Antenna pulsewidth distortion paradox explained

A paradox of why there can be no pulsewidth distortion for an antenna array which is receiving or transmitting a wide-bandwidth chirp waveform is presented and explained. When a very narrow pulse is received at an off-boresite angle by an antenna array using phase steering, the pulse becomes distorted, that is, dispersed. The pulsewidth spreading is equal to the difference in the times of arrival of the pulse at the opposite ends of the antenna. However, if a wideband chirp waveform instead is incident on the antenna, no dispersion can be made to occur if the antenna is resteered toward the signal source during the time the chirp waveform is being received. The steering prevents frequency scanning of the antenna beam because of the changing carrier frequency of the linear FM chirp waveform. This represents a paradox because the dispersion still exists over the antenna. The author explains why the chirp signal is received undistorted at the output of the antenna in spite of the dispersion     

相控阵和雷达技术的突破

许多人认为雷达是一个成熟的领域,不会发生任何新的变化,这种看法存在很久了,没有比这个看法更错误的了。当我1950年参与到雷达领域的时候,我也有过同样的看法,例如,我认为麻省理工学院的雷达丛书已经是包罗万象了,不需要增加任何新的内容。然而我是多么的错啊,从那时起雷达技术领域中已经发生了许多令人眼花嘹乱的发展,雷达一直受益于Moore′s定律和许多新的技术上的成果,例如,MMICGaAsT/R组件和相控阵组件。现在雷达技术发展得更快了,在这篇文章里,我将给出某些最近突破的例子,所要提到的主题在图1中示出。     

Equivalence between voltage-processing methods and discreteorthogonal Legendre polynomial (DOLP) approach

There are three methods for solving the least-squares estimation (LSE) problem. (1) the power method; (2) the voltage-processing method (square-root method); and (3) the discrete orthogonal Legendre polynomial (DOLP) method. The first involves a matrix inversion and is sensitive to computer round-off errors. The second and third do not require a matrix inversion and are not as sensitive to computer round-off errors. It is shown that the voltage-processing LSE methods (Givens, Householder, and Gram-Schmidt) become the discrete orthogonal Legendre polynomial (DOLP) LSE method when the data can be modeled by a polynomial function and the times between measurements are equal. Furthermore, when the data can be modeled by a polynomial function and the time between measurements are equal, the DOLP is the preferred method because it does not require an orthonormal transformation and it does not require the back-substitution method     

Deep-space optical communications

A major problem in deep-space communication systems is that of obtaining high data rates (of the order of 107 bits per second). This article proposes some design concepts that indicate the probable feasibility of achieving wide-band communications by means of the laser. The example selected here is a hypothetical mission to Venus, chosen because of its great brightness and, hence, high background-noise level. Since no earth satellite relay is assumed, the communication channel includes the atmosphere. The down-link is the one considered because of its high-information-rate requirement.     

Multidimensional ambiguity functions of linear, interferometer, antenna arrays

Greater insight into the resolution and accuracy, as well as the data processing, of an interferometer radar is obtained in this partly tutoral paper by the examination of the multidimensional ambiguity function. Two approaches are used for determining the multidimensional ambiguity function. First, it is determined by the classical and more standard procedure in which the signals at the target and at the receiver antenna output terminals are found by the superposition of the signals of each antenna array element. The second method considers the antenna as a network having a specified frequency transfer characteristic which is dependent on the azimuth spatial coordinate of the target and on the axis of the antenna beam. Prime consideration is given to signals having large time-bandwidth products and wide bandwidth. Extensive plots are made for the multidimensional ambiguity function of the linear, interferometer, antenna array system. The analysis verifies the previously obtained result that the grating lobes of an interferometer radar can be eliminated by the use of very wide band signals. The results also show that a trade off can be made between the signal bandwidth and the number of array elements in order to achieve a specified sidelobe level. Furthermore, it is found that increasing the spacing between the array elements results in an improvement in the angular accuracy and resolution in direct proportion to the increase in spacing. This improvement is accrued without degradation in the estimation of the other target parameters or in detectability.