RU2559828C1 - Method for short-range radar location - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to short-range location methods and can be used in aircraft landing, spacecraft approach and docking, driving safety and car parking radio systems. The method is based on use of a discontinuous pulsed signal, wherein parameters of the discontinuous pulsed signal are selected based on the required suppression of "diffraction" lobes (DL) of the autocorrelation function of said signal, for which the method includes determining the required number K_req of suppressed first (near) DL and their suppression by placing them in "zero" areas of the autocorrelation function, which is achieved through a defined selection of the repetition period of said lobes and corresponding durations, wherein K_req may be determined based on the required DL suppression value.

EFFECT: method of locating an object at short ranges using a discontinuous signal while suppressing parasitic lobes of the autocorrelation function thereof.

3 cl, 6 dwg

Description

The invention relates to methods for location at short distances (up to several kilometers) in radio systems for landing aircraft (LA), approaching and docking space objects, safe driving and parking of cars, monitoring the terrain, etc., when solving problems of detection and recognition of objects, especially small ones with small effective dispersion area (EPR), when determining their location, building a radar image (RLI) of the area with a given resolution, navigation in bad weather conditions, etc. .

In the locator, the duration of the probe signal is usually determined by energy considerations, and often, especially when using solid-state generators and power amplifiers, the required minimum duration of the probe signal significantly exceeds the delay of the echo signal at the minimum range of the locator. In this case, due to the imperfect isolation of the transceiver paths, when locating objects at short distances in the receiving path, a “creeping” probe signal is superimposed on the received echo signal and the problem arises of receiving echo signals reflected from the located objects against this parasitic interfering signal.

The amplitude of the echo signal decreases inversely with the 4th degree of increasing the range, and the level of interfering signals (“creeping” from the probe signal and the intrinsic noise of the receiving path) is constant. In this case, three options for admission may arise. The first case corresponds to the reception of echo signals at small "zero" ranges, when the echo signal significantly exceeds the spurious signal from the probe signal. In this case, you can use the usual probing signal, for example in the form of a single pulse.

As the range increases, especially when locating small-sized objects, the power of the echo signals becomes comparable or even less than the power of the "creeping" interference from the probing signal. In this second section, the work of the locator is impossible without increasing the isolation of the transceiver channels. Finally, the third section corresponds to the range when the delay of the echo signals exceeds the duration of the probe signal, and the location is carried out against the background of the intrinsic noise of the receiving path (and external interference, in the general case).

The second section requires special measures to decouple the received echo signals from the emitted. But when using spatial, frequency and polarization methods, isolation of more than 50 ... 70 dB is technically difficult to implement. This problem can be completely eliminated due to the time spread of the radiation of the probe signal and the reception of signals reflected from the located objects, i.e. when at any moment in time the system either emits a signal or receives it. In this case, an intermittent signal can be used to solve the problem (article G. Brooker, D. Birch, J. Solms "W-Band Airborne Interrupted frequency Modulated CW Imaging Radar", journal "Aerospace and Electronic Systems", vol. 41, no. July 3, 2005).

An intermittent signal at each sounding step has the form of a sequence of sub-pulses and is characterized by the duration of the sub-pulses, their repetition period, their number and modulation of the signals in the sub-pulses.

Similar signals are used in ultrasonic flaw detection (see, for example, V.G. Kartashev, I.V. Sokolov “Split signal, its characteristics and processing methods,” Journal of Radio Engineering, 2009, No. 1).

This article solves the problems of coordinated filtering of the probe signal in the form of a set of pulses (quasiharmonics, to use Kartashev's terminology) with an individual constant filling frequency and a given envelope (rectangular, Gaussian). In the article, in particular, it is shown that if the pulse does not fit an integer number of wavelengths of the filling frequency, the autocorrelation function (ACF) of such a signal gives side maxima at t = K × T _p , where K = 1, 2, 3 ..., and T _p is the pulse repetition period, i.e. in the general case, an uncertainty arises in the location of the located object, and mutual interference of echo signals from objects shifted in range by a value of cct _p / 2 is possible, where c is the speed of light.

At the same time, since the main task in this article is to reduce the volume of computational operations, the main attention is paid to a continuous signal and methods for suppressing side maxima for an intermittent signal are practically not discussed. Nevertheless, the considered application of an intermittent signal is the closest analogue to the prototype of the method proposed for solving problems in the conditions of a short range location.

The task of the invention is to develop a method for locating an object at short ranges using an intermittent signal while suppressing the side lobes of its ACF to the desired level. Thus for sensing selected intermittent pulse signal corresponding strobed (excision) of a rectangular pulse with a linear frequency modulation (LFM) and frequency deviation f _nine N podympulsov duration τ _and each and with a repetition period T _m, so that the length of the entire pack podympulsov τ _c = N × T _p . Moreover, the total duration of all subpulses is τ and _Σ = N × τ _and should be at least τ _{s_min_s / s} - the minimum allowable duration of the probe signal, determined by the required energy of the probe signal (energy potential of the locator). The deviation of the frequency f _dev is determined on the basis of the requirements for resolving ability of ranging in range, and upon reception, processing is carried out coordinated with the probing signal, as well as weight processing to reduce side lobes in range. The use of an intermittent signal and suppression of the side lobes of its ACF ensure, on the one hand, the complete isolation of the received echo signals from the probe signal locator “creeping” into the receiving path, and, on the other hand, the unambiguous location of objects at a given range of distances and suppression of interference from objects, located beyond this interval to the desired level.

The essence of the invention lies in the fact that in the short-range radar method, in which an intermittent pulse signal is used for sounding, the intermittent signal parameters are selected based on the required value of suppressing the "diffraction" lobes (DL) of the autocorrelation function (ACF) of this signal caused by the transition from a single chirped pulse from the edges podympulsov N, which define the required number K _Tp first DL suppressed suppression and carry them by placing them in a "null" areas ACF way selection period repetition of these lobes defined by the expression T _DL = N / f _nine and durations _and τ and τ _{max, and} where τ - duration _{podympulsa, τ max ≥2R max / c,} R max - maximum distance of locating and c - velocity light, and for the k-th suppressed DL in the range 1≤k≤K _Tr , the inequality ((k-1) τ _max + kτ _and ) <kT _DL <(kτ _max + (k-1) τ _and ) holds.

The number of suppressed DL K _Tr is determined by the expression:

where L _under is the required DL suppression value in dB, and E [x] is the integer part of x.

In addition, when choosing the parameters of the probing signal, the required number of subpulses N is first calculated at τ _max = 2R _max / c in accordance with the expression:

N = E [τ _max × f _maids ],

and then find the duration of the subpulse as τ _and = (τ _c _ _min _ _{c / w} ) / N and the number of suppressed DL corresponding to this τ _and :

$${\mathrm{TO}}_{P\mathrm{about}d}=\frac{{\tau }_{\max }}{{\tau }_{\mathrm{and}}}$$

and, if K _Tr ≤ K _under , then the obtained K _{Tr is} used to calculate τ _and

$${\tau }_{\mathrm{and}}=\frac{{\tau }_{\max }}{{\mathrm{TO}}_{tR}}$$

moreover, if the conditions K _Tr ≥ K are not met _{, they} increase R _max or decrease τ _s _ _{min_s / s} until this condition is met.

In addition, to take into account the length of the DL and its expansion during weighting, for the found signal parameters, correction corrections are calculated

и $$\Delta {\tau }_{и}=\Delta {\tau }_{\max }\times \left(\frac{{К}_{тр}-1}{{К}_{тр}}\right)$$

, $$\Delta {\tau }_{\max }=\frac{1.8}{f_{de\mathrm{at}}}$$

and $$\Delta {\tau }_{\mathrm{and}}=\Delta {\tau }_{\max }\times \left(\frac{{\mathrm{TO}}_{tR}-\mathrm{one}}{{\mathrm{TO}}_{tR}}\right)$$

,

and the final signal parameters are obtained from the expressions

, $${\tau }_{\mathrm{and}\_R\mathrm{but}b}=\frac{2R_{\max }}{c\ast {\mathrm{TO}}_{tR}}-\frac{1.8}{f_{de\mathrm{at}}}\times \left(\frac{{\mathrm{TO}}_{tR}-\mathrm{one}}{{\mathrm{TO}}_{tR}}\right)$$

,

. $$T_{P\mathrm{about}\mathrm{at}\_R\mathrm{but}b}=\frac{2({\mathrm{TO}}_{tR}+\mathrm{one})R_{\max }}{c\ast {\mathrm{TO}}_{tR}}+\frac{1.8}{{\mathrm{TO}}_{tR}\ast f_{de\mathrm{at}}}$$

.

The technical result of the application of the proposed method is to provide the ability to locate objects at short range when the ratio of the power of the echo signal and the interfering probe signal “creeping” into the receiving path is insufficient for radiolocation. This is achieved by using an intermittent LFM signal for location at short ranges, the processing and selection of parameters of which are carried out in accordance with the proposed method.

List of figures:

In FIG. Figure 1 shows two chirped signals shifted relative to each other, which illustrates the physical meaning of the difference frequency (f _different ) and its dependence on the time shift.

In FIG. 2 shows two subpulses of an intermittent signal and a difference frequency signal. The reason for the appearance of diffraction lobes during coherent summation is shown — the laying of a multiple of the difference frequency wavelengths during the repetition period of subpulses.

In FIG. Figure 3 shows a general view of the inter-correlation function obtained by convolving an intermittent LFM signal with a corresponding continuous signal of the same duration. All arising diffraction petals are visible here.

In FIG. Figure 4 shows a general view of the autocorrelation function obtained by convolving an intermittent LFM signal with exactly the same signal. “Zero zones” and suppression of some diffraction lobes due to getting into these zones are visible.

In FIG. Figure 5 shows the type of cross-correlation function for a calculation example.

In FIG. Figure 6 shows a view of the autocorrelation function for a calculation example showing the suppression of ten diffraction lobes.

The probe signal proposed for locating at short ranges in the form of an intermittent signal has a periodic structure. When using an intermittent signal with linear frequency modulation (LFM), its consistent processing can be represented as the sequential execution of two operations. First, the received signal is multiplied by the same, but time-shifted reference signal, and a difference frequency signal is obtained (see Fig. 1). Then, the difference signal is integrated over the duration of all subpulses of the reference signal. At certain mutual displacements of the received and reference signals, diffraction maxima - diffraction lobes (DL) will be observed. Indeed, this will happen when laying an integer number of waves of difference frequency λ _different in the repetition period T _p (see Fig. 2), therefore, the relation

, $$\mathrm{TO}\times {\lambda }_{R\mathrm{but}sn}=\mathrm{from}\times T_P,(\mathrm{one})$$

,

where K = 1, 2, 3 ...

These DLs have a negative effect, which, as already noted, is expressed in two factors: in the ambiguity in determining the location of the reflecting object and in the mutual influence (interference) of objects shifted in position by the period (s) of the DL repetition.

From FIG. Figure 1 shows the relationship between the subpulse shift and the difference frequency. From the similarity of triangles and taking into account the Doppler frequency offset f _add due to the movement of the aircraft, we can write

$$f_{R\mathrm{but}sn}=f_{de\mathrm{at}}\times \frac{{\tau }_{\mathrm{from}d\mathrm{at}}}{{\tau }_{\mathrm{from}\mathrm{and}g}}+f_{d\mathrm{about}P}(2)$$

Based on (2) and (1), for the K-th DL, the relation

$$\frac{\mathrm{TO}}{T_P}=f_{de\mathrm{at}}\times \frac{{\tau }_{\mathrm{from}d\mathrm{at}}}{N\ast T_P}+f_{d\mathrm{about}P}$$

$${\tau }_{\mathrm{from}d\mathrm{at}}=\frac{N}{f_{de\mathrm{at}}}(\mathrm{TO}-f_{d\mathrm{about}P}\times T_P),\mathrm{TO}=\mathrm{one,}23...$$

The Doppler frequency is of the order of kilohertz, and the time T _{p is of the} order of microseconds, therefore, the Doppler term, as a first approximation, can be neglected. As a result, the formula for the position of the Kth DL can be written as

$${\tau }_{\mathrm{from}d\mathrm{at}}\approx \mathrm{TO}\times \frac{N}{f_{de\mathrm{at}}}.(3)$$

и не зависит от временных параметров сигнала.It follows that the repetition period of DL is $$\frac{N}{f_{de\mathrm{at}}}$$

and does not depend on the time parameters of the signal.

At the same time, the presence of “zero zones” in the reference signal (the reference signal is 0), leads to the appearance of the so-called “zero zones” in the ACF. Within one period of repetition T _n podympulsov "zero zone" begins at time τ _and ends in (T _n - τ _u). Thus, it becomes possible to achieve such an overlap of two time sequences (repetition of “zero zones” and repetition of DL) so that some required number of DLs is suppressed due to their falling into the “zero zones” of the ACF. By selecting the difference between the periods of the DL repetition and the subpulses, the Kth DL can be superimposed on the Kth “zero zone”, i.e. when each DL coincides with its “zero zone”.

, поэтому для К-го ДЛ можно записать условия нахождения его в К-й «нулевой зоне» при заданной девиации сигнала:The distance between the two nearest diffraction maxima (the period of their repetition) is $$\frac{N}{f_{de\mathrm{at}}}$$

therefore, for the K-th DL, one can write down the conditions for finding it in the K-th “zero zone” for a given signal deviation:

where N _min is the number of subpulses at which the Kth DL is at the very beginning of the Kth “zero zone”, and N _max is the number of subpulses at which the Kth DL is at the very end of the Kth “zero zone”. Therefore, if you place the first DL at the end of the first “zero zone” of the ACF, then, since all subsequent DLs shift to the beginning of the corresponding zone, with optimal placement, some Kth DL will be at the beginning of the Kth zone. Equating the number of subpulses in the signal under the condition N _max1 = N _minK , we obtain the expression for the number of suppressed DL:

.The number of suppressed DL depends on the time parameters (τ _and , T _p ) of the sub-pulses and does not depend on the deviation and the number of sub-pulses, therefore, it is possible to change K _max without changing the position of the DL, the repetition period of which is equal to $$\frac{N}{f_{de\mathrm{at}}}$$

.

From the condition of finding the first DL at the end of the first "zero zone" we obtain the condition on the number of sub-pulses in the signal:

function E [x] is the integer part of x

Further, knowing the minimum total radiation time τ _{s_min s / s} obtained on the basis of the required energy potential of the locator, we can calculate the minimum duration of the subpulse

. Отсюда получаем выражение для требуемого количества ДЛ:and determine the maximum possible amount of suppressed DL K _max in accordance with expression (4). Next, you need to compare the obtained value of K _max with the required number of suppressed DL, which is determined by the set value of DL suppression. Because the distance between the DL is equal to the maximum range location, then the minimum (taking into account only the increase in range) suppression of the K-th DL will be equal

. From here we get the expression for the required number of DL:

where L _under is the required preset value of the DL suppression in dB, the function E [x] is the integer part of x. In this case, L _under is determined taking into account the existing spatial and frequency junctions of the receiving path from the probing signal.

If K _Tr ≤ K _max , then this means that the selected parameters of the intermittent sounding signal meet the set requirements and can only be refined based on the requirements of their technical implementation.

If K _Tr > K _max , then you need:

- increase R _max (thus increasing the time τ _max and the number of subpulses N),

- reduce the minimum duration of the subpulse τ _and (thereby setting more stringent requirements for the locator),

- reduce the required level of suppression of DL L _under , but in any way to achieve the fulfillment of the condition K _Tr ≤ K _max .

количество подымпульсов

, период повторения

.After fulfilling this condition, if necessary, specify the duration of the subpulse from the condition

number of subpulses

repetition period

.

The calculations were carried out under the assumption that the duration of the main lobe of the ACF (and also the DL) is much less than τ _max . In this case, theoretically, the maximum of the first DL was placed exactly at the end of the first “zero zone”. Moreover, about half of the DL falls into a nonzero zone. A similar situation is for K _{tr of the} DL, which is theoretically placed (in the worst case) at the beginning of the Kth “zero zone”. In practice, for large values of the frequency deviation, this is not significant. Nevertheless, in order to suppress DL completely, it is necessary to slightly change the position of the “zero zones”, i.e. change the parameters τ _and and τ _max .

We introduce the following notation:

Δτ _max - increment τ _max relative to the previously obtained value,

Δτ _and - increment τ _and relative to the initial value,

Δτ _cf is the half-width of the DL determined by the frequency deviation over the duration of the entire intermittent signal.

Note that to maintain the number of suppressed maxima, K _max τ _max should increase, and τ _and - decrease. That is, the new values will be

Then, to suppress the first DL completely, you need to expand the "zero zone" to the right. In this condition must be satisfied: Δτ _max ≥Δτ _{compression channel.}

We write the absolute position of the Kth maximum through the initial parameters of the signal and through the corrected

Expanding the brackets and removing the same terms, we get the result:

With a coordinated processing, the half-width of the obtained central compressed pulse, as well as the width of half the DL, are determined

During weight processing, the pulse expands 1.5-2 times, for example, modeling for the Hamming window gives a result of about 1.8. Then for the half-width of the DL we can write:

This implies the condition for the minimum Δτ _max and Δτ _and :

As an example, we can consider the choice of signal parameters at a near location in the range up to R _max = 3 km. For definiteness, assume that the desired level of suppression _by L dB = 40, _nine frequency deviation f = 10 MHz, the total duration of the radiation _with τ _ _min _ _{S / N} = 40 ms.

Wherein:

;time of receipt

;

number of subpulses

required amount of suppressed

the minimum value of the duration of the subpulse (based on energy considerations)

maximum number of suppressed

Since K _Tr <K _max , the duration of the subpulse can be increased (which does not contradict the energy considerations indicated above) to

When using weight processing (Hamming window):

округляем (в большую сторону) до 0,2 мкс,

round (up) to 0.2 μs,

округляем (в большую сторону) до 0,2 мкс.

round (up) to 0.2 μs.

The total signal parameters:

An intermittent signal with the obtained parameters can be quite easily implemented in practice. VKF and ACF of such a signal with rounded for practical implementation values of the parameters τ _{and_tog} = 1.8 μs, τ _max _ _total = 20.2 μs, τ _n _ _total = 22 μs are shown in FIG. 5 and FIG. 6 respectively. These figures confirm the suppression of a given number of DL and the effectiveness of the proposed method.

Claims (4)

1. A short-range radar method based on the use of an intermittent pulse signal, characterized in that the intermittent signal parameters are selected based on the required suppression of the "diffraction" lobes (DL) of the autocorrelation function of this signal caused by the transition from a single LF pulse to a burst of N podympulsov, which determine the required number K _Tp first DL suppressed suppression and carry them by placing them in a "null" areas of the autocorrelation function by selecting a lane ode repeating these lobes defined by the expression T _DL = N / f _nine and durations _and τ and τ _{max, and} where τ - duration _{podympulsa, τ max ≥2R max / c,} R max - maximum distance of locating and c - velocity of light moreover, for the kth suppressed DL in the range 1 ≤ k ≤ K _Tr , the inequality ((k-1) τ _max + kτ _u ) <kT _DL <(kτ _max + (k-1) τ _i ) holds. 2. The method according to p. 1, characterized in that the number of suppressed petals K _Tr is determined based on the expression:

where L _under is the required DL suppression in dB, the operator E [x] is the integer part of x. 3. The method according to p. 1, characterized in that when choosing the parameters of an intermittent signal, the required number of subpulses N is first calculated at τ _max = 2R _max / c in accordance with the expression:
N = E [τ _max × f _maids ],
and then find the duration of the subpulse as τ _and = (τ _c _ _min _ _{c / w} ) / N and the number of suppressed DL corresponding to this τ _and , as
$${\mathrm{TO}}_{P\mathrm{about}d}=\frac{{\tau }_{\max }}{{\tau }_{\mathrm{and}}}$$

and, if K _Tr ≤ K _under , then the obtained K _{Tr is} used to calculate τ _and :
$${\tau }_{\mathrm{and}}=\frac{{\tau }_{\max }}{{\mathrm{TO}}_{tR}}$$

moreover, if the conditions K _Tr ≥ K _{under are} not met, then R _max or decrease τ _s _ _min _ _{s / s} under this condition is met. 4. The method according to p. 3, characterized in that for the found signal parameters calculate the correction corrections
$$\Delta {\tau }_{\max }=\frac{1.8}{f_{de\mathrm{at}}}$$

and $$\Delta {\tau }_{\mathrm{and}}=\Delta {\tau }_{\max }\times \left(\frac{{\mathrm{TO}}_{tR}-\mathrm{one}}{{\mathrm{TO}}_{tR}}\right)$$

,
and the final signal parameters are obtained from the expressions
$${\tau }_{\mathrm{and}\_R\mathrm{but}b}=\frac{2R_{\max }}{c\ast {\mathrm{TO}}_{tR}}-\frac{1.8}{f_{de\mathrm{at}}}\times \left(\frac{{\mathrm{TO}}_{tR}-\mathrm{one}}{{\mathrm{TO}}_{tR}}\right)$$

,
$$T_{P\mathrm{about}\mathrm{at}\_R\mathrm{but}b}=\frac{2({\mathrm{TO}}_{tR}+\mathrm{one})R_{\max }}{c\ast {\mathrm{TO}}_{tR}}+\frac{1.8}{{\mathrm{TO}}_{tR}{f}_{de\mathrm{at}}}$$

.

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