RU2727793C1 - Ultra-wideband multifrequency radar with active phased antenna array and reduced level of side lobes in compressed signal - Google Patents

Abstract

FIELD: radar ranging.SUBSTANCE: invention relates to radar ranging and can be used in various radar systems, where high resolution on range is required. Radar comprises M active phased arrays (PAA), made in a certain way, wherein each PAA element emits and receives a phase-modulated signal (frequency modulation is considered to be a special phase event) with carrier frequency ƒ=ƒ+Δƒ (k-1), where ƒis lower carrier frequency; Δƒ is the interval between carrier frequencies, k=1…N, N is the number of carriers of the emitted multi-frequency signal (number of grid elements). At each carrier frequency ƒphase synchronization for all elements is carried out with frequency band B≤Δƒ. As a result, the entire radar band will be equal toFrequencies ƒare mutually coherent, which is achieved by means of common reference generator. Signals received by each PAA element after amplification and matched filtering are transmitted to a summing device, at the output of which a pulse signal is obtained. Signals from outputs of summing devices of all PAA are supplied to inputs of multiplier device, output of which is connected to input of output device. As a result, the level of side lobes in the received signal of such a locator is reduced to M×13.2 dB.EFFECT: reduced level of side lobes.1 cl, 6 dwg

Description

DESCRIPTION OF THE INVENTION

Invention title

An ultra-wideband multi-frequency radar with an active phased antenna array and reduced sidelobe levels in the compressed signal.

The technical field to which the invention relates

The invention relates to radar and can be used in various radar systems where high range resolution is required.

State of the art

Known ultra-wideband (UWB) radar with an active phased array (AFAR) [1]. In the transmitting channels of the AFAR, traditional amplifying devices of the microwave range (klystrons, amplitrons, transistor amplifiers) can be used. The disadvantage of such radars is the limited bandwidth of the power amplifiers, which means that the resolution is limited. For example, the bandwidth of one of the powerful broadband amplifying devices - continuous traveling wave tubes (TWT) does not exceed one octave in the frequency range 1 ... 4 GHz, and with an increase in the operating frequency it becomes even less. The frequency band of powerful pulsed TWT does not exceed 1 GHz at an operating frequency of 15 GHz [2].

The closest device in technical essence is a UWB radar with an active multi-frequency antenna array, which is selected as a prototype [3]. An increase in the frequency band and the range resolution of the locator is achieved due to the fact that the UWB signal is formed from narrow-band or wide-band signals emitted and received by different AFAR elements. Narrowband (wideband) signals are formed using phase or frequency modulation (keying) of the carrier [4].

The disadvantage of the prototype is the high level of side lobes in the received signal.

Disclosure of invention

The objective of the invention is to reduce the level of side lobes in the signal received by the UWB locator.

The block diagram of the proposed device is shown in Fig. 1.

The block diagram of the prototype is shown in Fig. 2.

Сигнал импульсной амплитудной модуляции поступает на AM с генератора импульсной модуляции (11) через распределительную систему (12).The prototype includes transceiver AFAR elements (15), matching devices (14), transceiving active modules (4), a summing device (3), an output device (21). To ensure mutual coherence, the carrier frequencies of the signals ƒ _k = ƒ ₁ + Δƒ (k-1) coming from the active modules (AM) to the transmitting and receiving elements in the radiation mode are formed from a common reference oscillator (22). Here ƒ ₁ is the lower carrier frequency; Δƒ is the interval between carrier frequencies, k = 1 ... N, N is the number of carriers of the emitted multifrequency signal. A signal with a frequency ƒ _{op is} fed to AM through the reference signal distribution system (23). Phase modulation (keying) generators (25) use a reference signal supplied from a reference baseband generator (26) through a reference baseband distribution system (27). Phase modulation (frequency modulation can be considered as its special case) is carried out with a frequency band B _k ≤Δƒ at each carrier frequency ƒ _k . As a result, the entire radar bandwidth will be equal to

The pulse amplitude modulation signal is fed to the AM from the pulse modulation generator (11) through the distribution system (12).

The maximum normalized envelope plot of the received signal at the output of one AM after matched filtering for a time of ± 75 ns of the maximum envelope in the case of chirp is shown in dotted line in FIG. 3. The calculation was carried out for the frequency band B = 2 GHz at N = 21 and the signal duration T = 1 μs. The expression describing the graph can be represented as [3]:

where τ is time; β = 2πB _k / Т is the rate of frequency change in the B _k band.

The solid line in FIG. 3 shows a normalized graph of the envelope of the sum of the signals at the output of the adder, provided that the amplitudes of the signals at the output of the active modules are equal. A fragment of this graph for a time range of ± 7 is not shown as a solid line in FIG. 4. The expression for the envelope of the sum of the signals of the lattice channels is:

where Δω = 2π Δƒ.

With equal signal amplitudes at all frequencies ƒ _{k, the} maximum sidelobe level (LBL) is -13.2 dB. The maximum LLL can be reduced by weighting signals with carriers ƒ _k . So when weighted according to Taylor, the maximum UBL will be equal to -40 dB, according to Hemming - -43 dB [4]. However, when weighing, the main lobe of the signal expands. If for an equal-amplitude frequency distribution the duration of the main lobe at a level of -3 dB is 0.886 / 5, then for Taylor weighting it is 1.2 B / V, and for Hamming weighting - 1.3 / V.

In order to reduce the maximum UBL without using weight processing, it is proposed to additionally introduce at least one APAR, built according to the prototype scheme, and a multiplication device. The total number of AFAA will thus be equal to M. In this case, the signals from the output of the adders (3) are fed not to the input of the output device (21), but to the inputs of the multiplier (29), the output of which is connected to the output device (21). The envelope of the signal at the output of the multiplier is described by the expression

Thus, the maximum SBL will be - 13.2M dB. FIG. 5, figs. 6 the dotted line shows the normalized envelope of the signal at the output of one adder for the above parameters, the solid line shows the normalized envelope of the signal at the output of the multiplier for M = 3. In this case, the maximum LFL is comparable to the LBL obtained with Taylor weighting, and the duration of the main lobe of the compressed sounding chirp signal decreases approximately 2 times, which makes it possible to double the range resolution.

Description of drawings

FIG. 1 shows a block diagram of the proposed device.

FIG. 2 shows a diagram of a prototype.

FIG. 3, fig. 4 the dotted line shows the normalized envelope of the chirp signal at the output of the prototype active module with the total signal frequency band B = 2 GHz, the number of frequencies N = 21 and the signal duration T = 1 μs, the solid line shows the signal envelope at the output of the prototype adder, for time ± 75 ns from the maximum of the envelope. The estimated time interval for FIG. 3 is ± 75 ns, for Fig. 4 - ± 7 ns.

FIG. 5, Fig. 6, the dotted line shows the normalized signal envelope at the output of the adder of one APAR, the solid line shows the normalized envelope of the signal at the output of the multiplier for the time ± 7 ns and ± 0.25 ns, respectively.

Implementation of the invention

The proposed radar contains M active HEADLIGHTS (at least two). Each phased array includes transceiving elements of the AFAR (15), matching devices (14), active modules (4), a summing device (3), an output device (21), a reference generator (22), a reference signal distribution system (23 ), a reference baseband signal generator (26), a baseband reference signal distribution system (27), a pulse modulation signal generator (11), a pulse modulation signal distribution system (12) (Fig. 1). The active module contains a frequency exciter ƒ _k = ƒ ₁ + Δƒ (k-1) (1), a phase shifter (5), a phase modulator (24), a phase modulation (manipulation) generator (25), the first and second preamplifiers (7) and (9), the first controllable attenuator (8), the power amplifier (10), the transmit-receive switch (13), the protective device of the receiving path (16), the first and second low-noise amplifiers (17) and (19), matched filter (18), second controlled attenuator (20), controlled delay line (28). The signals from the outputs of the active modules (4) are fed to the inputs of the adders (3), and from the outputs of the adders to the inputs of the multiplier (29). The output of the multiplier is connected to the input of the output device.

The device works as follows.

The exciter (1) of each active module (4) generates a carrier signal ƒ _k = ƒ ₁ + Δƒ (k-1), k = 1 ... N. The coherence of these frequencies is ensured by synchronizing all exciters using a common reference oscillator (22), the signal of which is fed to the exciters of all active modules through the reference signal distribution system (23). Since the proposed radar consists of M PAR, a signal with a carrier frequency ƒ _k will be generated by exciters of M active modules

Phase shifters (5) are needed to form the directional pattern of the radar. In this case, the maxima of the RP of all M active PARs must coincide in the direction in space.

Synchronous phase modulation of all carrier frequencies ƒ _{k is} achieved using a common reference baseband generator (26), the signal from which through the baseband reference signal distribution system (27) is fed to the phase modulation signal generators (25) of all active locator modules, and from these generators to phase modulators (24) of these modules.

The resulting phase-modulated signal is amplified by pre-amplifiers (7) and through the first controlled attenuators (8) of each active module and the second pre-amplifiers (9) is fed to the power amplifiers (10). Pulse modulation of the transmitted signal is carried out synchronously for all active modules using a common pulse modulation generator (11) and a common pulse modulation signal distribution system (12), the outputs of which are connected to the modulation signal input of the power amplifier (10) of each active module.

The generated signal is emitted by the transmitting and receiving elements (15) of the antenna array, which are connected to the active modules (4) using matching devices (14). The locator operating mode is carried out using the transmit-receive switches (13).

In the receiving mode, the receiving path of active modules operates, consisting of a protective device (16), a first low-noise amplifier (17), a matched filter (18), a second low-noise amplifier (19), a second controlled attenuator (20) and a controlled delay line (28) ... The matched filter compresses the received phase modulated signal (a special case of phase modulation - chirp).

The received signal of each of the M active arrays of the locator is obtained in a standard way - by summing the signals from the outputs of all N active modules that make up this array, in an adder (3). A decrease in the level of side lobes in the received signal is obtained using a multiplier (29), which multiplies the signals from the output of all M active gratings included in the device.

The output device (21) is designed to convert the received signal containing useful information into a form convenient for the recipient of this information.

Bibliographic data

1. Gostyukhin V.L., Trusov V.N., Gostyukhin F.V. Active phased antenna arrays / Ed. V.L. Gostyukhin. Ed. 3rd, rev. and add. - M .: Radio engineering, 2011. p. nineteen.

2. Generators and Microwave Amplifiers / Ed. I.V. Lebedev. - M .: "Radiotekhnika", 2005. p. 123 table 3.3., P. 47 table 1.9.

3. Vasiliev A.V., Verba B.C., Vorobiev N.V., Gryaznov V.A., Silkin A.T. Ultra-wideband radar with an active multi-frequency antenna array: Patent RU 2615996. Priority dated 09.02.2016.

4. Handbook on radar / Under. ed. M.I. Skolnik. Per. from English. under the general ed. B.C. Willows. In 2 books. Book 1. Moscow: Technosphere, 2014. Chapter 8.

Claims (1)

An ultra-wideband radar with an active multi-frequency antenna array and reduced sidelobe level in a compressed signal, consisting of an output device, a pulse modulation signal generator and a pulse modulation signal distribution system, a reference baseband generator and a reference baseband distribution system, a reference generator and a reference distribution system signal, active modules, the input-output of each of which is connected through a matching device to the transceiver element of the antenna array, and the outputs of the active modules are connected to the inputs of the adder; active modules include a transmit-receive switch, the input-output of which is the input-output of the active module, the receiving and transmitting paths; the transmitting path consists of a phase modulation signal generator and a series-connected exciter, a phase shifter, a phase modulator, the control input of which is connected to a phase modulation signal generator, a first pre-amplifier, a first controllable attenuator, a second pre-amplifier, a power amplifier, the output of which is connected to the input of the receive switch -broadcast; the receiving path of the active module consists of a series-connected protective device of the receiving path, the input of which is connected to the output of the transmit-receive switch, the first low-noise amplifier, a matched filter, the second low-noise amplifier, the second controllable attenuator and the controlled delay line, the output of which is the output of the active module; the spectrum of the transmitted and received signal, having a bandwidth B, is divided into N non-overlapping sub-bands with a bandwidth of B _k , k = 1 ... N, so that the condition

the signal in each subband is generated and received in a separate active module, emitted and received by a separate element of the antenna array, while the carrier frequencies of the subbands are mutually coherent and form a frequency grid ƒ _k = ƒ ₁ + Δƒ (k-1), where ƒ ₁ is the lower carrier frequency, Δƒ - the interval between carrier frequencies not exceeding the maximum band signal B _k, for each frequency band B _k is performed synchronous phase modulation (keying) signal, the mutual coherence of the carrier frequency provided by reference oscillator whose output is connected to the input distribution system reference signal, and each output of the reference signal distribution system is connected to the control input of the exciter of each active module, synchronous phase modulation is provided using a reference baseband generator, the output of which is connected to the reference distribution system of the reference signal, each output of the distribution system is reference The second baseband signal is connected to the input of the phase modulation signal generator of each active module, synchronous pulse modulation is performed in each active module using a pulse modulation signal generator, the output of which is connected to the input of the pulse modulation signal distribution system, each output of the pulse modulation signal distribution system is connected to input of the modulation signal of the power amplifier of each active module, characterized in that at least one active phased antenna array, built according to the scheme described above, and a multiplication device are additionally introduced, the inputs of which are connected to the outputs of the summing devices of each active array, and the output of the multiplication device is connected to the input of the output device, while the maxima of the radiation patterns of all active phased arrays coincide in the direction in space and for all phased arrays a common reference generator and a distribution a reference signal system, a common reference baseband generator and a baseband reference distribution system, and a common pulse modulation signal generator and a pulse modulation signal distribution system.

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