MIT辐射实验室丛书：电子时间测量技术

需积分: 0 33 浏览量更新于2024-07-21 收藏 24.91MB PDF 举报

"MIT辐射实验室丛书 V20-ELECTRONIC TIME MEASUREMENT" 该书是《雷达系统工程》丛书中的一卷，由美国麻省理工学院（MIT）的辐射实验室专家团队编写，该实验室在二战期间对雷达技术有着丰富的研发经验。这本书由麦克劳希尔出版社在1947年出版，旨在分享和总结他们在电子时间测量领域的专业知识。书中第一章“介绍”由Britton Chance撰写，探讨了极端短时间间隔和长时间间隔精确测量的技术。这些技术并不是新出现的，早在电气放电研究中就已有应用。作者列举了几种用于测量极短时间内隙的设备，如快速旋转光学系统（与摄影胶片配合使用）、克尔效应细胞装置和极高频示波器。这些设备能够达到大约10^-9秒的分辨率，即纳秒级别。另一方面，对于已知时间间隔的精确测量方法也经过了详尽研究，尤其是在光速或无线电波速度的测定中。最近且最精确的测量能实现大约五百万分之五的精度。这种高精度对于诸如测量电离层高度、雷达反射体距离以及物理仪器中核粒子速度等科学问题至关重要。在雷达技术中，需要结合上述两种方法的特点，以测量可变的时间间隔，这些间隔可能从10纳秒到更长。这反映了雷达系统设计中的核心挑战，即如何准确地确定信号从发射到反射回来所需的时间，进而计算目标的距离和速度。电子时间测量在雷达系统工程中的重要性不言而喻，它涉及到脉冲定时、信号处理和数据解析等多个关键环节。通过这些高级的时间测量技术，科学家和工程师能够开发出更为先进和精确的雷达系统，以应对各种军事和民用需求，例如空中交通管制、天气预报、地球观测以及空间探测等领域。

16 RADIO DISTANCE AND SPEED MEASUREMENTS

[SEC.27

preliminary data that indicate the potential usefulness of the combination

of phase and time demodulation for such a system.

Combinations of phase and time demodulation in micro}i ave radar

systems are not yet possible although phase demodulation may give a

very sensitive indication of increments of distance.

At this point it is desirable to refer to the accuracy of time discrimina-

tion obtainable with special displays involving superposition of two video

signals as in Loran. In an experimental test using synthetic signals free

from noise, the accuracy of time discrimination approached that obtain-

able by phase discrimination of the r-f pulse carrier (see Sec. 7.11). In

general, such accuracy would not be expected under practical conditions

of operation where appreciable noise would be present.

The accuracy of time and phase modulators used in measurement of

this type is discussed briefly in Sec. 3.14 and in considerable detail in

Chap. 5. It is sufficient to mention here that accuracies of 0.3 per cent

of full scale are readily obtainable with practical circuits.

With certain

arrangements, a cascade of a number of time- or phase-demodulation

circuits increases the accuracy by the product of the accuracies of the two

circuits that are cascaded (see Sees. 3.9 and 3.15 and Chap. 6). Consider-

ably less has been done to develop precision frequency modulators that

would be used for corresponding measurements in frequency-modula-

tion systems. The usual accuracies obtainable are approximately 1 per

cent and, as far as is known, no efforts have been made to cascade

frequency-demodulation systems as is usually done in time- and phase-

demodulation systems.

SPEED MEASUREMENTS

In radar systems having inadequate range and angle resolution, mov-

ing objects are sometimes distinguished from fixed objects—rocks, trees,

etc.—by speed measurements. The emphasis here is upon the means

for determining target speed as supplementary information to target

distance in order that prediction of future position of the target may be

obtained. In a number of special cases, prediction along a radial line is

sufficient, and the following discussion is confined to this subject. Rate

information can, of course, be obtained upon differentiation of displace-

ment measurements and this method is discussed in Sec. 2.11 and in

Chaps. 7 to 9. In scanning radar systems, the interval between dis-

placement measurements is often so great that a considerable time is

required before sufficient information is available to permit satisfactory

differentiation. Some aspects of this problem are re~-iewed in Sec. 2.14.

2.7. Continuous-wave Systems. —Figure 29 indicates a typical con-

tinuous-wave speed measurement system. It is based upon the elements

of Fig. 2.2 and takes advantage of the fact that the rate of change of the

RADIO DISTANCE AND SPEED MEASUREMENTS

[%c.

2.9

2.9. Pulse Systems.—Extemally -coherent Echo Interference.-In the

previously discussed systems the time delay between transmission and

reception of the pulse requires the maintenance of the phase of the trans-

mitted wave during this time interval in order to permit simultaneous

comparison of the phase of the transmitted and received waves.

The

necessity for the coherent oscillator derives from the fact that the trans-

mitted and received energies do not exist simultaneously at the transmit-

receive point. On the other hand, the incident and reflected energy are

coincident at the reflector for an interval equal to the pulse duration.

Extremely important methods of relative speed measurement, which

derive from this simple fact, are termed “external coherence. ” 1 External

coherence may be employed to measure the relative rate of a mov-

ing vehicle with respect to a stationary background or the relative

motion of portions of a large stationary object with respect to a moving

transmitter-receiver.

Retiive Speed of Vehicle and Ground.-The energy of the r-f pulse

incident upon a moving reflector is also incident upon the stationary

medium over which the object is moving. Experimental observations

and theoretical calculations have indicated that the phase shift due to a

large number of stationary scatterers is constant, even in the neighbor-

hood of a distinctive moving reflector;2 but the phase of the ener~

reflected from the moving object varies in accordance with the usual

doppler formula. The reflected energy then contains a component equal

to the sum or difference of the transmitted frequency and the frequency

corresponding to the rate of change of phase (doppler frequency) caused

by the motion of the object away from or toward the transmitter.

Although the speed of the moving object maybe determined by the dop-

pler frequency, information on its range must be obtained by time

demodulation.

Figure 2.12 shows the extreme simplicity of speed measurement by

this means. All the elements are parts of a conventional radar system

except the frequency meter. Since the energy reflected from the moving

and stationary targets contains both the transmitted frequency and this

frequency plus or minus the doppler frequency, phase discrimination is

accomplished in a simple detector. Practical considerations in the

design of these circuits are given in Vol. 19, Sec. 14.5, and in Vol. 1.

Time selection of the energy reflected from the desired target is, of

course, important in order to secure minimum target confusion and

1External coherence is often termed ‘‘noncoherent”

doppler detection. This

termisnot appropriatebecausetheenergyfrom stationaryscatterersis mhsrerdwith

the incidentradiation.

*A. J. F. Siegert,“Fluctuations in Return Signalsfrom Random Scatterers,”

RL Report No. 773, 1945.

剩余537页未读，继续阅读

和谐社区

粉丝: 9
资源: 16

MIT辐射实验室丛书：电子时间测量技术

MIT辐射实验室丛书 V17-COMPONENTS HANDBOOK

MIT辐射实验室丛书 V15-CRYSTAL RECTIFIERS

MIT-LCS-TR-212

dynamic locomotion in the mit cheetah 3 through convex model-predictive cont

超详细mit线性代数公开课笔记-完整

超详细mit线性代数公开课笔记-完整版

FileNotFoundError: [Errno 2] No such file or directory: 'D:\\作业\\一种典型心脏疾病的AI算法pychar\\代码\\data\\mit-bih-arrhythmia-database-1.0.0@.hea'

实验matlab对MIT-BIH心电信号处理，怎么才能处理的好

FileNotFoundError: [Errno 2] No such file or directory: 'mit-bih-arrhythmia-database-1.0.0/ANN.atr'

最新资源