Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-02-15
2001-12-04
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S846000
Reexamination Certificate
active
06326923
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circular polarized microstrip antenna having a dielectric substrate with a patch electrode formed on one surface thereof, and a ground electrode formed on another surface thereof.
2. Description of the Prior Art
Recently, there has been an active move to incorporate a GPS antenna in portable equipment to thereby build a portable navigation system or obtain position information and the like by Cellular Phone in urgent communications, resulting in an increasing demand for very small-sized antennas.
FIG. 11
is a plan view of a conventional circular microstrip antenna
101
in wide use. The microstrip antenna
101
has a nearly square dielectric substrate
104
with a nearly square patch electrode
102
formed on one surface thereof, and a ground electrode (not shown) formed on almost the whole of another surface thereof. The patch electrode
102
has a feeding point
105
formed slightly away from the center thereof, to which power is fed through a coaxial cable (not shown) from the ground electrode. The patch electrode
102
has a pair of notches
102
a
and
102
b
formed so that they are positioned 135 and 315 degrees, respectively, with respect to a direction toward the feeding point
105
from the center of the patch electrode
102
, which is defined as 0 degree. These notches
102
and
102
b
, called retraction-separation elements, function to separate two modes (M
1
and M
2
in
FIG. 11
) perpendicular to each other, retracted in the microstrip antenna
101
, and enable the microstrip antenna
101
to send or receive right-handed circular polarized radio waves.
In the square microstrip antenna
101
thus configured, its resonance frequency fr is generally given by the following expression (1).
[Expression 1]
fr
=
c
2
a
eff
ϵ
r
a
eff
=
a
{
1
+
0.824
h
(
ϵ
e
+
0.3
)
(
a
/
h
+
0.262
)
a
(
ϵ
e
-
0.258
)
(
a
/
h
+
0.813
)
}
ϵ
e
=
ϵ
r
+
1
2
+
ϵ
r
-
1
2
(
1
+
10
h
a
)
1
2
(1)
In the expression (1), c is a light speed, ∈r is the relative dielectric constant of a relative dielectric substrate
104
, h is the thickness of the relative dielectric substrate
104
, and a is the length of one side of the square patch electrode
102
.
It will be appreciated from the above expression (1) that a small-sized microstrip antenna
101
is achieved by using the dielectric substrate
104
having a large relative dielectric constant ∈r. For example, where the microstrip antenna
101
is used for GPS receiving, when ∈r=20, the length of one side of the dielectric substrate
104
is approximately 25 mm, while, when ∈r=90, the length of one side of the dielectric substrate
104
is reduced to approximately 12 mm. For this reason, as the dielectric substrate
104
, microwave dielectric ceramics (hereinafter simply referred to as ceramics) having large relative dielectric constants ∈r are often used.
FIG. 12
represents changes of resonance frequency fr for variations in the size of one side of a square patch electrode. In the drawing, the dashed line G is for the dielectric substrate when ∈r=20, and the dashed line H is for the dielectric substrate when ∈r=90. As seen from
FIG. 12
, the larger is the relative dielectric constant ∈r, the greater are the changes of the resonance frequency fr for variations of the size of the patch electrode. Herein, size variations of the patch electrode affect not only the length of one side but also, e.g., the notches
102
a
and
102
b
, resulting in changing not only the resonance frequency fr but also a circular polarized wave generation frequency and even its axis ratio.
FIG. 13
represents changes of the resonance frequency fr for variations of relative dielectric constant ∈r. In the drawing, the dashed line I is for the dielectric substrate when ∈r=20, and the dashed line J is for the dielectric substrate when ∈r=90. It will be appreciated from
FIG. 13
that although the magnitude of relative dielectric constants contributes less in comparison with the case of
FIG. 12
, the larger is the relative dielectric constant ∈r, the greater are the changes of the resonance frequency fr.
Therefore, although the above-described conventional microstrip antenna
101
is advantageous in that it can be miniaturized by using the dielectric substrate
104
having a large relative dielectric constant ∈r, it is disadvantageous in that since it is greatly affected by variations in production quality and other factors, it is afflicted by resonance frequencies fr remarkably far from desired values, a large axis ratio, and other problems, resulting in reduced yields.
As a conventional method for solving these problems, a circular polarized microstrip antenna
110
as shown in
FIG. 14
is proposed. The microstrip antenna
110
has a nearly square (or circular) patch electrode
112
formed on one surface of a dielectric substrate
114
wherein projections
116
a
to
116
d
for axis ratio adjustment, and projections
117
a
to
117
d
and conductor cutout portions
118
a
and
118
b
for frequency adjustment are formed in predetermined positions of the patch electrode
112
. The projections
116
a
to
116
d
for axis ratio adjustment, which are retraction-separation elements, are formed 45, 135, 225, and 315degrees, respectively, with respect to a direction toward the feeding point
115
from the center of the patch electrode
112
, which is defined as 0 degree. The projections
116
a
and
116
c
are formed longer than the projections
116
b
and
116
d
. The projections
117
a
to
117
d
for frequency adjustment are formed 0, 90, 180, and 270 degrees, respectively, and the conductor cutout portions
118
a
to
118
d
for frequency adjustment are formed in the vicinity of the bases of the projections
117
a
to
117
d.
In the microstrip antenna
110
configured in this way, the projections
116
a
to
116
d
for axis ratio adjustment are each cut by an equal amount to adjust an axis ratio so that it becomes equal to or smaller than a defined value. If a resonance frequency after the axis adjustment is below a target frequency, the projections
117
a
to
117
d
for frequency adjustment are each cut by an equal amount to gradually increase the resonance frequency so that it becomes equal to the target frequency. If the projections
117
a
to
117
d
for frequency adjustment have been excessively cut to such an extent that the resonance frequency exceeds the target frequency, the conductor cutout portions
118
a
to
118
d
for frequency adjustment are cut to gradually decrease the resonance frequency so that it becomes equal to the target frequency.
On the other hand, if a resonance frequency after the axis adjustment is already equal to or greater than the target frequency, the conductor cutout portions
118
a
to
118
d
for frequency adjustment are cut to gradually decrease the resonance frequency so that it becomes equal to the target frequency. If the resonance frequency has decreased below the target frequency as a result of this operation, the projections
117
a
to
117
d
for frequency adjustment are each cut by an equal amount to gradually increase the resonance frequency so that it becomes equal to the target frequency.
As described previously, in the conventional microstrip antenna
110
shown in
FIG. 14
, since the projections
116
a
to
116
d
for axis ratio adjustment, and the projections
117
a
to
117
d
and conductor cutout portions
118
a
to
118
d
for frequency adjustment are formed in predetermined positions of the patch electrode
112
, the projections
116
a
to
116
d
for axis ratio adjustment are cut to adjust the axis ratio so that it becomes equal to or smaller than the defined value, and then the projections
117
a
to
117
d
and conductor cutout portions
118
a
to
118
d
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Phan Tho
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