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991.
Taylor H.P. Haroules G.G. Brown W.E. 《IEEE transactions on aerospace and electronic systems》1969,(4):581-588
In angle tracking antenna applications, the angle sensing boresight accuracy capabilities are important. The ability of an antenna to precisely determine the bearing angle to a point source is determined by the slope of the control function pattern at boresight. In the presence of extraneous interference, the magnitudes of the sidelobe and backlobe responses are important. Control pattern slope (angular sensitivity) is primarily a function of aperture illumination. It can be described by a current distribution in intensity and phase at every point. Once distribution is defined, lobe structure is defined by the associated transform. When more than one feed is used, the distribution will be a vector sum of the individual feed distributions. The resulting secondary pattern can be defined in terms of the amplitude distribution and the phase center locations of the contributing feeds. With a four-horn monopulse configuration, the feed phase centers are displaced from the boresight axis. Placing the phase centers on the boresight axis by rotating the feeds through 45 degrees results in a different set of intensity and phase values. A quite different secondary pattern results. The control function obtained by the subtraction of the powers from a paired set of on-axis feeds results in a lower sidelobe level than that obtained with a conventional monopulse combiner for a given feed taper. 相似文献
992.
If accurate first-order corrections for ionospheric delay are applied to VHF ranging signals, the second-order terms become dominant. Only with abnormally large values of ionospheric electron content do the second-order terms lead to serious errors, however. Since these terms can be estimated to within 10 percent, further correction can lead to very small position errors. 相似文献
993.
An inverse filter, contained in a recently published paper by Senmoto and Childers, is improved by the application of a shaping function derived by Turin in an earlier paper. 相似文献
994.
We present the resuIts of manned studies in which test subjects were exposed to simulated zero g (water immersion or head-down tilt at -6 degrees) and head-to-feet acceleration. The findings give evidence that humans have different individual tolerances to an acceleration of +3 Gz after exposure to zero g, whether simulated by immersion or by head-down tilt. The paper discusses the role of functional relationship between water balance and cardiac output in the establishment of adaptive reactions to simulated zero g. 相似文献
995.
A distribution-free detection procedure for a multiplerange-bin radar is described. This procedure is based on the ranks of observations, but does not require elaborate equipment for rapidly ranking large amounts of data. Proposed equipment is described and analysis and results are given comparing this new procedure with certain practical (nondistribution-free) procedures. Comparisons with some "best" theoretical procedures are also given. 相似文献
996.
997.
998.
Mirmak E.V. Blumgold R.M. Grimes G. 《IEEE transactions on aerospace and electronic systems》1977,(5):546-548
An analysis of the saturation and quantization noise generated by analog-to-digital (A/D) conversion of radar returns from targets with log-normal radar cross sections is presented. The results of the analysis show that the high-cross-section tails of the log-normal distribution require higher saturation levels to be set in the A/D converter. The setting of the higher saturation level in the converter results in an increase in quantization noise. Thus the minimum achievable distortion in the output of the A/D converter signal is considerably higher than that for radar targets if their radar cross section had an exponential power distribution. 相似文献
999.
Earlier investigators of troposcatter propagation phenomena have suggested that aircraft-created interference patterns observed at the receiving site can be used to measure aircraft motion within and near the common volume region. A simplified signal and scattering model is used to show that these interference signatures are ambiguous unless prior knowledge of the aircraft trajectory is available. 相似文献
1000.
The present knowledge of the structure of low-mass X-ray binary systems is reviewed. We examine the orbital period distribution of these sources and discuss how the orbital periods are measured. There is substantial observational evidence that the accretion disks in low-mass X-ray binaries are thick and structured. In a number of highly inclined systems, the compact X-ray emitting star is hidden from direct view by the disk and X-radiation is observed from these only because photons are scattered into the line of sight by material above and below the disk plane. In such systems the X-ray emission can appear extended with respect to the companion star, which can lead to partial X-ray eclipses. There are substantial variations in the thickness of the disk rim with azimuth. These give rise to the phenomenon of irregular dips in the X-ray flux which recur with the orbital period, or to an overall binary modulation of the X-ray flux if the source is extended. The X-ray spectra of low-mass X-ray binaries can be used to probe the innermost emission regions surrounding the compact star. The spectra of the bright Sco X-1 variables can be fitted with two components which are provisionally identified as originating in the inner disk and the boundary layer between the disk and the neutron star respectively. The characteristic energy dependent flaring of the Sco X-1 sub-class may be a geometric effect triggered by an increase in the thickness of the inner disk or boundary layer. The X-ray spectra of the lower luminosity systems, including the bursters, are less complex, and in many cases can be represented by a single power law with, in some sources, a high energy cut-off. Iron line emission is a characteristic of most low-mass X-ray binaries, irrespective of luminosity. 相似文献