Aerospace and Electronic Systems Magazine August 2016 - 28

Pioneer Award The grounds for the SAT (theory of direct external problems) are completed by the consideration of the antenna field correlation properties. Knowledge of the correlation functions is necessary for solving a number of important practical problems such as defining the spread of amplitude and phase RPs at a certain angular sector, an analysis of reasonability of applications of angular diversity reception systems in the long-distance tropospheric propagation line, and estimation of the influence of field fluctuations in an incident wave on errors of the equi-signal-zone method. The correlation matrix of the field fluctuations for the linear antenna was investigated for different phase error variance and correlation radius values. The field correlation properties were thoroughly considered for a number of particular cases: c ≪ 1, α ≪ 1, and α ≫ 1, as well as for points that are symmetric with respect to the MMD. Examples that illustrate variations of a number of correlation dependences are given. The results of the field correlation properties analysis are then used for the correct definition of the SRL of an antenna with random errors. One can get an idea of the SRL of such an antenna by considering the mean level of SRL (by mean RP). However, this was not adequate to judge SRLs of separate RP realizations. Essentially more correct is an approach to the SRL estimate that is based on the calculation of functional FRP that characterizes the probability of the fact that the entire RP at a certain sector of angles y1-y2 will not go beyond some level characterized by the given function v(y). A procedure of functional FRP calculation is set forth and numerical examples are given. The antenna is considered good by side radiation if, at an acceptable shape of envelope function v(y), FRP is close to unity. The latter means that in practically any RP realization, a level of side radiation at a desired sector of angles y1-y2 will not go beyond the level v(y). In the second part of the book, a number of issues are investigated that concern the field statistics of four types of the antennas with random phase errors, which in some way differ from the simplest antenna that was presented in the first part of book. The following issues are considered in the second part of the book: C a linear antenna having arbitrary distribution laws of the source amplitudes and the variance of phase errors; C a linear equidistant array; C a rectangular aperture antenna; C a linear traveling-wave antenna (TWA). These were evaluated for mean power RPs, their widening, mean directivity, and MMD fluctuations. Results of these investigations are interesting on their own since these types of antennas find a wide application. Besides, a comparison of the obtained results with the analogous ones given in the first part of the book elucidates the influence of a number of factors on statistical characteristics of the antenna field. The results obtained for the first three antenna types, i.e., broadside antennas, qualitatively conform to those obtained for the simplest antenna. A procedure of calculations and their results for 28 TWA are of another character. The reason for this lies in the fact that in TWA antennas besides random local errors, nonlocal errors also take place, i.e., random disturbances of the system parameters, occurred at some place, influence the amplitude-phase distribution (APD) of all the consequent sources. Nonlocal errors affect the field statistics qualitatively in a different way than the local ones. Field statistics of TWA were investigated for the case of nonlocal phase errors. The third part of the book consists of two chapters. The first of them is devoted to a study of statistics of a diffraction image in the focal plane of an antenna (focusing system) when a wave with field amplitude and phase fluctuations impinges on it (see Figure 2(b)). This problem has a long history (a problem of scintillation and tremor of cosmic sources' image in telescopes) and is of interest for many specialists in radiophysics, antennas, acoustics, radiowave propagation, etc. This problem was theoretically considered (seemingly for the first time) by L. A. Chernov for the case of an incident wave propagating in the troposphere [3]. He obtained relations for the field mean intensity and fluctuations in the focal plane of the antenna. Further he restricted himself, by virtue of mathematical difficulties, by the consideration of a number of particular, sometimes trivial, cases. I managed to essentially supplement the results of Chernov's research. In particular, I obtained design formulas, suitable at arbitrary incident wave fluctuations, and built a series of plots for the mean intensity of the field, its fluctuations' variance, and correlation characteristics in the focal plane. When doing so, I essentially employed the results of the first part of book. This appeared to be possible because, as is shown in the book, at given statistics of the field in the aperture, formulas describing the field statistics in the focal plane of a paraxial focusing system and in its far-field region coincide. In the literature, this relation was almost not mentioned and moreover not employed. It, in essence, allowed uniting two earlier separate investigations into one common direction. Such a uniting is rather fruitful methodically and computationally. The second chapter of the third part of the book is devoted to application of SAT when analyzing antenna effects being observed at LDTP. As is known, the LDTP phenomenon, discovered in the 1950s, consists in the fact that a level of the field over the horizon is 5-6 orders in magnitude more than that calculated by Fock's diffraction formulas. Although the theory of this phenomenon is still debatable, it is accepted that LDTP is based on two mechanisms: scattering by turbulent inhomogeneities of the atmosphere (Figure 1) and scattering by lengthy inhomogeneities or by layers (the mechanism being close to coherent) in the atmosphere. The vagueness of the theory enhanced the importance of experimental investigations of LDTP. Such investigations were carried out at our chair under my leadership during the period 1957 to 1962. These investigations were widely supported by the ARTA leadership, as well as by the leadership of Anti-Aircraft Defense (AAD) Forces of Country. The investigations were carried out at 1.5 m, 10 cm, and 3 cm wave bands, totally in 40 lines of from 30 km to 350 km, at different daytimes, seasons of year, etc. High-quality radiolocation stations (RLS) of AAD Forces of Country were used at transmitting and receiving ends of the lines. The results of investigations were published in monograph [6] IEEE A&E SYSTEMS MAGAZINE AUGUST 2016

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine August 2016