IEEE Transactions on Aerospace and Electronic Systems

The tracking performance of a dithering loop in the presence of white Gaussian noise is analyzed and compared to the performance of a delay-lock loop. Performance curves are presented. View full abstract»

This paper describes two methods of generating an analog frequency-modulated waveform by the use of a small number of digital samples of the "chirp" waveform. The number of digital samples required is a function of the time-bandwidth product. For certain values of time-bandwidth product, this type of signal generation becomes extremely efficient. Several proofs are offered which show how to select... View full abstract»

Velocities of fluid flows and solid objects can be measured by performing photon count correlations on laser light scattered from the measuring region, the most common optical configuration being the laser Doppler system. A statistical analysis for the counting process is presented for both the constant velocity case and for turbulent fluid flows with formulations for specific laser Doppler config... View full abstract»

Recent developments in airborne Doppler and ground mapping navigation radars and ground and satellite based radio systems are described. Simultaneous lobing and slope tracking techniques can remove the well-known Doppler sea bias error in fast and slowly moving vehicles. Doppler velocity information can be extracted from coherent forward-looking mapping radars, and high position fixing accuracy ca... View full abstract»

This paper discusses the relationships that must be considered in analyzing the design and performance of typical precision stabilization systems. In particular, the disturbance inputs that are due to kinematic and geometrical coupling are examined in depth by considering systems implemented with either a conventional two-axis gimbal or a traditional half-angle mirror assembly. The disturbance cou... View full abstract»

In this paper an exact closed-form expression for the radar detection probability is derived and results are plotted for a frequency diversity radar receiver. The receiver model performs post-detection integration on all received pulses in all diversity channels. The target model assumed is the slow fluctuating Rayleigh-distributed (Swerling case I target) scatterer. Each of the M frequency divers... View full abstract»

Change in employment of engineers is shown to be related to the Deutsch and Shea Index of Engineering Demand. A relationship is given that shows the changes in engineering employment on a quarterly and annual basis. Engineering employment has turned upward for the first time since the last quarter of 1969. We have displaced and stored over 90 000 qualified engineers since 1969, in addition to disp... View full abstract»

A model is presented for the estimation of azimuth and elevation in a dispersive media where the signals come from a continuum of directions. These bounds depend upon the array ambiguity patterns and the channel spread function. Specific cases are discussed showing how the result reduces to an easily tractable analytical tool in many cases of interest. The model discussed is applicable to angular ... View full abstract»

The performance of angle of arrival estimates using an array in the presence of interfering signals is evaluated using the Cramer-Rao bound. To do this, a model for interference is developed which presents the interference as narrowband, temporally white, but spatially correlated, noise. The bound is evaluated and it is shown to depend upon the ambiguity function of the array and spatial correlati... View full abstract»

Sampling techniques provide a practical means of obtaining cross-correlation functions. In this paper, the correlation function is described by sums of the form Z = begin{equation*}Z = Sigma^{N}_{j=1}X_{j}Y_{j}end{equation*}. A general expression is derived for the probability density function of the random variable Z under the condition that Xj and Yj are stationary, jointly Gaussian random proce... View full abstract»

Future space exploration may involve communications between spacecraft moving at relativistic velocities. One of the significant problems associated with such communication is spectral distortion of signals which are propagated between relativistic frames. This distortion is generated by both changing propagation distances and purely relativistic electromagnetic field transformations. In this pape... View full abstract»

A statistical test is postulated for detecting, with an M-element hydrophone array, a Gaussian signal in spatially independent Gaussian noise of unknown power. The test is an extension of the uniformly-most-powerful (UMP) unbiased test for a two-element array. The output signal-to-noise ratio of the test is calculated and, for a large number of independent space-time samples, is shown to be no bet... View full abstract»

Several low-cost gyro-stabilized, bang-bang seeker assemblies for missile guidance and tracking applications have used similar physical structures. A magnetic dipole is an integral part of the gyro rotor assembly. The nominal spin axis of the gyro is colinear with the axis of a cylinder about which is wound a helix of wire. By properly modulating the current that is passed through that helix, the ... View full abstract»

Prominent among the commonly encountered gyro-stabilized assemblies used in guidance and tracking are those which are eddy-current torqued. Although eddy-current-torquecd lead- computing gunsights, which use spinning mirrors, have been well known for thirty years, it has been difficult to find an analysis of the torques developed by the precession mechanism. In this paper a model configuration of ... View full abstract»

The question of how multiple-pass data from the Navy Satellite System can be processed to yield an optimal estimate of the latitude, longitude, and elevation of a point on the Earth's surface is considered. It is demonstrated that the problem can be treated by use of modern estimation techniques. Two methods are considered: Kalman estimation and weighted least-squares estimation. The variance of t... View full abstract»

A mechanism by which an aircraft wake can interact strongly with the electromagnetic radiation present in an active elevated anomalous refractivity region (active feuillet) is analyzed. The aircraft wake structure, assumed to consist of twin contrarotating vortices plus entrained irrotational gas, trailing behind the wings of typical large aircraft is shown to be capable of descending a distance o... View full abstract»

In an earlier paper by the authors1 it was mentioned that atmospheric attenuation effects could be included by assuming that the attenuation is directly proportional to number of air masses. While this assumption is valid for the optical region, it is not true in the microwave region (1 to 40 GHz). For a clear atmosphere, the two constituents which absorb microwaves are oxygen and water vapor. An ... View full abstract»

Exact and approximate baseband models for the feedback FM demodulator are derived. Exact and approximate distortion equalizers that may be used to remove distortion in the output of the demodulator are also presented. View full abstract»

A comparison is made between optimum weighting, which maximizes Pd for a given α, and several MTI weightings. It is shown that a special case of the optimal weighting is approximately equal to the MTI weighting which maximizes the MTI improvement factor. View full abstract»

The performance of certain radars is degraded in environments with significant clutter returns, and since the clutter is signal-generated, increasing the transmitted power does not improve the situation. However, changing the pulse width and pulse period of the transmitted signal can increase the input signal-to-interference ratio. In this correspondence, the transmitted signal is made up of pulse... View full abstract»