Aerospace and Electronic Systems Magazine August 2016 - 31
Shifrin
thereto should be added an increase in the number of situations when
antennas of different radio technical stations (RTS) are in the Fresnel
region with respect to each other, and aggravation of the electromagnetic compatibility (EMC) problem. The enhanced interest in
antennas focused at the Fresnel region was driven by the intensification of their use in near radio communication and radiolocation, in
measurers of antenna parameters, and in medical devices.
The investigations statistical characteristics of the field in the
Fresnel region are more complicated than those in the far-field region. In the Fresnel region, statistical effects are subject not only to
spatial angles, but also to a distance between an observation point
and an antenna. Even more complicated is a study of the focused
antenna statistics because one more parameter must be taken into
account-the focal distance, a change of which entails a change of
the statistical picture of the field in the entire space.
These investigations were carried out using special software
and tables we calculated. Formulas were obtained, and plots were
built that illustrated the variations in field statistics both in the
transverse planes at different distances from the antenna and along
the focal axis. When studying the focused systems, significant
attention was paid to the focal spot statistics-variations of its intensity, bounds, and transverse and longitudinal fluctuations. The
results of the field statistics in the Fresnel region and the field statistics of focused systems are given in detail in [18].
Generalization of SAT to Circular Aperture Antennas (jointly
with Vladimir V. Dolzhikov) [19]
The investigations of circular aperture antenna are important because they are among the most widespread antenna types. Under
consideration was the circular aperture antenna with random phase
errors given arbitrary values of α and с. For generality, statistics
of the characteristics of the antenna focused at the Fresnel region
were studied. Calculations for a circular aperture antenna are
significantly more bulky than those for a linear antenna. We investigated all three groups of statistical characteristics-the mean,
fluctuation, and correlation. The results for the circular antenna aperture were compared with those for the linear antenna. The results
we obtained have wide applicability. The theory is suitable both
for focused antennas and for ordinary (nonfocused) antennas in
their Fresnel and far-field regions. It is also suitable to use when
analyzing field statistics in the focal plane of the antenna, on which
a wave with field fluctuations impinges.
Statistical Array Antenna Theory (jointly with Leonid
G.Kornienko) [20]
Urgency of these investigations was stipulated by a wide introduction in use of phased array antennas (PAA) of different purposes.
They are of key importance when designing and assessing potentialities of active PAAs, wherein a role of randomness is especially
significant. The theory was built under rather general assumptions
on both parameters of the array antenna and character of random
errors in it. Besides errors in excitation of the array antenna elements, errors in their placement were taken into account.
General relationships for random errors' statistics and expressions for mean power RPs and mean directivities of array antennas
AUGUST 2016
with arbitrary APD were analyzed. Errors statistics were investigated in coordination with mechanisms of their origin, as well as
with typical excitation schemes of the array antenna. It is shown
that errors in radiators' placement are equivalent to uncorrelated
phase errors.
The theory was set forth in detail as applied to a linear equidistant array antenna. The mean summary and difference RPs and
their parameters, mean directivity, as well as the fluctuations of
MMD for the summary RP and those of equi-signal direction for
the difference RP were studied. A peculiarity of the theory is the
fact that many of the formulas were obtained in the analytic form.
This enabled us to establish laws of behavior of field statistical
characteristics for a wide range of error parameters' variations. A
number of simple and physically obvious formulas are given that
allow estimating statistical effects in different, practically important cases. Statistical characteristics of the field were studied at any
orientations of the RP major lobe. We investigated the dependence
of the mean directivity on the array antenna spacing and were able
to introduce corrections in the conventional recommendations for
choosing array antenna spacing.
For array antennas with a great number of radiators, when the
condition of major lobe uniqueness is satisfied, universal curves
suitable for discrete and continuous systems were obtained. This
enabled the specific results for difference RPs to be used for continuous systems where such RPs had not previously been used.
It is noted that, like for continuous systems, the errors' correlation radius dependences of mean RP width and MMD variance have a resonant character. The maximum of their values is
achieved at "intermediate" correlation radius values of the order of
several shares of antenna length.
The procedure of analyzing statistical characteristics of linear
antennas is multipurpose. It is the same for other array antenna
types (plane, ring, etc), only mathematical computations become
more complicated, and the weight of numerical calculations increases.
Statistical Synthesis. Superdirectivity in SAT (jointly with Leonid
G.Kornienko).
By natural progression of problems of the deterministic antenna
synthesis is a deterministic-statistical antenna synthesis whose feature is in the fact that random errors in an antenna are taken into
account from the very beginning, i.e. at a stage of the synthesis
problem statement. The synthesis is then carried out employing
criteria that are analogous to those employed in the deterministic
antenna synthesis theory. However, the criteria are formulated in
"SAT language," that is, using the antenna parameters inherent in
SAT. Problems of statistical optimization constitute a special class
of problems, which allow estimating the antenna potentialities by
these or those integral parameters.
We proposed the generalized antenna energy quality factor,
which, being subject to the kind of weight functions entering it,
describes the mean directivity, mean power scattering coefficient,
etc. The criterion includes the mean RP. This allowed taking into
account, in the statistical sense, the influence of random errors in
the APD and placement of radiators on the aforementioned inte-
IEEE A&E SYSTEMS MAGAZINE
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