Radar Performance Review in Clear and Jamming Environments

The performance of electronically scanned radar systems is evaluated for clear and barrage jamming environments. Radar figures of merit in jamming are derived for search and track modes and are directly related to antenna pattern relative sidelobe levels. A random sidelobe model is analyzed with various numbers of independent jammers. Probability distributions of detection probability are derived to determine detection performance versus average jamming level and number of jammers.     

Experimental Detection of Anomalous Mode-C Reports Using Radar Data

A new methodology to scan automated radar terminal system (ARTS-III) data for aircraft tracks exhibiting probable mode-C encoder/transponder faults is described. The tracks of more than 8000 climbing or descending aircraft, recorded at the Seattle-Tacoma terminal area, were analyzed using this method. Based on this sample, the probability of the previously recognized "stuck C-bit" error is estimated to be 0.44 percent (0.31-0.61 percent, 95 percent confidence). In addition, a new, more subtle error, here termed the "deficient response," was discovered which is estimated to occur with a probability of 0.77 percent (0.59-0.98 percent, 95 percent confidence). Subsequent tests found this new error to have much less impact on traffic alert and collision avoidance system (TCAS) performance than does the stuck C-bit error.     

An Analytical Expression for Correlation Accuracy

An analytical closed-form expression for the uncertainty in aligning two images is derived as a function of image area, data fidelity, scene correlation length, limiting sensor resolution length, and degree of geometrical distortion between the two images.     

Software Maintenance Criteria for Small Microprocessor-Based Systems

Criteria is provided for designing and implementing small microprocessor-based programs with the objective of enhancing their maintainability properties. Since microprocessor-based programs typically have relatively short schedules and low budgets. it is necessary to adapt maintainability enhancing practices for these projects in such a manner that their impact in these critical areas is not excessive. Since many of the practices which can be used to enhance maintainability actually coincide with those which improve productivity during software development, application of those practices should incur little or no added cost or duration to a microprocessor-based program. This paper suggests practical steps which can be applied to the software design and implementation activities, to the software documentation, and to the development environment which will enhance the maintainability of the resultant computer programs.     

Effects due to an artificial earth satellite in rapid motion through the ionosphere or the interplanetary medium

Conclusion In this paper we have been concerned with the results of theoretical calculations of the interaction between a fast moving body and a tenuous plasma. Particular attention was paid to the case where the velocity of the body is much smaller than the velocity of neutral particles and ions, while the dimensions of the body are sufficiently large in comparison with the Debye radius. Such conditions are realized during the motion of artificial satellites or space rockets through the ionosphere, or through the interplanetary medium in the immediate neighborhood of the earth. Although this case has, on the whole, been investigated quite extensively, there are still a number of problems which require further analysis. Firstly, it is necessary to take into account the effect of the electric field on the motion of ions in the near zone at the rear of the body. Another important problem is that of magnetic disturbances. In the case of scattering of radio waves by the trail of the body, it would be interesting indeed to know the increase in the effective cross-section in the resonance region in which 0. A number of other research problems which arise in the analysis of phenomena in the neighborhood of a moving body have been noted in the Introduction.In the lower layers of the ionosphere it is important to allow for the fact that the dimensions of the body are comparable with the mean free path. Under these conditions there is the further interesting problem of the heating and additional ionization of the plasma, the disintegration of the surface, and the emission of waves. At large distances from the surface of the earth, the dimensions of the body may become comparable with the Debye radius, and the velocity of the body in the given region may become smaller than the thermal velocity of the particles. The character of the various disturbances introduced by the body under these conditions will also require a special investigation.Thus, the interaction of a moving body with plasma leads to special and exceptionally varied effects. Disturbances due to the body are very considerable, so that the physical state of the region surrounding the body is very different from the state of the undisturbed medium.The above results indicate that the phenomena in the neighborhood of satellites and space rockets in the ionosphere, or the interplanetary medium, must be taken into account, in the processing of experimental data when it is required to deduce information about the state of the undisturbed medium. This is particularly important in the analysis of the results of measurements obtained with various types of probes. Considerable errors may be introduced if these effects are not allowed for.Further extensive experimental and theoretical studies of the structure of the disturbed region in the neighborhood of moving bodies in plasma are clearly necessary. Such investigations will, in particular, lead to the development of the most effective methods of studying the properties of the media through which satellites and space rockets travel.Translated from the Russian: Ob effektah vyzyvaemyh iskusstvennym sputnikom bystro dviimsja v ionosfere ili meplanetnoj srede (Uspehi fizieskih nauk 79, 23–80) by Express Translation Service.     

Hydrodynamic forces resulting from liquid motion in capillary tubes

The wetting kinetics of model tubes of different geometrical shape has been investigated theoretically and experimentally under conditions of simulated zero-gravity (earthbound laboratory experiments) and low gravity (sounding rocket experiments within the TEXUS-programme). The present note deals with the hydrodynamic forces (capillary-, friction-, inertia forces, etc.) resulting from capillary rise in cylindrical, conical and sinusoidal tubes. The rôle of these forces is studied numerically in some detail.     

A Note on Dynamic Range of Quantizers

Based on the relationship between the inputand output correlation functions for a symmetric2N step optimum quantizer withGaussian noise inputs a computer programwas generated to obtain plots of the inputnumber of levels versus dynamic range of thequantizer. For it to be physically useful thedynamic range should be related to the distortionin the fundamental band and thedesired harmonic suppression. A definitionbased upon these considerations is suggestedand curves are plotted for two different fundamentaldistortion levels and three differentlevels of harmonic suppression. It is foundthat, for low levels of harmonic suppression(0-20 dB range), the dynamic range can beincreased by tolerating a higher level of fundamentaldistortion. In the medium range ofharmonic suppression (20-35 dB), any increasein the dynamic range due to higherfundamental distortion levels disappearsfor high level quantizers (typically 4 bitsor more). For still higher harmonic suppression(40 dB or higher), the dynamic range ofthe quantizer is independent of the acceptablefundamental distortion.     

Range Dependent Waveform of an Active Weighted Pulse Compression Receiver

This paper presents the output waveform of a correlation techniquewhich incorporates time domain amplitude weighting and matchedfiltering. This scheme may be used in pulse compression radars wherefine target detail is desired over an increment of range, the rangewindow. Analytic expressions describing the amplitude, phase, andfrequency modulation of the output waveform are obtained for thecosine-squared weighted spectrum, truncated Taylor weighted spectrum,and cosine-cubed weighted spectrum with weighting mismatchas a parameter. The effects of such mismatches on the amplitude,phase, and frequency modulation of the compressed waveform areplotted. However, the methods used to obtain these results are generalenough to obtain output waveforms of other weighting functions similarlymismatched.     

Switchless Control Strategies for Minimum Time Frequency Transitions in Phase-Locked Loops

The problem of minimum time frequency transitions in phase-locked loops with both phase and frequency controls applied is investigated using Pontryagin's maximum principle. Typically, a type II secondorder loop with a damping ratio of 0.707 subjected to a step change in the frequency of its input signal is considered and switchless control strategies that force the transients in the loop to settle down in minimum time are obtained.