Hypersonic vehicle-(HSV) borne synthetic aperture radar (SAR) with spiral trajectory has significant advantages, such as wide angle coverage, flexible observation geometry, and rich spatial information acquisition. However, the high mobility of the platform can cause many problems for SAR imaging. To address these issues, this letter first establishes a suitable vector model for HSV SAR with spiral trajectory. We proposed an innovative method based on 2-D Lagrange interpolation to address cross–coupling and spatial variation caused by rapid altitude and velocity changes. The performance of the method is demonstrated through simulations and real data experiments. The proposed solution has significant advancements in the application of HSV SAR.

Due to the large diving trajectory, the design of the imaging algorithm remains an exceptionally difficult task for hypersonic synthetic aperture radar (SAR). In this article, an accurate range model that accounts for the impact of higher-order motion factors on imaging performance is established. Based on the model, the signal characteristics are analyzed, which indicates that the design of the imaging approach faces greatly challenges such as severe cross-couplings and significant spatial variations (SVs). In view of these issues, a time–frequency hybrid domain imaging algorithm (TFHDIA) is proposed for hypersonic vehicle (HSV)-borne SAR systems with a large diving trajectory. The cross-couplings are significantly reduced by azimuth preprocessing. The 2-D SV in the range cell migration (RCM) and the first-order SV in the Doppler parameters (DPs) are eliminated through the fractional Fourier transform (FrFT) and the extended keystone transform (EKT). Additionally, the higher-order SVs of DPs are removed by the phase filter bank, which includes range, azimuth, and cross-coupling spatially variant phase error compensation filters. The proposed algorithm exhibits strong capabilities in eliminating SVs and effectively reducing cross-coupling, making it particularly suitable for HSV SAR systems with large diving trajectories. Simulation and actual acquired data results validate the efficacy of the proposed algorithm.

Compared with conventional synthetic aperture radar (SAR) systems, hypersonic vehicle-borne (HSV) SAR with a spiral trajectory offers unique advantages, including high maneuverability, large detection range, and diverse observation views, enabling precise three-dimensional (3-D) SAR coordinate positioning. However, the high maneuverability of the spiral trajectory poses significant challenges, such as model mismatch, image defocusing, and positioning algorithm failures. To address these challenges, a geometric vector model of HSV SAR with a spiral trajectory is established, and the corresponding signal and trajectory characteristics are analyzed. Subsequently, the 3-D coordinate positioning approach based on HSV SAR with spiral trajectory is proposed. The proposed method achieves target positioning via two-dimensional (2-D) multi-view imaging, SAR target matching, and 3-D coordinate calculation. This method is relatively novel and provides superior imaging and positioning performance. Simulation, real data, and semi-real data experiments are given to validate the effectiveness of the proposed method.

Maneuver provides flexibility for highly squinted synthetic aperture radar (SAR) and also means complicated signal characteristics in the echo, especially for ground moving target imaging (GMTIm). This article analyzes the interaction of parameters between the maneuvering platform and the moving target. The analysis suggests that three key factors should be taken into account: azimuth spectrum aliasing, Doppler centroid ambiguity, and high-order errors. To deal with these challenges, a novel GMTIm methodology for maneuvering platform is presented. The proposed approach employs an advanced parameter estimation method based on the extended generalized high-order ambiguity function (EGHAF), which enables simultaneous estimation of high-order phase coefficients across all orders in low signal-to-noise ratio (SNR) conditions through 2-D extension. Due to the estimation and compensation for higher order phases, which are usually ignored in conventional methods, the proposed method is more suitable for moving target imaging with maneuvering platforms. The superiority of the proposed approach is verified by simulation and real data results.

Hypersonic glide vehicle usually flies in a spiral trajectory to avoid being detected, reconnoitered, or jammed. However, due to its complex flight characteristics, the hypersonic glide vehicle-borne (HGV) synthetic aperture radar (SAR) faces several new challenges, including the complicated geometric model, serious cross-coupling, and significant spatial variation. To address these issues, a precise range model with large maneuvering parameters is first derived on the basis of the kinematic features, indicating that the signal properties change greatly. Then, a novel nonuniform fast Fourier transform (NUFFT)-based approach performed in the 2-D frequency domain is proposed. The cross-coupling terms are decoupled according to Lagrange mean value and the spatial variations are eliminated by 2-D NUFFT operation, which has a high depth-of-focusing and is more effective for HGV SAR with spiral trajectory. The effectiveness of the proposed approach is substantiated through a series of computer simulations and semi-real data experiments.

Abstract In this study, a dual‐function radar‐communications (DFRC) system based on the circulating code array is presented to address the contradiction between radar and communications system in beam scanning and beam coverage. Processed orthogonal frequency‐division multiplexing (OFDM) signal is transmitted by the circulating code array as the base signal to improve the data rate. Following the spatial angle of the communication receiver, the communication symbols are modulated to part of OFDM signal subcarriers occupying a specific frequency band. A significant property of the circulating code array, which provides a relationship between the baseband frequency of the base signal and the spatial angles, implements a basis for safe telecommunication transmission towards the cooperative receiver and demodulation. Moreover, the circulating code array transmits the same signal and introduces the same time interval between adjacent array elements. Therefore, the complex problems of multi‐dimensional orthogonal signal design in the traditional multiple‐input‐multiple‐output‐based DFRC system design are transformed into a simple base signal design. Finally, an omnidirectional coverage pattern is obtained. Thus, whether the communication receiver is in the mainlobe or the sidelobe of the radar beam, the communication connection can be established between the designed DFRC system and the communication users. The performance of the described DFRC system is verified through theoretical analysis and simulations.

As a frontier technology in radar imaging, hypersonic vehicle-borne (HSV) synthetic aperture radar (SAR) has several practical issues to be dealt with, namely, ground resolution capability, pulse repetition frequency (PRF) selection, and beam pointing description, especially for the near-vertical diving trajectory because of the extremely small angle between the velocity and slant range vectors. Moreover, its focusing approach design is greatly challenged by very large cross-couplings and spatial variations. Considering these practical problems, the constraints between system performance and parameter selection are analyzed firstly to obtain the parameter optimization procedure and avoid system design deviation. Then, a frequency radius/angle algorithm (FRAA) is devised, which is an extension of the radius/angle algorithm (RAA) performed in two-dimensional (2-D) frequency domain. In the FRAA, new range equation and 2-D frequency interpolation function are reconstructed with high accuracy by quadratic fitting and 3-D expansion. Compared with RAA, FRAA is more suitable for the HSV SAR with near-vertical diving trajectory. Simulation results verify the effectiveness of the proposed approach.

For synthetic aperture radiometer, radio frequency interference (RFI) seriously contaminates the observed data and affects the quality of the brightness temperature (BT) image. CLEAN algorithm is usually used to mitigate the Gibbs effect generated by RFI. However, the closely distributed RFI sources cannot be well mitigated by the original CLEAN algorithm. This letter proposes an improved adaptive CLEAN algorithm to enhance the performance of RFI mitigation, especially the closely distributed RFI sources. The loop factor is forced to synchronize with residual BT of RFI for every iteration to avoid over mitigation. Over mitigation can result in a BT vacancy area or an extra BT point generated at the position of RFI. Soil Moisture and Ocean Salinity (SMOS) L1B real data are applied to verify the effectiveness of the improved CLEAN algorithm. The simulation shows that the improved CLEAN algorithm can be competent in eliminating isolated and closely distributed RFIs better than the classic CLEAN algorithm, and the over mitigation problem is solved by the proposed method.

Unknown motions will make the synthetic aperture radar (SAR) images of ground moving targets defocused. The target signal easily exhibits Doppler ambiguity due to the limitation of pulse repetition frequency, which leads to the focusing difficulty of moving targets. To address these issues, a fast approach for SAR imaging of ground moving target with Doppler ambiguity is proposed. In this method, the first-order and quadratic phase are initially estimated by using proposed operations based on 2-D scaled Fourier transform and improved range frequency cross correlation function, respectively. With the estimated parameters, the moving target is then focused in the range–azimuth time domain by the matched filtering. The presented approach is fast, because its realization procedure does not have any parameter-searching step and can be sped up by nonuniform fast Fourier transform. Moreover, the proposed approach can handle Doppler ambiguity (including Doppler center blur and spectrum ambiguity), blind speed sidelobe, and scaled frequency spectrum aliasing. Both spaceborne and airborne real data-processing results are presented to confirm the effectiveness of the proposed method.

A large time-bandwidth product bistatic radar offers several advantages in high-resolution target detection and motion parameter estimation, but the scale factor and inner-pulse Doppler will also be introduced in the radar echoes when detecting high-speed targets. Under this condition, the conventional matched filter will cause a certain energy loss and a non-negligible shift of the range center, which is called mismatch effect. Considering the special geometries of the bistatic radar, we first establish the precise echo signal model to describe the radar echoes for high-speed targets in a space-air based bistatic radar system. By analyzing the mismatch effect within the pulse and the migration between pulses, we have obtained the mathematic relationship between the scale factor, inner-pulse Doppler shift, range, equivalent velocity and accelerate. Following that, we perceive that the parameters of the matched filter are related to the target motion parameters, i.e., a priori unknown, which inspires us to propose an iterative coherent integration method to achieve the intra-pulse and inter-pulse integration. A precise echo signal model matched filter with initial parameters is defined and a roughly motion parameter estimation is acquired by the precise echo signal model-based Keystone transform and inner-pulse chirp Fourier transform. The estimated parameters are used for matched filter construction and coherent integration. This process is performed over multiple iterations to provide an accurate motion parameter result. In the end, a target detection experiment is given to show the effectiveness of the proposed method using space-air based bistatic radar.

The medium- and large- scale global sea surface temperature (SSTs), which is an important ocean parameter, are mainly measured by the space-borne microwave radiometry. However, the resolution and sensitivity are greatly limited by antenna size, orbit altitude, and flight speed. In this paper, an airborne C-band one-dimensional (1-D) microwave interferometric radiometer (ACMIR) is developed to obtain the SSTs with a high resolution and sensitivity. The spatial resolution of the ACMIR ranges from 40.7m to 612m, corresponding to the flight height of 500m to 8000m, while the sensitivity varies from 0.25K to 0.36K, associating with the boresight to the edge of the field of view. In order to evaluate the performance of the ACMIR, an ocean aviation experiment was conducted in the coastal area of the Yellow Sea in September 2020. The land observation results indicate that typical ground objects can be clearly distinguished. Furthermore, thesea surface brightness temperatures acquired by the ACMIR are compared with the estimates based on the radiative transfer model, with SST retrieval error of 0.77°C. The ACMIR can offer a high-resolution and accuracy of SST especially in coastal areas, and can meet several application requirements related to SSTs.

The azimuth extent of imaged scene is relatively small under staring spotlight synthetic aperture radar (SAR) mode. The sliding spotlight SAR mode can enlarge the extent of the azimuth scene, but at the cost of azimuth resolution loss. In this paper, an intrapulse azimuth frequency scanning spotlight SAR mode is presented. Through azimuth frequency scanning, the proposed spotlight SAR mode can significantly enlarge the extent of the azimuth scene without causing any loss in the azimuth resolution. Moreover, the proposed mode can separate the azimuth ambiguities in the range frequency domain. Therefore, the extent of the azimuth scene can be enlarged without increasing the pulse repetition frequency (PRF). Then, the range swath width can be maintained. However, to overcome the reduction in the effective range-frequency bandwidth caused by frequency scanning, an ultrawideband transmitting signal is required. The signal model of the proposed mode is derived. Based on the analysis of the characteristics of the echo spectrum, the design criteria for this mode are developed, followed by a design example. Finally, an imaging algorithm for this mode is presented. Numerical simulations verify the effectiveness of the proposed mode.

Motion errors are inevitable in real-world scenarios and introduce significant phase errors in airborne synthetic aperture radar (SAR) imaging. Generally, these errors consist of the cross-coupling and spatially variant components. Cross-coupling errors can usually be eliminated by motion compensation (MoCo), whereas the latter are seldom addressed, which deteriorate the imaging qualities, especially for the high-resolution cases. To solve the problem, a novel approach based on 2-D range-Doppler expansion is proposed. First, an accurate range equation of the aircraft is obtained based on the inertial navigation system (INS) data. Then, the range-Doppler expansion corresponding to the slant range and Doppler centroid are performed, by which the echo signal is decoupled into two spatially variant parts in range and azimuth directions. Finally, the chirp-z transforms (CZTs) are employed to remove the range and azimuth spatial variations introduced, respectively, by the cross-track and along-track errors. Different from the conventional methods, our approach can greatly decrease the cross-coupling and spatially variant effects brought by motion errors in high-resolution cases. Computer simulation and real data experiments demonstrate the effectiveness of the proposed approach.

A space-based bistatic radar system, typically composed of a satellite as transmitter and an aircraft as receiver, has a larger surveillance area, stronger resistance to damage, and more superior early warning capability for high-speed targets when compared with monostatic radar system. However, the echo signal is more challenging to process because of the high speed of both receiver and transmitter. There are two main problems to be solved in space-based bistatic radar signal processing: constructing geometric model in line with the actual situation to derive the echo signal model and improving detection ability on the basis of the longtime coherent integration algorithm. This article addresses the problem of space-based bistatic radar echo signal modeling and coherent integration for detecting high-speed maneuvering targets. A novel algorithm based on generalized second-order keystone transform and modified product cubic phase function (GSKT-MPCPF) is proposed. First, the bistatic radar system model is constructed and the signal scattered from the moving target is derived. Aiming at seeking a general algorithm which is suitable for space-based bistatic radar system, the GSKT-MPCPF is presented to correct the linear range migration (LRM), the quadratic range migration (QRM), and the Doppler frequency migration (DFM), and estimate the motion parameters of targets simultaneously. The simulations of mono-target and multitargets validate the proposed method. Furthermore, we perform comparisons with several relative algorithms and results show that the proposed algorithm has superior performance.

The frequency dispersion of wideband phased array will lead to the variation of beam point angle with the frequency of transmit signal. In this letter, such phenomenon will be exploited for squint video SAR. Firstly, the frequency dispersion will make the centroid Doppler frequency independent from the range frequency. The spectrum support region will be rectangular in such case. Therefore, the different frequency components of the transmit signal will illuminate the same ground target in different slow time duration. A SAR video can be obtained through splitting the range frequency spectrum instead of the Doppler spectrum. Then, the azimuth resolution can be maintained. Meanwhile, the large bandwidth being employed can not only maintain the range resolution after splitting but also can enlarge the time duration of squint SAR video. Numerical simulations verify the effectiveness of the proposed method.

In this article, a novel 2-D scanning synthetic aperture radar mode for high-resolution and wide-swath imaging is introduced. Instead of the interpulse progressive azimuth beam scanning used in Terrain Observation by Progressive Scans (TOPS) mode, the intrapulse continuous azimuth frequency scanning is employed in this mode. The same azimuth resolution as the multichannel TOPS mode can be obtained through this mode in the case of single channel transmitting and receiving. And the wide-swath imaging in range is still achieved through the cyclically elevation beam scanning from burst to burst. Moreover, the antenna aperture can be fully exploited for transmitting in this mode. Therefore, it will outperform the multichannel TOPS mode especially in the case of active array antenna. The signal model of this mode is derived. Based on the analysis of the characteristics of echo spectrum, the design criteria for this mode are developed, followed by a design example. Finally, an imaging algorithm for this mode is presented. Theoretical analysis and numerical simulations verify the effectiveness of the proposed design criteria and imaging algorithm.

The synthetic aperture radar (SAR) image of ground moving targets will be typical smeared given the range migration (RM) and Doppler frequency migration (DFM). To deal with these issues, a new SAR ground moving target imaging method based on modified second-order keystone transform (MSOKT) and keystone transform (KT) is developed in this paper. Firstly, the time reversing process is utilized to separate the second-order phase. Secondly, the range curvature migration and DFM are removed by MSOKT, and then the second-order phase is estimated. Finally, the moving target is finely focused after eliminating residual RWM by KT. The main contributions of this paper are listed as follows: 1) the proposed method can effectively focus moving targets without residual errors; 2) the effects of Doppler ambiguity and blind speed sidelobe are further handled. The effectiveness of the proposed method is confirmed by the simulation and real data-processing results.

Elevation frequency scanning synthetic aperture radar (EF-SCAN SAR) can isolate range ambiguities in the range-frequency domain. Therefore, range ambiguity suppression can be accomplished through range-frequency bandpass filtering, which can outperform spatial filtering-based ambiguity suppression. In this article, the analytic space-time signal model of an intrapulse frequency scanning array is derived. Based on the analysis of the characteristics of this signal model, waveform design criteria for EF-SCAN SAR are developed to effectively separate the range ambiguities in the range frequency domain. The ground echo model of EF-SCAN SAR is also developed based on this space-time signal model. The impact of intrapulse frequency scanning on the performance of high-resolution and wide-swath (HRWS) imaging is analyzed based on the derivation and analysis of the echo spectrum. Finally, an imaging algorithm for EF-SCAN SAR is developed based on this analysis. Numerical simulations verify the effectiveness of the proposed waveform design criteria and imaging algorithm.

As a transition platform between aircraft and satellite, hypersonic vehicle-borne (HSV) synthetic aperture radar (SAR) could offer many advantages such as strong survival ability, fast response, and wide detection range. However, due to the complex aerodynamic configuration and flight characteristics of the hypersonic platform, the HSV SAR faces new challenges including serious cross-couplings and spatial variations. In order to deal with these issues, a radius/angle algorithm (RAA) is devised, which has a similar processing flow as that of the conventional polar format algorithm (PFA). In the RAA, a novel 2-D interpolation function, similar to that of the PFA which is performed in the Cartesian coordinates, is derived in the curvilinear coordinate system. Due to the high accuracy of the multi-decomposition by using the polar radius and polar angle, the RAA has a much larger depth-of-focus than that of the PFA. Moreover, the RAA approach is insensitive to the height variations for the HSV SAR with curved trajectory flight, whereas the PFA is not because of the out-of-plane projection effect. Simulation results verify the effectiveness of the proposed approach.

A non‐adaptive space‐time clutter canceller (NSCC) for multi‐channel (MC) synthetic aperture radar (SAR) was proposed. First, a new three‐part range equation was derived on the basis of the two‐dimensional Taylor series expansion. Then, each part of the model was analysed. By compensating of the high‐order coupling part and the compression of the Doppler extension part of the derived equation, the interlaced signal of a moving target and a clutter patch was easily separated in a space‐time domain. The clutter signal in different pulses only contained a constant phase difference. Using radar parameters, the authors constructed a non‐adaptive clutter canceller that prevented traditional space time adaptive processing (STAP) issues, such as secondary sample support, computational complexity burden, and unknown moving target information. Compared with the representative non‐adaptive method, that is displaced phase centre antenna (DPCA), NSCC is robust to a small degree of parameter error. It can be applied when DPCA condition is not satisfied. The effectiveness of the proposed method was validations through simulation.

In this study, a ground moving target focusing and motion parameter estimation method based on modified second‐order keystone transform (MSOKT) have been proposed for a synthetic aperture radar. Firstly, a cross‐track velocity matching compensation function is derived to remove range walk migration and estimate the cross‐track velocity of the moving target. Secondly, an MSOKT is proposed to remove the range curvature and Doppler frequency migration simultaneously. Lastly, a well‐focused result of the moving target is obtained, and the motion parameters of the moving target are estimated. Compared with the traditional KT‐based method, the proposed method works well in situations where Doppler centre blur and Doppler spectrum ambiguity are present. The computational complexity of the proposed method is considerably lower than that of the traditional optimum method, such as Radon‐Lv's distribution. Simulation and real data processing results validate the effectiveness of the proposed method.

Circulating code provides a simple way to achieve transmit diversity with stable gain along wide angular coverage, whereas this property is at costs of poor sidelobe signal suppression ability and degraded range resolution. In this paper, an angle dependent match filter combined with slow-time coding is proposed and investigated to solve the above problem. The angle dependent match filter is designed via convex optimization technique to suppress interfering signals from sidelobes with a controllable penalty in the target signal-to-noise ratio (SNR). Then the slow-time coding technique is used to recover range resolution. Numerical experiments are carried out using simulated data. The performance assessments show that the proposed technique is superior in interference suppression and range resolution improvement.

Long integration time (LIT) indicates high resolution and/or large scene for spaceborne synthetic aperture radar (SAR) imaging and also means that the effects, brought by curved orbit, cannot be ignored. In this paper, considering the curved orbit caused by the relative motion between an SAR sensor in orbit and targets on a rotating planetary surface, the impacts of the LIT on the imaging results are discussed in detail. The analysis suggests that the cross-coupling phase is two-dimensional (2-D) with spatial variation. Employing the 2-D Taylor series expansion, the 2-D linear relationships between the spatially variant and invariant coefficients are derived, which are exploited to improve the echo formulation. Then, we apply the keystone transform (KT) to process the LIT spaceborne SAR data. Unlike the traditional application of the KT, our two proposed methods, which operate, respectively, in azimuth time and azimuth frequency domains, can greatly remove the spatially variant cross-coupling phase. Moreover, implementation considerations including the curved orbit of LIT spaceborne SAR, applicability of two methods, postprocessing for topography error compensation, and computational load are discussed. Simulation results verify the effectiveness of the developed focusing approaches.

In geosynchronous (GEO) synthetic aperture radar (SAR), the high orbit height and the long integration time would lead to the significant round-trip delay time and the curved flight path, thus the traditional range model with `stop-go' assumption will be ineffective. In this Paper, based on the analysis of instantaneous Doppler frequency of GEO SAR, an equivalent midpoint mathematical model is proposed to accurately describe the range history, which takes the effect of `stop-go' assumption into account and is more applicable to SAR processing. Based on the equivalent model, the two dimensional (2-D) spectrum of the GEO SAR can be obtained easily by the method of series reversion (MSR). The simulations show the validity of the presented method.

In this paper, a target detector with frequency diverse array (FDA) multiple-input and multiple-output (MIMO) radar in a homogenous environment is proposed. Unlike the conventional MIMO radar, the system uses FDA transmitting array. The essence of the proposed technique is to formulate a range-angle dependent detector with FDA MIMO radar. The detector assumes the signals belonging to conic regions, and relies on secondary data. Then, the detector performance is evaluated via Monte Carlo simulations. The results show that our system has interesting detection capabilities with range-angle dependent property, and it could be easily adapted to real scenarios.

A huge limitation of the correlation analysis in existing scatterer model is that the former model, only consisting of uniformly distributed scatterers, ignores the variability of complex scattering intensity in real situation. In fact, each part of the target has a different scattering architecture. Moreover, the scattering intensity of pinnacle or boundary scattering structure is an order of magnitude larger than the normal scatterers. To solve this problem, this paper studies the correlation coefficient for scattering model which has several dominant scatterers in spatial-frequency diversity MIMO radar. And the positions of the dominant scatterers assumed to be variables to make an equivalent of different real targets. The proposed analysis enhances the authenticity of scattering model and can simulate the real model accurately. Simulation results show the effectiveness of the proposed approach.

A new wavenumber domain mapping method for the highly squinted beam steering synthetic aperture radar (BS-SAR) is analysed. After the mapping operation, the two dimensional (2-D) spectrums have a broadside form which can be regarded as an equivalent broadside SAR. Furthermore, a novel 2-D two-step approach is introduced to avoid spectral aliasing and skewing caused by the beam steering and the high squint angle. With the mapping operation being incorporated into the novel two-step approach, the baseband azimuth scaling (BAS) algorithm which is only used for broadside cases can be applied for the highly squinted BS-SAR without subaperture.

In the traditional model of monostatic synthetic aperture radar (SAR), the flying platform should have a uniform linear trajectory. In practice, the flight path of the SAR platform, which is highly nonlinear or curvy caused by 3-D velocity and acceleration, cannot be used in the traditional model. In this paper, a geometrical model of the monostatic SAR with general configurations is graphically illustrated by vector notation. Moreover, the gradient method is utilized to point out the effects of the motion parameters, namely, velocity vector and acceleration vector, on total bandwidth and image resolution. Based on the accurate model, a general frequency-domain algorithm, with the incorporations of pre- and postprocessing, is proposed to focus the raw data. Applicability is studied through theoretical analysis and numerical experiments. All these general analyses can be applied to different realizations of monostatic SAR mode, including spotlight SAR, sliding spotlight SAR, and Terrain Observation by Progressive Scans (TOPS) SAR.

This letter proposes an omega-K algorithm for missile-borne synthetic aperture radar (SAR) diving with constant acceleration. The essence of the novel method is to derive a reference function multiplication from the equivalent range history. The true range history is divided into two parts: range independent and range dependent. After compensating the range-independent part with considering all the terms, we can regard the range-dependent part as an equivalent range history with a form similar to that of conventional SAR. Then, an analytical 2-D spectrum can be used for the omega-K algorithm. The proposed algorithm can handle general missile configurations with wide swaths and high squint angles. Simulation results are presented to validate the proposed method.

General bistatic SAR (BiSAR) data are more challenging to process than their translational invariant counterparts because the transmitter and the receiver have unequal velocities or/and nonparallel tracks. Although several algorithms have been used to process the data in general cases, these can work only in small invariant regions of the azimuth-variant problem because of the complicated configurations. In this letter, an extended nonlinear chirp scaling (NLCS) is proposed to address this problem. The key is to use the vector analysis of the instantaneous slant ranges to extract the azimuth-variant components. Furthermore, a new perturbation function based on the principle of NLCS used to precompensate the data. The simulation results show that our algorithm can handle data with more complicated bistatic cases than the existing algorithms.

The most serious problem in processing highly squinted data is the strong range–Doppler coupling, which can be reduced by the linear range cell migration correction (LRCMC). After the LRCMC, however, targets with different azimuth frequency modulation (FM) rates are moved into the same range cell, blocking the efficient azimuth compression. In this letter, a new algorithm to equalize the FM rates is presented, which is referred to as azimuth extended nonlinear chirp scaling. The key is to derive a new perturbation function to handle the problem while introducing a negligible residual phase. The proposed method outperforms the existing algorithms, particularly in large bandwidth cases. Numerical simulations illustrate the performance of the proposed algorithm.

This paper deals with the adaptive detection of a signal of interest in the presence of Gaussian noise with unknown covariance matrix (CM). To this end, we resort to a Bayesian approach based on a suitable model for the probability density function (PDF) of unknown CM. Under this assumption, the maximum a-posteriori (MAP) estimation of CM is derived. The MAP estimate is in turn used to yield Bayesian version of Rao and Wald test. And the importance of the a priori knowledge can be tuned through scalar variable. Remarkably the devised detectors outperform Kelly's GLRT and non Bayesian Rao and Wald test in the presence of strongly heterogeneous scenarios (where a very small number of training data is available). Meanwhile, the coincidence of Bayesian GLRT and Wald test is proved.

A low-complexity ESPRIT method for direction-of-arrival (DOA) estimation is proposed in this paper. Unlike the conventional subspace based methods for DOA estimation, the proposed method only needs the training data of one signal to perform the forward recursions of the multi-stage Wiener filter (MSWF), does not involve the estimate of the covariance matrix or its eigendecomposition. Thus, the proposed method is computationally advantageous. Numerical results are given to illustrate the performance of the proposed method.

A novel approach called spatial-temporal correlator (STC) for code acquisition and beamforming weight acquisition in DS-CDMA mobile communication systems with adaptive antenna array is proposed in this paper. The STC uses the pilot symbol (channel) and incorporated Wiener filter with the conventional PN code correlator. The proposed STC exploits the spatial and temporal information of the received signal and thus achieve improved detection performance. The detection probability and false alarm probability of the STC is theoretically analyzed under spatial-temporal AWGN and Rayleigh fading environment. Simulation results are presented to verify the performance analysis. These results show that the proposed STC can effectively acquire the adaptive beamforming weight and have improved PN code acquisition performance.