RU2635875C2 - Method for generating and processing of radar modified phase-shift signals - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention is intended for generating and processing of radar modified phase-shift (FS) signals in radar stations. In the method, the generation, amplification and emission of FS signals with subsequent reception, filtering and processing are performed. During the generation the FS signal is divided into three FS pulses shifted in time with respect to each other. Two of them (the second and the third) are intended to generate narrow pulses filling the bulls at the phase inversion sites of the first FS pulse, for which the first FS pulse is applied to the first adder common to the three FS pulses, with a delay time t=τ/8, the second FS pulse with phase rotation at -90° and the third FS pulse with a delay time t=τ/4 and with a phase rotation of +90° are summed in the second adder, as a result of which a few short pulses appear in the first adder. The pulses fill the hulls at the phase inversion sites of the first (time-average) FS pulse, and the received signal is processed in the optimal filter.

EFFECT: minimum energy loss for transmission, and reception with the preservation of a single-channel discrete filter with small losses.

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Description

The invention relates to the field of radar and is intended for the formation and processing of radar modified phase-shift (FM) signals in radar stations.

One of the known methods for generating FM signals is based on the use of a balanced modulator (BM), in which the entire duration of the radio signal τ is divided into a series of partial radio pulses with a duration τ ₀ having certain phase shifts of 2π / k, where k is the code element number. For k> 2, the manipulation is multiphase, and for k = 2 it is antiphase, because only phase shifts 0 and π are possible. Phase rotation coding is often done according to the Barker code. The expression for the FM signal with an abrupt phase change is written as follows [1]:

where: n is the code size or signal base (the number of pulses of the sequence),

k is the code element number,

P _k is an element of a code sequence that takes the values +1 or -1 and defines a phase modulation code,

U (t) is the envelope of the FM signal,

- прямоугольная огибающая элементарного импульса длительностью τ₀ ФМ-сигнала с длительностью τ.

- a rectangular envelope of an elementary pulse with a duration of τ ₀ FM signal with a duration of τ.

Since BM is used to generate FM signals, in accordance with the Barker code, transients are minimized when switching phases from 0 to π and vice versa. It should be noted that with this method of generating FM signals at points of inversion of the carrier phase, its continuity is violated, leading to undesirable expansion of the effective width of the signal spectrum [2]. Usually, due to the requirements for electromagnetic compatibility (EMC), a band-pass filter is placed in front of the emitting cascade in the transmitter, which limits the spectrum width of the emitted signal. The presence of such a filter leads to the appearance of dips in the phase inversion region (Fig. 1), the width of which is proportional to the EMC filter bandwidth. This leads to a loss of energy of the emitted pulse. Losses also occur in the receiving module, where a filter with a narrower (in comparison with the EMC filter) optimal bandwidth ΔF = 1.37 / τ _{0 is} installed at the input, where τ ₀ is the duration of the partial pulse of the FM signal. According to the simulation results, energy losses can be about 1.5-2 dB.

One way to eliminate these losses is to use not a stepwise, but a smooth phase change between partial pulses [1]. A smooth phase change of 180 ° is achieved by changing the center frequency f ₀ by the value of F in a small interval Δτ = ξτ (ξ <1), covering the phase inversion region. The expression for the complex envelope of the FM signal with a smooth phase change between pulses can be represented as follows:

where: Ω = 2πF, and ΩΔτ = 2πFτ ₀ ξ = π;

- параметр, характеризующий наличие плавного изменения фазы между парциальными импульсами.

- a parameter characterizing the presence of a smooth phase change between partial pulses.

Based on the foregoing, this method of forming modified FM signals will be chosen as a prototype. The disadvantage of the prototype, as shown by its analysis in [1], is an increase in the width of the main lobe and the maximum levels of the first pair of side lobes of the spectral density of the signal. In addition, signal-to-noise losses are proportional to the duration Δτ of the region with a smooth phase change. These losses are associated with a violation of optimality when receiving a modified FM signal with a smooth phase change. In the receiving device, in order to reduce losses arising from the sampling of signals in an analog-to-digital converter (ADC) caused by different temporal positions of the analog signal relative to the sampling times, a set of discrete filters placed with a certain time step Δt is required, which leads to an increase in hardware costs.

The transition to a single-channel scheme along with the saving of computing resources entails losses in the detection of the information channel against the background of noise.

A way out of this situation was found [3] using an analog-discrete filter (ADF) with a transfer characteristic defined by the formula:

where: ω is the frequency;

Δt is the time sampling step;

S (ω) is the complex conjugate spectrum of the useful signal;

N (ω) is the spectral density of the noise power.

The use of ADP expands the signal pulse to discretization, while the signal-to-noise ratio decreases by a certain amount. As the simulation showed, when compressing the modified FM signal used in the proposed method for generating and processing radar modified FM signals, the pulse is wider than when compressing the FM signal, for example, with a smooth phase change. Therefore, in the proposed method, it is not required to use an additional analog filter with the characteristic described by formula (3).

The technical result of the invention is the formation of a modified FM signal having minimal energy loss in transmission, and reception while maintaining a single-channel discrete filter with low loss.

The specified technical result is achieved by the fact that in the known method, which consists in the formation, amplification and emission of FM signals, their subsequent reception, filtering and processing, division of the FM signal into three FM pulses shifted in time relative to each other is introduced during the formation, in this case, two of them (second and third) are intended for the formation of narrow pulses filling the dips in the places of phase inversion of the first FM pulse, for which the first FM pulse is fed to the first adder, which is common for three FM pulses, with time we have delays t = τ / 8, the second FM pulse with a phase rotation of -90 ° and the third FM pulse with a delay time of t = τ / 4 and with a phase rotation of + 90 ° are added to the second adder, as a result of which the first the adder there are several short pulses, filling the gaps in the places of phase inversion of the first (time-average) FM pulse, and the received signal is processed in an optimal filter.

For a better understanding of the proposed method for generating and processing radar modified FM signals, we consider a block diagram of its implementation, shown in FIG. 2, where the following notation is accepted:

1 - transmitting module;

2 - receiving module;

3 - balanced modulator (BM);

4 - EMC filter (F _ems );

5 - driver of a modified FM signal;

6 - delay line at τ / 8;

7 - the first adder;

8 - output stage;

9 - divider;

10 - phase shifter at -90 °;

11 - second adder;

12 - delay line at τ / 4;

13 - phase shifter + 90 °;

14 - filter (Ф ₀ );

15 is an optimal filter;

16 - delay line at τ / 8;

17 - the first adder;

18 - compression filter (SF);

19 - analog-to-digital Converter (ADC);

20 - a divider;

21 - phase shifter at -90 °;

22 - second adder;

23 - delay line at τ / 4;

24 - phase shifter + 90 °;

25 is a digital processing unit.

As can be seen from FIG. 2, the device includes transmitting 1 and receiving 2 modules. The transmitting module 1 consists of BM 3, F _emc 4 _{connected in series} , the shaper 5 of the modified FM signal and the output stage 8 of the transmitting module 1, the output connected to the antenna. Moreover, the shaper 5 of the modified FM signal consists of a divider 9, the input of which is connected to the output of the _emf 4, and the first output is to the input of the delay line 6 by τ / 8, the output of which is connected to the first input of the first adder 7, the output of which is connected to the input the output stage 8 of the transmitting module 1. The second output of the divider 9 is connected through the phase shifter 10 by -90 ° to the first input of the second adder 11, the output of which is connected to the second input of the first adder 7. The third output of the divider 9 is through τ / 4 connected in series to the delay line 12 and phases The spreader 13 is + 90 ° connected to the second input of the second adder 11.

The receiving module 2 consists of series-connected Ф ₀ 14 with the optimal band F = 1.37 / τ ₀ , the optimal filter 15, SF 18, ADC 19 and the digital processing unit 25, and the input Ф ₀ 14 is connected to the antenna. The optimal filter 15 contains a divider 20, the input connected to the output Ф ₀ 14, and the first output through the delay line 16 to τ / 8 - to the first input of the first adder 17 and then to the input of the SF 18. The second output of the divider 20 through the phase shifter 21 to - 90 ° is connected to the first input of the second adder 22, an output connected to the second input of the first adder 17. The third output of the divider 20 is connected in series with the delay line 23 by τ / 4, the phase shifter 24 by + 90 °, the second input of the second adder 22.

The principle of operation of a device that implements the proposed method is as follows.

An FM signal of duration τ, emerging from the BM 3 of the transmitting module 1, is fed through the F _emc 4 to the input of the divider 9 of the former 5 of the modified FM signal, where it is divided into three elementary pulses τ ₀ . The first pulse from the first output of the divider 9 through the delay line 6 with a delay time t = τ / 8 is fed to the first input of the first adder 7. The second pulse from the second output of the divider 9 with a phase rotation in the phase shifter 10 by -90 ° is fed to the first input of the second adder 11. The third pulse from the third output of the divider 9 through a series-connected delay line 12 to τ / 4 and the phase shifter 13 to + 90 ° is fed to the second input of the second adder 11.

As a result of the addition of the second pulse with the third pulse, several narrow pulses arise in the second adder 11, the duration of which is proportional to the width of the dips located at the phase inversion points of the first FM pulse, shown in FIG. 3. When they are fed to the first adder 7, they fill in the gaps in the first FM pulse and its general appearance becomes as shown in FIG. 4. From the output of the first adder 7, the generated FM signal is fed to the output stage 8 of the transmitting module 1, where it is amplified by power, and then it is emitted into the space through the antenna.

The signal received from the antenna goes to the filter Ф ₀ 14 of the receiving module 2 and then to the optimal filter 15, matched with the modified FM signal, similar in structure to the former 5 of the modified FM signal, complex conjugate with it. Complex coupling is provided by the negative sign of the signal coming from the output of the second adder 22 to the second input of the first adder 17. From the output of the first adder 17, the signal is fed to the input of the SF 18, and then through the ADC 19 to the input of the digital processing unit 25. The type of signal at the output of the SF 18 is shown in FIG. 5.

In FIG. Figure 6 shows a compressed FM signal that has not passed through an optimal filter matched with a modified FM signal. From their comparison it can be seen that the signal passed through the optimal filter is wider, and, therefore, has less sampling loss.

Analysis of the proposed method for the formation and processing of modified radar FM signals showed its advantages relative to the prototype. Due to the absence of dips, there are no energy losses, and due to the presence of an optimal filter that is consistent with the modified FM signal, there are no losses associated with the modification of the FM pulse, in contrast to the prototype, where the loss is related to the duration of the portion of the FM pulse, on which the phase change and there is no optimal filter when receiving such a modified FM signal. With discrete processing of the FM signal in the proposed method, the losses are minimal because the compressed FM signal is wider relative to the FM signal with a smooth phase change, therefore, when using the prototype method, it is necessary to install a filter to expand it to avoid losses.

Information sources

1. G.S. Nachmanson, A.V. Suslin “Correlation and spectral characteristics of a radar phase-shifted signal with a smooth phase change”, “Advances in modern radio electronics” No. 4, 2012, pp. 7-11;

2. C. Cook, M. Bernfeld "Radar signals", "Soviet Radio", Moscow, - 1971, p. 262;

3. RF patent No. 2291463 "Method for analog-discrete processing of radar pulse signals", published January 10, 2007, author P.V. Mikheev.

Claims (1)

A method of generating and processing radar modified phase-shift (FM) signals, which consists in generating, amplifying and emitting FM signals, their subsequent reception, filtering and processing, characterized in that when generating the FM signal is divided into three FM pulses, time-shifted relative to each other, while the second and third FM pulses are intended for the formation of narrow pulses filling the dips in the places of phase inversion of the first FM pulse, for which the first FM pulse is fed to the first adder, I common for three FM pulses, with a delay time of t = τ / 8, and a second FM pulse with a phase rotation of -90 ° and a third FM pulse with a delay time of t = τ / 4 and a phase rotation of + 90 ° summarize, resulting in the first adder there are several short pulses, filling the dips in the places of phase inversion of the first FM pulse, and the received signal is processed in an optimal filter.

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