共查询到20条相似文献,搜索用时 15 毫秒
1.
Beam Steering with Linear Arrays 总被引:7,自引:0,他引:7
The principles and techniques of real-time imaging with phased array ultrasound scanners are reviewed. Topics include 1) the geometric optics of beam steering and focusing with a linear array in the transmit and receive modes; 2) limitations on image data acquisition due to ultrasound propagation velocity; 3) optical diffraction theory for linear arrays including effects of amplitude grating lobes. Limitations on the image quality of phased array imaging systems are also discussed, including 1) nonideal response of array transducers; 2) target ambiguities caused by phase error grating lobes; 3) refraction errors; 4) delay line design. Finally, an analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatial compounding, frequency compounding, and parallel processing. 相似文献
2.
When designing a dipole 'panel', a unit building block for a TV transmitting dipole array, there are several constraints which need to be met viz. beamwidth, sidelobe levels, front to back ratio and input impedance. Theories on reflector backed dipole arrays have so far dealt with idealised or thin dipoles and with infinite reflector. They are not very useful for predicting sidelobe levels and front to back ratios nor would they be of any use to calculate the input impedance of an array of relatively thick dipoles which are often used in practice. Experimental procedures are usually employed by the designer and these have proved to be very time consuming. 相似文献
3.
介绍了两种适于毫米波应用的RF MEMS实时延时线的设计。首先,在设计中采用了一种新颖的RF MEMS拓宽调节范围的变容器结构,得到了最大变容比为5.39的在片测试结果。其工艺设计基于表面微机械工艺,采用了由5个掩模版组成的工艺流程。然后,在RF MEMS变容器设计的基础上,完成了用于原理论证的Ka波段RF MEMS实时延时线的仿真设计、工艺流片和在片测试。Ka波段RF MEMS实时延时线的在片测试结果显示,在28GHz时处于下降状态的插入损耗为-2.36dB;两端口在28GHz时的回波损耗都小于-15dB,而在5~40GHz的整个测试频率范围内的回波损耗都小于-10dB。在Ka波段RF MEMS实时延时线设计基础上,60GHz RF MEMS实时延时线的仿真设计已经完成并准备投片。 相似文献
4.
介绍了相控阵雷达天线在大扫描角及大瞬时带宽应用场景下延时补偿技术的发展概况。对天线阵列的波束色散现象以及延时补偿技术对天线方向图的影响进行了分析,并介绍了国内外的一些延时方案。依据延时实现架构,将其分为微波延时、表面声波延时、光延时以及数字延时四类。重点对微波延时的几种不同类型的实现形式进行了描述,并根据微波延时线实现载体的不同,分为GaAs 芯片、射频电缆、印制板和微同轴四种。另外,针对延时拓扑电路进行理论推导分析,说明单延时路径在电路设计上的优势,并分析了基态链路对延时路径的幅度、相位补偿和介质材料对延时量的误差引入。对相控阵雷达天线在大扫描角及大瞬时带宽应用场景下的延时补偿技术研究有一定参考价值。 相似文献
5.
LI Zheng 《半导体光子学与技术》2007,47(1):53-57
The system of a true-time delay line for X-band and 8-unit phased array antennas is introduced. Changing the length of a chirp grating with piezotranslator(PZT), the variable delay is obtained. The scheme is applied to X-band phased array radar whose searching data rate is 56/s. It is simulated that the beam squinting is influenced by the error of real time delay. The relation between the beamforming mode and its modifying volt is discussed. 相似文献
6.
实延时是相控阵天线波束合成的一种重要手段,而随着带宽和阵列单元数目的增加,光学实延时技术的采用已成为一种重要趋势.介绍了受激光子回波的物理现象,分析了这一现象产生的原理,说明了光实延时的产生方法. 相似文献
7.
A new optical configuration for switching light beams called a spherical Fourier cell is explained. Its use for optical true time delay is outlined. An experimental apparatus was constructed for a 6-bit delay system, with 2 bits demonstrated. Delays of 0, 2.1, 4.1, and 6.2 ns were measured. Loss and crosstalk measurements are also given. 相似文献
8.
光实时延时技术与相控阵技术的融合,解决了传统相控阵雷达的瞬时大带宽受限和波束偏斜问题.文中给出了光实时延时技术的思想,讨论了光实时延时技术出现的背景.分析了应用于光实时延时技术中的光纤光栅的原理,着重讨论了均匀光纤光栅和线性啁啾光栅,分别给出了基于两种光纤光栅的光实时延时的技术方案,在此基础上,讨论了受控于应变和温度的光纤光栅在光实时延时技术中的应用.最后讨论了一些技术上存在的问题.Abstract: Optical true time delay technology (OTTD) is the key technology for phase array antennas (PAA).By using OTTD,the beam squint and the restriction of instantaneous bandwidth are resolved.The principles of OTTD are given,the emergence background of OTTD is discussed.The theory of fiber Bragg grating(FBG) used in OTTD is analyzed,especially on uniform fiber bragg grating and linear chirped fiber Bragg grating.Two OTTD schemes based on FBG is presented,then some new kinds of FBG used in OTTD are discussed.Some technique hurdles are analyzed as well. 相似文献
9.
This paper shows how the mechanical panel displacement technique can be used effectively in order to smooth out omnidirectional patterns of TFD TV panel antenna arroys fed by progressive phase shift currents (Fig. la). 相似文献
10.
一种模糊函数时频差联合估计快速算法 总被引:1,自引:0,他引:1
直接相关时延估计方法仅适用于接收站和辐射源都相对静止的情况,若接收信号存在多普勒频差则会严重影响时差(TDOA)估计精度,为解决相关时延估计方法的局限性,采用基于模糊函数的时频差联合估计方法,并针对模糊函数计算量巨大的问题,提出一种变时频分辨率峰值搜索方法。利用GPU并行计算架构实现来实现算法,以提高算法效率,加快算法收敛速度。仿真试验结果表明了算法的有效性。 相似文献
11.
高精度快速可控光纤真延迟线实验研究 总被引:1,自引:0,他引:1
在相控阵雷达中使用光纤实时延迟技术,可实现大角度瞬时宽带扫描.利用半导体光放大器和法拉第旋转镜实现了快速切换的延迟线,此技术具有切换速度快,延迟精度高,输出功率恒定,偏振不相关等优点.实验结果表明,此结构能够实现1 ps的延时精度,误差不超过0.1 ps. 相似文献
12.
A new method is presented on constrained power synthesis for reconfigurable arrays of arbitrary geometry. Given a number of suitable masks, the algorithm yields excitation vectors whose array patterns belong to such masks, and for each array element the excitation amplitude holds constant during the pattern reconfiguration, so as to ensure phase-only control. Each excitation amplitude is optimized, and the method allows to control the dynamic range ratio (DRR) of the excitations. The solution to the synthesis problem is found as a point of the intersection between two suitable sets, by using the method of successive projections. The proposed method can also be used to solve problems of constrained beam scanning. To this aim it is sufficient to select a high number of masks, close to each other in the angular sector of interest and shaped in such a way as to reproduce the desired scanning beam. The algorithm yields array patterns belonging to these masks, thus performing a discrete scanning by phase-only control, and allows to control the DRR. Several numerical examples show the effectiveness and the capabilities of the method. 相似文献
13.
Passivity Analysis of Neural Networks With Time Delay 总被引:4,自引:0,他引:4
《Circuits and Systems II: Express Briefs, IEEE Transactions on》2005,52(8):471-475
The passivity conditions for delayed neural networks (DNNs) are considered in this paper. We firstly derive the passivity condition for DNNs without uncertainties, and then extend the result to the case with time-varying parametric uncertainties. The proposed approach is based on a Lyapunov–Krasovskii functional construction. The passivity conditions are presented in terms of linear matrix inequalities, which can be easily solved by using the effective interior-point algorithm. Numerical examples are also given to demonstrate the effectiveness of the theoretical results. 相似文献
14.
15.
16.
17.
《Antennas and Propagation, IEEE Transactions on》2009,57(5):1367-1372
18.
在长基线多站时差定位系统中,由于辐射源相对于不同的站存在不同飞行速度,导致各站接收信号存在多普勒差异,从而影响对辐射源的精确时延测量。研究了采用联合时延多普勒估计和广义互相关方法进行多普勒补偿并准确估计时延的方法。分析结果表明联合时延多普勒估计更适合于精确时延估计的要求。 相似文献
19.
20.
A True Time Delay Beamforming System Incorporating a Wavelength Tunable Optical Phase-Lock Loop 总被引:1,自引:0,他引:1
A true time delay (TTD) beamforming system incorporating a wavelength tunable optical phase-lock loop (OPLL) module is proposed and experimentally demonstrated. In the proposed system, instead of using a high-frequency intensity modulator to modulate the optical carrier with an RF signal, we use two laser diodes (LDs) that are phase locked to generate an RF signal, which is then sent to a fiber Bragg grating (FBG) prism to produce different time delays. Since no optical intensity modulator is used, the system can operate at much higher frequencies with a reduced cost. In addition, the use of only two wavelengths eliminates the power-penalty problem caused by chromatic dispersion. In the proposed approach, the wavelengths from the two LDs are phase-locked using a frequency-discriminator-aided OPLL. A TTD beamforming system, using the OPLL in combination with an FBG prism to achieve tunable time delays, is investigated. Experimental time-delay results are provided. 相似文献