Three-dimensional images can accurately reflect the target’s posture and structure, providing rich feature information for spatial target recognition. However, challenges arise in image registration and phase reconstruction for interferometric inverse synthetic aperture radar (InISAR) 3-D imaging when observation perspectives significantly differ, the target size is relatively large, or the squint model is present. Therefore, we propose a target 3-D reconstruction method based on phase-derived technology. For the issue of image distortion misregistration caused by differing observation perspectives, we propose transforming the traditional image registration problem into a multiscatterer association problem by extracting target scatterer information from inverse synthetic aperture radar (ISAR) 2-D images and using the iterative closest point (ICP) algorithm to achieve scatterer association between different ISAR images. To tackle the interference phase ambiguity problem caused by large target size or squint model in InISAR 3-D imaging, we propose transforming the 3-D reconstruction problem into a 3-D positioning problem for each scatterer and achieving 3-D reconstruction through a 3-D positioning method based on phase-derived angle measurement (PDAM) and phase-derived range measurement (PDRM). In cases where the extracted scatterers are generally nonideal, the nonideal scatterers can be treated as a whole, and cross correlation processing can be performed between different antennas to extract the interferometric phase. Both simulation and measured data have verified the effectiveness of the proposed method.

Compared with traditional synthetic wideband signals, synthetic ultrawideband (UWB) signals with higher range resolution can obtain more information for target identification. The stepped-frequency chirp signal (SFCS) based on dechirp processing can simultaneously achieve a UWB, a high data rate and a low sampling rate. In this paper, a synthetic UWB range profiling method for high-speed targets based on phase-derived velocity measurement (PDVM) is proposed. High-precision velocity compensation is key to synthetic UWB range profiling for high-speed targets. Thus, the PDVM based on the pulses at the same carrier frequency is adopted to obtain high-precision velocity measurement results. Then, based on PDVM results, the synthetic UWB range profiling method in the time domain is analyzed in detail, which mainly contains time shift, linear phase correction and constant phase correction. In the phase correction process, the compensation of intrapulse Doppler modulation, range migration and tracking gate movement is emphatically analyzed. In addition, to guide the implementation in radar systems, the phase hopping caused by parameter estimation error is theoretically derived. Finally, simulation results and raw data are presented to verify the performance of the proposed method.

The micromotion features of a target contain unique structural information and motion information about the target, which can be used as an important basis for target classification and recognition. To achieve high-accuracy three-dimensional micromotion measurements in the clutter environment, a stationary clutter suppression method for three-dimensional micromotion measurements based on wideband radar amplitude and phase information is proposed in this paper. This method is capable of accurately measuring the trajectory of small amplitude micromotion with the high-accuracy phase-derived angle measurement (PDAM) and phase-derived range measurement (PDRM). However, the measurement accuracy of three-dimensional micromotion deteriorates sharply when clutter exists. Thus, the main challenge that we overcome is achieving high-accuracy clutter estimation based on wideband radar measurements. The clutter suppression method is proposed by utilizing wideband radar amplitude and phase of multiple range cells jointly. Finally, simulation and experiment are presented to validate the feasibility and effectiveness of the proposed method under stationary clutter conditions.

The phase-derived velocity measurement (PDVM) technique can achieve a high measurement accuracy at the phase level and thus has great application prospects in the field of micromotion feature extraction and target recognition. To achieve a PDVM with a low signal-to-noise ratio (SNR), a PDVM method based on the generalized Radon–Fourier transform (GRFT) is proposed in this article. The main challenges that we overcome are phase extraction and phase ambiguity resolving under the condition of a low SNR. By utilizing the GRFT to estimate the target motion parameters, the echo peak position can be reconstructed, and then the peak phase value can be extracted. In the meantime, the phase ambiguity integer can be resolved based on the rough velocity estimation results obtained by the GRFT, and the phase ambiguity resolving can be realized at a low SNR. In addition, to suppress the influence of noise on the extracted phase, a filter design method based on the target motion characteristics is proposed to further improve the accuracy of the PDVM. In the simulation, the performance of the proposed method under different motion models and different SNR conditions is analyzed, and the effectiveness of the proposed method under low-SNR conditions is verified. Compared with directly using the GRFT, the proposed method has the advantages of strong applicability to different motion models and low computational load.

In this article, we propose a phase-derived velocity measurement (PDVM) method for high-speed spatial targets based on the stepped-frequency chirp signal (SFCS). This method is capable of accurately measuring the velocity of high-speed targets and yields root-mean-squared error values at the level of centimeters per second; therefore, it has great potential for measuring the micromotion of targets and is of significant importance for target recognition. The traditional phase-derived measurement method is not applicable for high-speed targets. The main challenge that we have solved is how to extract the echo phase from the high-resolution range profile, which is corrupted by range migration, intrapulse motion, and range straddling under high-speed target conditions. To guide the implementation of the proposed method in radar systems, constraint conditions for the compensation accuracy are thoroughly derived and systematically justified under different radar parameter settings. The simulation results are presented to validate the high accuracy of the method under various circumstances. In addition, the small-amplitude micromotion measurement capability of the proposed method is verified, and reconstruction of the target micromotion trajectory is demonstrated.

This paper proposes a phase-derived velocity measurement (PDVM) method for high-speed targets based on wideband direct sampling linear frequency modulated radar. First, a high-speed target echo model considering intrapulse Doppler modulation is developed. Then, a PDVM model considering acceleration is established. The key to realizing PDVM is resolving phase ambiguity. Under low signal-to-noise ratio (SNR) conditions, a joint processing method combining acceleration information and multiframe data to solve phase ambiguity is proposed, which can significantly reduce the SNR requirement for PDVM. In this paper, the small-amplitude micromotion measurement capability of the proposed method is verified by simulation. Moreover, the measured data of a Ku-band ground-based radar are used to verify the applicability of the PDVM method under low SNR conditions and its feasibility to be applied to complex multi-scattering point targets. Both the simulation and experimental results show that the proposed method is suitable for high-speed targets with radial motion, including acceleration and jerk, and that the PDVM precision can reach the order of magnitude of centimeters per second or millimeters per second.

The existing methods for motion compensation in inverse synthetic aperture radar (ISAR) imaging are generally limited to the low-order target motion model, and require iterative optimization with limited velocity estimate precision and heavy computational burdens. This paper proposes a high-precision method of phase-derived velocity measurement (PDVM) and applies it to motion compensation of ISAR imaging. The method applies PDVM based on range profiles cross correlation to the translational velocity estimation of targets, and converts the velocity measurement results to the corresponding range increment. The equivalent phase-derived range measurement precision can reach the order of magnitude of millimeter (mm) or even sub-mm, which can satisfy the precision requirements of both envelope alignment and phase adjustment. The key to realizing PDVM is resolving phase ambiguity. The traditional method for resolving ambiguity has very high requirements for the signal-to-noise ratio (SNR). This work resolves ambiguity by combining multiframe data, i.e., by resolving ambiguity of multiframe data simultaneously instead of resolving ambiguity of single-frame data independently and correcting the above ambiguity-resolving results using a minimum-entropy method. Therefore, phase ambiguity can be correctly resolved under a relatively low SNR. Experimental results of an ISAR imaging of an airplane show that the method proposed in this paper can obtain high-quality ISAR imagery, and can efficiently realize robust imaging under the conditions of low SNR.

The micro-Doppler is an effective tool for target recognition. It is hard to detect micro-Doppler induced by vibration for its small value. In our system, phase-modulated stepped-frequency waveform is used. The method of matching pursuit (MP) is introduced to compensate translation. Translation trajectory is approximated by Chebyshev polynomial to improve approximation accuracy under low signal-to-noise ratio. The parameters in the polynomial are estimated by MP. To improve the performance of MP, simulated annealing is used. The operation of translation parameters estimation is performed in frequency domain before pulse compression. After translation compensation and pulse compression, Doppler component induced by rotation is mitigated by phase fitting. After compensation of translation and rotation, micro-Doppler is extracted from the result of motion compensation based on vibration model. Simulation and experiment data are used to testify our method.

OFDM-CDMA, the orthogonal frequency division multiplexing-code division multiple access, is a promising technology in mobile communication because of its abilities to combat the multi-path fading and narrowband interference. It has been proposed to use in many future communication systems. However, the high ratio of the peak power to the average power (PAPR) of the OFDM-CDMA signal, a special drawback of multi-carrier transmission, has prohibited its wider application. In this paper we focused on a new OFDM-CDMA system structure, which combines the time spreading structure and frequency spreading structure, called time-frequency spreading OFDM-CDMA. This system can achieve a much lower BER and paper compared to frequency spreading OFDM-CDMA. In this paper we give this simulation results of the new system, and show the performance improvement.