Theoretical aspects of radar imaging using stochastic waveforms

In this work, we develop the theory of radar imaging using stochastic waveforms, such as random noise or chaotic signals. Specifically, we consider one-dimensional (1-D) (range profiles) and two-dimensional (2-D) (range-Doppler) radar imaging performed with a random signal radar, in which the transmit signals are assumed to be stationary random processes. We calculate the 1-D and 2-D point-spread functions as the expected value of the radar return. We show that the 2-D point-spread function is spatially invariant; however, the reduction in height and broadening of the mainlobe is small in the case of bandlimited noise. We also derive a formula that is useful in calculating the variance of the radar return under the assumption that the transmit signal is real valued and Gaussian     

Ultra-wideband radar signals generated technology with two-channel

Synthesis of ultra-wideband (UWB) linear frequency modulation radar signals is a very important technology for microwave imaging, target identification and detection of low radar-cross-section (RCS) targets. In this paper a new method of UWB radar signals generation with two-channel is presented. The realization structure is given, and the principle of signal synthesis is analyzed. At the same time, an automatic adjustment measure of signal phase is proposed for phase discontinuity of waveform in this method. The simulation experiment and analysis results show that radar signals with large instantaneous bandwidth can be generated by means of this method.     

Orthogonal wideband hybrid-coding radar waveforms design

To obtain wideband orthogonal waveforms of radar systems with high-range resolution and good correlation properties, this paper proposes two types of orthogonal wideband hybrid-coding waveforms, polyphase discrete frequency (PDF) waveforms and polyphase signed-chirp (PSC) waveforms. Using an intra-pulse hybrid modulation, high-range resolution can be obtained, and good correlation properties between different waveforms are easier to optimize within a larger optimization space. Specifically, good correlation properties of the PDF waveforms are indeed easier to achieve without a loss of range resolution, as occurs with a discrete frequency coding waveform. Compared with polyphase coding waveforms, the signal bandwidth of each PSC waveform is twice as large as that of sub-pulse chirp signals, and superior correlation properties are obtained. Finally, various designed waveforms optimized by the genetic algorithm are provided to demonstrate the effectiveness of these proposed wideband hybrid-coding waveforms.     

UWB雷达杂波物理建模与仿真分析

利用子带合成和物理平板模型,将超宽带(UWB)雷达分别在不同地貌(植被或裸地)和中心频率条件下进行地杂波建模、仿真、杂波统计分布拟合及其分析。通过获得的杂波仿真数据拟合出地杂波的统计模型,分析发现:UWB雷达地杂波随着地貌或中心频率的变化,杂波并不服从同种统计分布;但统计分布具有低重心和重拖尾的共性,且随着相对带宽的增加,拖尾加重。仿真结果与UWB雷达杂波定性分析的规律基本符合。     

Multi-view synthesized aperture radar

This article considers synthesized aperture radar (SAR), developed and manufactured in Radio Astronomy Institute of Ukrainian Academy of Sciences. SAR operates in 3 cm frequency band and it intended for obtaining multi-view images from light-motor planes. Technical and scientific solutions found during design of this radar are described. Characteristics examples of obtained images are provided.     

基于双谱特征的超宽带雷达人体目标识别

为了在人体微多普勒特征不明显条件下识别静态人体目标及人体姿态,提出了一种结合双谱对角线起伏特性与目标强散射点分布特征进行人体目标识别的方法。首先,通过分析静态人体目标双谱,提取双谱对角线起伏特性作为分类特征,降低了双谱数据的维数,减少了双谱特征冗余。然后,结合目标强散射点分布特征从不同角度描述目标,并构造用于目标识别的特征向量。最后,用支持向量机实现目标识别。仿真和实测结果均表明,双谱对角线起伏特性与目标强散射点分布特征融合的方法可以有效识别出静态人体目标并且实现人体姿态识别。     

Improved design of unimodular waveforms for MIMO radar

This paper proposes a novel method of unimodular transmitting waveforms design for multiple-input multiple-output (MIMO) radar to strengthen the detection performance in the presence of clutter and white Gaussian noise. An improved iterative algorithm is put forward to maximize the signal-to-clutter-plus-noise ratio (SCNR) under the constant modulus constraint. During iterations, the optimization of unimodular waveforms with filters fixed is a nonconvex fractional quadratically constrained quadratic program problem, which is NP-hard and not able to be solved in polynomial time. An algorithm based on semidefinite programming relaxation combined with bisection and Gaussian randomization is introduced to provide the high-quality suboptimal solutions with a polynomial time computational complexity. The analysis on the approximation bound is given to prove the tightness of the semidefinite programming relaxation and so the correctness of the proposed algorithm. The simulation results show that the improved method is efficient in designing unimodular waveforms for MIMO radar to achieve a better SCNR performance.     

On the design of optimum radar waveforms for clutter rejection

The problem to be considered in this paper is that of designing radar signals and receivers that are optimum for detecting a point target masked by a background of clutter returns and thermal noise. The problem of choosing an optimum signal when no constraints are placed on the type of signals allowed is discussed briefly, but the remainder of the paper is restricted to signals and receiver impulse responses that are uniformly spaced, phase and amplitude-tapered pulse trains. Expressions for the signal-to-interference ratio obtained when a signal is used with its matched filter (pm/) and with the optimum filter or clutter filter(rho_{cf})are then derived together with an explicit expression for the clutter filter. An iterative technique for maximizingrho_{cf}is devised. This scheme has the useful property that it generates a sequence of signals whoserho_{cf}'s form a monotone, nondecreasing sequence. This is followed by an application of the calculus of variations to derive the Euler equations for the stationary points ofrho_{cf}andrho_{mf}. The form of the Euler equations suggests iterative techniques for their solution; in fact, the technique suggested for the solution of the Euler equation associated withrho_{cf}is essentially the iterative technique that was described above.     

Effects of signal decorrelation on pulse-compressed waveforms fornadir-looking spaceborne radar

Pulse-compressed waveforms for partially coherent radar return signals are formulated with an incoherent-scatter autocorrelation function, ρ(τ). Numerical calculations are made for a nadir-looking spaceborne radar with linear FM pulses, and effects of signal decorrelation on the compressed waveforms are qualitatively evaluated. The calculations indicate that the transmitted pulse width should be shorter than half the correlation time, defined as the time at which ρ(τ) decreases by 0.1, in order to keep signal decorrelation effects negligible     

The design of clutter-resistant radar waveforms with limited dynamic range

The problem of designing radar signals and receivers that are optimum for detecting a point target masked by thermal noise and clutter returns is considered. In a previous paper, the authors described an iterative algorithm for designing such signals subject to an energy constraint. This paper describes an algorithm for the case where the energy constraint is replaced by a dynamic-range constraint, that is, the ratio of maximum to minimum signal amplitude is limited. The signal to which the algorithm converges satisfies the Kuhn-Tucker conditions, which are necessary for optimality. Examples of the application of both algorithms to radar signal design problems are given.     

波形具有任意相关性时MIMO雷达的检测性能

基于Neyman-Pearson准则,研究了空间分集MIMO(多输入多输出)雷达发射波形相关时的自、互相关旁瓣对MIMO雷达检测性能的影响.首先,分析了波形的相关性,导致了在空间上和时间上的白高斯噪声变为相关色噪声,同时,使得接收的回波信号具有一定的相关性,影响了空间分集的效果;然后,通过理论分析得到了MIMO雷达在波形具有任意相关性时的检测概率和虚警概率的解析表达式.通过数值计算,得到如下结论:与发射正交波形相比,在高信噪比(SNR)工作时,M1MO雷达波形相关时的自、互相关旁瓣使得MIMO雷达的检测性能下降;在低SNR时,波形的相关性能够改善检测性能;波形的低自、互相关旁瓣对MIMO雷达的检测性能影响不大.     

Ultra-wideband bandpass filter using CPW-to-microstrip coupling structure

A novel ultra-wideband bandpass filter based on a back-to-back microstrip-CPW transition structure is presented. The filter is composed of two microstrip-CPW transitions and a section of microstrip line used as a multiple-mode resonator. The filter has been investigated numerically and experimentally. Both simulated and measured results show that the filter has a good performance, including a small insertion loss, a group delay variation of less than 0.2 ns, stopband of up to 16.0 GHz at high frequencies, and an out-of-band rejection level of below -20.0 dB.     

Ultra-wideband bandpass filter using back-to-back CBCPW-to-CBCPW transition

A new ultra-wideband bandpass filter using a back-to-back CBCPW-to-CBCPW transition structure is presented. The filter is composed of two CBCPW-to-CBCPW transitions and a section of a CBCPW line section used as a multiple-mode resonator. Using this transition, a new ultra-wideband filter prototype was designed, fabricated and measured. Obtained results show that the proposed filter can easily cover the band from 3.1 to 10.6 GHz.     

Ultra-wideband slotline dispersion measurements using ring resonator

The design for an ultra-wideband coplanar waveguide-fed slotline ring resonator is presented. The broadband feed system permits dispersion measurements to be made over the frequency range 2?220 GHz using a single circuit and coplanar waveguide probes connected to a vector network analyser. Measured effective dielectric constant data from a number of different rings using thin-film copper on alumina is presented, and compared with a theoretical prediction using the spectral domain approach, the agreement being better than 3.5%.     

Ultra-wideband bandpass filter using back-to-back microstrip-to-CPW transition structure

A novel ultra-wideband bandpass filter is proposed on a back-to-back microstrip-to-CPW transition structure. A multiple-mode resonator on a CPW is formed to allocate its first three resonant modes around the lower-end, centre and upper-end of the 3.1 to 10.6 GHz UWB passband. Its two sides are fed by two microstrip-to-CPW transitions with enhanced frequency-dispersive coupling degree. The designed filter exhibits good UWB passband behaviour with insertion loss <0.5 dB and group delay variation <0.35 ns.     

Generation of arbitrary optical waveforms by Fourier synthesisusing three continuous-wave semiconductor lasers

Arbitrary optical waveforms have been successfully generated by Fourier synthesis using three independent continuous-wave semiconductor lasers. The lasers were phase-locked to each other using a nonlinear phase-locking scheme. By controlling their amplitude and phase, triangular and trapezoidal waveforms as well as ordinary pulses have been generated     

Time-domain reflectometry using arbitrary incident waveforms

A novel time-domain reflectometry technique is developed for detecting the physical structures of transmission lines by using arbitrary waveforms. By discretizing both incident and reflected waves, we formulate the reflection coefficient of a nonuniform transmission line as a polynomial ratio in the Z-transform, wherein the numerator and denominator represent the reflected and incident waves, respectively. A reconstruction scheme is derived to obtain the characteristic impedance profile of a transmission line. Some examples are presented to illustrate the validity of this new technique.     

Blind velocities mitigation for MIMO GMTI radar with Doppler division multiple access waveforms

Multiple-input multiple-output (MIMO) radar with multiple transmitters and multiple receivers can achieve a larger virtual antenna array and more system degrees of freedom; thus applying it to ground moving target indication (GMTI) radar can improve the performance of GMTI. Doppler division multiple access (DDMA) waveforms are approximately orthogonal providing good minimum detectable velocity (MDV) performance. However, in such DDMA systems, a sufficient pulse repetition frequency (PRF) design freedom is required. Furthermore, these waveforms suffer from blind velocities which are serious problems, especially in radar systems with high carrier frequency or low PRF. This paper analyses the blind velocities problem and show that blind velocities are relative to variation of the PRF and/or the carrier frequency. Variable PRF techniques are widely used in conventional GMTI radar including multiple PRFs and variable pulse repetition intervals (PRI). Combined with the characteristics of the DDMA MIMO GMTI radar, this paper proposed two methods to mitigate blind velocities: “multi-PRF DDMA” which employs multiple PRFs over successive coherent processing intervals, and “PRI-dithered DDMA” which employs nonuniform sampling by dithered PRI in slow time. Simulation results demonstrate that both the methods are effective ways to mitigate blind velocities in DDMA MIMO GMTI radar systems.