Communications: radio wave antennas – Antennas – Including magnetic material
Reexamination Certificate
2003-04-21
2004-09-14
Vannucci, James (Department: 2821)
Communications: radio wave antennas
Antennas
Including magnetic material
C343S748000
Reexamination Certificate
active
06791505
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to radio engineering, in particular—to wave-systems, and can be suitably used for designing small-size antenna devices of diverse applications.
Emission and absorption of the electromagnetic wave energy using the known antenna devices can be carried out optimally when dimensions of an antenna are equal to, or multiple of quarter of wavelength of the emitted or received signal. In the real practice of construction of antenna devices it is often necessary to reduce the antenna dimensions, especially for their operation on low frequencies, and provide the directional effect of an antenna.
These goals are achieved using the known techniques of lengthening of antennas and construction of sophisticated directional effect antennas.
BACKGROUND OF THE INVENTION
A technique for lengthening of antennas is discussed below basing on the example of conventional vibrator
1
performing the role of an antenna having length l and oriented along axis z (FIG.
1
). Generator
2
of harmonic oscillations provides pumping of current I(&ohgr; t) into an antenna. Distribution of current along the antenna corresponds to I(z). Such antenna is characterised by parameter h of the antenna effective height:
h=
(∫
I
(
z
)
dz
)/
I
o
(1) (1)
where I
o
is operating value of the current at antenna pedestal.
When l=&lgr;/4, where &lgr; is wavelength of the emitted signal, it follows from (1) that
h=
(2/&pgr;)/
l=&lgr;/
2&pgr;
=h
opt
(2)
i.e. the effective height of antenna, h
opt
, in the optimum case is 0.637 of the actual height l.
FIG. 1
b
shows the spatial distribution of the electric and magnetic fields of vibrator
1
.
If l<&lgr;/4 (shortened antenna), then h<h
opt
, said inequality being maintained also using the techniques of artificial lengthening of antennas, shown in
FIGS. 2
a, b, c
that illustrate, respectively, antenna
3
of T-type, antenna
4
of &Ggr;-type, antenna
5
that has an additional inductance L at its pedestal. Such antenna lengthening techniques allow to provide the optimal distribution of current I(z) along an antenna. As regards the effective height h, for antennas
3
and
4
of T- and &Ggr;-types, when l<&lgr;/4, h=1, i.e. it is equal to the height of an antenna itself; and in case of antenna
5
having an additional inductance L (
FIG. 2
c
): h=l/2, i.e. the effective height is equal to half the antenna height.
Power of emission of dipole antennas is known to be determined by the following ratio:
P=
(
k h
2
I
o
2
)/&lgr;
2
(3)
where k≈1600. Value of (k h
2
)/&lgr;
2
is the effective resistance r
ef
of an antenna. Emission resistance r
em
≈2r
ef
. If l=&lgr;/4, i.e. h=h
opt
, then r
ef
≈40 Ohm.
If l<&lgr;/4, then, as it is obvious from expression (3), the emission resistance drops sharply (r
ef
≡h
2
). Thus, for example, when h=(⅓) h
opt
, then resistance r
ef
decreases almost ten times. When l<<&lgr;/4, then r
em
is negligible and, consequently, to provide a predetermined value of P
em
, current I
o
must be very strong, which results in difficulties in practical realisation. Further, a significant difference of value of r
ef
from the optimum value sharply reduces the possibility to match an antenna with a feeder path.
The directional effect of antennas is known to be provided by an appropriate spatial arrangement of a number of antenna elements. At that, the optimum value of P
em
is achieved when the distance between the antenna elements is multiple of &lgr;/4. Such arrangement also provides a required phase shift in separate antenna elements (vibrators), when in their spatial combination the passive antenna elements are present.
FIG. 3
a
shows a diagram of arrangement of symmetrical half-wave vibrator
6
and reflector
7
in plane (x, z), and
FIG. 2
b
shows pattern of such antenna in plane (x, y)
Thus, a decrease in the solid angle of propagation of the antenna-emitted (or received) electromagnetic energy (antenna gain) involves an increase in dimensions of an antenna system, which often results in serious technical problems in designing communication devices, in particular in case of the necessity to use signals in a relatively long-wave range
Hence, the objective of the invention consists in providing an antenna device that will be free of said drawbacks of the known antennas and provide a possibility to increase the antenna effective height, with small dimensions of a device and decreased dimensions in the wave propagation direction for the directional effect antennas
SUMMARY
More specifically, the objective of the invention consists in providing an antenna device wherein the nature of the electrodynamic processes effected therein will ultimately result in an increase in the effective resistance, i e an increase in the effective height, and, furthermore, the nature of the spatial-temporal distribution of electromagnetic field in such antenna device will provide directionality of propagation of the emitted waves, with electrical interrelationship between an antenna device and passive vibrators at the distances much less than &lgr;/4
The technical result to be attained is a significant growth of the antenna device emission resistance, and, consequently, an increase in the antenna effective height with dimensions of l<&lgr;/4 and l<<&lgr;/4, and a possibility to create a directional effect antenna device having the dimensions, in the direction of predominant propagation of the emitted and absorbed electromagnetic waves, that are much less than quarter of wavelength
Said technical result is achieved as follows in a method of increasing the effective height of a small-size antenna device, according to the invention,
formed is an antenna element in the form of an oscillating loop consisting of a reactive element and inductance coil that are connected in series, inductance value of which coil being selected such that to provide resonance of the oscillating loop at a predetermined frequency of a signal; the reactive element being provided in the form of a capacitor having a pair of metallic plates, the space between said plates being filled with a material containing particles of a conductive substance, which particles are separated by a dielectric filler, the distance between the capacitor plates being selected to be less than value &lgr;/4, where &lgr; is wavelength of the signals acting on the antenna device, the conductive substance being selected such that to meet the following conditions:
(&ohgr;&rgr;
2
&egr;&mgr;/x
o
)·10
−11
≧1, (1/&rgr;&ohgr;) 10
10
>>&egr;,
where &ohgr; is frequency of the operating signal; &rgr; is specific conductance of the conductive substance (Ohm·m); &egr;, &mgr; are, respectively, relative electric and magnetic permeabilities of a medium; x
o
is the least one of dimensions of cross-section of a conductive substance particle, which cross-section is perpendicular to direction of the acting electric field vector, (cm);
to the oscillating loop applied a signal, which signal causes a loop voltage to develop across the reactive element and brings about the loop voltage electric field in the space that surrounds the reactive element; thereby, in the signal transmission mode, provided is accumulation of the applied signal energy in the reactive element material, which accumulation is caused by the electrodynamic interaction of said material and electromagnetic field of the operating signal, with subsequent transformation of the accumulated energy into that of the emitted electromagnetic field in the proximate zone of the antenna device; and a flux of emission of electromagnetic power is formed;
and in the signal reception mode provided is absorption of the energy flux of the external electromagnetic field, which absorption is caused by interaction of said external electromagnetic field with electric field of the loop voltage in the proximate zone of the antenna device, with subsequent accumulation of the supplied en
A Minh Dieu
Advanced Micro Antennas LLC
Burns Doane Swecker & Mathis L.L.P.
Vannucci James
LandOfFree
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