Description:TECHNICAL FIELD
[0001] The present disclosure relates, in general, to radars, and more specifically, relates to system and methodology to classify radar and decoy radar emissions causing modulation on pulse (MOP).

BACKGROUND
[0002] Radars in general, operate in different spot frequencies, in a wide RF bandwidth by hopping the frequency. Generally, radars are not equipment which can be expended with and hence needs to be protected against incoming threats which seek RF signals emitted by radar. These threats will be ejected to destroy the radar by homing on to the radar. Radar, when detects an incoming threat, within a certain distance will switch off to avoid detection by the incoming threat. Usually, to protect the main radar from destruction, decoy radar will also be placed adjacent to the radar at a distance such that the main radar when switched off, decoy radar which comprises just a transmitter takes over and transmits the same emissions as done by main radar so as to mislead the incoming threat.
[0003] Complex radar needs to be protected against threats and seekers that home in on to RF emissions from the radar. To protect the main radar system, a decoy radar system will be deployed that transmits the same radar pulse as the main radar system. When an incoming threat such as an anti-radiation missile is approaching the main radar system, it will switch off the main radar after which the same pulse will be transmitted by the decoy radar which is a low-cost system as compared to the main radar; thus the threat gets confused.
[0004] A few examples of such radar are recited in Chinese patent CN114460547A that discusses passive active induced bias resisting method based on a DOA clustering algorithm, which judges whether a radiation source targets exist or not by jumping of power and phase difference of received signals and carries out DOA estimation; accumulating angle results of DOA estimation and carrying out dynamic distance clustering within a period of time; judging whether the clustering result meets the condition of judging the isolated point; and performing repetition frequency stability calculation on the clustering result, and outputting a target angle. Also, the method accurately judges whether the actively induced deviation exists in the current environment, has high real-time performance and low algorithm complexity, and realizes the identification and judgment of the target of the active induced deviation system, which is suitable for the direction-finding and identification of the airborne/missile-borne passive to the target of the radiation source at the ground fixed position, belongs to a ground target accurate guidance system and has a high real-time requirement and low misjudgement rate.
[0005] This method judges the presence of radiation based on the power level of the signal received and suffers when multiple radiations are emitted by different sources from an equal radial distance as the power received by the receiver is the same in a wide band scenario. Also, the method does not disclose the wide bandwidth requirements when sources are hopping, which are addressed as part of the scope of the present disclosure. Also, the method classifies the emissions after clustering the characterized emissions for a period of time wherein the present method and system classify in a single pulse repetition period for all the pulses.
[0006] Another example is recited in the European patent EP1167995A2 discusses a method and system for identifying the locations of plural targets lying within a main beam of a mono pulse antenna including four ports for generating sum, elevation difference, azimuth difference and double difference signals. The method comprises the steps of forming a mono pulse ratio matrix from the sum, elevation difference, azimuth difference and double difference signals; and determining eigenvalues of the mono pulse ratio matrix. These eigenvalues are then used to determine the angular locations of the plural targets. Preferably, the eigenvalues are determined by performing an Eigenvalue decomposition of the mono pulse ratio matrix to generate eigenvalues, and the angles of the targets may be determined from the eigenvalues by the use of a look-up table.
[0007] The above method suffers from estimating the direction of arrival in a single pulse repetition period as it calculates the Eigenvectors that call for a matrix inversion process, requiring a lot of processor clock computations, as compared to the proposed method and its system for realization, which classifies the similar emissions with different direction of arrival within a pulse period, and on pulse-by-pulse basis without using matrix inversion for calculations & computations
[0008] Therefore, it is desired to overcome the drawbacks, shortcomings, and limitations associated with existing solutions, and develop a means to perform the classification of radar and decoy emissions within a single pulse repetition period causing modulation on the pulse.

OBJECTS OF THE PRESENT DISCLOSURE
[0009] An object of the present disclosure relates, to radars, and more specifically, relates to system and methodology to classify radar and decoy radar emissions causing modulation on pulse (MOP).
[0010] Another object of the present disclosure is to provide a system that performs under sampling the RF signals with three different sampling frequencies.
[0011] Another object of the present disclosure is to provide a system that estimates the frequency using a look-up table based on cost function minimization.
[0012] Another object of the present disclosure is to provide a system that performs an estimation of the direction of arrival without complex matrix inversions.
[0013] Yet another object of the present disclosure is to provide a system that performs classification of radar and decoy emissions within a single pulse repetition period causing modulation on pulse i.e., time domain and frequency domain overlap.

SUMMARY
[0014] The present disclosure relates to radars, and more specifically, relates to the system and methodology to classify radar and decoy radar emissions causing modulation on pulse (MOP). The main objective of the present disclosure is to overcome the drawback, limitations, and shortcomings of the existing system and solution, by providing a system to classify exactly similar pulses emitted by a radar system and its decoy system causing modulation on pulse for a wideband receiver. The present disclosure relates to the development of test equipment for the validation and testing of radar and decoy systems when they emit the signal simultaneously.
[0015] The system for classifying emissions within a single pulse repetition period, the system includes a radar and decoy that are installed at a predefined distance. Electronic warfare (EW) receiver with an instantaneous bandwidth (IBW) is installed at a predefined distance in a triangular fashion, the EW receiver detects the radar and decoy signal within a wide radio frequency (RF) bandwidth, the EW receiver having an antenna array coupled to a plurality of ADCs to process at least three channel data from a set of channel data received from the antenna arrays for coarse frequency estimation using under-sampling with predefined sampling frequencies to form digital samples.
[0016] The EW receiver determines the indexes of peaks with respect to corresponding sampling frequencies using a 512-point fast Fourier transform (FFT) on the acquired digital samples, obtains the corresponding actual frequency from the look-up table (LUT) values pre-calculated using a minimum distance process based on the frequency bin indexes. The EW receiver stores the set of channel data for the length of coarse frequency estimation in a memory, down-convert at least one of the channels data by mixing with the frequency estimated by the coarse frequency estimation, band limit the down-converted channel data, estimates fine frequency and phase across all the set of channel data, combine the stored set of channel data with weight vectors, estimate power spectrum and normalize the values to find the peak in the respective degree of the direction of arrival.
[0017] Further, the EW receiver calculates the power spectrum for all the array of weight mixed signals for all the degrees under consideration, compares the peak for all the power spectra, and the higher peak estimated is considered the direction of arrival parameter of the emission, forms pulse descriptor word for the degree indicated with the highest peak and classify the radar and decoy radar signal emissions based on the pulse descriptor word formed on the single pulse by pulse case basis within pulse repetition interval period of the radar.
[0018] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0020] FIG. 1 illustrates an exemplary system to classify pulses emitted by a radar system and decoy system, in accordance with an embodiment of the present disclosure.
[0021] FIG. 2 illustrates an exemplary block diagram of the EW receiver, in accordance with an embodiment of the present disclosure.
[0022] FIG. 3 illustrates an exemplary schematic view of coarse frequency estimation, in accordance with an embodiment of the present disclosure.
[0023] FIG. 4 illustrates an exemplary schematic view of fine frequency estimation and phase estimation, in accordance with an embodiment of the present disclosure.
[0024] FIG. 5 illustrates an exemplary schematic view of the direction of arrival estimation, in accordance with an embodiment of the present disclosure.
[0025] FIG. 6 illustrates an exemplary flow chart of the method for classifying emissions within single pulse repetition period, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0026] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0027] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0028] The present disclosure relates, to radars, and more specifically, relates to the system and methodology to classify radar and decoy radar emissions causing modulation on pulse (MOP). The proposed system disclosed in the present disclosure overcomes the drawbacks, shortcomings, and limitations associated with the conventional system providing a wideband passive receiver system which is used to test the arrangement wherein main radar and decoy radar are connected and synchronized by a fibre optic link; transmit the radar pulses simultaneously; causing modulation on pulse (MOP). The system and methodology adapted to classify the radar and its duplicate spaced by varying distances, in a wide bandwidth scenario are disclosed. The system is compact and low cost; the process of estimating the radar pulse parameters along with their direction of arrival, classification of main radar signal and decoy signal strictly within the single pulse repetition period of radar pulse more particularly on the occurrence of MOP. The present disclosure can be described in enabling detail in the following examples, which may represent more than one embodiment of the present disclosure.
[0029] The present disclosure relates to a receiver which acts as a typical electronic warfare receiver that operates in huge instantaneous wide bandwidths, of about 500 MHz, and works as a test and validation instrument that detects and classifies the radar, its decoy signals along with the direction of arrival estimation of both the radar and decoy radar waveforms based on proposed techniques detailed more particularly for modulation on pulse cases.
[0030] The advantages achieved by the system of the present disclosure can be clear from the embodiments provided herein. The system performs under sampling the RF signals with three different sampling frequencies, estimates the frequency using a look-up table based on cost function minimization, performs estimation of the direction of arrival without complex matrix inversions and performs classification of radar and decoy emissions within a single pulse repetition period causing modulation on pulse i.e., time domain and frequency domain overlap. The description of terms and features related to the present disclosure shall be clear from the embodiments that are illustrated and described; however, the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents of the embodiments are possible within the scope of the present disclosure. Additionally, the invention can include other embodiments that are within the scope of the claims but are not described in detail with respect to the following description.
[0031] FIG. 1 illustrates an exemplary system to classify pulses emitted by a radar system and decoy system, in accordance with an embodiment of the present disclosure.
[0032] Referring to FIG. 1, system 100 is configured to classify exactly similar pulses emitted by a radar system 102 (also referred to as radar, 102 herein) and its decoy system 104 (also referred to as decoy 104, herein) causing modulation on the pulse for a wideband receiver 106. This work relates to the development of test equipment for the validation and testing of radar 102 and decoy system 104 when they emit the signal simultaneously. The radar system 102 and its decoy system 104 are installed at a distance of around 100 meters geographically apart and a wide band electronic warfare (EW) receiver 106 (also referred to as EW receiver 106, herein) with an instantaneous bandwidth (IBW) of around 500 MHz as per hopping bandwidth of radar spot frequencies is installed at a distance of 100 meters in a triangular fashion as shown in FIG. 1. Although the test setup is explained with a triangular pattern, it may be applicable to any pattern; with a restriction that EW receiver 106 should have radar 102 and decoy 106 in its field of view.
[0033] In the proposed configuration, radar frequency is considered to be hopping from 5.4 GHz to 5.9 GHz within a bandwidth of 500 MHz and whose spot frequencies are hopping with a jump of 30 MHz with nearly 16 hops. As shown in FIG. 1, radar 102 and the decoy radar are connected by an optical link for clock transport and synchronization of both systems.
[0034] The present disclosure relates to the test equipment which acts as passive electronic warfare (EW) receiver that detects the radar and its decoy signal, which are hopping within a wide radio frequency (RF) bandwidth; sensing by using multiple antennas; estimating the radar and decoy signal parameters like frequency by direct under-sampling techniques and estimate the direction of arrival using 8 elements of antennae within accuracy as good as 1 degrees of separation, within the pulse period of the incoming radar signal.
[0035] The present techniques are proposed in determining the coarse frequency and fine frequency estimations, coded the coarse frequency estimation in the form of a look-up table (LUT) using minimum distance; fine frequency estimation; phase difference estimation and digital beam forming; novel method of maximizing signal to noise ratio using Fourier transform; followed by the direction of arrival estimation for the pulse-on-pulse condition from radar and decoy system.
[0036] FIG. 2 illustrates an exemplary block diagram of the EW receiver, in accordance with an embodiment of the present disclosure.
[0037] In the EW receiver setup, 106 under consideration can include a plurality of antennas 202 connected in a linear array with a predefined spacing of 70mm. The EW receiver setup 106 can include a plurality of low noise amplifiers 204, a plurality of filter banks 206 to band limit the signal to the specified range of 5.4GHz to 5.9 GHz and Radiofrequency system-on-chip (RFSOC) device 208. In an exemplary embodiment, the plurality of antennas 202 can be eight numbers of Vivaldi antennas.
[0038] The RFSOC device 208 is an integrated chip with 16 ADCs and FPGA whose analog bandwidth is 6GHz, with maximum sampling frequency of 2.5GSPS. The signals from antennas are amplified, filtered as per bandwidth requirement, and sampled by individual ADCs. The RFSOC device 208 includes software to configure the parameters of ADC 210 like sampling frequency.
[0039] The RFSOC 208 is a device with 16 number of ADC channels 210, with associated down converters for frequency translation to baseband and a programmable logic 212 is used to realize the method to classify radar and its decoy signal within a single pulse repetition period for all the pulses captured using the proposed techniques for estimation of frequency using under sampling, and estimation of direction of arrival of the emissions without complex mathematical computations.
[0040] The RFSOC device 208 can include 16 ADCs which aids in miniaturization compared with the conventional hardware radio frequency down converters and mono pulse antenna systems including phase shifters and do spatial combining and filtering. The proposed methodology and systems are quick enough to classify the radar and decoy radar pulses within the pulse period time interval being realized on the proposed systems for modulation on pulse conditions.
[0041] The three parallel signal processing steps are followed to run the entire design in less number of clocks and such a method is chosen to complete the whole computations in a single pulse repetition period of radar under consideration.
[0042] FIG. 3 illustrates an exemplary schematic view 300 of coarse frequency estimation, in accordance with an embodiment of the present disclosure.
[0043] As depicted in FIG. 3, the coarse frequency estimation is as follows. In an embodiment, the three different ADCs are configured for three different sampling frequencies namely 1100 MHz, 1300 MHz, 2000 MHz. The acquired ADC samples are transformed into the frequency domain. Using a dynamic threshold frequency detection of the signal is determined using a 512-point FFT. The Index numbers with respect to individual sampling frequencies as per the Nyquist zones are estimated and using the above index numbers frequency is obtained by using the reference look-up table pre-calculated using a novel minimum distance method.
[0044] FIG. 4 illustrates an exemplary schematic view 400 of fine frequency estimation and phase estimation, in accordance with an embodiment of the present disclosure.
[0045] Referring to FIG. 4, one of the channel data from the antenna is stored for the length of coarse frequency estimation which is around 768 clock cycles in a block RAM of the PL of RFSOC. One of the channel data from the antenna is down-converted to 600 -1100 MHz bandwidth using digital down conversion by mixing with the frequency estimated by the above coarse frequency estimation. The down-converted channel data is band limited to around 30 MHz using a Polyphase filter bank. Finally, the fine frequency and phase are estimated for the coarse frequency of the radar detected.
[0046] FIG. 5 illustrates an exemplary schematic view of the direction of arrival estimation 500, in accordance with an embodiment of the present disclosure.
[0047] Assuming some prior coarse angle information is available, parallel 32 beams are formed around that coarse DOA. The FOV for beam forming is ± 15° assuming the coarse DOA is at bore sight.
[0048] Considering the signal arriving at the antenna element 1 to have a phase = 0, while the signal that arrives at the antenna “n” leads in phase with ξnd*sin(α). Array propagation vector containing angle information of the emission is defined by

Array factor can be defined by

[0049] Individual array factor matrices shown in FIG. 5 are stored in the PL 212 of FPGA which corresponds to the weights of 1 degree of phase against the bore sight of the antenna arrays. The power spectrum is calculated for the array of weight-mixed signals for all the degrees under consideration. The peak is compared for all the power spectra, and the higher peak estimated is considered the direction of arrival parameter of the emission. A pulse descriptor word is formed for the degree indicated with the highest peak. Two peaks identified within the operating frequency by maximizing signal-to-noise ratio without using any matrix inversion may classify the radar and decoy radar signal.
[0050] Since these algorithms run in parallel entire operations of the methodology can be executed within a single pulse repetition period of radar as a number of clock cycles consumed is around 1000 clocks, given design is optimized for a 300 MHz clock, which can as well operate within time period of the order of microseconds.
[0051] Thus, the present invention overcomes the drawbacks, shortcomings, and limitations associated with existing solutions, and provides the system that performs under sampling the RF signals with three different sampling frequencies, estimates the frequency using a look-up table based on cost function minimization, performs estimation of direction of arrival without complex matrix inversions and performs classification of radar and decoy emissions within a single pulse repetition period causing modulation on pulse i.e., time domain and frequency domain overlap.
[0052] FIG. 6 illustrates an exemplary flow chart of the method for classifying emissions within single pulse repetition period, in accordance with an embodiment of the present disclosure.
[0053] Referring to FIG. 6, the method 600 includes at block 602, the EW receiver having an antenna array coupled to a plurality of ADCs can process at least three channel data from a set of channel data received from the antenna arrays for coarse frequency estimation using under-sampling with predefined sampling frequencies, wherein the EW receiver is installed at a predefined distance in a triangular fashion and detects the radar and decoy signal within a wide radio frequency (RF) bandwidth, a radar and decoy are installed at a predefined distance.
[0054] At block 604, the EW receiver can determine the indexes of peaks with respect to corresponding sampling frequencies using a 512-point fast Fourier transform (FFT) on the acquired digital samples. At block 606, the EW receiver can obtain the corresponding actual frequency from the look-up table (LUT) values pre-calculated using a minimum distance process based on the frequency bin indexes.
[0055] At block 608, the EW receiver can store the set of channel data for the length of coarse frequency estimation in a memory. At block 610, the EW receiver down-converts at least one of the channels data by mixing with the frequency estimated by the coarse frequency estimation. At block 612, the EW receiver can estimate fine frequency and phase across all the set of channel data.
[0056] At block 614, the EW receiver combines the stored set of channel data with weight vectors. At block 616, the EW receiver estimates the power spectrum and normalizes the values to find the peak in the respective degree of the direction of arrival. At block 618, the EW receiver calculates the power spectrum for the array of weight-mixed signals for all the degrees under consideration.
[0057] At block 620, the EW receiver compares the peak for all the power spectra, and the higher peak estimated is considered the direction of arrival parameter of the emission. At block 622, the EW receiver forms a pulse descriptor word for the degree indicated with the highest peak; and At block 624, the EW receiver classifies the radar and decoy radar signal emissions based on the pulse descriptor word formed on a single pulse by pulse case basis within pulse repetition interval period of the radar.
[0058] It will be apparent to those skilled in the art that the system 100 of the disclosure may be provided using some or all of the mentioned features and components without departing from the scope of the present disclosure. While various embodiments of the present disclosure have been illustrated and described herein, it will be clear that the disclosure is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the disclosure, as described in the claims.

ADVANTAGES OF THE PRESENT INVENTION
[0059] The present invention provides a system that performs under sampling the RF signals with three different sampling frequencies.
[0060] The present invention provides a system that estimates the frequency using a look-up table based on cost function minimization.
[0061] The present invention provides a system that performs an estimation of direction of arrival without complex matrix inversions.
[0062] The present invention provides a system that performs classification of radar and decoy emissions within a single pulse repetition period causing modulation on pulse i.e., time domain and frequency domain overlap.
, Claims:1. A system for classifying emissions within a single pulse repetition period, the system comprising:
a radar (102) and decoy (104) that are installed at a predefined distance;
an electronic warfare (EW) receiver (106) with an instantaneous bandwidth (IBW) is installed at a predefined distance in a triangular fashion, the EW receiver detects the radar and decoy signal within a wide radio frequency (RF) bandwidth, the EW receiver having an antenna array coupled to a plurality of analog to digital converter (ADCs) to:
process at least three channel data from a set of channel data received from the antenna arrays for coarse frequency estimation using under-sampling with predefined sampling frequencies to form digital samples;
determine the indexes of peaks with respect to corresponding sampling frequencies using a 512-point fast Fourier transform (FFT) on the acquired digital samples;
obtain the corresponding actual frequency from the look-up table (LUT) values pre-calculated using a minimum distance process based on the frequency bin indexes;
store the set of channel data for the length of coarse frequency estimation in a memory;
down-convert at least one of the channels data by mixing with the frequency estimated by the coarse frequency estimation, band limit the down-converted channel data;
estimate fine frequency and phase across all the sets of channel data;
combine the stored set of channel data with weight vectors;
estimate power spectrum and normalize the values to find the peak in the respective degree of the direction of arrival;
calculate power spectrum for all the array of weight mixed signals for all the degrees under consideration;
compare the peak for all the power spectra, and the higher peak estimated is considered the direction of arrival parameter of the emission;
form pulse descriptor word for the degree indicated with the highest peak; and
classify the radar and decoy radar signal emissions based on the pulse descriptor word formed on a single pulse by pulse case basis within the pulse repetition interval period of the radar.
2. The system as claimed in claim 1, wherein the predefined sampling frequencies comprise 1100 MHz, 1300 MHz, and 2000 MHz.
3. The system as claimed in claim 1, wherein the memory comprises Random-access memory (RAM) of the programmable logic (PL) of Radiofrequency system-on-chip (RFSOC).
4. The system as claimed in claim 1, wherein the EW receiver comprises polyphase filter bank configured to down-convert at least one of channel data by mixing with the frequency estimated by the coarse frequency estimation.
5. The system as claimed in claim 1, wherein the weight vectors correspond to all degrees of direction with required resolution; wherein the weight vectors are pre-calculated and stored to form multiple beams in parallel.
6. The system as claimed in claim 1, wherein the EW receiver computes the transform on the above phase mixed and beam formed channel data for all degrees of direction of arrival.
7. The system as claimed in claim 1, wherein the EW receiver estimates parameters of radar and decoy signal with their phase differences as two distinct peaked phases indicating their direction from the bore sight of the antenna array
8. The system as claimed in claim 1, wherein individual look-up tables are stored in the PL which corresponds to the weights of 1 degree of phase against the bore sight of the antenna arrays
9. A method (600) for classifying emissions within a single pulse repetition period, the method comprising:
processing (602), by EW receiver having an antenna array coupled to a plurality of ADCs, at least three channel data from a set of channel data received from the antenna arrays for coarse frequency estimation using under-sampling with predefined sampling frequencies, wherein the EW receiver is installed at a predefined distance in a triangular fashion and detects the radar and decoy signal within a wide radio frequency (RF) bandwidth, a radar and decoy are installed at a predefined distance;
determining (604) the indexes of peaks with respect to corresponding sampling frequencies using a 512-point fast Fourier transform (FFT) on the acquired digital samples;
obtaining (606) the corresponding actual frequency from the look-up table (LUT) values pre-calculated using a minimum distance process based on the frequency bin indexes;
storing (608) the set of channel data for the length of coarse frequency estimation in a memory;
down-converting (610) at least one of channel data by mixing with the frequency estimated by the coarse frequency estimation;
estimating (612) fine frequency and phase across all the set of channel data;
combining (614) the stored set of channel data with weight vectors;
estimating (616) power spectrum and normalizing the values to find the peak in the respective degree of the direction of arrival;
calculating (618) power spectrum for all the array of weight mixed signals for all the degrees under consideration;
comparing (620) the peak for all the power spectra, and the higher peak estimated is considered the direction of arrival parameter of the emission;
forming (622) pulse descriptor word for the degree indicated with the highest peak; and
classifying (624) the radar and decoy radar signal emissions based on the pulse descriptor word formed on a single pulse by pulse case basis within the pulse repetition interval period of the radar.