Stationary coherent (hologram) radar and sonar

This letter enlarges on an earlier suggestion that the synthetic aperture of a moving, coherent (side-looking) radar (or sonar) could be replaced by a stationary, "hologram" form of receiving array.     

Ambiguity functions of laser-based chaotic radar

The ambiguity functions of a newly developed laser-based chaotic radar (CRADAR) system are studied. In the CRADAR system, the chaotic waveforms can be generated either by an optically injected (OI) semiconductor laser, or a semiconductor laser with optoelectronic feedback (OEF). The ambiguity functions of the chaotic pulsation and chaotic oscillation waveforms obtained experimentally from the CRADAR system with the respective OEF and the OI schemes are examined and compared. In the cross-ambiguity functions, both types of the chaotic waveforms demonstrate their excellent capabilities in the electrical counter-countermeasures (ECCM) that civilian and military applications desire. In the auto-ambiguity functions, the chaotic oscillation waveform shows better unambiguous detection quality than the chaotic pulsation waveform that an ideal thumbtack-like ambiguity function with minimal sidelobes is found. Moreover, variations in the peak value and the full width at half-maximum of the auto-ambiguity function of the chaotic oscillation waveform along the principal axes are also investigated. By having the features of both ultrawideband radar and random signal radar, the chaotic oscillation waveform of the CRADAR system with the OI scheme is shown to possess the advantages of high range resolution, excellent ECCM capability, ideal thumbtack-like ambiguity function, and uncoupled range and range rate resolution functions.     

Ambiguity function of interpulse Costas FH radar signal

A new radar waveform utilizing Costas sequences and interpulse Frequency Hopping (FH) technique is developed, which is a good high range resolution radar signal. The interpulse Costas FH coherent pulse train is introduced and the system block diagram using the interpulse Costas FH waveform is given. In the paper, ambiguity function is employed to study interpulse Costas FH radar. The mathematical expression of the ambiguity function for this waveform is derived. The advantages of the waveform are interpreted by computer simulation.     

基于剩余定理和一维集法的PD雷达解模糊处理

脉冲多普勒雷达在目标检测时常常存在距离和速度模糊问题,目前比较成熟的解模糊算法有余差查表法、剩余定理和一维集法。这几种算法各有优点和不足,适合不同的解模糊情况。根据距离、速度模糊的特点结合算法的优缺点,这里利用剩余定理解距离模糊,一维集法解速度模糊。     

Target position estimation in radar and sonar, and generalized ambiguity analysis for maximum likelihood parameter estimation

Target position estimation in radar and sonar means joint estimation of range and angle in the presence of noise and clutter. The global behavior of a maximum likelihood (ML) position estimator, and the clutter suppression capability of the system, can be written in terms of a range-angle ambiguity function. This function depends upon signal waveform and array configuration, i.e., upon both temporal and spatial characteristics of the system. Ambiguity and variance bound analysis indicates that system bandwidth can often be traded for array size, and direction-dependent signals can be used to obtain better angle resolution without increasing the size of the array. Wide-band direction-dependent signals (temporal diversity) can be traded for large real or synthetic arrays (spatial diversity). This tradeoff is apparently exploited by some animal echolocation systems. The above insights are obtained mostly from the properties of the range-angle ambiguity function. In general, an appropriate ambiguity function should be very useful for the design and evaluation of any ML parameter estimator. System identification methods and radio navigation systems, for example, can be optimized by minimizing the volume of a multiparameter ambiguity function.     

Signal analysis by means of time-frequency (Wigner-type)distributions-applications to sonar and radar echoes

Time series data have been traditionally analyzed in either the time or the frequency domains. For signals with a time-varying frequency content, the combined time-frequency (TF) representations, based on the Cohen class of (generalized) Wigner distributions (WD's) offer a powerful analysis tool. Using them, it is possible to: (1) trace the time-evolution of the resonance features usually present in a standard sonar cross section (SCS), or in a radar cross section (RCS) and (2) extract target information that may be difficult to even notice in an ordinary SCS or RCS. After a brief review of the fundamental properties of the WD, we discuss ways to reduce or suppress the cross term interference that appears in the WD of multicomponent systems. These points are illustrated with a variety of three-dimensional (3-D) plots of Wigner and pseudo-Wigner distributions (PWD). The plots are all obtained from an extensive analysis we have made over the years of the resonance acoustic echoes backscattered by a variety of elastic shells submerged in water, when they are excited by various types of incident pressure waves, including the short pulses generated by explosive charges. We also review studies we have made of the echoes returned by conducting or dielectric targets in the atmosphere, when they are illuminated by broadband radar pings. These short incident pulses are used to analytically model the performance of ultrawide band (UWB) radars, often called impulse radars. A TF domain analysis of these impulse radar returns demonstrates their superior information content     

Improvements in near-field discrimination for radar or sonar systems by the use of separate transmitting and receiving arrays

A recent letter described how the near-field discrimination of a radar or sonar could be improved by the use of multiplicative signal processing. This letter shows that similar improvements can be obtained by the use of a much simpler technique employing separate transmitting and receiving arrays.     

Random-signal sonar

The possibility of applying some random-signal radar proposals made by Poirier to a random-signal sonar is discussed A proposal for obtaining bearing information is presented, together with some experimental results. It appears that the limitations inherent in this type of random-signal system severely restrict the useful operation of a practical sonar.     

Extended sonar sequences

Sonar sequences were introduced by Golomb and Taylor in 1982. We introduce the concept of extended sonar sequences, which is similar to that of sonar sequences except that blank columns are permitted. Several constructions for extended sonar sequences are offered here. Some of these are close to constructions for ordinary sonar sequences, but they provide improvements to the list of best sonar sequences with up to 100 symbols     

Improved near-field discrimination by the use of multiplicative signal processing in c.t.f.m. radar or sonar

It is shown that the improved near-field lateral discrimination, already shown to be obtainable in a pulse radar or sonar by the use of multiplicative signal processing, can be obtained in a c.t.f.m. (continuous-transmission frequency-modulated) system.     

Tunable sonar transducer

Details are given of an underwater transducer which is tunable over the frequency range 250 kHz to 700 kHz. The structure comprises a pair of 50 mm-diameter lead zirconate titanate ceramic plates suitably mounted. The resonant frequency of the structure is electronically controlled by varying in a predetermined manner the amplitude and phase of the voltage applied to one of the ceramics.     

PZT铁电厚膜声纳换能器

综述了 PZT厚膜单元声纳换能器和 8× 8阵列声纳换能器的制备方法、结构和性能 ,并介绍了 PZT厚膜声纳换能器的应用及发展前景。该厚膜是利用改进的 sol- gel工艺制备的 ,厚度为 4～ 12 μm。4μm厚的 PZT厚膜的纵向压电系数 d3 3 为 140～ 2 40 p C/ N,剩余极化强度 Pr为 2 8× 10 - 6 C/ cm2 ,矫顽场强 EC为 30× 10 3 V/ cm,相对介电系数 εr为 140 0。     

Ambiguity resolution in self-cohering arrays

Two approaches to resolving the phase ambiguity associated with phase multilateration of self-cohering antenna arrays are described and the probability of ambiguity error is derived for each approach. For the minimum least square error method an efficient computational technique is introduced which permits element position uncertainties as large as one wavelength in the presence of phase measurement errors in the order of one rad. The multiple frequency method permits element position uncertainties significantly larger than one wavelength, at some increase in bandwidth. The probability of ambiguity error is shown to be acceptably small if the root mean square (rms) phase measurement errors are in the order of 0.5 rad or smaller.     

Ambiguity function simulator

It is shown that the magnitude of the ambiguity function can be easily displayed on a spectrum analyzer. The technique used employs delay lines operating only on the modulation waveform. Examples of measured ambiguity functions are given for FM sine waves. These results are shown to be in agreement with theory.     

基于模糊图的相位干涉仪解模糊方法

当基线长度大于半波长时,相位干涉仪测角系统存在相位差测量模糊的问题。针对此问题,首先推导出双基线相位干涉仪测角系统相位差模糊图的表达式,说明了相位差解模糊余量与正确解模糊概率的关系,指出了正确解模糊的限制条件,并提出一种基于相位差模糊图的解模糊方法。仿真分析验证了该方法的有效性。     

N-Sequence RSNS Ambiguity Analysis

The robust symmetrical number system (RSNS) is a modular system formed using Nges2 integer sequences and ensures that two successive RSNS vectors (paired terms from all N sequences) differ by only one integer. This integer Gray-code property reduces the possibility of encoding errors and makes the RSNS useful in applications such as folding analog-to-digital converters (ADCs), direction finding antenna architectures, and photonic processors. This paper determines the length of combined sequences that contain no vector ambiguities. This length or longest run of distinct vectors we call the RSNS dynamic range (Mcirc). The position of Mcirc which is the starting point in the sequence is also derived. Computing Mcirc and the position of Mcirc allows the integer Gray-code properties of the RSNS to be used in practical applications. We first extend our two-sequence results to develop a closed-form expression for Mcirc for a three-sequence RSNS with moduli of the form 2^r-1,2^r,2^r+1. We then extend the results to solving the N-sequence RSNS ambiguity locations in general     

A single-chip monolithic sonar system

A 12-W 200-kHz RF transmitter, a 10-W neon lamp display, and novel circuitry have been combined to realize a complete sonar system on a single monolithic chip which does not require any costly alignment adjustments. A single inductance-capacitance (LC) resonator is time-shared between the receiver and the transmitter to reduce external parts, to eliminate alignment labor, and to guarantee that the received signal is always the proper frequency.     

Digital signal processing for sonar

This paper is a tutorial which describes "main stream" sonar digital signal processing functions along with the associated implementation considerations. The attempt is to promote further cross-fertilization of ideas among digital signal processing applications in sonar, radar, speech, communications, seismology, and other related fields.     

前视声纳系统成像视觉改进与实现

视觉效果良好的声纳图像可以更加清晰地呈现水下场景,是目标定位与识别的重要依据.本文在多波束扫描成像模型的基础上,分析了影响前视声纳系统成像视觉的主要因素,并对系统进行了优化与实现.通道幅相校正改善了成像波束的指向性能,使得图像显示地更加均匀细腻;成像波束优化采用二阶锥规划方法设计了接收波束;动态范围优化采用开方处理,在保证灰度等级的同时,增强了图像细节信息的显示效果;扇形视图转换使得图像切合实际场景,更加符合人类的视觉感官,大大提升了用户体验.最后通过对复杂场景的成像测试验证了图像视觉效果改进方法的有效性.