Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
2001-11-13
2004-05-25
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S815000, C343S817000
Reexamination Certificate
active
06741220
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a cross dipole antenna suitable for being installed in telecommunication equipment employing circularly polarized waves, and to a composite antenna suitable for being used in a communication system employing both circularly polarized waves and linearly polarized waves.
BACKGROUND ART
Various proposals have been made on satellite communication systems for the purpose of mobile communication employing circularly polarized waves. As the satellite communication system, there are a geosynchronous mobile satellite system employing a geosynchronous satellite and a non-geosynchronous mobile satellite system employing a non-geosynchronous satellite.
As the non-geosynchronous mobile satellite system, there are a system employing a low/medium-earth orbit satellite, a system employing a highly elliptical orbit satellite and a system employing an inclined geosynchronous orbit. Among the above, there is the LEO (Low Earth Orbit) communication system as the system employing a low/medium-earth orbit. This LEO communication system is a system having a small propagation delay time. Moreover, as the propagation loss is also small, there is an advantage in that the transmission power can be reduced and it is easy to miniaturize the size and lighten the weight of the terminal.
In addition, with this LEO communication system, there are a small scale LEO (Little LEO) for handling only data transmission and a large scale LEO (Big LEO) capable of voice transmission. The Iridium system and ICO (Intermediate Circular Orbit) system (Project
21
) are included in this Big LEO. The communication method of the Iridium system is a TDMA (Time Division Multiple Access) method employing a frequency in a 1.6GHz band, and conducts communication with (66+6) non-geosynchronous satellites launched to an altitude of 780 km so as to cover the entire globe. These non-geosynchronous satellites are disposed at longitudinal 30° intervals for orbiting. In addition, the ICO system disposes 6 orbiting satellites in orthogonally inclined orbits of 10390 km, respectively, and the portable terminal thereof is a dual terminal capable of sharing satellite system networks utilizing satellites and existing ground system mobile phone systems.
With such satellite mobile communication systems, although numerous satellites are required, real-time voice and data communication is possible since the delay time can be disregarded. It is further possible to make the terminal portable since the transmission power of the terminal can be reduced. Thus, carrying a portable wireless device of such satellite mobile communication system will realize real-time communication and data transmission with telephones and mobile phones around the world. Circularly polarized waves suitable for portable wireless devices is employed in satellite mobile communication systems.
Incidentally, across dipole antenna or micro strip antenna capable of transmission and reception is employed in a portable wireless device of such satellite mobile communication systems since it is necessary to receive circularly polarized waves.
A cross dipole antenna is structured from two half-wavelength dipole antennae in which dipole antennae are orthogonally disposed in a cross shape. By mutually shifting the phase of two half-wavelength dipole antennae 90 degrees and exciting the same, circularly polarized waves are generated in a direction perpendicular to the face of the two half-wavelength dipole antennae. Here, as mutually opposing circularly polarized waves are generated in the two directions perpendicular to the face of the two half-wavelength dipole antennae, it is standard to place a reflecting plate at the position of approximately ¼ wavelength rearward of the two half-wavelength dipole antennae for unidirectional use. Further, in order to obtain circularly polarized waves within the range of a wide elevation angle, employed is an inverted V-shaped or inverted U-shaped dipole antenna which shows small directional change in the electric field face and magnetic field face.
FIG.
20
and
FIG. 21
show a fundamental structure of a conventional cross dipole antenna capable of transmitting and receiving this type of circularly polarized waves.
FIG. 20
is a diagram showing the fundamental structure of a cross dipole antenna
100
employing an inverted V-shaped dipole antenna, and
FIG. 21
is a diagram showing the fundamental structure of a cross dipole antenna
200
employing an inverted V-shaped dipole antenna.
The cross dipole antenna
100
employed in the inverted V-shaped dipole antenna shown in
FIG. 20
is structured of a reflecting plate
106
, an inverted V-shaped first dipole antenna formed of dipole elements
102
a,
102
b
disposed on such reflecting plate
106
, and an inverted V-shaped second dipole antenna formed of dipole elements
102
c,
102
d
disposed approximately orthogonal to the first dipole antenna.
This cross dipole antenna
100
, although not shown, comprises a phase shifter circuit in the inverted V-shaped first dipole antenna and inverted V-shaped second dipole antenna for mutually shifting the phase approximately 90 degrees and exciting the same. The cross dipole antenna
100
can thereby be used as a an antenna capable of transmitting and receiving circularly polarized waves, and it can further obtain circularly polarized waves in a range of a wide elevation angle since it is formed of an inverted V-shaped first dipole antenna and an inverted V-shaped second dipole antenna.
The cross dipole antenna
200
employed in the inverted U-shaped dipole antenna shown in
FIG. 21
is structured of a reflecting plate
206
, an inverted U-shaped first dipole antenna formed of dipole elements
202
a,
202
b
disposed on such reflecting plate
206
, and an inverted U-shaped second dipole antenna formed of dipole elements
202
c,
202
d
disposed approximately orthogonal to the first dipole antenna. This cross dipole antenna
200
, although not shown, comprises a phase shifter circuit in the inverted U-shaped first dipole antenna and inverted U-shaped second dipole antenna for mutually shifting the phase approximately 90 degrees and exciting the same. The cross dipole antenna
200
can thereby be used as an antenna capable of transmitting and receiving circularly polarized waves, and it can further obtain circularly polarized waves in a range of a wide elevation angle since it is formed of an inverted U-shaped first dipole antenna and an inverted U-shaped second dipole antenna.
Since the aforementioned cross dipole antennae are capable of transmitting and receiving circularly polarized waves, they may be employed in communication systems utilizing circularly polarized waves, such as satellite communication antennae and so on. Next, FIG.
22
and
FIG. 23
show the concrete structure of the conventionally proposed cross dipole antenna capable of transmitting and receiving circularly polarized waves.
FIG. 22
, however, is a plan view of the cross dipole antenna and
FIG. 23
is the front view thereof. This cross dipole antenna may be installed in automobiles, ships and vessels, aircraft, portable devices, and so forth.
The cross dipole antenna
300
illustrated in these diagrams is structured of two dipole antennae disposed to be approximately orthogonal and a reflecting plate
306
. The diameter D
3
of the approximately circular reflecting plate
306
is approximately &lgr;/2 to &lgr; when the wavelength of the center frequency in the used frequency band is set to &lgr;. The two dipole antennae disposed to be approximately orthogonal are structured from a first inverted U-shaped dipole antenna and a second U-shaped dipole antenna being orthogonally disposed. The first inverted U-shaped dipole antenna is structured from a dipole element
302
a
and a dipole element
302
b,
and the second inverted U-shaped dipole antenna is structured from a dipole element
302
c
and a dipole element
302
d.
Dipole elements
302
a
to
302
d
are formed of metal plates, and the approximate center thereof is folded
Connolly Bove & Lodge & Hutz LLP
Nippon Antena Kabushiki Kaisha
Phan Tho
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