range-Doppler Coupling Effect Research Articles

Photonic generation of terahertz dual-chirp waveforms ranging from 364 to 392 GHz.

In this paper, we propose and experimentally demonstrate a photonic scheme based on frequency doubling and photo-mixing to generate dual-chirp signals in the terahertz (THz) band. A broadband dual-chirp THz signal with 28 GHz bandwidth, ranging from 364 GHz to 392 GHz, is successfully generated in the proof-of-concept experiment, resulting in a chirp rate of 0.028 GHz/ns for both up chirp and down chirp signals. THz dual-chirp signals featuring a large bandwidth are beneficial to enable high resolution and high accuracy by mitigating the range measurement error induced by the range-Doppler coupling effect. Therefore, the proposed system is expected to have a great potential for future THz radar applications.

Research of a Radar Imaging Algorithm Based on High Pulse Repetition Random Frequency Hopping Synthetic Wideband Waveform.

Aiming at the imaging algorithm of high-pulse-repetition random-frequency-hopping synthetic wideband radar on a supersonic/hypersonic aircraft platform, this study established an echo simulation model of target and clutter, analyzed the special range-Doppler coupling effect and its influence on imaging, and proposes a method of imaging with pipeline-parallel processing based on generalized 2D matched-filtering and Doppler pre-processing. In the method, Doppler-beam-sharpening was advanced to be performed with the pulse compression process in each frame, and the special range-Doppler coupling effect caused by high dynamic motion of platform and random frequency hopping in bandwidth synthesis was well suppressed; several modes of random frequency hopping were designed and the pipeline-parallel image processing algorithm was optimized for each mode. Theoretical analysis and simulation results show that the proposed imaging method can effectively avoid the divergence of 2D range-Doppler images in the range direction, and can meet the requirements of real-time imaging.

Investigation on reason of range profile distortion of plasma sheath target

The range profile of the plasma sheath target is always found to be distorted when using the linear frequency modulation signal as the radar detection signal. As a result, the detection and tracking of the target became hard, or even failure. Here, three possible reasons of the range profile distortion is investigated in detail: (i) The broadening of the particles in the radial direction of the radar detection when the plasma sheath is produced; (ii) The scatterers in one range gate have different radial velocities that the range profile is dispersion due to the range-Doppler coupling effect; (iii) The amplitude and frequency of the echo signal are modulated by the time-varying plasma sheath. Here, the influence of the above three mechanisms on the range profile is simulated. In addition, for the accurate detection and tracking of these targets, the reason of the distortion should be distinguished. Therefore, several methods are proposed to distinguish the different mechanisms for the range profile distortion.

Photonic Generation of Dual-Chirp Waveforms With Improved Time-Bandwidth Product

We present a photonic method for the generation of dual-chirp signals. In this approach, a single-tone RF signal is first modulated using a modulator in order to generate two optical carriers, which are further modulated by a linearly chirped signal by another modulator. Square-law detection in a photodiode then generates a dual-chirp signal whose center frequency and time-bandwidth product (TBWP) are fourfold increased. The dual-chirping and the improved TBWP can improve the range resolution of the radar system and help avoid the range measurement error caused by the range-Doppler coupling effect. The generation of bandwidth-quadrupled S-band dual-chirp waveforms is demonstrated experimentally. The processing of the dual-chirp signal is also discussed, in order to show its advantages over single-chirp signals. We believe that the proposed approach is a potential solution for the generation of dual-chirp signals with high center frequency and large bandwidth in modern radar systems.

A novel range-Doppler imaging algorithm with OFDM radar

Traditional pulse Doppler radar estimates the Doppler frequency by taking advantage of Doppler modulation over different pulses and usually it requires a few pulses to estimate the Doppler frequency. In this paper, a novel range-Doppler imaging algorithm based on single pulse with orthogonal frequency division multiplexing (OFDM) radar is proposed, where the OFDM pulse is composed of phase coded symbols. The Doppler frequency is estimated using one single pulse by utilizing Doppler modulation over different symbols, which remarkably increases the data update rate. Besides, it is shown that the range and Doppler estimations are completely independent and the well-known range-Doppler coupling effect does not exist. The effects of target movement on the performances of the proposed algorithm are also discussed and the results show that the algorithm is not sensitive to velocity. Performances of the proposed algorithm as well as comparisons with other range-Doppler algorithms are demonstrated via simulation experiments.

Zonal Imaging Algorithm of Range-Speed Target Based on the LMSF Radar Signal

The automatic recognition of range-spread target is based on its range profile. When obtaining its range profile by using synthetic wideband radar signal, the different-range scatters would be overlapped because of the range-doppler coupling effect. The overlapping effect affects the ability of the automatic recognition algorithm. According to this, based on the Linearly Modulated Stepped Frequency (LMSF) radar signal, coherent processing of range profiles to obtain zonal image of range-spread target is proposed in this paper, which avoids the overlapping effect. The theoretical model of the zonal image of range-spread target is presented, the signal processing flow is derived, and the simulation result of zonal image is also given in this paper.

Nonuniform stretch processing for the range profile of a target with micro-motion

Abstract Complex motions such a micro-motions induce complex range-Doppler coupling effect in radar imaging. Hence it is a challenge to reconstruct a clear range profile of a target with micro-motion. Stretch processing with fine motion compensation cannot perform well while it tics to eliminate the distortion of range profile caused by Doppler effect, because it is difficult to accurately estimate each scattering center velocity during coherent processing interval. Based on nonuniform stretch processing (NSP), a new technology is proposed to decouple range, time and Doppler and then achieve range profile of target with micro-motion. The new technology uses a new synthetic wide-band waveform and has an innovative mathematic interpretation. Statistical properties of the new approach are primarily examined. Typical models of target with micro-motion for high resolution rader are presented. Monte Carlo simulations demonstrate the performance of the new technology and the simulation result confirm our expecta...

A New Approach for Synthesizing the Range Profile of Moving Targets via Stepped-Frequency Waveforms

In radar target imaging, motion induces a range-Doppler coupling effect, which results in distortion in synthesizing a range profile for a moving target. To eliminate or suppress the distortion of the synthetic range profile, conventional technology such as motion compensation requires velocity estimation. Unfortunately, for a high-speed moving target, it is difficult to achieve real-time accurate estimation of the velocity of the target. Based on phase cancellation, a new technology is proposed to achieve a motion target range profile via stepped-frequency waveform. The new technology does not need the estimation of the velocity. Hence, its computational cost can be minimized. It is also easier to use. The simulation result confirms the effect of the new technology