Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2001-09-17
2002-08-20
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000
Reexamination Certificate
active
06437744
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circularly polarized wave antenna device used for e.g., communication equipment of a mobile unit.
2. Description of the Related Art
Satellite communication using an artificial satellite is being utilized in aircraft, cars, etc. and employs circularly polarized radio waves in order to eliminate regional difference. Particularly, small-sized circularly polarized wave antenna devices are required as antennas for radio equipment using circularly polarized waves, such as GPS (Global Positioning System), DAB (Digital Audio Broadcast) using S-band, ETC (Electrical Toll Collection) or the like. To meet this requirement, the present applicant has proposed a surface-mount circularly polarized wave antenna device and radio equipment using the same, in Japanese Patent Application Publication No. 2000-183637.
FIG. 11
shows the circularly polarized antenna proposed in the above-mentioned patent application.
In
FIG. 11
, the circularly polarized antenna has a flat-plate shaped substrate formed of a dielectric body. On one main surface of this substrate
1
, radiation conductor
2
which has a substantially rectangular shape in a plan view, and of which two diagonally opposite comer portions are cut off, is formed, while, on the other main surface thereof, a ground conductor
3
is formed substantially over the entire surface, except for a wraparound portion of a feeding conductor as described later. On one side surface of the substrate
1
, there is provided a strip-shaped feeding conductor
4
which extends from the main surface on which the ground conductor
3
is formed, to the main surface on which the radiation conductor
2
is formed, and each of the ends of the feeding conductor
4
are formed so as to wrap around one of the main surfaces. On opposite sides of the feeding conductor
4
, capacitive loading conductors
5
and
6
are formed substantially over the entire remaining surfaces while securing electrical isolation from the feeding conductor
4
, and these capacitive loading conductors
5
and
6
are connected to the ground conductor
3
.
In the circularly polarized wave antenna device with these features, a stray capacitance is formed between the feeding conductor
4
and the radiation conductor
2
, while a load capacitance or an electrostatic capacitance is formed between each of the capacitance loading conductors
5
and
6
and the radiation conductor
2
. In this case, since the corner portion of the radiation conductor
2
on the capacitive loading conductor
6
side is cut off, a load capacitance or an electrostatic capacitance between the capacitive loading conductors
6
and the radiation conductor
2
is smaller than that between the capacitive loading conductors
5
and the radiation conductor
2
.
When the power of a transmitting signal is supplied to the feeding conductor
4
, a resonant current in a linear polarization mode does not flow through the radiation conductor
2
, but resonant currents separated into two resonant circuits, that is, a high-frequency resonant circuit formed by the radiation conductor
2
and the capacitive loading conductor
5
, and that formed by the radiation conductor
2
and the capacitive loading conductor
6
, in other words, resonant currents in a degeneration-separated mode flow through the radiation conductor
2
. These two resonant currents in the degeneration-separated mode have a predetermined phase difference &thgr;
1
, generate two radiation electric fields having mutually different frequencies (f
1
and f
2
), and radiate circularly polarized electromagnetic waves from the radiation conductor
2
in the normal direction thereto.
However, in the circularly polarized wave antenna with the above-described features, the width L of the capacitive loading conductors
5
and
6
with respect to the length of the edge
2
a
of the radiation conductor
2
is large, so that the paths through which two resonant currents in the degeneration-separated mode flow, depends on the width L of the capacitive loading conductors
5
and
6
, the width L determining the load capacitance or electrostatic capacitance between the radiation conductor
2
and each of the capacitive loading conductors
5
and
6
. As a consequence, two radiation electric fields in the degeneration-separated mode do not have a phase difference of 90° therebetween, and the two radiation electric fields do not spatially intersect each other orthogonally. This results in elliptically polarized waves, and causes deterioration of the antenna characteristic.
Also, since the feeding conductor
4
and each of the capacitive loading conductors
5
and
6
are close to each other, the electromagnetic coupling between the feeding conductor
4
and each of the capacitive loading conductors
5
and
6
becomes large, and thereby the power of transmitting/receiving signals using the radiation conductor
2
becomes small, so that it is necessary accordingly to increase the power of transmitting/receiving signals to be supplied to the feeding conductor
4
.
Furthermore, under the condition that the dielectric constant of the substrate
1
is constant, when the area of the capacitive loading conductors
5
and
6
is increased, the load capacitance or electrostatic capacitance between the radiation conductor
2
and each of the capacitive loading conductors
5
and
6
becomes large, so that the resonant frequency in the degeneration-separated mode decreases. This causes a problem in that a desired frequency cannot be obtained.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above problems, and an object of the present invention to provide a circularly polarized wave antenna device which has improved the orthogonality of two radiation electric fields in the degeneration-separated mode.
In order to achieve the above-described object, the present invention uses the following configurations to solve the above-described problems. The circularly polarized wave antenna device in accordance with a first aspect of the invention comprises a substrate formed of dielectric material; a radiation conductor having a quadrangular shape in plan view, the radiation conductor being formed on one main surface of the substrate; a ground conductor formed on the other main surface of the substrate, the other main surface being opposed to the radiation conductor; and a feeding conductor formed on the substrate so as to extend from the other main surface toward the one main surface. In this circularly polarized wave antenna device, the radiation conductor is formed into a shape wherein the electric lengths in two orthogonal directions on the radiation conductor are equal to each other. On the substrate, capacitive loading conductors which generate load capacitance between the radiation conductor and the capacitive loading conductors, are provided at positions in the diagonal directions on the radiation conductor, the load capacitance determining the frequency difference between two resonant currents flowing through the radiation conductor.
The circularly polarized wave antenna device in accordance with a second aspect of the present invention comprises a substrate formed of dielectric material; a radiation conductor formed on one main surface of the substrate; a ground conductor formed on the other main surface of the substrate, the other main surface being opposed to the radiation conductor; and a feeding conductor formed on a side surface of the substrate so as to extend from the other main surface toward the one main surface. In this circularly polarized wave antenna device, the radiation conductor is formed into a square shape in a plan view, or an electrical square shape in a plan view. On the substrate, capacitive loading conductors which are formed between the ground conductor and the radiation conductor, and which have mutually different shapes between one of the diagonal direction and the other thereof, are provided at the extended positions of the two diagonal lines on the rad
Akiyama Hisashi
Itoh Shigekazu
Kawahata Kazunari
Yuasa Atsuyuki
Le Hoang-anh
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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