of alternating layers of ferrite film of different thicknesses along the direction of propagation of a surface magnetostatic wave in the film; the self-oscillator contains a variable attenuator placed between the linear resonator and the nonlinear dispersive delay line; the resonant frequency of the cavity resonator is tuned to the central frequency of the first band gap of the periodic ferromagnetic structure.

To generate chaotic microwave pulses, the magnitude of the external constant magnetic field and magnetization of the MC are selected in such a way that the frequency of the first Bragg resonance of the MC coincides with the natural frequency of the resonator, and at the frequency of the first Bragg resonance of the MC, parametric processes of the first order exist, leading to the decay of the dipole surface magnetostatic wave ( PMSV) to exchanged spin waves. In addition, to generate a chaotic signal with an almost continuous spectrum, it is necessary that in the MSSW excitation frequency band there is a delay of the signal passing through the dispersion delay line. In such a self-oscillator, synchronization of the self-modulation frequencies of spin waves is maintained when the ring gain is changed mechanically using a variable attenuator, which causes a change in the duty cycle of the generated chaotic pulse sequence over a wide range.

The disadvantage of this generator of chaotic microwave pulses is the lack of the ability to dynamically control the duty cycle of the pulse sequence.

The technical problem of the claimed invention is the creation of a self-generating chaotic pulse, which allows for dynamic control of the duty cycle of the pulse sequence.

The technical result consists in ensuring a change in the level of nonlinear losses of a magnetostatic wave (MSW) propagating in a dispersive delay line with an MC using a direct electric current.

By locally changing the internal magnetic field of the 1D MC due to the applied direct electric current of different polarity, it is possible to control the duty cycle of pulse sequences generated at the frequency of the 1D MC stopband.

To achieve a technical result, a self-oscillator of chaotic pulses containing a linear microwave amplifier, a directional coupler, a variable attenuator, a nonlinear delay line connected to the linear microwave amplifier with a magnon crystal made in the form of a ferrite film, on the surface of which a periodic structure is formed in the form of alternating layers of ferrite films of different thicknesses along the direction of propagation of a surface magnetostatic wave in the film, the source of an external magnetic field, according to the invention , additionally contains a nonlinear amplifier, the input of which is connected to the output of the linear amplifier, and the output is connected to a directional coupler; the nonlinear delay line additionally contains a metal conductor placed on the surface periodic structure and connected to a direct current source, while the nonlinear amplifier is configured to operate in the maximum output power mode, and the linear amplifier is a multi-cavity system, the resonant frequency of which is tuned to the central frequency of the stopband of the periodic structure.

The linear amplifier can be made in the form of a multicavity span klystron.

The present invention is illustrated by drawings, where:

- in fig. 1 shows a block diagram of the proposed self-oscillator of chaotic microwave pulses;

- in fig. Figure 2 shows a schematic representation of a delay line based on a one-dimensional magnon crystal, along the longitudinal axis of symmetry of which a current-carrying conductor is located;

- in fig. Figure 3 shows the dependence of the transmission coefficient S ₂₁ on the frequency f of a delay line based on a one-dimensional magnon crystal with dynamic control (a) and a linear microwave amplifier (b) (a resonant active element);

- in fig. Figure 4 shows the dependence of the transmission coefficient S ₂₁ on the signal power at _the input ( Pin ) of the delay line based on a one-dimensional magnon crystal with dynamic control, obtained at several values of direct electric current I;

- in fig. Figure 5 shows the dependences of the output power ( Pout ) on the _input power ( Pin ) of a nonlinear microwave amplifier (a) (nonlinear active element) and a resonant active element ₍ b);

- in fig. 6 - shows the time series of chaotic microwave pulses generated in a self-oscillator based on a one-dimensional magnon crystal with dynamic control at several values of direct electric current I: 0 (a), +320 mA (b) and -200 mA (c).

Positions in the drawings indicate:

1 - linear microwave amplifier (an active resonant element capable of operating in linear amplification mode of a microwave signal);

2 - nonlinear microwave amplifier (an active element capable of operating in maximum output power mode);

3 - directional coupler;

4 - variable attenuator;

5 - nonlinear delay line based on a magnon crystal with dynamic control;

6 - metal screen;

7 - polycor substrate;

8 - yttrium iron garnet film with a periodic structure;

9 - metal conductor;

10 - gadolinium gallium garnet substrate;

11 - input microstrip converter;

12 - output microstrip converter;

13 - grounding;

14 - direct current source;

15 - dependence of the transmission coefficient S ₂₁ of a one-dimensional magnonic crystal with dynamic control on the input power Pin , _measured at the central frequency of the first stopband at a value of direct electric current I = 0;

16 - dependence of the transmission coefficient S ₂₁ of a one-dimensional magnonic crystal with dynamic control on the input power Pin , measured at the central frequency of _the first stopband at a constant electric current I = +500 mA;

17 - dependence of the transmission coefficient S ₂₁ of a one-dimensional magnon crystal with dynamic control on the input power Pin , _measured at the central frequency of the first stopband at a constant electric current I = -500 mA.

The device contains (see Fig. 1) a linear microwave amplifier 1, a nonlinear microwave amplifier 2, a directional coupler 3, a variable attenuator 4, a nonlinear delay line 5 with a one-dimensional magnon crystal (1D) made in the form of an iron film, connected in series in a ring. yttrium garnet (YIG) 8 grown on a gadolinium gallium garnet 10 substrate. A periodic structure is formed on the surface of the YIG film in the form of alternating layers of ferrite film of different thicknesses along the direction of propagation in the PMSW film. The nonlinear delay line 5 contains a metal conductor 9 placed on the surface of the periodic structure and connected to a direct current source 14. The self-oscillator contains input 11 and output 12 microstrip converters, which are deposited on a polycor substrate 7, shielded on the opposite side using screen 6.

A one-dimensional (1D) MC with dynamic control (see Fig. 2) is made of YIG film with a thickness of 10 μm, a width of 4 mm, a length of 10 mm and a saturation magnetization of 1750 Gauss. A periodic structure in the form of columns and grooves with a period of 200 μm is formed on the surface of the YIG film using etching and lithography methods. The pillars and grooves have the same width - 100 µm. The grooves are characterized by an etching depth of 1 µm. The length of the periodic structure is 4 mm. For dynamic control of the 1D MK, a copper wire with a diameter of 100 microns and a length of 4.5 mm is used, located along the longitudinal axis of symmetry of the 1D MK and connected to a direct current source. The distance between the copper wire and the surface of the YIG film is 100 μm, which eliminates the influence of heating on the propagation of MSW. Depending on the polarity of the current, the internal magnetic field of the 1D MK in the area of the wire conductor can either increase or decrease. The excitation and reception of MSSW propagating in a 1D MC is carried out using input and output microstrip converters, which are deposited on a polycor substrate 500 μm thick, shielded on the opposite side. Each of them is 30 µm wide and 6 mm long. The distance between them is 6 mm. An external constant magnetic field H ₀ is applied tangentially to the surface of the 1D MK and parallel to the microstrip converters. The choice of field strength H ₀ =356 Oe is due to the need to create conditions for the development of three-wave parametric decay of MSSW in a 1D MC, which leads to chaotization of the microwave signal generated in the ring self-oscillator.

In addition to the 1D MK with dynamic control, a cascade of two active elements is introduced into the feedback circuit of the circular microwave oscillator, one of which is a resonant active element and operates in the mode of linear amplification of the microwave signal (linear amplifier), and the other in the mode of maximum output power of the microwave signal (non-linear amplifier). A five-cavity fly-through klystron can be used as a resonant active element, and a transistor amplifier can be used as a nonlinear amplifier. A linear resonant amplifier serves to isolate the dominant ring mode and amplify the generated chaotic microwave signal on it to a power level at which the nonlinear amplifier operates in the maximum output power mode. A nonlinear amplifier limits the growth of the amplitude of a chaotic microwave signal, which leads to the formation of relatively narrow dips of nanosecond duration in the time domain on the signal envelope, which are “dark” pulses of the envelope. Applying a direct electric current of different polarity to a wire conductor located on the surface of a 1D MC leads to a change in the magnitude of the internal magnetic field in that region of 1D MC space that borders the wire conductor. This causes a frequency shift in the MC stopband and, as a consequence, a change in the level of nonlinear losses of MSSW, on which the duty cycle of the generated “dark” microwave pulses depends.

Thus, to achieve the claimed result, the following conditions must be met.

The direction of the external constant magnetic field _H0 is chosen tangent to the surface of the 1D MK and parallel to the input and output microstrip converters.

The magnitude of the external constant magnetic field H ₀ is chosen in such a way that for an MSSW not bordering metal screens, it is determined as

Н ₀ < 2πM ₀ ,

where M ₀ is the magnetization of the 1D MC.

The power level of the microwave signal at the input of the 1D MC is set so that it exceeds the threshold power level corresponding to three-wave nonlinear spin-wave interactions at the MSSW.

The power level of the microwave signal at the input of the nonlinear amplifier is set so that the amplifier operates at maximum output power.

In fig. Figure 3 shows the amplitude-frequency characteristics (AFC) of a multicavity transit klystron and a delay line based on a 1D MC with dynamic control, measured in linear mode and in the absence of direct current in the region of a dynamic linear defect. It can be seen that the frequency response of the transit klystron is resonant in nature and is characterized by a central frequency f ₀ =2797 MHz, at which the gain of the transit klystron is maximum. On the frequency response of the delay line with a 1D MC, a stopband is observed, which, with the selected direction and strength of the external constant magnetic field, is in the MSSW spectrum and coincides not only with the central frequency of the first Bragg resonance f _b1 , but also with the frequency of the transit klystron f ₀ .

In fig. Figure 4 shows the dependence of the transmission coefficient of a delay line based on a 1D MC with dynamic control on the signal power at its input, measured at several values of direct electric current applied to the wire conductor. Three cases are considered: 1) current is not applied to the conductor (curve 15); 2) a current of positive polarity is applied to the conductor (curve 16) and 3) a current of negative polarity is applied to the conductor (curve 17). From those shown in FIGS. 4 results it follows that in the absence of direct electric current, the dependence S ₂₁ (P _in ) contains both linear and nonlinear sections. The threshold at which the delay line based on a 1D MC with dynamic control switches to a nonlinear operating mode is observed at an input power of -15 dBm, which corresponds to the beginning of the three-wave parametric decay of the MSSW. If a direct electric current of positive polarity is applied to a wire conductor, this leads to an increase in both the linear loss level and the nonlinear threshold. This fact is due to an increase in the internal magnetic field of the 1D MC in the area of current flow. With a current of negative polarity, the level of linear losses of the MSSW and the value of the nonlinear threshold decrease. This is due to a decrease in the internal magnetic field of the 1D MC in the area of current flow. Thus, by applying a direct electric current of different polarity to a wire conductor, it is possible to control not only the level of linear, but also nonlinear MSSW losses at a fixed frequency due to the frequency shift of the 1D MK bandgap. For selected values of current polarity, the dynamic range of linear loss changes is ~4 dB, and the dynamic range of threshold power changes is ~2 dB. It should be noted that at frequencies far from the bandgap, direct electric current does not have a noticeable effect on the levels of linear and nonlinear losses of the MSSW.

In fig. Figure 5a shows the dependence _of Pout ( Pin ) of the transistor amplifier, measured at frequency ƒ _{0 .} It can be seen that its output power deviates by 1 dB from the linear dependence (compression point) and begins to saturate at P _thor2 =+5 dBmW. In a ring oscillator, _the transistor amplifier operates in output power saturation mode when Pin > _Ppor2 by 5 dB.

In fig. Figure 5b shows the dependence _of Pout ( Pin ) of a five-cavity fly-by klystron _, measured at frequency ƒ ₀ . It can be seen that its output power deviates by 1 dB from _the linear dependence (compression point) and begins to saturate at Pthr3 = +16 dBm. _In a ring oscillator , the output amplifier operates in linear signal amplification mode when Pin >> _Pport3 .

In fig. Figure 6 shows the results obtained by including a delay line based on a 1D MC with a dynamic linear defect, as well as two microwave amplifiers (multi-resonator fly-through klystron and transistor amplifier) in the feedback circuit of an active ring resonator. Shown in FIGS. 6, the time series are measured at the ring gain G=KA=31 dB (where K is the gain of the amplifier stage, consisting of two amplifiers, A is the total loss level in the ring). In this case, the integral signal power at the input of the delay line based on a 1D MC with dynamic control has the value _Pin = +3 dBm, which exceeds the nonlinear threshold by 18 dB, and the output amplifier of the stage (transistor amplifier) operates in the maximum output power mode.

From those shown in FIGS. 6a results show that in the absence of direct current (I=0), a chaotic sequence of pulse packets with a duration of ~0.9 μs is formed, each of which contains “dips” in the form of dark envelope pulses. For some “dark” pulses the envelope amplitude drops to zero, while for others it does not drop strictly to zero. The repetition rate of chaotic pulse packets, averaged over the implementation length, has a value of ~100 kHz and corresponds to the self-modulation frequency of parametrically excited SWs generated as a result of the three-wave decay of MSSWs. The duty cycle of such a pulse sequence has a value of q~11.

In fig. 6b and fig. Figure 6c shows chaotic pulse sequences obtained when a direct electric current of different polarity is applied to a wire conductor. From the presented results it follows that with a positive current polarity, the SW self-modulation frequency increases to a value of ~250 kHz (the duty cycle decreases to q~4), and with a negative current polarity, on the contrary, it decreases to a value of ~13 kHz (the duty cycle increases to q~80 ).

Thus, by locally changing the internal magnetic field of the 1D MC due to the applied direct electric current of different polarity, it is possible to control the duty cycle of pulse sequences generated at the frequency of the 1D MC stopband.

Claims (2)

1. Autogenerator of chaotic pulses containing a linear microwave amplifier, a directional coupler, a variable attenuator, a nonlinear delay line connected to the linear microwave amplifier with a magnon crystal made in the form of a ferrite film, on the surface of which a periodic structure is formed in the form of alternating layers of ferrite film of different thickness along the direction of propagation of a surface magnetostatic wave in the film, a source of external magnetic field, characterized in that it additionally contains a nonlinear amplifier, the input of which is connected to the output of the linear amplifier, and the output is connected to a directional coupler; the nonlinear delay line additionally contains a metal conductor placed on surface of the periodic structure and connected to a direct current source, while the nonlinear amplifier is configured to operate in the maximum output power mode, and the linear amplifier is a multi-cavity system, the resonant frequency of which is tuned to the central frequency of the stopband of the periodic structure. 2. Self-oscillator according to claim 1, characterized in that the linear amplifier is made in the form of a multi-resonator flight klystron.