Performance Of Radar System Research Articles

Constrained Radar Waveform Design for Range Profiling

Range profiling refers to the measurement of target response along the radar slant range. It plays an important role in automatic target recognition. In this paper, we consider the design of transmit waveform to improve the range profiling performance of radar systems. Two design metrics are adopted for the waveform optimization problem: one is to maximize the mutual information between the received signal and the target impulse response (TIR); the other is to minimize the minimum mean-square error for estimating the TIR. In addition, practical constraints on the waveforms are considered, including an energy constraint, a peak-to-average-power-ratio constraint, and a spectral constraint. Based on minorization-maximization, we propose a unified optimization framework to tackle the constrained waveform design problem. Numerical examples show the superiority of the waveforms synthesized by the proposed algorithms.

Clutter Mitigation Based on Spectral Depolarization Ratio for Dual-Polarization Weather Radars

In this article, a spectral polarimetric filter named moving spectral depolarization ratio (MsDR) filter is proposed to mitigate the effects of clutter and noise for dual-polarization weather radar without cross-polar measurements. The filter is based on a spectral polarimetric variable termed as spectral depolarization ratio (sDR). sDR can be estimated by any polarimetric weather radar, making the MsDR filter widely applicable. Taking advantage of the spectral polarimetric features and the range-Doppler continuity of precipitation, the MsDR filter is implemented in the range-Doppler spectrogram. The performance of the MsDR filter is assessed using data collected by 1) an X-band full-polarimetric radar interfered by narrow-band clutter (both stationary and moving) and sidelobe wind turbine clutter; 2) a C-band operational dual-polarization radar affected by radio frequency interference. In addition, the implementation of the MsDR filter is straightforward, and the computational complexity is relatively low. Hence, the MsDR filter has great potential to be applied in real-time for operational radar systems at different frequencies.

Suppressing Range Ambiguity by Pattern Synthesis for SAR via Semidefinite Relaxation

Range ambiguities severely degrade the performance of the synthetic aperture radar (SAR) system. To make an improvement without increasing the system complexity, antenna pattern synthesis is a feasible method. To this end, a novel algorithm that can shape the mainlobe and suppress the range ambiguities simultaneously by relaxing the problem as a semidefinite relaxation (SDR) programming problem is proposed here for the first time. Compared to the algorithm with global optimization, the presented algorithm could find the desired pattern without the large occupation of computing resources and has great potential in raising the performance of SAR system. In addition, some simulations are carried out, and the results prove that the proposed algorithm has the superior ability to suppress the range ambiguities while controlling the beamwidth and dynamic range ratio (DRR).

Radar Main-Lobe Jamming Suppression Based on Adaptive Opposite Fireworks Algorithm

In the presence of the main lobe jamming, the performance of the modern radar system would degrade significantly. In this study, a blind source separation (BSS) method based on an Adaptive Opposite Fireworks Algorithm (AOFWA) is proposed to address the problem of ineffective target echo detection when the radar is subjected to main lobe jamming. First, a signal model for BSS applied in the anti-main lobe jamming is provided, and the number of source signals is estimated. Then, an adaptive opposite learning operator is designed to improve the optimization capability and convergence speed of the basic Fireworks Algorithm (FWA). Finally, pulse compression is performed for separated signals to achieve peak detection. The simulation result shows that the proposed algorithm can effectively extract target echo under suppression jamming and deception jamming, and the separation precision is relatively high, and its convergence speed is superior.

Radar code design to optimise detection under whitened similarity constraint

An active sensing system, such as radar, extracts the useful features of the targets of interest, by transmitting a certain waveform to a particular area and analysing the returned signal. There are two factors that are critical to the system performance, namely the receive filter and the transmitted waveform. Transmitted signal is among the most interesting factor affecting the radar system performance in complex environments. The waveform design problem is an important stage in the performance of cognitive radars. Here, the matched illumination approach is studied which specially addresses the issue of adaptive waveform design to maximise the signal-to-disturbance ratio that finally leads to an increased probability of detection. Different constraints on the designed waveform have been introduced in the literature. However, the focus is on the similarity constraint that controls the ambiguity function and modulus variations of the devised code. In more details, it is shown that this kind of constraint should be written based on the estimated background covariance matrix leading to a proposed whitened similarity constraint. It is shown by simulation that the proposed whitened constraint outperforms the well-known similarity one in resultant ambiguity function properties and probability of detection, assuming the same environmental conditions.

Modeling of Monopulse Radar Signals Reflected from Ground Clutter in a Time Domain Considering Doppler Effects

To evaluate the performance of a monopulse radar system, it is necessary to accurately model radar return signals from the ground surface in a time domain. In this paper, we propose a numerical method to model these return signals including radar radio frequency specifications, such as the pulse repetition interval, frequency, and polarization, as well as the antenna geometry, the ground clutter backscattering characteristics, and so on. The Doppler effect is also incorporated into the signal generation scheme because of the dynamics of the platform/clutter and the antenna orientation. The Doppler frequency shift caused by the ground clutter is modeled by employing the time correlation of the received signals. In some scenarios, the monopulse signals are generated and numerically examined. For real radar application, the effect of the platform’s roll stabilization on the monopulse signals is investigated based on the proposed signal generation scheme.

Compressed Sensing MIMO Radar System for Extended Target Detection

The article presents a multiple-input–multiple-output (MIMO) radar system for which transmit-receive beamforming in conjunction with a compact frequency domain representation of the radar signals yields a sparse representation of the radar scene. Compressed sensing (CS) methods are then applied to design the radar waveforms for detecting the presence within the radar scene of multiple extended targets with known impulse responses, as well as for designing the receiver filters to reconstruct the radar scene. The detection performance of the MIMO radar system based on noisy scene reconstruction is illustrated with numerical examples obtained from simulations. These show that the receiver operating characteristic curves obtained using the MIMO radar waveforms and receiver filters designed based on CS methods outperform those obtained when statically defined waveforms and receiver filters are used for target detection in the reconstructed scene.

Calibration of an Airborne Interferometric Radar Altimeter over the Qingdao Coast Sea, China

Calibration/Validation (Cal/Val) of satellite altimeters is fundamental for monitoring onboard sensor performance and ensuring long-term data quality. As altimeter technology has been evolving rapidly from profile to wide swath and interferometric altimetry, different requirements regarding Cal/Val have emerged. Most current Cal/Val technology has been developed for conventional profile altimeters, whereby satellite observations are compared against measurements at one point along orbit lines. However, the application of this type of Cal/Val technique to swath interferometric altimeters with two-dimensional measurements is difficult. Here, we propose a new strategy for the evaluation of interferometric altimeters based on comparison of wave-induced sea surface elevation (WSSE) spectra from one- and two-dimensional measurements. This method assumes that the WSSE variance of an equilibrium wave field is uniform and can be measured equivalently in the space or time domains. The method was first tested with simulated data and then used to evaluate the performance of an airborne interferometric radar altimeter system (AIRAS) using Global Navigation Satellite System (GNSS) buoy measurements. The differences between the WSSE variances from the AIRAS and two GNSS buoys were below 8 cm2, corresponding to a standard deviation of 2.8 cm, which could serve as a reference for the WSSE error over the scale range of waves. The correlation coefficient between the AIRAS and GNSS buoys was approximately 0.90, indicating that the error was small relative to the WSSE signals. In addition, the sea surface height (SSH) difference measured by the AIRAS was compared with that derived from the GNSS buoys at two sites. The results indicated that the error of the SSH difference was 3 cm. This approach represents a possible technique for the Cal/Val of future spaceborne/airborne interferometric altimeters; however, additional experiments and applications are needed to verify the feasibility of this method.

Time and Aperture Resource Allocation Strategy for Multitarget ISAR Imaging in a Radar Network

In modern high-dynamic battlefield environments, the time and aperture resources of multifunction radar systems are often viewed as important system resources. In this paper, a time and aperture resource allocation strategy for multitarget inverse synthetic aperture radar (ISAR) imaging that incorporates requirements for distributed network radar multitarget imaging tasks is proposed to improve the efficiency of a radar system. First, the resolution requirement of the target is determined based on the feature recognition of the target, and an allocation model of the aperture resource for the distributed networking conditions is established by analyzing the relationship between the resolution and the aperture resource. Second, by analyzing the requirements of target sparse ISAR imaging, time resources are incorporated into the resource allocation model. Third, a multiobjective function model for the multitarget imaging of networked radars with the least resource consumption and the largest number of imaging tasks is established. Finally, the objective function is sorted according to the degree of importance by a lexicographic strategy, and a lexicographic genetic algorithm is proposed to solve the optimization problem. The simulation results show that the proposed algorithm outperforms the traditional algorithm in terms of the effective utilization of radar resources and the radar system performance.

Monitoring the differential reflectivity and receiver calibration of the German polarimetric weather radar network

Abstract. It is a challenge to calibrate differential reflectivity ZDR to within 0.1–0.2 dB uncertainty for dual-polarization weather radars that operate 24∕7 throughout the year. During operations, a temperature sensitivity of ZDR larger than 0.2 dB over a temperature range of 10 ∘C has been noted. In order to understand the source of the observed ZDR temperature sensitivity, over 2000 dedicated solar box scans, two-dimensional scans of 5∘ azimuth by 8∘ elevation that encompass the solar disk, were made in 2018 from which horizontal (H) and vertical (V) pseudo antenna patterns are calculated. This assessment is carried out using data from the Hohenpeißenberg research radar which is identical to the 17 operational radar systems of the German Meteorological Service (Deutscher Wetterdienst, DWD). ZDR antenna patterns are calculated from the H and V patterns which reveal that the ZDR bias is temperature dependent, changing about 0.2 dB over a 12 ∘C temperature range. One-point-calibration results, where a test signal is injected into the antenna cross-guide coupler outside the receiver box or into the low-noise amplifiers (LNAs), reveal only a very weak differential temperature sensitivity (<0.02 dB) of the receiver electronics. Thus, the observed temperature sensitivity is attributed to the antenna assembly. This is in agreement with the NCAR (National Center for Atmospheric Research) S-Pol (S-band polarimetric radar) system, where the primary ZDR temperature sensitivity is also related to the antenna assembly (Hubbert, 2017). Solar power measurements from a Canadian calibration observatory are used to compute the antenna gain and to validate the results with the operational DWD monitoring results. The derived gain values agree very well with the gain estimate of the antenna manufacturer. The antenna gain shows a quasi-linear dependence on temperature with different slopes for the H and V channels. There is a 0.6 dB decrease in gain for a 10 ∘C temperature increase, which directly relates to a bias in the radar reflectivity factor Z which has not been not accounted for previously. The operational methods used to monitor and calibrate ZDR for the polarimetric DWD C-band weather radar network are discussed. The prime sources for calibrating and monitoring ZDR are birdbath scans, which are executed every 5 min, and the analysis of solar spikes that occur during operational scanning. Using an automated ZDR calibration procedure on a diurnal timescale, we are able to keep ZDR bias within the target uncertainty of ±0.1 dB. This is demonstrated for data from the DWD radar network comprising over 87 years of cumulative dual-polarization radar operations.

Versatile Dual-Receiver 94-GHz FMCW Radar System With High Output Power and 26-GHz Tuning Range for High Distance Applications

Airborne applications demand exceptional overall radar system performance and eminently high output power for high range target detection. The frequency modulated continuous wave (FMCW) radar system presented in this article is capable of achieving this task due to its high output power at 94-GHz center frequency with over 26-GHz tuning range. Nevertheless, the radar still provides a small form factor and low power consumption of 4.25 W at 5 V single Universal Serial Bus (USB) supply. The key system component is a Silicon Germanium (SiGe) bipolar complementary metal-oxide-semiconductor (BiCMOS) monolithic microwave integrated circuit (MMIC) that contains a 94-GHz voltage-controlled oscillator (VCO), and a 27-GHz VCO for dual-loop phase-locked loop (PLL) stabilization, a power amplifier (PA), and two receive mixers. It generates frequency ramps between 83- and 109-GHz with a maximum output power of 19.7 dBm at its output after the bond wires on the printed circuit board (PCB) and 14.8-dBm output power at the radar’s transmit (TX)-waveguide WR-10-flange. The sensor was also tested in a temperature range from −40 °C to +70 °C with menial deviation. Thus, the system offers high system dynamic range and far distance target detection range. Following a detailed system description, we finally present the FMCW range and Doppler measurements performed with the presented radar sensor as well as the application on unmanned aerial vehicles (UAVs) for flight altitude control and as airborne collision avoidance system (ACAS).

A methodology for optimal deployment and effectiveness evaluation of air defence resources using game theory

Planning for the deployment of air defence (AD) assets in areas of operation to achieve maximum protection coverage against enemy air threats is an important problem in military science. A three-stage approach to address the problem is proposed: a static methodology to deploy AD resources to maximize the coverage and performance of radar systems under various terrain conditions is studied, followed by the second stage that considers the dynamics of enemy air attacks and Electronic Warfare (EW) conflict that ensues between the attacker and defender modeled using game theory. In the final stage the conflict scenarios modelled using game theory are represented as AD wargames and experimented on a battlefield simulation test-bed called Air Warfare Simulation System (AWSS) to assess the AD effectiveness in operations. The first stage uses a coverage-based optimization, and the second stage is modelled using game theory. The strategies of the attacker (enemy aircraft) and defender (sensors-radars grid and weapons-missiles grid) in the EW operations as Electronic Counter Measures and Electronic Counter-Counter Measures in a game-theoretic setting are illustrated using several scenarios.

Main lobe jamming suppression via blind source separation sparse signal recovery with subarray configuration

The performance of the modern radar systems will degrade significantly in the presence of main lobe jamming. In this study, a new methodology is introduced to suppress multiple main lobe jammings while accomplishing the directions of arrival (DOAs) estimation of the multiple targets. Specifically, the signal model of a specific subarray configuration accounting for jamming and target signals is developed. Then, blind source separation method is utilised to separate the target and jamming signals in each subarray. Furthermore, the separated target signals of all subarrays are jointly imposed to estimate DOAs of targets through resorting to sparse signal recovery approach. Finally, numerical simulations are provided to assess the performance of the proposed algorithm exhibiting the favourable capabilities in terms of the strong main lobe jamming suppression and the DOAs estimation of multiple targets.

다기능 레이다의 디지털 능동 위상 배열 안테나에 최적화된 이중 채널 부엽 차단 빔 패턴 형성에 관한 연구

To prevent the detection performance of radar systems from being degraded by interference signals appearing in the side-lobe of the antenna, an additional side-lobe blanking(SLB) antenna is often added and operated alongside the main antenna. In this paper, the SLB antenna composed of array elements within the main antenna is discussed. Using the structural features of the digital active phased array antenna implies that no additional antenna is physically added. Optical channels are also employed to simultaneously form multiple digital beams for the main and the SLB antennas. A structure for the SLB antenna to cover all the side-lobes of the main antenna pattern was designed using two SLB beam patterns, and weight distributions corresponding to each element were calculated. Applying the weight distributions of the designed SLB antenna, the far-field pattern was reviewed through near field tests. As a result and as shown in the simulation, it was confirmed that, even during beam steering, all the side-lobes of the main antenna were covered by the beam patterns of the dual-channel SLB antenna in all regions of the 2D space.

Simultaneous Radar-Communication Systems Using Controlled Chaos-Based Frequency Modulated Waveforms

With the increase in demand for spectral resources and bandwidth constraints, efficient solutions for the coexistence of radar and communication systems are needed. Simultaneously, the development of multifunctional radio frequency (RF) systems with less hardware have received considerable attention. Most previous work on coexistence has focused on hardware design and mitigation of interference between radar and communication systems. This work proposes, a novel method for controlling a chaotic trajectory, which allows for the coexistence of both radar and communication systems. Binary information can be encoded in a chaotic state by adjusting its trajectory. In this approach, a state variable is selected to control the trajectory and generate a controlled chaos-based frequency modulated (CCBFM) waveform for joint radar-communication system signal transmission. We also design a communication receiver to decode the information and a radar receiver that extracts the signature of the target are designed accordingly. The performance of the controlled chaotic communication system is assessed in terms of the bit error ratio (BER). The analysis of the communication system shows that the CCBFM receiver performs reasonably well compared to a half-sine pulse frequency modulated (HSPFM) receiver. Analysis of the radar system performance is assessed using the entropy of the target's signature. The use of a CCBFM waveform leads to accurate target detection and classification for a signal-to-noise ratio as low as -30 dB. These analyses demonstrate that a CCBFM waveform can be successfully used for joint radar-communication systems in a shared spectrum.

Radar Waveform Optimization for Joint Radar Communications Performance

We develop and present a radar waveform design method that optimizes the spectral shape of the radar waveform so that joint performance of a cooperative radar communications system is maximized. The continuous water-filling (WF) spectral-mask shaping method presented in this paper is based on the previously derived spectral-mask shaping technique. However, the method presented in this paper is modified to utilize the continuous spectral water-filling algorithm to improve communications performance. We also introduce additional practical system constraints on the autocorrelation peak side-lobe-to-main-lobe ratio and radar waveform spectral leakage. Finally, we perform a numerical study to compare the performance of the continuous WF spectral-mask-shaping method with the previously derived method. The global estimation rate, which also accounts for non-local estimation errors, and the data rate capture radar and communications performance respectively.

Reinforcement Learning-Based Anti-Jamming in Networked UAV Radar Systems

The networked unmanned aerial vehicle (UAV) radar system may exploit inter-UAV cooperation for enhancing information acquisition capabilities, meanwhile its inter-UAV communications may be interfered with by external jammers. This paper is devoted to quantifying and optimizing the anti-jamming performance of networked UAV radar systems in adversarial electromagnetic environments. Firstly, instead of using the conventional metric of signal-to-interference ratio (SIR), this paper explores use of the theory of radar information representation as the basis of evaluating the information acquisition capabilities of the networked UAV radar systems. Secondly, this paper proposes a modified Q-Learning method based on double greedy algorithm to optimize the anti-jamming performance of the networked UAV radar systems, through joint programming in the frequency-motion-antenna domain. Simulation results prove the effectiveness of the algorithm in two different networking scenarios.

Effects of Plasma Sheath on Parameter Estimations of Linear Frequency Modulation Pulse Signal

A space vehicle traveling in the atmosphere at hypersonic speed is enveloped by a time-varying plasma sheath, and the performance of onboard radar reconnaissance system will be significantly interrupted. Plasma sheath would generate parasitic modulations of the amplitude and phase of radar signals. Therefore, based on the transmission coefficient of radar wave in time-varying plasma sheath, the Wigner–Hough transform and autocorrelation time-domain signal detection method are used to estimate the frequency- and time-domain parameters of the linear frequency modulation (LFM) pulse signal statistically. A variation rule of the estimation errors of signal parameters is established under various plasma characteristics parameter and frequency and bandwidth of LFM waves. The critical signal-to-noise ratio that is the threshold value for failure of signal parameter estimation has been accurately obtained for different electron densities and radar frequencies. The calculation results could provide useful information for onboard electronic reconnaissance system in further applications.

Calibration of MIMO Fully Polarimetric Imaging Radar Systems with Passive Targets

Abstract The performance of polarimetric imaging radar systems depends greatly on how well they are calibrated. The complexity of the calibration procedure scales with the number of send and receive antennas, i. e. the size of the antenna array. This article proposes a practical and effective approach for calibrating a polarimetric near field MIMO imaging radar using only two simple passive targets. The calibration requires four measurement steps: An empty space measurement for suppressing direct mutual coupling between the channels. An offset short calibration with the specular reflection of a planar metal plate for the co-polarized channels. Two measurements with a dihedral reflector inclined at different angles for the cross-polarized calibration.

Non-searching coherent integration method for maneuvering target detection by using non-uniformly resampling technique

It is well known that, long-time integration improves the detection performance of radar system, which is however limited by the range migration (RM) and Doppler frequency migration (DFM) caused by target's high velocity and acceleration. To solve this problem, this paper proposed a three-dimensional modified cross correlation function (3DMCCF) method for maneuvering radar targets. In this method, we define a new cross correlation function under a designing frame based on non-uniformly resampling technique. By using the new function, the target's RM and DFM can be eliminated at the same time. The resulting signal is a three-dimensional complex sinusoid. Finally the integration is achieved efficiently by performing inverse fast Fourier transforms (IFFTs) and fast Fourier transforms (FFTs). The proposed method can work in low signal to noise ratio (SNR) environment and is applicable for multi-target scene. Compared with the generalized Radon Fourier transform (GRFT) and the Radon Lv's distribution (RLVD) algorithms, the proposed method is free from searching approach and has lower computational complexity. The effectiveness of the proposed method is demonstrated by simulations and real-data processing.