Multi-input Multi-output Synthetic Aperture Radar Research Articles

Inter-Pulse Phase Modulation Waveform Scheme for Spaceborne MIMO SAR Systems

Special attention has been devoted to multi-input multioutput synthetic aperture radar (MIMO SAR) systems over the past decades. However, performances of such systems are seriously limited by the imperfect orthogonal waveforms. The nonideal orthogonality would introduce ambiguous energy, and therefore degrades the signal to clutter ratio dramatically. In order to suppress the ambiguous energy, the interpulse phase modulation (IPPM) and range-Doppler decouple filtering scheme was proposed. However, this scheme requires a multiplied pulse repeat frequency (PRF), and thus degrades the swath width and/or the azimuth resolution. In this article, the IPPM waveform scheme is further developed to avoid the required increasing of the PRF. With the developments, the MIMO SAR can simultaneously produce multiple higher signal to noise ratio image data without degrading the ambiguities. The multiple images can be used either to realize multimodal operation or to further enhance the noise equivalent sigma zero. Theoretical analysis is validated by numerous simulations.

Research on Rebound Jamming Against Multi-Input Multi-Output Synthetic Aperture Radar

Multi-Input Multi-Output Synthetic Aperture Radar (MIMO-SAR) emits orthogonal waveform, which reduces the probability of signal interception. Using multiple antennas to receive echoes, spatial filtering can be performed to avoid interference. MIMO-SAR waveform and structure characteristics determine that it has a certain anti-jamming ability with good prospect of application. For effective jamming MIMO-SAR, a theoretical model of rebound jamming against MIMO-SAR is established by taking the space-borne MIMO-SAR as object, the similarities and differences of rebound jamming against MIMO-SAR and conventional SAR are analyzed. Then, the effects of different signal systems on rebound jamming are discussed. Finally, the interference parameter selection for rebound jamming against the MIMO-SAR is analyzed. Simulation result verifies the validity and correctness of the proposed jamming method.

A Two-Dimensional Mixed Baseline Method for Recognizing Deceptive Jamming Based on MIMO-SAR

Abstract Aiming at the current methods of range delay and azimuth Doppler frequency modulation used in deceptive jamming, this paper proposes a two-dimensional mixed baseline method for deception jamming recognition based on multi-input multi-output synthetic aperture radar (MIMO-SAR). In this paper, on the basis of MIMO-SAR phase coding method which makes the multi-channel signal orthogonal, we propose to detect the deceptive jamming phenomenon by employing multi-dimensional phase information. Among them, the intersection-orbit interferometric phase is used to identify the range-delay deception jamming, and the along-orbit interferometric phase is used to identify the azimuth Doppler frequency modulation deception jamming. The combination of the two methods can identify two-dimensional deception jamming. Experimental results demonstrate the validity of our method.

Imaging and micro‐Doppler analysis of vibrating target in multi‐input–multi‐output synthetic aperture radar

The micro-Doppler (m-D) signature induced by the micro-motion dynamics of a component or structure on a radar target can provide additional information for classification, recognition, and identification of the object. Since the m-D signature from conventional synthetic aperture radar (SAR) is insufficient for further application, attention centred on multi-input–multi-output (MIMO) SAR. MIMO SAR employs diversity to improve SAR performance and shows great potential in applications including high-resolution wide-swath remote sensing, slow moving target detection, and three-dimensional (3D) imaging. Take vibration for research, because vibration is a basic kind of micro-motion and it occurs commonly such as vehicle engine. In this study, the vibration signal modelling is deduced and the m-D signature of vibrating target is analysed, based on short-term shift-orthogonal waveform in MIMO SAR. Simulations verify the influence of vibration parameters on imaging and time–frequency profile and show the m-D signature difference through different MIMO channels. The results demonstrate the potential of MIMO SAR for 3D micro-motion estimation.

Impact of radar systematic error on the orthogonal frequency division multiplexing chirp waveform orthogonality

Orthogonal frequency division multiplexing (OFDM) chirp waveform, which is composed of two successive identical linear frequency modulated subpulses, is a newly proposed orthogonal waveform scheme for multiinput multioutput synthetic aperture radar (SAR) systems. However, according to the waveform model, radar systematic error, which introduces phase or amplitude difference between the subpulses of the OFDM waveform, significantly degrades the orthogonality. The impact of radar systematic error on the waveform orthogonality is mainly caused by the systematic nonlinearity rather than the thermal noise or the frequency-dependent systematic error. Due to the influence of the causal filters, the first subpulse leaks into the second one. The leaked signal interacts with the second subpulse in the nonlinear components of the transmitter. This interaction renders a dramatic phase distortion in the beginning of the second subpulse. The resultant distortion, which leads to a phase difference between the subpulses, seriously damages the waveform’s orthogonality. The impact of radar systematic error on the waveform orthogonality is addressed. Moreover, the impact of the systematic nonlinearity on the waveform is avoided by adding a standby between the subpulses. Theoretical analysis is validated by practical experiments based on a C-band SAR system.

An improved OFDM chirp waveform used for MIMO SAR system

Special attention has been devoted to multi-input multi-output (MIMO) synthetic aperture radar (SAR) systems in recent years. The applications of MIMO SAR systems which involve 3D imaging, highresolution wide-swath remote sensing, and multi-baseline interferometry are seriously limited to the orthogonal waveforms. Although orthogonal frequency division multiplexing (OFDM) chirp waveforms can be used for MIMO SAR systems to avoid intra-pulse interferences, there is a small frequency shift between the transmitted OFDM pulses. This vulnerable shift, which can not only affect the waveform orthogonality, but also introduce residual phase error, renders the OFDM waveforms impractical. In this paper, an improved OFDM chirp waveform which works without the mentioned shift is presented, along with the novel modulation and efficient demodulation procedures. Comparison between the improved and the conventional OFDM chirp waveforms is detailed. The influence of random noise, quantization error, and Doppler shift on the orthogonality of OFDM waveform is also investigated in this paper. Theoretical analysis and simulation results illustrate the feasibility of this waveform scheme.

Brief Analysis on the Development and Application of Multi-Input Multi-Output Synthetic Aperture Radar

多发多收合成孔径雷达(MIMO-SAR)是近年来提出并备受关注的一种新型雷达成像模式，通过多天线同时发射、多天线同时接收的工作方式能够获得远多于实际天线数目的等效观测通道，为解决常规SAR 面临的方位向高分辨率与宽测绘带指标相互矛盾、弱小慢速运动目标难以检测等难题提供了更为有效的技术途径。该文围绕MIMO-SAR 成像技术及其应用展开论述，从距离分辨率增强、3 维下视成像、高分辨率宽测绘带成像以及动目标检测等方面综述了MIMO-SAR 的研究状况，分析了系统的体制优势和不足，进而归纳了MIMO-SAR 研究中的若干关键技术问题，最后对其应用前景进行了展望。

A Novel Algorithm For MIMO SAR Imaging

A Multi-Input Multi-Output (MIMO) Synthetic Aperture Radar (SAR) system has been considered for its potential to simultaneously improve the performance of stationary scene imaging and ground moving target indication (GMTI) by utilizing multiple subarrays both at transmission and reception. To successfully exploit the potential benefits of MIMO SAR for practical imaging application, a signal model for MIMO SAR system with colocated arrays is presented in this paper, then we propose a novel procedure for imaging processing by coherently combining the returns from multiple receive subarrays. Our approach can make efficient use of the transmitted waveform power, and resulting in higher Signal-to-Noise Ratio (SNR) images. The effectiveness of model and MIMO SAR imaging method proposed in this paper are demonstrated by simulation experiments.

SIGNAL MODEL AND MOVING TARGET DETECTION BASED ON MIMO SYNTHETIC APERTURE RADAR

Recent years, a new SAR concept based on Multi-Input Multi-Output (MIMO) conflguration has demonstrated the potential advantages to simultaneously improve the performance of Synthetic Aperture Radar (SAR) imaging and ground moving target detection by utilizing multiple antennas both at transmission and reception. However, the precise signal model, as well as the efiect of ground moving target in image domain and the approaches for moving target indication based on MIMO SAR system are rarely investigated. Our paper has three main contributions. Firstly, we present a detailed signal model for stationary scene and moving target based on a colocated MIMO SAR conflguration, and analyze the motion efiect of the moving target. Secondly, we provide an algorithm of phase compensation to combine the multiple virtual channel data in order to enhance the image quality. Thirdly, an adaptive optimal approach is applied for clutter suppression, then the velocity of the moving target is estimated via Delay-and-Sum (DAS) beamforming approach. Finally, several numerical experiments are provided to illustrate the derivation and analysis in this paper.