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Editor Work2012 Vol. 1, No. 3
Previous Issue
2012, 1(3): 217-224.
Abstract
2720KB
The antenna pattern uncertainty is the main error of SAR system. The technique for inflight antenna pattern measurement of spaceborne SAR is one of the most important technique of SAR calibration. This paper discusses the development courses of the inflight antenna pattern measurement of spaceborne SAR, analyses its development trend and compares the main inflight antenna pattern measurement techniques. This paper will be an important reference for designing a project of inflight antenna pattern measurement of spaceborne SAR.
The antenna pattern uncertainty is the main error of SAR system. The technique for inflight antenna pattern measurement of spaceborne SAR is one of the most important technique of SAR calibration. This paper discusses the development courses of the inflight antenna pattern measurement of spaceborne SAR, analyses its development trend and compares the main inflight antenna pattern measurement techniques. This paper will be an important reference for designing a project of inflight antenna pattern measurement of spaceborne SAR.
2012, 1(3): 225-231.
WiFi (Wireless Fidelity) is widely deployed all the world. When it is utilized as external illuminaor in Passive Radar, its broadband singal make the high resolution of detection be obtained in both the range and Doppler domains. In this paper, the typical WiFi signal format and its characters are analyzed, then the theoretical signal model is setup. Based on the theory of bistatic passive radar, the relationship between typical IEEE 802.11 signals format and the characters of its Ambiguity Function (AF) is analyzed. Moreover, the position and amplitude of side peaks in time and frequency domain is analyzed and its causes from the signal structure is also discussed. In this paper, a method for suppressing the side peaks based on the correction of direct-path reference signal is proposed, therefore to avoid the false alarm brought in target detection caused by side peak interference. Experimental results valid the proposed signal processing method.
WiFi (Wireless Fidelity) is widely deployed all the world. When it is utilized as external illuminaor in Passive Radar, its broadband singal make the high resolution of detection be obtained in both the range and Doppler domains. In this paper, the typical WiFi signal format and its characters are analyzed, then the theoretical signal model is setup. Based on the theory of bistatic passive radar, the relationship between typical IEEE 802.11 signals format and the characters of its Ambiguity Function (AF) is analyzed. Moreover, the position and amplitude of side peaks in time and frequency domain is analyzed and its causes from the signal structure is also discussed. In this paper, a method for suppressing the side peaks based on the correction of direct-path reference signal is proposed, therefore to avoid the false alarm brought in target detection caused by side peak interference. Experimental results valid the proposed signal processing method.
2012, 1(3): 232-237.
Two-Dimensional (2D) projection in temporal-Doppler plan is utilized to solve the effects of range-Doppler coupling and Doppler dispersion on radial velocity estimation for Linear Frequency Modulation (LFM) Ultra-WideBand (UWB) radar. First, temporal-Doppler 2D plane is got via 2D Fourier transform in fast-slow time domain. Second, 2D projection is performed to obtain energy focusing in UWB Doppler domain through mapping the UWB signal into narrow signal. Finally, radial velocities of moving targets are obtained according to the Doppler frequencies of the narrow signal after the mapping. This method not only solves the negative impacts of UWB radar Doppler dispersion on velocity estimation, but also voids that energy can not be accumulated in slow time since targets move along range resolution bins. Range profile of targets can also be got via the corresponding compensation with the estimated velocities. Besides, the velocity restriction is further derived according to the corresponding requirements. The simulation results illustrate the effectiveness of this method.
Two-Dimensional (2D) projection in temporal-Doppler plan is utilized to solve the effects of range-Doppler coupling and Doppler dispersion on radial velocity estimation for Linear Frequency Modulation (LFM) Ultra-WideBand (UWB) radar. First, temporal-Doppler 2D plane is got via 2D Fourier transform in fast-slow time domain. Second, 2D projection is performed to obtain energy focusing in UWB Doppler domain through mapping the UWB signal into narrow signal. Finally, radial velocities of moving targets are obtained according to the Doppler frequencies of the narrow signal after the mapping. This method not only solves the negative impacts of UWB radar Doppler dispersion on velocity estimation, but also voids that energy can not be accumulated in slow time since targets move along range resolution bins. Range profile of targets can also be got via the corresponding compensation with the estimated velocities. Besides, the velocity restriction is further derived according to the corresponding requirements. The simulation results illustrate the effectiveness of this method.
2012, 1(3): 238-245.
The existing multiple model hypothesis density filter can estimate the number and state of maneuvering targets at the same time. Yet its Sequential Monte Carlo (SMC) implementation involves clustering algorithm, which is unstable and time consuming, and may result in tracking target loss. To solve the problem, this paper proposes a Multiple Model (MM) Cardinality Balanced Multiple target Multi-Bernoulli (CBMeMBer) filter. When the clutter number of per-scan is less than 20 and detection probability is higher than 0.9, this lgorithm transmits the posterior density of maneuvering targets through a set of time-varying Bernoulli parameters, according to which, the targets state can be computed by simple operations, thus effectively avoids the clustering algorithm. Simulation results shows that compared with multiple model hypothesis density filter, the algorithm proposed decreased the OSPA distance which chooses to estimate tracking errors.
The existing multiple model hypothesis density filter can estimate the number and state of maneuvering targets at the same time. Yet its Sequential Monte Carlo (SMC) implementation involves clustering algorithm, which is unstable and time consuming, and may result in tracking target loss. To solve the problem, this paper proposes a Multiple Model (MM) Cardinality Balanced Multiple target Multi-Bernoulli (CBMeMBer) filter. When the clutter number of per-scan is less than 20 and detection probability is higher than 0.9, this lgorithm transmits the posterior density of maneuvering targets through a set of time-varying Bernoulli parameters, according to which, the targets state can be computed by simple operations, thus effectively avoids the clustering algorithm. Simulation results shows that compared with multiple model hypothesis density filter, the algorithm proposed decreased the OSPA distance which chooses to estimate tracking errors.
2012, 1(3): 246-252.
Deceptive jamming can get vivid jamming effect on Multiple-Input Multiple-Output (MIMO) radar with very low power. In order to remove those deceptive targets, one method based on signal jittering, data fusion and fake target notch filtering is proposed in this paper. Multiple orthogonal binary phase codes are used as transmitted signals, before each time of transmission each transmitter will choose one signal from all the orthogonal codes, images of echoes of all kinds of codes are detected with constant false alarm rate. Targets detected in images of echoes of all different signals are fused to determine to be real or not, fake targets will be nulled by notch filtering in the image, therefore, weak real targets can be detected in the next round of detection, in this way fusion and notch filtering are implemented again and again until no fake targets exist. The effect of deceptive jamming on radar will be removed completely. Simulation result testifies that the method based on signal jittering, data fusion and notch filtering can help MIMO radar remove deceptive jamming completely.
Deceptive jamming can get vivid jamming effect on Multiple-Input Multiple-Output (MIMO) radar with very low power. In order to remove those deceptive targets, one method based on signal jittering, data fusion and fake target notch filtering is proposed in this paper. Multiple orthogonal binary phase codes are used as transmitted signals, before each time of transmission each transmitter will choose one signal from all the orthogonal codes, images of echoes of all kinds of codes are detected with constant false alarm rate. Targets detected in images of echoes of all different signals are fused to determine to be real or not, fake targets will be nulled by notch filtering in the image, therefore, weak real targets can be detected in the next round of detection, in this way fusion and notch filtering are implemented again and again until no fake targets exist. The effect of deceptive jamming on radar will be removed completely. Simulation result testifies that the method based on signal jittering, data fusion and notch filtering can help MIMO radar remove deceptive jamming completely.
2012, 1(3): 253-261.
Aiming at the requirement of real-time signal detection in the passive surveillance system, a wideband array signal detection algorithm is proposed based on the concept of power focusing. By making use of the phase difference of the signal received by a uniform linear array, the algorithm makes the power of the received signal focused in the Direction Of Arrival (DOA) with improved cascade FFT. Subsequently, the probability density function of the output noise at each angle is derived. Furthermore, a Constant False Alarm Rate (CFAR) test statistic and the corresponding detection threshold are constructed. The theoretical probability of detection is also derived for different false alarm rate and Signal-to-Noise Ratio (SNR). The proposed algorithm is computationally efficient, and the detection process is independent of the prior information. Meanwhile, the results can act as the initial value for other algorithms with higher precision. Simulation results show that the proposed algorithm achieves good performance for weak signal detection.
Aiming at the requirement of real-time signal detection in the passive surveillance system, a wideband array signal detection algorithm is proposed based on the concept of power focusing. By making use of the phase difference of the signal received by a uniform linear array, the algorithm makes the power of the received signal focused in the Direction Of Arrival (DOA) with improved cascade FFT. Subsequently, the probability density function of the output noise at each angle is derived. Furthermore, a Constant False Alarm Rate (CFAR) test statistic and the corresponding detection threshold are constructed. The theoretical probability of detection is also derived for different false alarm rate and Signal-to-Noise Ratio (SNR). The proposed algorithm is computationally efficient, and the detection process is independent of the prior information. Meanwhile, the results can act as the initial value for other algorithms with higher precision. Simulation results show that the proposed algorithm achieves good performance for weak signal detection.
2012, 1(3): 262-269.
Location precision of radiant source is the primary performance of passive location system, and how to improve location precision is an important problem which always attracts attention. In three satellites TDOA (Time Difference Of Arrival) passive location system, location precision of single pulse location is limited by the error of TDOA measure. For improving location precision of radiant source, multi-TDOA location algorithm which estimates the position of target combining all the TDOAs is proposed in this paper. The new algorithm calculates three satellites positions at the arrival time of each pulse firstly, and then combines all pulsesTDOA equations and earth equation, lastly estimates the position of radiant source using least square algorithm. The result of simulations shows that the new algorithm can improve location precision of radiant source, and it is a steady and effective location method with higher location precision.
Location precision of radiant source is the primary performance of passive location system, and how to improve location precision is an important problem which always attracts attention. In three satellites TDOA (Time Difference Of Arrival) passive location system, location precision of single pulse location is limited by the error of TDOA measure. For improving location precision of radiant source, multi-TDOA location algorithm which estimates the position of target combining all the TDOAs is proposed in this paper. The new algorithm calculates three satellites positions at the arrival time of each pulse firstly, and then combines all pulsesTDOA equations and earth equation, lastly estimates the position of radiant source using least square algorithm. The result of simulations shows that the new algorithm can improve location precision of radiant source, and it is a steady and effective location method with higher location precision.
2012, 1(3): 270-276.
Sidelobe Suppression (SS) can be found on almost every Linear Frequency Modulated (LFM) pulse radar receiver|Shift-Frequency Jamming (SFJ) is an important method to realize deception jamming using the inherent coupling property between time-delay and frequency-shift of this LFM signal. So, the inter-ambiguity function (IAF) of LFM with SS using normalized parameters including time-delay rate and shift-frequency rate is analyzed. Then the 3:1 cone than weighted, Hamming weighted and cosine square weighted are focused and some parameters related to detection are analyzed. Compared with the none SS, the weighted shift-frequency signal to Jamming loss and the weighted shift-frequency jamming to noise loss are present like M function having the max shift-frequency rate point equal to 0.29. And the impact of weighted shift-frequency pulse-width loss are decide by none shift-frequency.
Sidelobe Suppression (SS) can be found on almost every Linear Frequency Modulated (LFM) pulse radar receiver|Shift-Frequency Jamming (SFJ) is an important method to realize deception jamming using the inherent coupling property between time-delay and frequency-shift of this LFM signal. So, the inter-ambiguity function (IAF) of LFM with SS using normalized parameters including time-delay rate and shift-frequency rate is analyzed. Then the 3:1 cone than weighted, Hamming weighted and cosine square weighted are focused and some parameters related to detection are analyzed. Compared with the none SS, the weighted shift-frequency signal to Jamming loss and the weighted shift-frequency jamming to noise loss are present like M function having the max shift-frequency rate point equal to 0.29. And the impact of weighted shift-frequency pulse-width loss are decide by none shift-frequency.
2012, 1(3): 277-282.
In this paper, theories of electromagnetic reflection and transmission as well as transmission line are adopted, a simulation method is designed to calculate power transmission coefficient and insertion phase shift, and also the mathematical formulas are deduced that the electromagnetic parameters of material used in radomes must be satisfied to remove the depolarization phenomenon, a single magnetic slab is used to discuss and verify the formulas. A special A sandwich radome, as a example, is calculated to analysis the effects of the magnetic and dielectric materials on the power transmission coefficient and the insertion phase shift. It is found that the phenomenon of depolarization can be avoided for A sandwich radome structure once when r r = (the relative complex permittivity of the magnetic material equals its relative complex permeability), and the power of transmission coefficient for magnetic material is better, the insertion phase shift is smoother, and the property of transmission performance is better than those of the electric material. Finally, the commercial software HFSS further verifies the correctness of the conclusions and validity of the method.
In this paper, theories of electromagnetic reflection and transmission as well as transmission line are adopted, a simulation method is designed to calculate power transmission coefficient and insertion phase shift, and also the mathematical formulas are deduced that the electromagnetic parameters of material used in radomes must be satisfied to remove the depolarization phenomenon, a single magnetic slab is used to discuss and verify the formulas. A special A sandwich radome, as a example, is calculated to analysis the effects of the magnetic and dielectric materials on the power transmission coefficient and the insertion phase shift. It is found that the phenomenon of depolarization can be avoided for A sandwich radome structure once when r r = (the relative complex permittivity of the magnetic material equals its relative complex permeability), and the power of transmission coefficient for magnetic material is better, the insertion phase shift is smoother, and the property of transmission performance is better than those of the electric material. Finally, the commercial software HFSS further verifies the correctness of the conclusions and validity of the method.
2012, 1(3): 283-291.
To resolve the problem of sampling speed and real-time continuous mass storage in large instantaneous bandwidth radar signal direct Intermediate Frequency (IF) sampling, a wideband radar intermediate frequency signal acquisition and real-time storage system is developed in this paper. Firstly, according to bandpass signals alias-free sampling theorem, the sampling frequency is determined. And then the digital quadrature demodulation, buffer and high speed real-time continuous mass storage design scheme is proposed. Based on chassis server platform, this system uses QDRII SRAM as the buffer storage, and adopts PCIe to be the data transmission channel. It is verified in a phased array radar experimental system that this system makes a good performance and gives a feasible schema for wideband radar data acquisition.
To resolve the problem of sampling speed and real-time continuous mass storage in large instantaneous bandwidth radar signal direct Intermediate Frequency (IF) sampling, a wideband radar intermediate frequency signal acquisition and real-time storage system is developed in this paper. Firstly, according to bandpass signals alias-free sampling theorem, the sampling frequency is determined. And then the digital quadrature demodulation, buffer and high speed real-time continuous mass storage design scheme is proposed. Based on chassis server platform, this system uses QDRII SRAM as the buffer storage, and adopts PCIe to be the data transmission channel. It is verified in a phased array radar experimental system that this system makes a good performance and gives a feasible schema for wideband radar data acquisition.
2012, 1(3): 292-300.
A novel algorithm for larger size target imaging in sparse aperture is presented in this paper for Inverse Synthetic Aperture Radar (ISAR). In the proposed method, azimuth compressing is done in the range frequency domain to avoid Migration Through Range Cell (MTRC), and Compress Sensing (CS) is introduced to take place of FFT to reduce the Peak Side Lobe Ratio (PSLR), meanwhile a basis matrix changing with the range frequency is constructed to eliminate the coupling between range frequency and azimuth time. Simulation results validate the feasibility of the approach.
A novel algorithm for larger size target imaging in sparse aperture is presented in this paper for Inverse Synthetic Aperture Radar (ISAR). In the proposed method, azimuth compressing is done in the range frequency domain to avoid Migration Through Range Cell (MTRC), and Compress Sensing (CS) is introduced to take place of FFT to reduce the Peak Side Lobe Ratio (PSLR), meanwhile a basis matrix changing with the range frequency is constructed to eliminate the coupling between range frequency and azimuth time. Simulation results validate the feasibility of the approach.
2012, 1(3): 301-308.
The Pixel Relativity (PR) measurement of SAR image, which is the key of the despeckling techniques based on weighted average, is researched in three aspects. Firstly, the rationality of ratio PR model is expounded, and two new ratio PR models, which are the LOG-domain Gaussian model and the pixel similarity probability model, are proposed. Meanwhile, the Probability Density Function (PDF) of SAR image and the PDF of the ratio between pixels are transformed into ratio PR models. Then, in order to evaluate the four ratio PR models, the weighted maximum likelihood filters are designed using the PR. Finally, a novel method, performed by calibrating the maximum location of the PR model, is introduced to improve the radiation preservation of those models whose maximum do not locate at 1. The effectiveness of the two proposed PR models and the approach to calibrate the maximum location of the PR model, are indicated by the theoretical analysis and experimental comparison.
The Pixel Relativity (PR) measurement of SAR image, which is the key of the despeckling techniques based on weighted average, is researched in three aspects. Firstly, the rationality of ratio PR model is expounded, and two new ratio PR models, which are the LOG-domain Gaussian model and the pixel similarity probability model, are proposed. Meanwhile, the Probability Density Function (PDF) of SAR image and the PDF of the ratio between pixels are transformed into ratio PR models. Then, in order to evaluate the four ratio PR models, the weighted maximum likelihood filters are designed using the PR. Finally, a novel method, performed by calibrating the maximum location of the PR model, is introduced to improve the radiation preservation of those models whose maximum do not locate at 1. The effectiveness of the two proposed PR models and the approach to calibrate the maximum location of the PR model, are indicated by the theoretical analysis and experimental comparison.
2012, 1(3): 309-313.
Time-domain algorithms have great application prospect in Ultra Wide Band Synthetic Aperture Radar (UWB SAR) imaging for its advantages such as perfect focusing and perfect motion compensation. We could adopt the flat surface assumption to simplify the imaging geometric model, when undulating terrain is imaged using time-domain algorithms. Nevertheless, the flat surface assumption leads to geometric errors, thereby affecting the imaging results. This paper studies the effects of this assumption on time-domain imaging algorithms, points out that it leads to position offset problem in the case of linear aperture, and it even leads to target defocusing problem in the case of non-linear aperture. The expression of position offset is given in this paper, as well as the restriction of the maximal offset of the non-linear aperture and the maximum elevation of the area in order to focus the targets. The conclusions are validated by simulated data, which is processed by one kind of time-domain algorithms, namely Back Projection (BP) algorithm.
Time-domain algorithms have great application prospect in Ultra Wide Band Synthetic Aperture Radar (UWB SAR) imaging for its advantages such as perfect focusing and perfect motion compensation. We could adopt the flat surface assumption to simplify the imaging geometric model, when undulating terrain is imaged using time-domain algorithms. Nevertheless, the flat surface assumption leads to geometric errors, thereby affecting the imaging results. This paper studies the effects of this assumption on time-domain imaging algorithms, points out that it leads to position offset problem in the case of linear aperture, and it even leads to target defocusing problem in the case of non-linear aperture. The expression of position offset is given in this paper, as well as the restriction of the maximal offset of the non-linear aperture and the maximum elevation of the area in order to focus the targets. The conclusions are validated by simulated data, which is processed by one kind of time-domain algorithms, namely Back Projection (BP) algorithm.
2012, 1(3): 314-322.
GEOsynchronous Circular SAR (GEOCSAR), having a high orbit, operating in a slant ellipse, and imaging in spherical surface, should be newly modeled to assess the resolution performance. In this paper, starting from modeling geometry, a function of slant range difference and orientation angle is deduced. Then we can obtain the three dimensional point spread function and make a conclusion of resolution affected by both sinc function and bessel function of first kind. Lastly, resolution with the variation of location of target, bandwidth, radius of orbit, and integral time is analyzed detailedly. Finally raw signal simulations show the validity of theoretical model.
GEOsynchronous Circular SAR (GEOCSAR), having a high orbit, operating in a slant ellipse, and imaging in spherical surface, should be newly modeled to assess the resolution performance. In this paper, starting from modeling geometry, a function of slant range difference and orientation angle is deduced. Then we can obtain the three dimensional point spread function and make a conclusion of resolution affected by both sinc function and bessel function of first kind. Lastly, resolution with the variation of location of target, bandwidth, radius of orbit, and integral time is analyzed detailedly. Finally raw signal simulations show the validity of theoretical model.
2012, 1(3): 323-328.
The single-transmitting-dual-receiving polarimetric SAR system has only two receving channels, which induces lack of prior information forcalibration. Due to the polarization diversity of this kind of system (which operates on different dual and compact polarimetric modes), there has not a general algorithm currently. In this paper, a new general calibration algorithm is proposed for single-transmitting-dual-receiving polarimetric SAR system, which can be widely applied to diverse polarization modes. The transmitting and receiving distortion can be estimated using trihedral, 0 dihedraland 45 dihedral as ideal point targets without any assumption on the scene and system. The basic principle of this new algorithm is induced theoretically. The effect of calibrator error on the distortion estimation is analyzed by simulation. Point targetscalibration results and polarization signatures verify this algorithm.
The single-transmitting-dual-receiving polarimetric SAR system has only two receving channels, which induces lack of prior information forcalibration. Due to the polarization diversity of this kind of system (which operates on different dual and compact polarimetric modes), there has not a general algorithm currently. In this paper, a new general calibration algorithm is proposed for single-transmitting-dual-receiving polarimetric SAR system, which can be widely applied to diverse polarization modes. The transmitting and receiving distortion can be estimated using trihedral, 0 dihedraland 45 dihedral as ideal point targets without any assumption on the scene and system. The basic principle of this new algorithm is induced theoretically. The effect of calibrator error on the distortion estimation is analyzed by simulation. Point targetscalibration results and polarization signatures verify this algorithm.
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