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l/λ
,
d/λ
and
h/λ
,
i.e. they are defined by exclusively geometrical system size. (Here
l
- length of a
vibrator shoulder,
d
- distance between vibrators of the antenna,
h
- spacing
between the panel antennas and
λ
- wavelength).
The active and reactive components of mutual resistance depending on the
relative distance
d/λ
between vibrators are accepted both the positive, and the
negative values and in case of some
d/λ
values pass through zero. Similar
dependence is noticed in case of change of
h/λ
. Respectively, the active component
of the induced resistance can be positive or negative.
Radio signal propagation and, therefore, value of the induced resistance is
influenced by the restriction placed between antennas. Therefore, it is possible to
assume that the restriction-shield placed between panel antennas of mobile
network allows reducing vertical distance between antennas without
communication quality deterioration. There is a matter of the restriction-shield
shape. Indeed the restriction in the shape of, say, cutting-edge will not reduce but
increase the cross impact of antennas. Therefore, a smoothly changing shape of a
restriction-shield was selected for further research, so as wave’s diffraction on it
will have considerable loose as, for example, on a shield in the shape of a sphere,
cylinder or an ellipsoid of rotation.
An experimental installation has been created for these purposes. The
transmitting part consisted of the microwave generator G4-83 connected to funnel-
shaped antenna by coaxial cable and coaxial-to-waveguide transition.
The receiving part consisted of the funnel-shaped antenna connected to
Agilent E4407B spectrum analyzer through waveguide-to-coax transition and the
coaxial cable, as well. The restriction-shield was placed between the receiver and
transmitter. Frequency of the generator was selected equal to 10GHz (
λ
= 3 sm),
and simulation coefficient - equal to 11 that corresponded to operating frequency
range of GSM standard – 900MHz.
Block diagram of the installation to weakening an electromagnetic field on
restrictions of different shape is given in fig.2.
Experiments discovered that the power level on the receiver input decreases
in case of installation of restriction-shield in the shape of a sphere or cylinder in
average by twenty and more dB, i.e. 100 times and more. Therefore, the
restriction-shield in the shape of a sphere or cylinder gives an increase in
decoupling between antennas more than 100 times.
A great interest for us represents also an influence of value of the relative
spacing of
h/λ
between an antenna and a restriction as well as between two
116
antennas on value of the induced resistance, i.e. on value of the standing wave ratio
(SWR) in the panel antenna feeder.
Fig.2. Block diagram of the experimental installation on research of weakening a field on
restriction (1 – G4-83 microwave generator, 2 – coaxial cable, 3 – transmitting funnel-shaped
antenna, 4 – restriction-shield, 5 - receiving funnel-shaped antenna, 6 - spectrum analyzer)
A mobile panel antenna, restriction-shield made full-scale of the metal lath
with cells of 35 mm and a spectrum analyzer FSH-6 have been used for this
experiment. The spectrum analyzer had built-in generator which was connected to
the antenna, and dependence of SWR values on frequency was displayed on the
analyzer display.
Block diagram of the experimental installation on restriction-shield
influence on the SWR value in the feeder of transmitting panel antenna is shown in
fig. 3.
Fig.3. Block diagram of the experimental installation on research of restriction-shield influence
on the SWR value in the feeder of transmitting panel antenna (1 – spectrum analyzer FSH-6, 2 –
coaxial cable, 3 - antenna, 4 - restriction-shield)
A distance between antenna and a restriction-shield changed during the
experiment. It was discovered that existence of a restriction-shield brings an
increase of the SWR value in the feeder from 1,20 to 1,21. In case of increasing the
size of a restriction-shield from 40cm up to 75cm in diameter the SWR value
increased only for 0,05. That is, the extremely feeble dependence of the antenna
matching on value of
h/λ
and the size of a restriction has been observed.
A diagram of such an installation option of different mobile operators
antennas on one mast with use of a spherical shield is given in fig. 4.
Fig.4. A diagram of different mobile operators antennas on one mast with use of a spherical
restriction-shield (1 - panel antennas, 2 - a mast, 3 - feeder paths, 4 and 5 – BS transceivers, 6 –
a building roof, 7 – a restriction-shield)
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Also, one of the factors influencing on the value of antennas diversity is
spatial selectivity of antennas. But, since mobile station antennas have a wide
range of directivity, this factor can be neglected.
Thus, using restriction-shields between different mobile operators’ panel
antennas allows to considerably reducing the distance between antennas when
installing them on one mast and it can decrease a concentration of antenna masts
installation on roofs, especially in central representative areas of the cities. And
this, in turn, will improve esthetic architectural image of our cities.
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