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and Xu Zhen-zhong formed a chaos system for weak signal detection using
Dungfunction.Byintroducingtheauto-correlationmethodandcross-correlation
method respectively, the lowest signal to noise ratio was reduced to -77dB. The
combination of chaos and auto-correlation or cross-correlation detection method
has the advantages of time-domain such as simple, intuitionistic and feasible in
hardware, while reducing the detection threshold of normal detection ones[21].
The surfaces of traditional High-gain antennas are usually of parabola shape
with the caliber usually being circular. American scientist Nathan made the first
fractal antenna in the year 1988. But it didn't gain much attention until an ar-
ticle on studies of fractal antenna written by him was reported[22].The newly
developed fractal antenna has the characters of small size and multiband. Koch
fractal antenna is studied most in antenna miniaturization, as Koch monopole
performs better in space-filling than straight wire monopole at the same res-
onance frequency. While the number of iterations on the small fractal Koch
monopole is increased, the Q of the antenna approaches the fundamental limit
for small antennas[23].
Scatter communication happened mostly in troposphere, which is near to the
earth surface. Being the densest layer of earth atmosphere, 75% quality of at-
mosphere is contained in it with almost all the vapor and aerosol. So scatter
communication may be affected by clouds and rainfalls. Since 1960's,the prop-
agation of radio waves in the earth's atmosphere involving multiple frequency
bands has been widely studied[24]]. But it was dicult to forecast and calculate
the absorption and scattering of electromagnetic waves in rains because of the
lack of adequate statistical description of rains. To fill this vacancy in a certain
degree, S. A. Zhevakin built the fractal model of spatio-temporal chaos of rain
intensity permitting to calculate the fluctuations of electromagnetic wave inten-
sity by its passage through the rain with a few parameters. It was of help in
developing the physics of rains[25].
In humid atmospheric environments, soot aggregates frequently acquire a wa-
ter coating which effect the radiation of electromagnetic waves. Chao Liu et al
studies the influence of water coating on the scattering properties of fractal soot
aggregates. Through building fractal aggregates and using effective medium ap-
proximations to the models, their studies shows that water coating of the fractal
aggregates increases the forward scattering, extinction and absorption cross sec-
tions, and single-scattering albedo, but decreases the backward scattering [26].
Apart from all above, applications of chaos and fractal in scatter communica-
tion proposed involve signal encoding, encrypion or mapping, multiple access
techniques, constructing reproducible broadband waveforms, image compression
frequency selective channels and so on[27].
3.5 The Application of Chaos and Fractal in Other EM Scattering
Fields
Chinese scientist Zhen-song Wang and Bao-wei Lu developed the general the-
ory of multiple scattering of electromagnetic wave in fractal media by modifying
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