Communications: radio wave antennas – Antennas – With coupling network or impedance in the leadin
Reexamination Certificate
2001-07-18
2002-07-16
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
With coupling network or impedance in the leadin
C343S853000, C343S895000
Reexamination Certificate
active
06421026
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to antenna devices and, more particularly, to an antenna device composed of a multi-element antenna, operated at a plurality of frequencies and provided with matching circuits adapted for reflection coefficients.
2. Description of the Related Art
FIG. 1
shows a construction of a conventional antenna device-disclosed, for example, in U.S. Pat. No. 5,828,348; this example is the case of a 4-element antenna operated at two frequencies, and matching circuits connected to the 4-element antenna are the same.
In
FIG. 1
, symbols
101
a,
101
b,
101
c
and
101
d
denote antenna elements, symbols
102
a,
102
b,
102
c
and
102
d
denote parasitic antenna elements, symbols
103
a,
103
b,
103
c
and
103
d
denote matching circuits connected respectively to the antenna elements
101
a,
101
b,
101
c
and
101
d,
symbols
104
a
and
104
b
denote divider/combiner circuits using double branch line circuits for dividing an inputted signal into two signals with a phase difference of 90 degrees, numeral
105
denotes a 180-degree divider/combiner circuit for dividing an inputted signal into two signals with a phase difference of 180 degrees, and numeral
106
denotes an input/output terminal.
FIG. 2
shows a cylindrical dielectric
30
on the surface of which an antenna portion composed of the antenna elements
101
a,
101
b,
101
c,
101
d
and parasitic antenna elements
102
a,
102
b,
102
c,
102
d
of
FIG. 1
is provided. As shown in the figure, the antenna elements
101
a,
101
b,
101
c
and
101
d
are formed on the outer surface of the cylindrical dielectric
30
, while the parasitic antenna elements
102
a,
102
b,
102
c
and
102
d
are formed on the inner surface of inside diameter of the cylindrical dielectric
30
.
The operation of the antenna device will now be described.
A signal inputted to the input/output terminal
106
is divided by the 180-degree divider/combiner circuit
105
as signals having phases of 0 degree and −180 degrees. Thereafter, one of the signals is divided by the divider/combiner circuit
104
a
as signals having phases of 0 degree and −90 degrees, and the other is divided by the divider/combiner circuit
104
b
as signals having phases of −180 degrees and −270 degrees. At two operating frequencies f
1
and f
2
, the 180-degree divider/combiner circuit
105
realizes a phase distribution of 0 degree and −180 degrees, while the divider/combiner circuits
104
a
and
104
b
realize a phase distribution of 0 degree and −90 degrees.
In order to realize matching for each of the antenna elements
101
a,
101
b,
101
c
and
101
d
at the two frequencies f
1
and f
2
, a scattering matrix of the antenna is determined empirically or by calculation, and reflection coefficients in operation are determined using excitation amplitude and excitation phase. In this example, due to symmetry of the scattering matrix of the antenna and symmetry of the excitation phase, the reflection coefficients of the antenna elements
101
a,
101
b,
101
c
and
101
d
are equal. Accordingly, the matching circuits
103
a,
103
b,
103
c
and
103
d
connected respectively to the antenna elements
101
a,
101
b,
101
c
and
101
d
are the same.
The entire divider/combiner circuit composed of the 180-degree divider/combiner circuit
105
and the divider/combiner circuits
104
a
and
104
b
is large in size, as shown in FIG.
1
. Thus, as shown in
FIG. 2
, the entire divider/combiner circuit cannot be formed on the cylindrical dielectric
30
, and, therefore, only the antenna portion composed of the antenna elements
101
a,
101
b,
101
c,
101
d
and the parasitic antenna elements
102
a,
102
b,
102
c,
102
d
is formed on the cylindrical dielectric
30
.
FIG. 3
shows a conventional small-type divider/combiner circuit constructed by combining T branches with lines of unequal lengths. In the figure, symbols
107
a,
107
b,
107
c
and
107
d
denote excitation terminals, numeral
108
denotes an input/output terminal, and symbols
109
a,
109
b,
109
c
and
109
d
denote lines having lengths according to desired excitation phases. The lengths of the lines are such that
109
a
<
109
b
<
109
c
<
109
d,
and the excitation phase is progressively delayed in the order of
107
a,
107
b,
107
c
and
107
d.
In the small-type divider/combiner circuit composed of T branches and lines of unequal lengths shown in
FIG. 3
, where the antenna device is operated at a plurality of frequencies, it is difficult to realize excitation with progressive phase shifts of a predetermined angle at all the frequencies. For example, where the lines
109
a,
109
b,
109
c
and
109
d
are set for excitation with symmetric phases by providing progressive phase shifts of 90 degrees at a frequency f
1
, the progressive phase shifts of 90 degrees cannot be achieved but asymmetric excitation results at a frequency f
2
different from the frequency f
1
, and, therefore, the reflection coefficients at the antenna elements
101
a,
101
b,
101
c
and
101
d
are not equal to each other.
Since the conventional antenna devices are constituted as described above, there is the problem that the 180-degree divider/combiner circuit
105
and the divider/combiner circuits
104
a
and
104
b
for excitation with progressive phase shifts of a predetermined angle at operational frequencies f
1
and f
2
become very large, as shown in FIG.
1
.
Therefore, where the antenna elements
101
a,
101
b,
101
c,
101
d,
the matching circuits
103
a,
103
b,
103
c,
103
d,
the divider/combiner circuits
104
a,
104
b
and the 180-degree divider/combiner circuit
105
shown in
FIG. 1
are formed on respective substrates and the substrates are connected to each other by cables or other connecting mechanisms, there is the problem that the antenna device as a whole becomes very large.
Besides, in the case of the small-type divider/combiner circuit composed of the T branches and the lines of unequal lengths shown in
FIG. 3
, there is a problem that it is difficult to achieve excitation with progressive phase shifts of a predetermined angle at both the operational frequencies f
1
and f
2
, so that the reflection coefficients at the antenna elements
101
a,
101
b,
101
c
and
101
d
are not equal to each other, so that matching cannot be attained.
SUMMARY OF THE INVENTION
Accordingly, a general object of the present invention is to provide an antenna device in which the aforementioned disadvantages are eliminated.
Another and more specific object is to provide an antenna device which realizes smallness in size by using a small-type divider/combiner circuit such as the one shown in FIG.
3
and it is possible to attain matching of a multi-element antenna at a plurality of operational frequencies by connecting different matching circuits respectively to the antenna elements
101
a,
101
b,
101
c
and
101
d.
Still another object of the invention is to obtain an antenna device which is reduced in overall size by integrally forming antenna elements, matching circuits and divider/combiner circuits on a cylindrical dielectric.
According to the present invention, there is provided an antenna device comprising a plurality of antenna elements operated at a plurality of frequencies, a divider/combiner circuit for exciting the plurality of antenna elements at desired phases, and matching circuits each connected to the antenna element at one end and connected to the divider/combiner circuit at the other end, the matching circuits corresponding to reflection coefficients of the antenna elements determined by taking into account the coupling between the antenna elements occurring when the antenna elements are excited with corresponding excitation amplitudes and excitation phases at each of the frequencies.
This is effective in that it is possible to attain impedance matching of each of the antenna elements at the plurality of operational frequencies.
According to the present invention, there is p
Endo Tsutomu
Miyazaki Moriyasu
Nishino Tamotsu
Ohwada Tetsu
Ho Tan
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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