Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
1998-09-23
2001-10-23
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
Reexamination Certificate
active
06307508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a flat antenna, and more particularly to an improved feeding method suitable for a coaxial cable connected to the feeder point of a flat antenna.
2. Description of the Related Art
Recently, simple flat antennas which can be manufactured at low costs have been developed as widespread antennas for the mobile communication system.
The flat antenna or thin antenna is configured, for example, by disposing a patch conductor cut to a predetermined size over a grounded conductive plate through a dielectric material. This structure allows an antenna with high sensitivity over several GHz rf waves to be fabricated in a relatively simple structure. Such an antenna can be easily mounted to appliances.
However, a problem arises in using the flat antenna resonating at a receive frequency and in designing a radiation resistance, or the impedance at the feeder point having a real-part component. That is, when received rf waves are taken out of the antenna or the coaxial cable for supplying transmission power to the antenna is connected to the patch antenna, various kinds of machining are required to match the impedance of the feeder point.
The above-mentioned problem will be described below with reference to FIG.
5
. FIG.
5
(
a
) is a cross sectional view partially illustrating a flat antenna. Referring to FIG.
5
(
a
), numeral
10
represents a patch antenna section made of a conductive plate sized so as to resonate to a received frequency,
11
represents a dielectric material, and
12
represents a grounded conductive plate.
Numeral
13
represents a center conductor of a coaxial cable disposed to feed power to the patch antenna section
10
. The outer conductor of the coaxial cable is grounded within the opening
12
A of the grounded conductive plate
12
.
The dielectric material
11
with a high dielectric constant is used to miniaturize the antenna. A thick dielectric material
11
of a large thickness generally provides a higher receive sensitivity and a wider receive band.
However, the center conductor
13
inserted into the dielectric material
11
induces an inductive impedance component L at the opening. In designing, the impedance at the feeder point of the patch antenna resonating at a specific receive frequency is usually set to have only a radiation resistance component. Hence, in order to cancel the inductive impedance L added to the terminal impedance of the coaxial cable, the center conductor
13
of the coaxial cable is disposed to pass though the feeder point of the patch antenna, as shown in
FIG. 5
, and the tip thereof is connected to a chip conductor
15
. The coaxial cable is matched with the patch antenna by means of the capacitive impedance C formed between the chip conductor
15
and the patch antenna section
10
.
FIG.
5
(
b
) shows a circular patch antenna in which like elements are represented with like numerals as shown in FIG.
5
(
a
). In the case of the conventional structure shown in FIG.
5
(
b
), in order to cancel the inductive impedance L added by the center conductor
13
of the coaxial cable penetrating the dielectric material, an island conductor
10
B insulated from the patch antenna is disposed at the feeder point of the patch antenna
10
A. The patch antenna
10
A is matched with the coaxial cable by means of the capacitance C defined by the gap t between the island conductor
10
B and the patch antenna
10
A.
Referring to FIG.
5
(
c
), an insulating material
15
is disposed between the patch antenna portion
10
and the dielectric material
11
. The center conductor
13
of the coaxial cable is connected to the chip conductor
16
disposed underneath the insulating layer
15
. Thus, the matching configuration which cancels the inductive impedance L is provided by adding the capacitive impedance C between the chip conductor
16
and the patch antenna section
10
.
As described above, in order to feed power with the coaxial cable, the conventional flat antenna is electrically matched to cancel the inductive impedance L of the center conductor penetrating the dielectric material
12
. Hence, the problem is that the patch antenna section must be machined to some degree so that the structure of the flat antenna is complicated.
SUMMARY OF THE INVENTION
The present invention is made to overcome the above-mentioned problems. The object of the invention is to provide a simplified flat antenna which can reduce fabrication costs.
According to the present invention, the flat antenna comprises a patch antenna section which is set to resonate at a predetermined frequency; a dielectric plate having one surface in contact with the patch antenna section and the other surface in contact with a grounded plate; and a coaxial feeder connected to the patch antenna section through both the grounded plate and the dielectric plate; the coaxial feeder having its center conductive portion which penetrates the dielectric plate and is connected to a feeder point of the patch antenna section; wherein the resonance frequency of the patch antenna section is set to a value higher than receive frequencies in such a manner that an inductive impedance component of said center conductive portion is nearly equal to a capacitive impedance component of the feeder point of the patch antenna portion over use frequencies.
In the flat antenna according to the present invention, the patch antenna section comprises a circular conductive plate.
In the flat antenna according to the present invention, the patch antenna section comprises a rectangular conductive plate.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.
REFERENCES:
patent: 4160976 (1979-07-01), Conroy
patent: 4218682 (1980-08-01), Yu
patent: 4386357 (1983-05-01), Patton
Futaba Denshi Kogyo Kabushiki Kaisha
Ho Tan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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