Information
-
Patent Grant
-
6563469
-
Patent Number
6,563,469
-
Date Filed
Thursday, December 27, 200122 years ago
-
Date Issued
Tuesday, May 13, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Frishauf, Holtz, Goodman & Chick, P.C.
-
CPC
-
US Classifications
Field of Search
US
- 343 741
- 343 742
- 343 743
- 343 744
- 343 866
- 343 867
- 343 895
- 343 853
- 343 700 MS
- 343 850
- 343 857
- 343 858
-
International Classifications
-
Abstract
In order to feed at four points to a loop portion (12) made of conductor formed around a central axis (O) in a loop fashion along a peripheral surface of a cylindrical body (11) formed by rounding a flexible insulator film member (20) around the central axis in a cylindrical fashion, each of four feeders (13) formed on the peripheral surface of the cylindrical body comprises a vertical feeding portion (131) having one end (131a) grounded and another end (131b) extending toward the loop portion, a zigzag line (132) disposed between the other end of the vertical feeding portion and the loop portion, a tap (133) for feeding from a feeding terminal (13a) to the vertical feeding portion.
Description
BACKGROUND OF THE INVENTION
This invention relates to a digital radio receiver for receiving an electric wave from an artificial satellite (that may be called a “satellite wave”) or an electric wave on the ground (that may be called a “ground wave”) to listen in a digital radio broadcasting and, in particular, to a loop antenna for use in the digital radio receiver.
In recent years, a digital radio receiver, which receives the satellite wave or the ground wave to listen in the digital radio broadcasting, has been developed and is put to practical use in the United States of America. The digital radio receiver is mounted on a mobile station such as an automobile and can receive an electric wave having a frequency of about 2.338 gigahelts (GHz) to listen in a radio broadcasting. That is, the digital radio receiver is a radio receiver which can listen in a mobile broadcasting. In addition, the ground wave is an electric wave in which a signal where the satellite wave is received in an earth station is frequently shifted a little.
In order to receive such an electric wave having the frequency of about 2.338 GHz, it is necessary to set up an antenna outside the automobile. Although a variety of antennas having various structures have been proposed, the antennas of cylindrical-type are generally used rather than those of planer-type (plane-type). This is because a wider directivity is achieved by forming the antenna into a cylindrical shape.
A loop antenna is known in the art as one of the antennas of the cylindrical-type. The loop antenna has structure where one antenna lead member is wound around a peripheral surface of a hollow or solid cylindrical (which is collectively called “cylindrical”) member in a loop fashion, namely, is an antenna having the form of a loop. The cylindrical member may be merely called a “bobbin” or a “dielectric core” in the art. In addition, the antenna lead member may be merely called a “lead.” It is known in the art that the loop antenna acts as an antenna having a directivity in a longitudinal direction thereof if the antenna lead member has an all around length which is selected to about one wavelength. This is because the antenna lead member has a sinusoidal distribution of a current.
Although it is necessary for the loop antenna to feed to it, a four-point feeding is generally adopted to the loop antenna. In order to receive circular polarization, feeding is carried out at four points having a phase difference of 90 degrees from one another. The loop antenna with the four-point feeding is called in the art a four-point feeding loop antenna. In a conventional four-point feeding loop antenna, a feeding is directly carried out to a loop portion.
More specifically, the conventional four-point loop antenna comprises a cylindrical body formed by rounding a flexible insulation film around a central axis in a cylindrical fashion, a loop portion made of conductor that is formed on the cylindrical body along a peripheral surface thereof around the central axis in a loop fashion, and four feeders formed on the peripheral surface of the cylindrical body to feed the loop portion at four points. In addition, each of the four feeders consists of a vertical feeding portion and the loop portion is directly connected with each of the four feeders.
After the electric wave is received by the loop portion as a received wave, the received wave is divided through the four feeders into four partial received waves which are phase shifted and combined by a phase shifter so as to match phases of the four partial received waves to obtain a combined wave, and then the combined wave is amplified by a low-noise amplifier (LNA) to obtain an amplified wave which is delivered to a receiver body. A combination of the four-point feeding loop antenna, the phase shifter, and the low-noise amplifier is called an antenna unit.
In the manner which is described above, inasmuch as the conventional four-point feeding loop antenna comprises the four feeders each consisting of the vertical feeding portion and directly feeds to the loop portion from the four feeders, the conventional four-point feeding loop antenna is disadvantageous in that it has a too high feeding impedance. Thus, the conventional four-point feeding loop antenna is disadvantageous in that a special matching circuit for obtaining an impedance match is required aside from the four-point loop antenna.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a four-point feeding loop antenna into which a matching circuit is integrated.
Other objects of this invention will become clear as the description proceeds.
According to an aspect of this invention, a four-point feeding loop antenna comprises a cylindrical body formed by rounding a flexible insulator film member around a central axis in a cylindrical fashion. The cylindrical body has a peripheral surface. Made of conductor, a loop portion is formed on the cylindrical body along the peripheral surface around the central axis in a loop fashion. In order to feed to the loop portion at four points, four feeders are formed on the peripheral surface of the cylindrical body. Each of the four feeders comprises a vertical feeding portion having one end grounded and another end extending toward the loop portion, a zigzag line disposed between the other end of the vertical feeding portion and the loop portion, a tap for feeding from a feeding terminal to the vertical feeding portion.
In the above-mentioned four-point feeding loop antenna, the flexible insulator film member may substantially have a rectangular shape having an upper side, a lower side, a first lateral side, and a second lateral side. In this event, the cylindrical body is formed by connecting the first lateral side with the second lateral side. The loop portion may be formed on one surface of the flexible insulator film member in the vicinity of the upper side. The one end of the vertical feeding portion may lie on the lower side.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1A
is a plan view showing a four-point feeding loop antenna according to an embodiment of this invention;
FIG. 1B
is a front view of the four-point feeding loop antenna illustrated in
FIG. 1A
;
FIG. 2
is development of the four-point feeding loop antenna illustrated in
FIGS. 1A and 1B
; and
FIG. 3
is a plan view showing a circuit board for use in the four-point feeding loop antenna illustrated in FIGS.
1
A and
1
B.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to
FIGS. 1A
,
1
B,
2
, and
3
, the description will proceed to a four-point feeding loop antenna
10
according to an embodiment of this invention. The illustrated four-point feeding loop antenna
10
has a central axis O and comprises a cylindrical body
11
, a loop portion
12
, four feeders
13
.
The cylindrical body
11
is formed by rounding a flexible insulator film member (which will later be described) around the central axis O in a cylindrical fashion in the manner which will later be described. The loop portion
12
is made of conductor and is formed on the cylindrical body
11
along a peripheral surface thereof around the central axis O in a loop fashion. The four feeders
13
are formed on the peripheral surface of the cylindrical body
11
to feed to the loop portion
12
at four points. As the conductor of the loop portion
12
, for example, copper foil is used. In addition, the flexible insulator film member for use in the cylindrical body
11
, for example, plastic such as polyimide resin is used. In the example being illustrated, the cylindrical body
11
ha a diameter of 20 mm.
As shown in
FIGS. 1A and 1B
, the cylindrical body
11
has a longitudinal lower end which is fixed on a circuit board
14
. The circuit board
14
has a main surface
14
a
on which a phase shifter
15
is formed. The circuit board
14
has a back surface
14
b
on which a ground conductive pattern (not shown) is formed. In addition, the four feeders
13
have four feeding terminals
13
a
which are electrically and mechanically connected to input terminals of the phase shifter
15
by means of solder
16
.
Referring to
FIG. 2
, the flexible insulator film member
20
for use in forming the cylindrical body
11
substantially has a rectangular shape which has an upper side
20
U
, a lower side
20
L
, a first lateral side
20
S1
, and a second lateral side
20
S2
. By connecting the first lateral side
20
S1
with the second lateral side
20
S2
, the cylindrical body
11
is formed as shown in
FIGS. 1A and 1B
. This connection between the first lateral side
20
S1
and the second lateral side
20
S2
is carried out, for example, by using double-sided adhesive tape or an adhesive agent.
In addition, the loop portion
12
is formed on one surface of the flexible insulator film member
20
in the vicinity of the upper side
20
U
. While the cylindrical body
11
is formed by rounding the flexible insulator film member
20
, both ends of the loop portion
12
are electrically connected to each other.
In the example being illustrated, each of the four feeders
13
comprises a vertical feeding portion
131
, a zigzag line
132
, and a tap
133
. The vertical feeding portion
131
has one end
131
a
which is grounded and another end
131
b
which extends toward the loop portion
12
. The zigzag line
132
is disposed between the other end
131
b
of the vertical feeding portion
131
and the loop portion
12
. The tap
133
is for feeding from the feeding terminal
13
a
to the vertical feeding portion
131
. As shown in
FIG. 2
, the one end
131
a
of the vertical feeding portion
131
lies on the lower side
20
L of the flexible insulator film member
20
.
In addition, formed on one surface of the flexible insulator film member
20
, the loop portion
12
and the four feeders
13
may be made the same conductive material (e.g. copper foil).
As shown in
FIG. 3
, the circuit board
14
has four through holes
18
at positions which correspond to the respective ends
131
a
of the vertical feeding portion
131
. The ends
131
a
of the vertical feeding portion
131
are electrically connected through the through holes
18
to the ground conductive pattern formed on the back surface
14
b
of the circuit board
14
by means of solder
19
. As a result, the ends
131
a
of the vertical feeding portion
131
are grounded.
With this structure, by providing the feeder
13
with the zigzag line
132
, the vertical feeding portion
131
is added with an inductance component and it results in compensating a reactance component of the feeder
13
. In addition, by feeding through the tap
133
, it is possible to obtain an impedance match of the feeder
13
by adjusting a height of the tap
133
. When the height of the tap
133
increases, the impedance becomes higher. When the height of the tap
133
decreases, the impedance becomes lower. In other words, by providing the feeder
13
with the zigzag line
132
, it is possible to make the impedance at the feeding terminal
13
a
a pure resistance and it is possible to easily obtain the impedance match due to the tap
133
. Accordingly, it is unnecessary to provide the four-point feeding loop antenna
10
with a special matching circuit which is required in the conventional four-point feeding loop antenna.
In general, in the four-point feeding loop antenna, it is necessary to make the feeding impedance 50Ω. In the four-point feeding loop antenna
10
according to the embodiment of this invention, it is possible to lower an impedance at each feeding terminal
13
a
because the feeder
13
comprises the zigzag line
132
and the tap
133
as well as the vertical feeding portion
131
. It is therefore possible to make an impedance at an output terminal
15
a
of the phase shifter
15
50Ω.
On the contrary, a conventional four-point feeding loop antenna has a too high impedance at each feeding terminal
13
a
because the conventional four-point feeding loop antenna comprises feeders each of which consists of a vertical feeding portion alone but not includes a zigzag line and a tap. Thus, in the conventional four-point feeding loop antenna, a special matching circuit for obtaining an impedance match at an output terminal
15
a
of the phase shifter
15
is required aside from the four-point loop antenna, as mentioned in the preamble of the instant specification.
While this invention has thus far been described in conjunction with a preferred embodiment thereof, it will now be readily possible for those skilled in the art to put this invention into various other manners. For example, although the feeders
13
substantially extend in a normal direction to the lower side
20
L
of the flexible insulator film member
20
in the above-mentioned embodiment, they may substantially extend in an oblique direction to the lower side
20
L
of the flexible insulator film member
20
. In addition, although the taps
133
are formed on the flexible insulator film member
20
in the above-mentioned embodiment, they may formed as special separated lines independent of the flexible insulator film member.
Claims
- 1. A four-point feeding loop antenna comprising:a cylindrical body formed by rounding a flexible insulator film member around a central axis in a cylindrical fashion, said cylindrical body having a peripheral surface; a loop portion made of conductor, said loop portion being formed on said cylindrical body along said peripheral surface around said central axis in a loop fashion; and four feeders formed on the peripheral surface of said cylindrical body to feed to said loop portion to four points, each of said four feeders comprising a vertical feeding portion having one end grounded and another end extending toward said loop portion, a zigzag line disposed between the other end of said vertical feeding portion and said loop portion, a tap for feeding from a feeding terminal to said vertical feeding portion.
- 2. A four-point feeding loop antenna as claimed in claim 1, wherein said flexible insulator film member substantially has a rectangular shape having an upper side, a lower side, a first lateral side, and a second lateral side, said cylindrical body being formed by connecting said first lateral side with said second lateral side,said loop portion being formed on one surface of said flexible insulator film member in the vicinity of the upper side, and said one end of said vertical feeding portion lying on said lower side.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2001-300099 |
Sep 2001 |
JP |
|
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
5134422 |
Auriol |
Jul 1992 |
A |
5986616 |
Edvardsson |
Nov 1999 |
A |
6075501 |
Kuramoto et al. |
Jun 2000 |
A |