RU2501157C2 - Apparatus for generating chirp signals - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: apparatus includes a transmitting optical unit, a fibre-optic splitter with N outputs, N binary fibre-optic structures, (N-1) fibre-optic delay lines, a fibre-optic connector with N inputs, an optical amplifier, a receiving optical unit, a band-pass filter, an amplitude limiter, an electronic amplifier and a low-pass filter.

EFFECT: high rate of frequency modulation, which is equivalent to reducing the duration of a chirp signal while maintaining high values of the radio signal base.

15 dwg

Description

The present invention relates to techniques for the formation of radio signals and can be used in radar, secure communications, radio, geo-reconnaissance, etc.

A device for generating linear frequency-modulated (LFM) signals is known [US Patent 4633185, MKI H03K 005/159, Hugh McPherson (Great Britain); John P. Blakely (UK)].

The forming device includes a serially connected single pulse generator, a delay line on surface acoustic waves, an amplitude limiter, an electronic amplifier, and an expander. The control input of the single pulse generator is the input of the shaper, the output of which is the output of the expander.

Signs of an analogue that coincide with the features of the claimed technical solution are series-connected amplitude limiter and electronic amplifier.

The disadvantages of the analogue are:

- upper limit of the central frequency of the chirp signal;

- upper limit on the value of the frequency deviation of the chirp signal;

- the impossibility of the formation of radio pulses with intrapulse LFM nanosecond duration with a central frequency of more than 1.5 GHz;

- speed limitation of frequency modulation.

The reasons that impede the achievement of the required technical result are the limited capabilities of the delay lines on surface acoustic waves. The high attenuation and limited capabilities of micron technology photolithography (at a frequency of 1 GHz requires a resolution of 1 μm) make it difficult to create devices on surface acoustic waves at frequencies of more than 1.5 GHz, which does not allow the generation of chirp signals in the range above 1.5 GHz. In this case, the relative passband of the delay line on surface acoustic waves varies from 1 to 100%, which limits the frequency deviation of the generated LFM signal to 1.5 GHz.

Considering that the duration of the signal at the output of the single pulse generator is much shorter than the duration of the generated signal (20-30 times), it can be concluded that, taking into account the above-mentioned limitation, the duration of the generated pulses exceeds 18 ns, while the central frequency of the generated signal does not exceed 1 5 GHz.

Limitations of the frequency deviation and the duration of the generated signals do not allow to obtain high values of the frequency modulation speed.

A device for generating chirp signals is also known [Patent 5428361 118, MKI G01S 7/28; H03B 23/00; Charles H. Hightower (USA), Ralph I. Kratzer (USA)].

The forming device includes a crystal oscillator, a frequency divider by 4, a frequency divider by 5, a frequency multiplier by 2, two phase detectors, two frequency-phase detectors, twelve electronic amplifiers, four multipliers, two loop filters, three voltage-controlled oscillators, two isolators, four power dividers, three attenuators, two programmable dividers, a bandpass filter, a synchronization and control unit, an expander, two modulation characteristic selectors, a noise reduction unit, a phase auto selector frequency adjustment of the generator.

The input of the shaper is the control input of the crystal oscillator, the output of the shaper is the output of the fourth multiplier.

Signs of an analogue that coincide with the features of the claimed technical solution are a band-pass filter and an electronic amplifier.

The disadvantages of the analogue are:

- the impossibility of the formation of pulses of nanosecond duration;

- upper limitation of the frequency deviation of the chirp signal;

- speed limitation of frequency modulation;

- the complexity of the device.

The reasons that impede the achievement of the required technical result are as follows.

The technical solution scheme does not provide for the formation of signals of nanosecond duration, since the resulting pulse is composed of sub-pulses in order to increase the signal base. The insufficient broadband of the phase detectors and the voltage-controlled generator limits the deviation of the generated signal and also does not allow for the nanosecond duration of the generated signal.

Limitations of the duration and frequency deviation of the generated signals do not allow to obtain high values of the frequency modulation speed.

A large number of feedbacks in the device leads to a reduction in the speed of the driver and additional attenuation of the signal. A large number of multipliers in the device introduces additional signal distortion and makes high demands on the frequency stability of the crystal oscillator.

Of the known technical solutions, the closest in technical essence to the claimed one is the driver of frequency-modulated signals [Patent 2282302 RU, MKI H03C 3/00, A. Bortsov (RF), Ilyin Yu.B. (RF)].

The frequency-modulated signal generator consists of a generator, a functional converter and a phase interferometer having three inputs and one output and can also generate chirp signals.

The generator is connected to the first input of the deflector in the functional converter. The functional converter consists of a deflector having two inputs and one output, a first receiving optical module, a first electronic amplifier having one input and two outputs, a transmitting optical module included in the first output of the first electronic amplifier, two optical fibers. In this case, one of the optical fibers at the output is optically coupled to the first receiving optical module, the other optical fiber at the input is optically coupled to the transmitting optical module, and at the output with the deflector. A phase shifter is additionally introduced into the functional converter, the second input of which is connected to the output of the receiver, a low-pass filter, three directional couplers, four optical fibers, one of which is with a polymer sheath. In this case, the phase interferometer is connected by inputs to the second outputs of the directional couplers, and its output is connected to the second input of the phase shifter. A low-pass filter is located between the phase shifter and the first electronic amplifier, the second output of which is the output of the functional converter. Three optical fibers are arranged in series so that one of them is optically coupled to the deflector output at the input, and a fiber with a polymer cladding is located between the other two. In this case, the directional couplers are connected in series so that the first and third optically coupled respectively to the output and input from the optical fibers, the first and second directional couplers are rigidly connected to each other, and the second and third through the optical fiber located between them.

The transmitting optical module contains an optical source and a modulator, the first input of which is the input of the transmitting optical module, the second input is connected to the optical source. The output of the modulator is the output of the radiation source.

The phase interferometer is designed according to a two-arm scheme and contains two phase shifters, three optical fibers, two receiving optical modules, one of which has two inputs and one output, two amplifiers and a mixer having two inputs and an output, while the second and third phase shifters are connected to the second by inputs the outputs of the third and second directional couplers, respectively, and the outputs to the second receiver, which, in turn, is connected to the second amplifier, with optical fibers installed between the phase shifters and the second receiver, and the third receiver The detector is connected to the second output of the first directional coupler and a fiber is installed between them, while the second amplifier and the third receiver are connected respectively to the first and second inputs of the mixer, which, in turn, is connected to the third amplifier, which transmits a signal to the second input of the first phase shifter.

The signs of the prototype, coinciding with the features of the claimed technical solution, are a receiving optical module, a transmitting optical module, an electronic amplifier and a low-pass filter.

The disadvantages of the prototype are:

- lower restriction on the duration of the generated LFM radio signals;

- upper limitation of the frequency deviation of the chirp radio signal;

- speed limitation of frequency modulation;

- the complexity of the device.

The reasons that impede the achievement of the required technical result are as follows.

The use of an acousto-optical deflector based on tellurium oxide does not allow controlling the deflector with a frequency above 200 MHz, which limits the minimum duration of the generated signal (taking into account the reduced value of the control signal frequency and delays in the device path, the minimum duration of the generated signal is at least 30 ns).

The frequency deviation in the prototype is limited by the upper operating frequency of the electro-optical modulator, which is part of the transmitting optical module, the value of which for modern serial models based on the material declared in the prototype is about 8 GHz.

Limitations of the duration of the generated signals and frequency deviation do not allow achieving high values of the frequency modulation rate.

The use of a phase interferometer with a high identity of shoulder lengths, due to the complexity of manufacturing and tuning, complicates and increases the cost of the device.

The use of phase shifters places high demands on the accuracy of manufacturing optical fibers.

The problem to which the invention is directed, is to increase the frequency modulation speed, which is equivalent to reducing the duration of the chirp radio signal while maintaining high values of the radio signal base.

To achieve a technical result, a fiber optic splitter, N binary fiber optic structures, (N-1) fiber optic delay lines, a fiber optic connector, an optical amplifier, a bandpass filter and an amplitude limiter are additionally introduced into the known device.

The technical result is achieved by the fact that a fiber-optic splitter with N optical outputs, N binary fiber-optic structures, (N-A) is additionally introduced into the device for generating chirp signals, which contains a transmitting optical module, a receiving optical module, a low-pass filter and an electronic amplifier. 1) fiber-optic delay lines, a fiber-optic connector with N optical inputs, an optical amplifier, a band-pass filter and an amplitude limiter, the optical output of the transmitting optical the muzzle is connected to the optical input of the fiber optic splitter, the first output of which through the first binary fiber optic structure is connected to the first optical input of the fiber optic connector, the second output of the fiber optic splitter through the second binary optical fiber structure and the first fiber optic connected in series the delay line is connected to the second input of the fiber optic connector, and the i-th output of the fiber optic splitter through series-connected e i-th binary fiber-optic structure and (i-1) -th fiber-optic delay line is connected to the i-th input of the fiber-optic connector, the optical output of which is connected through the optical amplifier to the optical input of the receiving optical module, the electrical output of which through a series-connected bandpass filter, an amplitude limiter and an electronic amplifier are connected to the electrical input of the low-pass filter, and all N binary fiber-optic structures contain a dividing directional a Y-type curl coupler, Q-type X-directional fiber couplers, (Q + 1) additional fiber-optic delay lines and a summing Y-type directional fiber coupler, the input of a Y-type directional fiber coupler being an input of a binary optical fiber structure the first output of which is combined with the first input of the first directional X-type fiber coupler, and the second output is connected to the second input of the first direction through the first additional fiber-optic delay line X-type fiber coupler, the first output of which is connected to the first input of the second X-type directional fiber coupler, and the second output through the second additional fiber optic delay line is connected to the second input of the second X-type fiber coupler, the first output j- of the X-directional directional fiber coupler is connected to the first input of the (j + 1) -th X-type directional fiber coupler, and the second output of the jth X-type directional fiber coupler through the jth additional fiber the optical delay line is connected to the second input of the (j + 1) th directional X-type fiber coupler, the first output of the last Qth directional X-type fiber coupler being connected to the first input of the summing Y-type directional fiber coupler the output of the last Qth directional X-type fiber coupler through the (Q + 1) -th fiber optic delay line is connected to the second input of the summing directional Y-type fiber coupler, and the output of the low-pass filter is the output of the device Properties.

The analysis of the essential features of analogues, prototype and the claimed technical solution revealed the following new significant features regarding the technical solution for the claimed object:

- introduced fiber optic splitter BOP 2 with one input and N outputs for the simultaneous formation of optical pulses on all of its N optical outputs;

- N binary optical fiber structures of BVOS 3-1 ... 3-N are introduced for replication of input optical pulses with high copy identity. At the output of the i-th binary optical fiber structure of the BVOS 3-i, a sequence of K non-overlapping optical pulses is formed, following with a frequency f _{trace i} . Moreover, the sequences at the output of the i-th and (i + 1) -th binary fiber-optic structures differ only in the repetition rate;

- introduced (N-1) fiber optic delay lines VOLZ 4-1 ... 4- (N-1). The delay time in the rth and (r + 1) th fiber-optic delay lines differs by

$$\Delta {\tau }_{\left(r+\mathrm{one}\right)}=\frac{K+\mathrm{one}}{f_{\mathrm{from}led}\left(r+\mathrm{one}\right)}.\left(\mathrm{one}\right)$$

Due to this, the pulse sequences of different binary fiber-optic structures are spread in time to exclude their overlap during further processing;

- introduced fiber optic connector BOC 5, having N inputs and one output, combining the sequence of pulses of various binary fiber optic structures into a single sequence of non-overlapping pulses with a linearly changing repetition rate;

- an optical amplifier ОУ 6 was introduced, which makes it possible to compensate for the loss of optical radiation when dividing the signal of the transmitting optical module POM 1 in the fiber-optic splitter BOP 2, as well as losses in the binary fiber-optic structures of the BVOS 3-1 ... 3-N, fiber-optic lines delays VOLZ 4-1 ... 4- (N-1) and fiber optic connector BOC 5;

- the bandpass filter PF 8 is introduced to highlight the spectrum of the chirp signal from the obtained sequence;

- introduced an amplitude limiter AO 9, eliminating spurious amplitude modulation of the signal.

Thus, the formation of a radio signal with an intrapulse LFM is carried out in the optical wavelength range, where the used optical fibers having a linear attenuation of 0.2 dB / km and a linear passband exceeding hundreds of terahertz per kilometer can minimize losses during signal formation and achieve a reduction in duration of the generated signal, and the use of binary fiber-optic structures allows you to replicate copies of the pulse of the transmitting optical module with high identity in amplitude, which creases generated signal quality.

Evidence of a causal relationship between the claimed combination of features and the achieved technical result is given below.

The essence of the proposed device is illustrated by drawings.

Figure 1 presents a structural diagram of a device for generating chirp signals.

Figure 2 presents the structural diagram of the binary fiber optic structure BVOS 3-i.

Figure 3 shows the voltage diagrams at the output of the functional nodes of the chirp signal generation device: POM 1 (a), BVOS 3-1 (b), BVOS 3-i (c), BVOS 3-N (g), VOLZ 4- 1 (e), BOC 5 and OS 6 (e), PF 8 (g), AO 9 (h), EU 10 (s), low-pass filter 11 (k).

Figure 4 presents the time dependence of the frequency of the chirp signal in the device for generating chirp signals.

Figure 5 shows the spectrum and autocorrelation characteristic of the LFM signal generated in the inventive device.

Figure 6 shows the limiting values of the generated chirp signal depending on the size of the technological tolerance in the manufacture of fiber-optic delay lines for binary fiber-optic structures.

7 shows the results of calculating the dispersion length of the optical fiber.

On Fig shows a graph of the dependence of the dispersion length on the duration of the pulse generated by the transmitting optical module T ₀ for three types of optical fiber.

Figure 9 shows the results of calculating the value of the nonlinear length for various values of the peak power of the transmitting optical module.

Figure 10 shows the results of calculating the threshold power for various values of the spectrum width of the emission line of the transmitting optical module.

Figure 11 illustrates the time shifts of copies of binary fiber structures under the influence of increasing ambient temperature.

Fig. 12 shows a block diagram of a device for generating chirp signals with the parameters specified by the model.

13 is a structural diagram of a binary fiber optic structure device with parameters specified by the model.

On Fig shows the values of the delay time for various fiber-optic delay lines in the composition of the device for generating chirp signals on binary fiber-optic structures with the parameters specified by the model.

Figure 15 shows the spectrum and the autocorrelation characteristic of the LFM signal generated on binary fiber-optic structures with parameters specified by the model.

The device for forming the LFM radio signals (Fig. 1) contains a transmitting optical module POM 1, a fiber optic splitter BOP 2 with N outputs, N binary fiber optic structures BVOS 3-1, ..., 3-N, (N-1) fiber-optic delay lines, fiber-optic connector BOC 5 with N inputs, optical amplifier OU 6, receiving optical module PROM 7, bandpass filter PF 8, amplitude limiter AO 9, electronic amplifier EU 10 and low-pass filter low-pass filter 11. Optical output POM 1 is connected to the optical input of BOP 2. The first optical output B P 2 through the first binary optical fiber structure BVOS 3-1 with a time constant τ _BVOS1 connected to a first optical input BOC 5. The second optical output BOP via series connected second binary optical fiber structure BVOS 3-2 with a time constant τ and a first _BVOS2 fiber optic delay line VOLZ 4-1 with a time constant τ _{back1 is} connected to the second optical input of BOC 5, and the i-th optical output of BOP 2 through a series i-connected binary fiber-optic structure of BVOS 3-i with time constant τ _{BV OSi} and (i-1) -th fiber optic delay line VOLZ 4- (i-1) with time constant τ _{back (i-1) is} connected to the i-th optical input of BOC 5.

The optical output of BOC 5 through a series-connected optical amplifier OU 6, a receiving optical module PROM 7, a bandpass filter 8, an amplitude limiter AO 9 and an electronic amplifier EU 10 is connected to a low-pass filter of the low-pass filter 11. The output of the low-pass filter 11 is the output of the device for generating LFM signals,

In this case, the i-th binary optical fiber structure of the BVOS 3-i (Fig. 2) contains a dividing directional fiber coupler of the HBO of the Y-type 12-i, Q directional fiber couplers of the HBO of the X-type 14-i1 ... 14-iQ, (Q +1) additional fiber optic delay lines VOLZ 13-i1 ... 13-i (Q + 1) and a summing directional fiber coupler HBO Y-type 15-i. The input of the Y-type 12-i HBO directional fiber coupler is the input of the BVOS 4-i binary optical fiber structure, the first output of which is combined with the first input of the first X-type HBO 14-i1 directional fiber coupler, and the second output through the first additional fiber the optical delay line VOLZ 13-i1 with a time constant τ _{back1 is} connected to the second directional fiber coupler of the HBO X-type 14-i2, the first output of which is connected to the first input of the second directional fiber coupler of the HBO X-type 14-i2, and the second output through the second additional fiber optic delay line VOLZ 13-i2 with a time constant τ _{rear i2} connected to the second input of the second directional fiber coupler HBO X-type 14-i2. The first output of the jth directional fiber coupler of the HBO X-type 14-ij is connected to the first input of the (j + 1) -th directional fiber coupler of the HBO X-type 14-i (j + 1), and the second output of the jth directional fiber coupler X-type HBO 14-i-coupler coupler through the j-th additional fiber optic delay line of the VOLZ 13-ij delay with a time constant τ _{back ij is} connected to the second input of the (j + 1) -th directional X-type HBO 14-i fiber coupler +1). The first output of the last Qth directional fiber coupler of the HBO X-type 14-iQ is connected to the first input of the summing directional fiber coupler of the HBO Y-type 15-i, and the second output of the last Qth directional fiber coupler of the HBO X-type 14-iQ The (Q + 1) th fiber optic delay line VOLZ 13-i (Q + 1) with a time constant τ _{rear (Q + 1) is} connected to the second input of the summing directional fiber coupler HBO Y-type 15-i.

The device for generating chirp signals works as follows.

Let the optical pulse with energy E ₀ and duration T _{0 be} generated by the transmitting optical module POM 1 (see Fig. 3.a). Moreover, T ₀ << τ _LFM .

In the BOP 2 fiber-optic splitter, the optical pulse is divided into N optical pulses of duration T ₀ and energy E ₀ / N, which simultaneously appear on the N outputs of the BOP 2 fiber-optic splitter. From the i-th output of the BOP 2 fiber-optic splitter, the pulse fed to the input of the i-th binary optical fiber structure of the BVOS 3-i, forming K copies of the input optical pulse with a duration of T ₀ and a copy energy of E ₀ / N (figure 3, b-g). The copy repetition rate for the i-th binary optical fiber structure of the BVOS 3-i is selected in accordance with the formula

$$f_{\mathrm{from}ledi}={\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="00000041.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\frac{\beta }{\pi }\left[\left(i-\mathrm{one}\right)K+0.5K\right]\frac{\mathrm{one}}{{\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="00000041.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+\sqrt{{\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="00000041.png"\; state="\{\{state\}\}">f</figure-callout>}}_0^2+\frac{\beta \left[\left(i-\mathrm{one}\right)K+0.5K\right]}{\pi }}},\left(2\right)$$

where f ₀ is the initial frequency, β is the frequency modulation rate.

As a result, at the output of the i-th binary optical fiber structure of BVOS 3-i there is a packet of K pulses with a repetition period

$${\tau }_{B\mathrm{AT}\mathrm{ABOUT}\mathrm{FROM}i}=\frac{\mathrm{one}}{f_{\mathrm{from}ledi}}.\left(3\right)$$

The time constant of the additional fiber optic delay line VOLZ 13-ij ... 13-i (Q + 1) is determined by the formula

$${\tau }_{s\mathrm{but}dij}=2^{j-\mathrm{one}}{\tau }_{s\mathrm{but}di\mathrm{one}},j=\overline{\mathrm{one,}\left(Q+\mathrm{one}\right)}.\left(\mathrm{four}\right)$$

The time constant of the fiber optic delay line VOLZ 4- (i-1) is determined by the formula

$${\tau }_{s\mathrm{but}d\left(i-\mathrm{one}\right)}=\left(K+\mathrm{one}\right){\displaystyle \sum _{m=\mathrm{one}}^{i-\mathrm{one}}{\tau }_{s\mathrm{but}dm\mathrm{one}}.\left(5\right)}$$

From the output of the first binary optical fiber structure of the BVOS 3-1, a packet of pulses is fed to the fiber-optic connector BOC 5, from the output of the binary fiber-optical structures of the BVOS 3-2 ... 3-N copies are fed to the fiber-optic connector BOC 5, respectively, through the fiber Optical delay lines VOLZ 4-1 ... 4- (N-1) (see figure 3, d). In the fiber optic connector of BOC 5, the pulse packets formed by all N binary fiber optic structures of BVOS 3-1 ... 3-N are combined into a single sequence (see Fig. 3, f), after which it is amplified in OA 6 and converted from the optical to the electrical signal in the receiving optical module PROM 7. To select the spectrum of the chirp signal, the pulse sequence is passed through a band-pass filter PF 8 (figure 3, g). The received signal is fed to the amplitude limiter AO 9 to eliminate spurious amplitude modulation (Fig. 3, h), is additionally amplified by an electronic amplifier EU 10 (Fig. 3, and) and is fed to the low-pass filter LPF 11 (Fig. 3, )

The generalized time dependence of the frequency of the chirp signal is shown in Fig. 4, where t ₀ is the start time of the radio signal, t ₁ is the end time of the signal, τ _n is the step of changing the time interval, f ₀ is the minimum value of the signal frequency, f ₁ is the maximum frequency value signal, Δf _n is the step of changing the frequency interval.

The design features of the binary fiber optic structure are determined by the parameters of the generated RF signal with the LFM: the initial frequency of the LFM signal f ₀ , the frequency modulation rate β, the duration τ of the _{LFM of the} generated LFM signal.

If the number of copies of K formed by each of the binary optical fiber structures of the BVOS 3-1 ... 3-N is specified, then the number of outputs of BOP 2 is determined by the formula

$$N=\lfloor \frac{{\tau }_{LHM}\left({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="00000041.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+0.5\beta {\tau }_{LHM}\right)}{K}\rfloor .\left(6\right)$$

The number of copies of K formed in the i-th binary optical fiber structure of BVOS 3-i is always a multiple of two: K = 2 · j. Moreover, the condition must be met

$$2^j\le K=\sqrt{\frac{2\mathrm{<figure-callout\; id="0"\; label="\pi \; f"\; filenames="00000041.png"\; state="\{\{state\}\}">\pi \; </figure-callout>}{f}_{}^{}{}_0^2}{\beta }}+\frac{\mathrm{one}}{2}\le 2^{j+\mathrm{one}}.\left(7\right)$$

The delay time of the i-th FOCL 3-i is determined by the formula

$${\tau }_{s\mathrm{but}di}=\left(K+\mathrm{one}\right){\displaystyle \sum _{m=\mathrm{one}}^{i-\mathrm{one}}{\tau }_{B\mathrm{AT}\mathrm{ABOUT}\mathrm{FROM}m}}.\left(8\right)$$

The delay time of the j-th additional FOCL 13-ij in the i-th binary optical fiber structure of the BVOS 3-i is determined by the formula

$${\tau }_{s\mathrm{but}dij}=2^{j-\mathrm{one}}{\tau }_{s\mathrm{but}di\mathrm{one}},j=\overline{\mathrm{one,}Q}.\left(9\right)$$

The number Q is determined by the formula

$$Q={\log }_{2}K-\mathrm{one.}\left(10\right)$$

To analyze the obtained chirp signal, we compare its spectral and correlation characteristics with the characteristics of the classical chirp signal with the same output parameters (see Fig. 5). The level of the side lobes of the autocorrelation function of the resulting signal does not differ from the corresponding value for the classical chirp signal (minus 13.4 dB).

When analyzing the possibility of generating LFM signals based on binary fiber optic structures, the limit values of the central frequency, deviation and duration of the generated LFM signal were obtained for various technological tolerances in the manufacture of delay lines in binary fiber optic structures (see Fig. 6).

There are several limitations to the implementation of the above scheme.

Firstly, to select the spectrum of the LFM signal with a band-pass filter, the value of the initial frequency of the LFM signal must be chosen more than half the value of the frequency deviation f ₀ > 0.5Δf.

Secondly, the duration of the input optical pulse must satisfy the condition T ₀ ≤0.5 / f _max , where f _max is the maximum frequency of the radio pulses in the sequence. In addition, since the parameters of the input LFM signal must be consistent with the structural features of the construction of binary fiber-optic structures, it is advisable to use binary fiber-optic structures to synthesize a matched filter for the LFM signal provided that the LFM signal is generated on the same synthesized structure.

Thirdly, the limiting factor in the frequency range of the input signal in binary fiber-optic structures during the formation of copies, and, therefore, in the device for generating LFM signals, is the dispersion of the optical fiber.

Since the inventive device for generating LFM signals uses a single-mode optical fiber, chromatic dispersion is predominant. To assess the degree of influence of chromatic dispersion on the waveform, we use the dispersion length parameter L _D , determined by the formula for a radiation source with a frequency spectrum width Δω, pulse width of the transmitting optical module POM 1 T ₀ and group velocity dispersion parameter β ₂

$$L_D=\frac{{\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="00000041.png"\; state="\{\{state\}\}">T</figure-callout>}}_0^2/\left|{\mathrm{<figure-callout\; id="2"\; label="\beta "\; filenames="00000038.png,00000039.png"\; state="\{\{state\}\}">\beta </figure-callout>}}_2\right|}{\sqrt{\mathrm{one}+{\left(\Delta \omega \right)}^2{\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="00000041.png"\; state="\{\{state\}\}">T</figure-callout>}}_0^2}}.\left(\mathrm{eleven}\right)$$

Relation (11) is valid for pulses of any shape. If the maximum distance z _max , at which the influence of dispersion can be neglected, is assumed to be 0.1 L _D , then the pulse duration T _{z · max} after passing a fiber of length z _max , expressed through the pulse duration of the transmitting optical module POM 1 T ₀ , will be T _{z · Max} ≈ 1.0057 °, and the relative "broadening" of the pulse does not exceed 0.5%.

We calculate the values of the dispersion length for various types of single-mode fiber and values of duration T ₀ . Moreover, we take into account that

$${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="00000041.png"\; state="\{\{state\}\}">T</figure-callout>}}_0\le 0.5/f_{\max }.\left(12\right)$$

The minimum possible value of the pulse duration of the transmitting optical module POM 1 taking into account (12)

$${\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="00000041.png"\; state="\{\{state\}\}">T</figure-callout>}}_{0\min }=\frac{\mathrm{one}}{2\cdot f_{\max }}.\left(13\right)$$

In this case, the maximum possible value of the length of the optical fiber is determined by the maximum number of copies K _max formed by binary fiber-optic structures:

$$z_{\max .OB}=\left(K_{\max }+\mathrm{one}\right){\displaystyle \sum _{r=\mathrm{one}}^{N-\mathrm{one}}\frac{\mathrm{one}}{f_r}.\left(\mathrm{fourteen}\right)}$$

Given the above data, the minimum possible values of the input pulse duration T ₀ = 38 ps and the length of the optical fiber z _max.OB = 37 m were _obtained .

The results of calculating the dispersion length according to (11) for various types of optical fiber and pulse length are shown in Fig.7.

The dependence of the dispersion length on the pulse duration T ₀ and the type of optical fiber is graphically presented in Fig. 8.

From Fig. 7 and Fig. 8 it can be seen that for pulse durations exceeding 38 ps, the dispersion lengths for various types of optical fiber differ slightly and exceed 63 km.

Taking into account the value of the maximum length of the optical fiber in the inventive device for generating LFM signals z _max.OB (the length of the fiber-optic delay line connecting the outputs of the Nth binary fiber-optic structure of BVOS 3-N and fiber-optic connector BOC 5), we can conclude that z _max.OB << 0.1 · L _D for any type of optical fiber, which allows not to take into account the effect of chromatic dispersion when considering the properties of the inventive device for generating chirp signals. In addition, in order to reduce the cost of the device, it is advisable to use an optical fiber with unbiased dispersion SF.

Since for use in the inventive device for generating LFM signals, it is assumed to use single-mode fibers with a low chromatic dispersion value and lasers with a narrow spectral band of radiation, it is also necessary to take into account the polarization mode dispersion.

, а усредненная во времени дифференциальная групповая задержка между двумя ортогональными состояниями поляризации Δτ_ПМД растет с ростом расстояния по законуThe specific dispersion coefficient T is normalized per km and has a dimension $$\left(P\mathrm{from}/\sqrt{\mathrm{to}m}\right)$$

, and the time-averaged differential group delay between two orthogonal polarization states Δτ _PMD increases with increasing distance according to the law

$$\Delta {\tau }_{PMD}=T\cdot \sqrt{z}.\left(\mathrm{fifteen}\right)$$

Typical value of the specific polarization mode dispersion for an individual single-mode fiber with a step profile

. Следовательно, для заявляемого устройства формирования ЛЧМ-сигналов, в котором осуществляется большое количество соединений индивидуальных волокон, необходимо учитывать поляризационную модовую дисперсию протяженной линии (квадратично усредненная поляризационная модовая дисперсия для соединенных волокон), типовое значение которой для одномодового волокна составляет $$\mathrm{0,2}\dots \mathrm{1,0}пс/\sqrt{км}$$

.refraction is not more than 1550 nm $$0.02P\mathrm{from}/\sqrt{\mathrm{to}m}$$

. Therefore, for the inventive device for generating chirp signals, in which a large number of compounds of individual fibers are carried out, it is necessary to take into account the polarization mode dispersion of the extended line (squared averaged polarization mode dispersion for connected fibers), the typical value of which for a single-mode fiber is $$0.2...\mathrm{1,0}P\mathrm{from}/\sqrt{\mathrm{to}m}$$

.

составитThe previously calculated maximum length of a single-mode fiber with unbiased SF dispersion and the minimum input signal duration at which the influence of chromatic dispersion can be neglected is about 6.3 km (0.1 · L _D ). Moreover, the time-averaged differential group delay between two orthogonal polarization states Δτ _PMD for a typical value of the specific polarization mode dispersion of the extended line for a single-mode fiber of this type $$T=0.4P\mathrm{from}/\sqrt{\mathrm{to}m}$$

will make

$$\Delta {\tau }_{PMD}\approx 0.4\cdot \sqrt{6.3}\approx \mathrm{one}P\mathrm{from}.\left(16\right)$$

For the duration of the input optical pulses T ₀ = 38 ps, the delay between two orthogonal polarization states Δτ _PMD calculated by formula (16) is about 3.6% of the signal duration. Considering the fact that the actual maximum optical fiber length in the shaper does not exceed z _max.OB = 37 m, it can be concluded that when using a single-mode fiber with unbiased SF dispersion in a binary optical fiber structure, the polarization mode dispersion can be neglected.

When considering the issue of providing the required bandwidth of the device for generating chirp signals, it is also necessary to take into account the restrictions imposed by nonlinear phenomena in the optical fiber.

To assess the phenomenon of self-modulation (SPM) there is the concept of non-linear length:

$$L_{NL}=\frac{\mathrm{one}}{{\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="00000041.png"\; state="\{\{state\}\}">P</figure-callout>}}_0}\cdot \frac{{\lambda }_0{\mathrm{<figure-callout\; id="2"\; label="S\; e"\; filenames="00000038.png,00000039.png"\; state="\{\{state\}\}">S\; </figure-callout>}}_e}{2\pi \overline{n}},\left(17\right)$$

). Влиянием SPM на импульсы можно пренебречь в том случае, когда импульсы распространяются на расстояние z<<L_NL.where P ₀ is the peak power of the optical pulse, W; S _e is the effective region of the fiber cross section (as a rule for single-mode optical fibers S _e = 50 μm ² ), n is the coefficient of nonlinearity of the refractive index (for quartz fiber $$\overline{n}=3.2\cdot {10}^{-8}m\mathrm{to}{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="00000038.png,00000039.png"\; state="\{\{state\}\}">m</figure-callout>}}^2/\mathrm{AT}t$$

) The influence of SPM on the pulses can be neglected in the case when the pulses propagate to a distance z << L _NL .

The result of calculating the nonlinear length for various values of the peak power of the optical pulse of the quantum generator is shown in Fig.9.

Given that the maximum length of the optical fiber in the shaper z _max.OB = 37 m, we can state that the self-modulation phenomenon in the inventive device for generating LFM signals can be neglected if the peak power of the optical pulse P ₀ does not exceed 1 W, which is sufficient for most applications .

To assess the Brillouin scattering phenomenon (SBS), the concept of threshold power P _pore is introduced, which is usually calculated using the following approximate expression:

$$R_{P\mathrm{about}R}\approx 21\frac{S_e}{g_B{L}_e}\left(\mathrm{one}+\frac{\Delta f_s}{\Delta f_B}\right),\left(\mathrm{eighteen}\right)$$

where g _B is the SBS gain of approximately 4 × 10 ^-11 m / W and does not depend on the wavelength, Δf _s is the width of the frequency spectrum of the optical signal source, L _e is the effective fiber length, Δf _B is the frequency band of interaction with acoustic phonons (20 MHz).

We calculate the threshold power values for various values of the emission line spectrum width Δλ, which determines the width of the frequency spectrum of the optical signal source Δf _s , at which stimulated Brillouin scattering into the optical fiber can be neglected. The calculation result is shown in Fig.10.

As can be seen from the calculation results, at a working wavelength of λ ₀ = 1550 nm and a radiation line spectrum width of the order of Δλ> 0.1 nm, the threshold power P _then has values that are acceptable for practical use.

In addition to dispersion and dispersion, one of the key factors affecting the properties of the optical fiber in the composition of the inventive device for generating chirp signals is the temperature factor.

The refractive index of the core of the optical fiber in the absence of deformation (tension, compression) of the fiber depends on the temperature:

$$\Delta n=\left[{\left(\frac{\partial n}{\partial T}\right)}_T+{\left(\frac{\partial n}{\partial T}\right)}_R\right]dT,\left(19\right)$$

- частная производная по температуре.where n is the refractive index of the core of the optical fiber; dT — temperature change, K; $$\left(\frac{\partial n}{\partial T}\right)$$

- partial derivative with respect to temperature.

от температуры (0,68·10^-5°C для кварцевого стекла).The first term of formula (19) is analyzed in the literature, which presents the dependence of the component of the change in the indicator $$\frac{\mathrm{one}}{n}{\left(\frac{\partial n}{\partial T}\right)}_T$$

temperature (0.68 · 10 ^-5 ° C for quartz glass).

To calculate the second term characterizing changes in the refractive index of the core of the optical fiber due to deformations, you can use the formula

where a is the radius of the fiber core, taken as the radius of the mode field; R is the bending radius of the fiber in the coil; T _N - conditional temperature at which the length of the optical fiber would be equal to the nominal length.

Based on formula (20), we can conclude that the relative change in the refractive index of the core of the optical fiber caused by bending or torsion due to thermal expansion is about 10 ^-5 . Given the variation in the refractive index of the core of the optical fiber of various brands, this value will be in the range (0.8 ... 1) · 10 ^-5 . Thus, according to (20), taking into account (19), we obtain the resulting change in the value of the refractive index of the core for optical fibers of various grades is in the range (1.79 ... 1.99) · 10 ^-5 dT.

On the other hand, with increasing ambient temperature, the length of the optical fiber segment increases due to thermal expansion

$$\Delta z=z\cdot \rho \cdot dT,\left(21\right)$$

where z is the length of the optical fiber, m; ρ is the temperature coefficient of linear expansion, which characterizes the change in the length of the optical fiber, ρ = 0.54 · 10 ^-6 ° C ^-1 .

The resulting change in the delay time due to temperature fluctuations in the refractive index and the length of the optical fiber will be

$$\Delta t=z\frac{1.9\cdot {10}^{-5}\cdot dT}{c}+z\cdot \rho \cdot dT\cdot 4.88\cdot {10}^{-9},\left(22\right)$$

where c is the speed of light in vacuum (3 ·· 10 ⁸ m / s).

The value of the second term of expression (22) is extremely small (much less than the value of the first term), which allows us to exclude it from further consideration.

The process of changing the delay time of various fiber optic delay lines in the device for generating the chirp signal is illustrated in Fig.11.

The time shift of each copy at the input of the fiber-optic connector BOC 5 as a result of changes in ambient temperature has two components:

;- change the delay time of additional fiber-optic delay lines VOLZ 13-i1 ... 13-iQ as part of the i-th binary optical fiber structure of the BVOS $$3-i{\tau }_{V_{ik}}$$

;

- change the delay time of the fiber-optic delay line connecting the i-th binary optical fiber structure of the BVOS 3-i and fiber-optic connector BOC 5 τ _Bi .

The time shift of the copy due to a change in the delay time of the additional fiber optic delay lines of the VOLZ 13-il ... 13-i (Q + 1) in the i-th binary optical fiber structure of the BVOS 3-i is determined by the number of copies K formed by the BVOS, changes in temperature value dT, the number of binary optical fiber structure i and repetition frequency copies the binary optical fiber structure _sdeduet f _r

$${\tau }_{Bi}=\frac{0.389\cdot {10}^{\mathrm{four}}\cdot \left(K+\mathrm{one}\right)\cdot dT}{c}{\displaystyle \sum _{r=\mathrm{one}}^{i-\mathrm{one}}\frac{\mathrm{one}}{f_{\mathrm{from}ledr}}}.\left(23\right)$$

и τ_Bi двум условиям:From figure 11 it is obvious that a sufficient condition for eliminating the imposition of pulses with increasing ambient temperature is the satisfaction of the choice of values $${\tau }_{V_{ik}}$$

and τ _{Bi to} two conditions:

$$\{\begin{array}{l}{\tau }_{V_{ik}}<\frac{\mathrm{one}}{f_{\mathrm{from}ledi}}+{\tau }_{V_i\left(k+\mathrm{one}\right)};\\ {\tau }_{Bi}+{\tau }_{V_{ik}}<\frac{\mathrm{one}}{f_{\mathrm{from}ledi}}+{\tau }_{B\left(i+\mathrm{one}\right)}+{\tau }_{V\left(i+\mathrm{one}\right)\mathrm{one}}.\left(24\right)\end{array}$$

Inequality (24) is valid for any value of dT.

The frequency modulation rate of the proposed technical solution reaches 2478070 MHz / μs (Kukuyashny A.V. Features of the generation of chirp signals using fiber optic structures // Information Counterterrorism Threats. - 2007. - No. 9. - P.75-88) with the duration of the generated pulses and frequency deviation up to 5.65 GHz, and that allows to provide high resolution in range (up to 20 mm with the duration of the chirp signal 3 ns) and significantly reduce the minimum range of the device using these signals (up to 45 cm).

Verification of the effectiveness of the inventive device for generating chirp signals was carried out through simulation.

The model is synthesized on the basis of a block diagram of a device for generating an LFM signal with a duration of τ _LFM = 30 ns, a central frequency f _c = 10 GHz and a frequency modulation rate β = 153333 MHz / μs.

According to formula (12), the pulse duration of the transmitting optical module POM 1. will be T _0min = 40.6 ps.

In accordance with formulas (6) and (7), we find the number of binary fiber-optic structures N = 18 and the number of generated copies K = 16 for the desired chirp signal. Thus, the composition of the forming device should include a POM 16 transmitting optical module (pulse duration 40 ps), a fiber optic splitter VOR 17 for 32 outputs, 18 binary fiber-optic structures BVOS 18-1 ... 18-18. 17 fiber optic delay lines VOLZ 19-1 ... 19-17, fiber optic connector BOC 20 with 32 inputs, optical amplifier OU 21, receiving optical module PROM 22, bandpass filter PF 23, amplitude limiter AO 24, electronic amplifier EU 25 and a low-pass filter low-pass filter 26 (see Fig.12).

Each binary fiber-optic structure contains one dividing directional fiber coupler of HBO Y-type 27-1, one summing directional fiber coupler of HBO Y-type 30-i, (log ₂ K-1) = 3 directional fiber couplers of HBO Y-type type 28-i1 ... 28-i3, log ₂ K = 4 additional fiber-optic delay lines VOLZ 29-i1 ... 29-i4 (see Fig.13).

The time constant for each of the binary optical fiber structures of BVOS 18-1 ... 18-18. VOLZ fiber optic delay lines 19-1 ... 19-17 and additional VOLZ fiber optic delay lines 29-i1 ... 29-i4 are calculated according to formulas (3), (4) and (5), and the calculation results are shown in FIG.

The gain of the OS 21 is selected taking into account the compensation of losses in the device for generating chirp signals and taking into account the sensitivity of PROM 22.

The passband of the band-pass filter PF 23 is determined according to the calculated frequency deviation of the generated signal. With the given parameters of the generated LFM signal, the bandwidth value is 4.6 GHz.

The simulation was carried out in the MATLAB package. On Fig shows the spectrum and the correlation function of the resulting signal. The level of the side lobes of the autocorrelation function was minus 13.6 dB, which confirms the effectiveness of the formation device when generating a signal for the purposes indicated above.

The width of the spectrum of the resulting chirp signal is determined by the expression:

$$\Delta f=\frac{\beta NK}{\pi }\cdot \frac{\mathrm{one}}{f_{\mathrm{one}}+\sqrt{f_{\mathrm{one}}^2+\frac{\beta NK}{\pi }}}.\left(25\right)$$

The center frequency of the spectrum of the chirp signal is determined by the expression:

$$f_c=f_{\mathrm{one}}+\frac{\mathrm{<figure-callout\; id="2"\; label="\beta \; N\; K"\; filenames="00000038.png,00000039.png"\; state="\{\{state\}\}">\beta \; </figure-callout>}NK}{2\pi }\cdot \frac{\mathrm{one}}{f_{\mathrm{one}}+\sqrt{f_{\mathrm{one}}^2+\frac{\beta NK}{\pi }}}.\left(26\right)$$

The duration of the resulting impulse is determined by the expression:

$$f_c=\frac{\mathrm{one}}{N\text{A.}K}\left(f_{\mathrm{one}}+\frac{\mathrm{<figure-callout\; id="2"\; label="\beta \; N\; K"\; filenames="00000038.png,00000039.png"\; state="\{\{state\}\}">\beta \; </figure-callout>}NK}{2\pi }\cdot \frac{\mathrm{one}}{f_{\mathrm{one}}+\sqrt{f_{\mathrm{one}}^2+\frac{\beta NK}{\pi }}}\right).\left(27\right)$$

Thus, the use of the inventive device for generating LFM signals made it possible to generate an LFM pulse with a duration of τ _LFM = 29 ns, a central frequency f _s = 9.92 GHz, a deviation of Δf = 4.45 GHz, and a frequency modulation rate of β = 153448 MHz / μs.

Let us prove the presence of a causal relationship between the claimed combination of features and the achieved technical result. To this end, we will conduct a comparative analysis of the claimed device and prototype in terms of the duration of the generated pulses, the frequency deviation and the frequency modulation speed.

The duration of the generated impulse.

The manufacturing material of the deflector, which serves to delay the optical signal in the prototype device, provides a maximum frequency of the control signal of about 200 MHz. Thus, without taking into account the signal delay in the device path, one cycle of the frequency change at the output of the electronic amplifier has a duration of at least 5 ns. Taking into account the signal delay in the optical fiber and processing in the interferometer, the duration of one cycle of the frequency change can be up to 10 ns. Since the formation of the chirp signal requires several such cycles, the minimum duration of the generated signal exceeds the value of a similar parameter in the claimed technical device (from 40 not in the prototype and from 2.28 s in the claimed device).

Frequency deviation.

The frequency deviation in the prototype is limited by the upper working frequency of the electro-optical modulator, the value of which for modern serial models based on the material declared in the prototype is about 8 GHz (Ivanov AB Fiber optics: components, transmission systems, measurements. - M.: Publishing House "Syrus System", 1999. P.175). The deviation of the proposed technical solution with a minimum duration of the generated signal does not exceed 5.65 GHz.

Frequency Modulation Rate.

Based on the values of the duration of the generated pulse and the frequency deviation, the value of the frequency modulation speed for the prototype does not exceed 200,000 MHz / μs, and for the claimed technical solution - 2478070 MHz / μs. Thus, it is obvious the improvement of the duration and speed of the frequency modulation of the claimed technical solution in comparison with the prototype.

In addition to the traditional use in radiolocation, short LFM radio signals can be used in secure communications, surveillance in dense environments (geolocation), medicine and sonar.

For example, the use of chirp signals in communication systems compared to digital systems CDMA (Code Livision Multiply Access) allows you to simplify processing and reduce the cost of devices with the same technical characteristics.

The relevance and industrial relevance is confirmed by a large number of patent documents on the formation of chirp signals (for example, patents 2033685 RU 7791415 US, 5428361 US, 5557241 US and others).

The functional elements of the chirp signal generation device satisfy the criterion of industrial use.

As a transmitting optical module, for example, an injection semiconductor laser operating in a pulsed mode and capable of generating pulses of picosecond duration, for example, manufactured by Laser2000, can be used.

The physical features of the operation of the injection semiconductor laser and the propagation of optical radiation in the optical fiber impose certain restrictions on the spectral line width and the mode of radiation of the injection semiconductor laser and determine additional requirements for the radiation source of the following nature:

- single-mode single-frequency radiation mode with a minimum spectral line width;

- high quantum efficiency, i.e. the absence of noticeable leaks and other internal losses that can cause local overheating of the laser structure;

- high power stability and low intrinsic noise;

- small emitting area to increase the coupling coefficient with the optical fiber.

Given this, and also on the basis of assessing the influence of the physical factors of the optical fiber on the functioning of the inventive device for generating chirp signals above, the transmitting optical module should have the following characteristics:

- working wavelength of optical radiation 1550 nm;

- the duration of optical pulses is more than 37 ps;

- spectral radiation width of more than 0.1 nm;

- peak optical pulse power: not more than 1 W;

- relative intensity noise of 140 dB / Hz;

- operating temperature in the range - 40 ... + 60 ° C.

As a fiber-optic splitter, industrial optical splitters can be used for 2, 4, 8, 16, 32, 64 and 128 outputs, for example, manufactured by ZAO Component. They are planar and rafted. Planar optical splitters are made by etching a waveguide layer grown on the basis of lithium niobate on a silicon single crystal corresponding to the configuration of the splitter tree. Planar splitters have more stable and accurate parameters compared to alloy splitters.

Requirements for fiber optic splitters with N outputs in the inventive device for the formation of chirp signals are as follows:

- branching ratio 4, 8.16, 32, 64, 128;

- working wavelength of optical radiation 1550 nm;

- excess losses of 0.4.0.8, 1.6, 3.2, 6.4, 12.8 dB, respectively;

- isolation: not less than 50 dB;

- operating temperature in the range - 40 ... + 60 ° С.

Optical fibers can be implemented on the basis of quartz single-mode optical fibers (Ivanov A. B. Fiber optics: components, transmission systems, measurements. M: Publishing House "Syrus System", 1999. - P.50-52).

The requirements for optical fiber in the inventive device for generating chirp signals taking into account the assessment of the influence of physical factors of the optical fiber on the functioning of the inventive device for forming chirp signals above are as follows:

- single-mode optical fiber with unbiased dispersion (SF);

- maximum attenuation no more than 0.2 dB / km;

- specific dispersion coefficient less than 0.06 ps / km ^-1 ;

- specific chromatic dispersion of less than 18 ps / (nmkm);

- the accuracy of the manufacture of segments of the optical fiber is not less than 1 mm;

- operating temperature in the range - 40 ... + 60 ° C.

Directional fiber couplers can be implemented, for example, on the basis of directional single-mode couplers (O. Sklyarov. Modern fiber-optic transmission systems, equipment and components. - M.: Solon R., 2001. - p.194). Requirements for directional fiber couplers in the inventive device for generating chirp signals:

- transient attenuation minus 3 dB;

- working wavelength of optical radiation 1550 nm;

- excess losses of not more than 0.1 dB;

- isolation of at least 50 dB;

- operating temperature in the range - 40 ... + 60 ° C.

The fiber-optic connector can be implemented in the form of industrial optical adders for 2, 4, 8, 16, 32, 64 or 128 inputs, for example, manufactured by ZAO Component.

The requirements for fiber-optic connectors with M-inputs in the inventive device for the formation of chirp signals are as follows:

- excess losses: 0.4, 0.8, 1.6, 3.2, 6.4, 12.8 dB, respectively;

- isolation: not less than 50 dB;

- operating temperature in the range - 40 ... + 60 ° C.

The optical amplifier is implemented as an Erbium Doped Fiber Optic Amplifier (EDFA). A number of amplifiers are produced, operating in the optical range of 1530 ... 1560 nm and providing optical amplification of 22 ... 30 dB with a noise figure of not more than 4 dB (Ivanov A.B. Fiber optics: components, transmission systems, measurements. - M.: Publishing House "Syrus System", 1999. - S.104-105).

The requirements for the optical amplifier in the inventive device for generating chirp signals are as follows:

- working wavelength of optical radiation 1550 nm;

- amplification of the optical signal of at least 13.3 dB;

- input signal power of at least 1 μW;

- noise figure no more than 6 dB;

- operating temperature in the range - 40 ... + 60 ° C.

The receiving optical module is usually a combination of a photodiode and a pre-amplification stage of the photoresponse signal. The maximum band of detected signals of serial photodiodes reaches 10 GHz, with a sensitivity of optical radiation power of the order of minus 30 dBm, a dynamic range of 20 ... 25 dB and a steepness of the detection characteristics of 0.5 ... 0.8 A / W current (Strucheva O.F. Bezborodova T.M. Products of fiber-optic technology: Catalog. - M .: Ekos, 1993. - 142 p.)

The requirements for the receiving optical module in the inventive device for generating chirp signals are as follows:

- working wavelength: 1550 nm;

- the range of spectral sensitivity is not higher than 13.3 GHz;

- the steepness of the detector characteristics of 0.7 ... 0.9 A / W;

- bandwidth or information reception rate of not more than 6.6 GHz;

- response time no more than 10 ps;

- operating temperature in the range - 40 ... + 60 ° C.

A band-pass filter and a low-pass filter can be implemented on strip and microstrip lines (Zikiy AN Lecture notes on the course “Receiving and processing microwave signals.” Taganrog: Publishing house of TRTU, 2005, p.24-41).

Requirements for the bandpass filter in the inventive device for the formation of chirp signals:

- the center frequency is not higher than 10 GHz;

- relative bandwidth not more than 50%;

- insertion attenuation no more than 1 dB;

- coefficient of squareness: <1.3;

- unevenness of the introduced attenuation in the passband below 10 dB;

- operating temperature in the range - 40 ... + 60 ° C.

The requirements for a low-pass filter in the inventive device for generating chirp signals:

- bandwidth not more than 13.3 GHz;

- insertion attenuation not higher than 1 dB;

- attenuation band of not more than 13.3 GHz;

- attenuation level in the attenuation band of at least 50 dB;

- operating temperature in the range - 40 ... + 60 ° C.

The amplitude limiter can be implemented on a two-sided diode circuit.

The most widely used as broadband electronic amplifiers are transistor amplifiers operating in the frequency range of 0.1 ... 25 GHz and having a gain band of 4 ... 80%, a gain per cascade of 5 ... 30 dB, a noise figure of 2 ... 6 dB and the dynamic range of the input signal 80 ... 90 dB (Microelectronic Microwave Devices / Edited by G.I. Veselov.- M.: Higher School, 1988. - P.78-86, 225).

Requirements for the electronic amplifier in the device for generating chirp signals:

- operating frequency range of not more than 13.3 GHz;

- noise temperature no more than 5K;

- gain of at least 10 dB;

- operating temperature in the range - 40 ... + 60 ° C.

Thus, the practical feasibility of the inventive device for generating chirp signals is proved.

Claims (1)

A device for generating chirp signals containing a transmitting optical module, a receiving optical module, a low-pass filter and an electronic amplifier, characterized in that it additionally includes a fiber optic splitter with N optical outputs, N binary fiber optic structures, (N-1 ) fiber-optic delay lines, a fiber optic connector with N optical inputs, an optical amplifier, a bandpass filter and an amplitude limiter, the optical output of the transmitting optical module being connected to optical input of the fiber optic splitter, the first output of which is connected through the first binary fiber optic structure to the first optical input of the fiber optic connector, the second output of the fiber optic splitter through the second binary optical fiber structure and the first fiber-optic delay line connected in series to the second input of the fiber optic connector, and the ith output of the fiber optic splitter through the i-th binary wave connected in series the window-optical structure and the (i-1) -th fiber-optic delay line is connected to the i-th input of the fiber-optic connector, the optical output of which is connected through the optical amplifier to the optical input of the receiving optical module, the electrical output of which is through a series-connected bandpass filter , an amplitude limiter and an electronic amplifier are connected to the electrical input of the low-pass filter, and all N binary fiber-optic structures contain a dividing directional fiber branch Y-type fiber, Q directional X-type fiber couplers, (Q + 1) additional fiber-optic delay lines and a summing Y-type directional fiber coupler, wherein the input of the Y-type directional fiber coupler is an input of a binary optical fiber structure, the first output of which is combined with the first input of the first directional X-type fiber coupler, and the second output through the first additional fiber-optic delay line is connected to the second input of the first directional fiber X-type coupler, the first output of which is connected to the first input of the second X-type directional fiber coupler, and the second output through the second additional fiber-optic delay line is connected to the second input of the second X-type directional fiber coupler, the first output of the jth X-type directional fiber coupler is connected to the first input of the (j + 1) -th X-type directional fiber coupler, and the second output of the j-type X-type directional fiber coupler through the jth additional fiber optic the delay line is connected to the second input of the (j + 1) th directional X-type fiber coupler, the first output of the last Qth directional X-type fiber coupler being connected to the first input of the summing Y-type directional fiber coupler The Qth directional X-type fiber coupler is connected via the (Q + 1) -th fiber delay line to the second input of the summing Y-type directional fiber coupler, and the output of the low-pass filter is the output of the device.

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