Information
-
Patent Grant
-
6549177
-
Patent Number
6,549,177
-
Date Filed
Wednesday, September 5, 200123 years ago
-
Date Issued
Tuesday, April 15, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Frishauf, Holtz, Goodman & Chick, P.C.
-
CPC
-
US Classifications
Field of Search
US
- 343 895
- 343 702
- 343 700 MS
- 343 841
- 455 90
-
International Classifications
-
Abstract
In an antenna unit (10) comprising a circuit board (11) having a principal surface (11a) and a back surface (11b) and an antenna element (12) mounted on the principal surface of the circuit board, a helical antenna having an axial direction extending in substantially parallel with the principal surface is used ad the antenna element (12). A shield cover (13) is added to the circuit board at the back surface (11b) so as to cover circuit elements (17) and shields the circuit elements arranged on the back surface of the circuit board. An output cable (14) is connected to the circuit elements inside the shield cover and is pulled out of the shield cover. The circuit elements include a low-noise amplifier (LNA) circuit (172).
Description
BACKGROUND OF THE INVENTION
This invention relates to an antenna unit used as a GPS (Global Positioning System) antenna.
As well known in the art, a GPS receiver is an apparatus for detecting a current position of a mobile station for a user by receiving electric waves radiated on an earth from a plurality of GPS (Global Positioning System) satellites which go over the earth.
As well known in the art, the GPS (Global Positioning System) is a satellite positioning system using military satellites under Department of Defense in Unite States control that comprise twenty-four non-geostationary satellites in total in six orbit surfaces every four satellites at an orbit height of about 20,000 km. The above-mentioned non-geostationary satellites (military satellites) are called GPS satellites. If the GPS receiver receives electric waves from four GPS satellites, it is possible to carry out a three-dimensional positioning. In this connection, if the GPS receiver receives electric waves from three GPS satellites, it is possible to carry out a two-dimensional positioning.
In other words, the GPS is a global positioning system comprising twenty-four artificial satellites launched by Department of Defense in United States, a control station on earth, and mobile stations for users. By using the global positioning system, it is possible to calculate a position, a moving direction, and a moving speed of the mobile station by measuring distances between the mobile station and three or more GPS satellites on the basis of time intervals taken for arrival of the electric waves. Although the global positioning system is originally used for military affairs, presently, it is widely applied to car navigation systems or the like. In addition, the mobile stations may be not only automobiles but also airplanes, ships, or the like.
Now, “car navigation” means to provide a driver information by displaying a position of a driver's driving car on a map of a car mounted machine at a real time, by displaying road traffic information, and by calculating the most suitable route up to a driver's destination.
A current used car navigation system calculates a latitude, a longitude, a height, and a time instant on capturing four or more GPS satellites and calculates the latitude, the longitude, and the time instant with the height fixed on capturing only three GPS satellites. In addition, the current used car navigation system calculates the latitude and the longitude using a time instant of an internal clock with the height fixed on capturing only two GPS satellites. Furthermore, the current used car navigation system carries out an error indication on capturing only one GPS satellite or no GPS satellite (see Japanese Unexamined Patent Publication Tokkai No. Hei 9-236650 or JP-A 9-236650.
Now, inasmuch as an electric wave called a GPS signal, which is generated by the GPS satellite and is arrived on the ground, has a very weak strength, the GPS signal may be buried in or covered with noises of electric waves on the ground. Accordingly, as the GPS signal, a PSK (Phase Shift Keying) wave which spread spectrum modulated by using a PN (Pseudo Noise) code is used and the GPS receiver comprises a LNA (Low Noise Amplifier) circuit for extracting the GPS signal from the noises and for amplifying an extracted GPS signal.
Attention will be directed to the car navigation system where the mobile station is a car or an automobile. In this event, a GPS antenna (or an antenna unit) is mounted on an outer surface of a body of the car by using magnets or the like. Specifically, it will be assumed that the GPS antenna (or the antenna unit) is a planer-type antenna. The planer-type antenna may be mounted on a metallic roof panel of the car or the like by magnetically attracting the planer-type antenna to the metallic roof panel. The GPS antenna (or the antenna unit) comprises an antenna element and a circuit board on which accompanied circuit elements including the above-mentioned LNA circuit are mounted. The planer-type antenna is called a patch antenna in the art.
In the manner which will later be described in conjunction with
FIG. 3
, the planer-type antenna has almost no gain (directivity) in a horizontal direction. Accordingly, it is difficult or unsuitable to mount the planer-type antenna on an inclined place.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an antenna unit which is capable of mounting the antenna unit on not only a horizontal place but also an inclined place such as a rear window or a front window of a car.
Other objects of this invention will become clear as the description proceeds.
According to a first aspect of this invention, an antenna unit comprises a circuit board on which circuit elements are mounted. The circuit board has a principal surface. Mounted on the principal surface of the circuit board, an antenna element is connected to the circuit elements. The antenna element comprises a helical antenna having an axial direction which extends in a direction in substantially parallel to the principal surface of said circuit board.
According to a second aspect of this invention, an antenna unit comprises a circuit board having a principal surface and a back surface opposite to the principal surface. Circuit elements are arranged on the back surface of the circuit board. Mounted on the principal surface of the circuit board, an antenna element is connected to the circuit elements. The antenna element comprises a helical antenna having an axial direction which extends in a direction in substantially parallel to the principal surface of the circuit board. Added to the back surface of the circuit board so as to cover the circuit elements, a shield cover shields the circuit elements.
According to a third aspect of this invention, an antenna unit comprises a circuit board having a principal surface and a back surface opposite to the principal surface. Circuit elements are arranged on the back surface of the circuit board. Mounted on the principal surface of the circuit board, an antenna element is connected to the circuit elements. The antenna element comprises a helical antenna having an axial direction which extends in a direction in substantially parallel to the principal surface of the circuit board. Added to the back surface of the circuit board so as to cover the circuit elements, a shield cover shields the circuit elements. An output cable is connected to the circuit elements inside the shield cover. The output cable is pulled out of the shield cover.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1
is a schematic side view showing an antenna body of a planer-type antenna which is used as an existing GPS antenna;
FIG. 2
is a schematic side view showing the exterior of the planer-type antenna illustrated in
FIG. 1
;
FIG. 3
is a view showing a radiation pattern (directional pattern) indicative of directive of the planer-type antenna (patch antenna);
FIG. 4
is a schematic sectional side view showing an antenna unit (GPS antenna) according to an embodiment of this invention;
FIG. 5
is a schematic perspective view showing an antenna body of the antenna unit illustrated in
FIG. 4
;
FIG. 6A
is a side view showing the antenna body illustrated in
FIG. 5
;
FIG. 6B
is a bottom view showing the antenna body illustrated in
FIG. 6A
;
FIG. 7A
illustrates a radiation pattern (directional pattern) of a four-phase helical antenna in a state where the four-phase helical antenna is stood up; and
FIG. 7B
illustrated the radiation pattern (directional pattern) of the fore-phase helical antenna in a state where the four-phase helical antenna is brought down.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to
FIGS. 1 and 2
, the description will proceed to a basic structure of a general planer-type antenna
20
which is used as a GPS antenna.
FIG. 1
is a schematic side view showing an antenna body of the planer-type antenna
20
.
FIG. 2
is a schematic side view showing the exterior of the planer-type antenna
20
.
As shown in
FIG. 1
, the antenna body of the planer-type antenna
20
comprises a circuit board
21
having an upper (a principal) surface
21
a
and a lower (back) surface
21
b
, an antenna element
22
, an a shield cover
23
. The circuit board
21
has an upper surface (a principal surface)
21
a
and a lower surface (a back surface)
21
b
opposite to the upper surface
21
a
. Circuit elements (not shown) including a low-noise amplifier (LNA) circuit are mounted or arranged on the lower surface (back surface)
21
b
of the circuit board
21
. The antenna element
22
is mounted on the upper surface (principal surface)
21
a
of the circuit
21
and is connected to the circuit elements. The shield cover
23
is added to the lower surface
21
b
of the circuit board
21
so as to cover the circuit elements and is for shielding the circuit elements. In addition, an output cable (a coaxial cable)
24
is pulled out of the circuit elements through the shield cover
23
.
The antenna body, which comprises the circuit board
21
, the antenna element
22
, and the shield cover
23
) is received between an upper case
25
and a lower case
26
as shown in FIG.
2
. The output cable
24
is pulled between the upper and the lower cases
25
and
26
through a gap (not shown) to the exterior of the planer-type antenna
20
and may be connected to a receiver body (not shown) of a GPS unit.
In addition, the lower case
26
has a bottom surface
26
a
on which permanent magnets (not shown) are mounted to enable the planer-type antenna
20
to magnetically attract on a surface of a roof panel of a car. The principal surface
21
a
of the circuit board
21
and the bottom surface
26
a
of the lower case
26
substantially extend to be parallel with each other. Accordingly, the principal surface
21
a
of the circuit board
21
in the planer-type antenna
20
substantially extends along a horizontal direction.
In addition, the antenna element
22
comprises a ceramic body
221
having a substantial rectangular shape, a reception surface
222
mounted on an upper surface of the ceramic body
221
, and a feeding pin
223
. The feeding pin
223
penetrates the ceramic body
221
and the reception surface
222
to connect the reception surface
222
with the circuit elements. The antenna element
22
having such a structure is called a “patch antenna” in the art.
Now, the planer-type antenna
20
(the patch antenna
22
) illustrated in
FIGS. 1 and 2
has a directivity as shown in FIG.
3
. More specifically, the planer-type antenna
20
has a radiation pattern (a directional pattern) which has the largest value (the maximum gain) in a vertical direction to the principal surface
21
a
of the circuit board
21
. However, it is seen that the radiation pattern (directional pattern) of the planer-type antenna
20
has almost no gain (directivity) in a direction in parallel with the principal surface
21
a
of the circuit board
21
. This means that the planer-type antenna
20
cannot receive any electric wave in the direction in parallel with the principal surface
21
a
of the circuit board
21
(i.e. any electric wave having an angle of elevation of zero from GPS satellites).
On the other hand, as described above, it is necessary for a car navigation system to capture at least four GPS satellites (or receive GPS signals from the at least four GPS satellites) in order to position an almost collect current position in a mobile station for a user. In addition, inasmuch as the GPS satellites always move, an angle of elevation of the GPS satellite to be captured is not always high.
Accordingly, in order to capture not only the GPS satellites having a high angle of elevation but also the GPS satellites having a low angle of elevation, it is necessary to mount the planer-type antenna
20
on the car so that the principal surface
21
a
of the circuit board
21
is put into as horizontally as possible. This is because it is impossible to receive an electric wave in a direction in parallel with the principal surface
21
a
of the circuit board
21
if the planer-type antenna
20
is mounted or fixed on the car with the principal surface
21
a
of the circuit board
21
slanted off the horizontal. Therefore, a mounted place of the existing GPS antenna (planer-type antenna)
20
is restricted to a horizontal position such as the roof panel of the car. In other words, it is unsuitable and not desirable that the planer-type antenna
20
is mounted on an inclined place such as a rear window or a front window of the car.
Users for the car navigation systems wish that an antenna unit (GPS antenna) may be mounted not only on such as a horizontal place but also on an inclined place and want degrees of freedom as regards the mounted place.
The present inventors have been made extensive studies and considered various ideas in order to achieve a structure which enables an antenna unit to be mount not only on a horizontal place but also on an inclined place. As described above, inasmuch as the existing antenna element (patch antenna) has the radiation pattern (directional pattern) which has the largest value (the maximum gain) in a vertical direction to the principal surface of the circuit board and which has almost no gain (directivity) in a horizontal direction, it is practically difficult to mount the planer-type antenna with the planer-type antenna put into an inclined state. Accordingly, the present inventors arrived at an idea to use, as the antenna element, ones having a gain (directivity) in a direction in parallel with the principal surface of the circuit board and having a different directivity compared with the existing one.
So, the present inventors looked for candidacy for an antenna element having such as a directivity. The present inventors realized that a helical antenna is suitable for the candidacy. This is because the helical antenna has a radiation pattern (directional pattern) which has the largest value (the maximum gain) in an inclined direction to an axis (a slant transverse) without in an axial direction (longitudinal) of the helical antenna. In addition, the helical antenna comprises a cylindrical member made of insulator and at least one antenna lead wound around an outer peripheral surface of the cylindrical member in a helix fashion. Accordingly, the present inventors arrived at a conclusion that if the helical antenna is mounted on a circuit board so that the helical antenna has an axial direction in parallel with a principal surface of the circuit board, such an antenna unit ought to have a gain (directivity) in a direction in parallel with the principal surface of the circuit board (in the axial direction of the helical antenna).
Referring to
FIGS. 4
,
5
,
6
A, and
6
B, the description will proceed to an antenna unit
10
according to a preferred embodiment of this invention.
FIG. 4
is a schematic sectional view showing the antenna unit
10
.
FIG. 5
is a schematic perspective view showing an antenna body of the antenna unit
10
.
FIG. 6A
is a side view showing the antenna body illustrated in FIG.
5
.
FIG. 6B
is a bottom view showing the antenna body illustrated in FIG.
6
A. The illustrated antenna unit
10
is used as a GPS antenna of a GPS receiver for use in a car navigation system.
The antenna unit
10
comprises a circuit board
11
, an antenna element
12
, a shield cover
13
, and an output cable (a coaxial cable)
14
. The circuit board
11
has an upper surface (a principal surface)
11
a
and a lower surface (a back surface)
11
b
opposite to the upper surface
11
a.
As shown in
FIGS. 6A and 6B
, various circuit elements
17
including a phase shifter circuit
171
, a low-noise amplifier (LNA) circuit
172
, and so on are mounted or arranged on the lower surface (back surface)
11
b
of the circuit board
11
. The antenna element
12
is mounted on the upper surface (principal surface)
11
a
of the circuit board
11
and is connected to the circuit elements
17
. The shield cover
13
is added to the lower surface
11
b
of the circuit board
11
so as to cover the circuit elements
17
and is for shielding the circuit elements
17
. The output cable (coaxial cable)
14
is pulled out of the circuit elements
17
to the exterior through the shield cover
13
. A combination of the circuit board
11
, the antenna element
12
, and the shield cover
13
serves as the antenna body received between an upper case
15
and a lower case
16
both of which are made of resin. The output cable
14
is pulled out of the lower case
16
to the exterior through a gap (not shown) and is connected to a receiver body (not shown) of the GPS receiver.
According to this invention, a four-phase helical antenna is used as the antenna element
12
. More specifically, the four-phase helical antenna
12
comprises a cylindrical member
121
made of insulator. The cylindrical member
121
may be called a bobbin or a cylindrical dielectric core. The cylindrical member
121
has an outer peripheral surface
121
a
. The four-phase helical antenna
12
further comprises four antenna leads
122
which are wound around the outer peripheral surface
121
a
of the cylindrical member
121
in a helix fashion. The four-phase helical antenna
12
is mounted on the principal surface
11
a
of the circuit board
11
so that four-phase helical antenna
12
has an axial direction in substantially parallel with the principal surface
11
a
of the circuit board
11
. In addition, in the manner known in the art, the helical antenna may receive circular polarization.
The four antenna leads
122
are connected to the phase shifter circuit
171
. After the GPS signal from the GPS satellite is received by the four antenna leads
122
as four received waves, the four received waves are phase shifted and combined by the phase shifter circuit
171
so as to match phases of the four received waves to obtain a combined wave, and then the combined wave is amplified by the low-noise amplifier (LNA) circuit
172
to obtain an amplified wave.
In addition, the antenna element
12
may comprise a single-phase helical antenna having only one antenna lead. In this event, the phase shifter circuit
171
is removed from the circuit elements
17
.
Referring to
FIGS. 7A and 7B
, attention will be directed to a radiation pattern (directional pattern) of the four-phase helical antenna
12
.
FIG. 7A
illustrates the radiation pattern (directional pattern) of the four-phase helical antenna
12
in a state where the four-phase helical antenna
12
is stood up.
FIG. 7B
illustrated the radiation pattern (directional pattern) of the four-phase helical antenna
12
in a state where the four-phase helical antenna
12
is brought down.
As apparent from
FIG. 7A
, in a case where the four-phase helical antenna
12
is stood up, the four-phase helical antenna
12
has the radiation pattern (directional pattern) having the largest value (the maximum gain) in an inclined direction to the axial direction (slant sidewise) or the inclined direction to a horizontal plane by a predetermined angle θ without the axial direction of the four-phase helical antenna
12
(a vertical direction). In the example being illustrated, the predetermined angle θ is equal to about 30 degrees.
Accordingly, the four-phase helical antenna
12
has a directivity (gain) laterally (that is, in a direction in parallel with the principal surface
12
a
of the circuit board
12
or the axial direction of the four-phase helical antenna
12
) although the four-phase helical antenna
12
is brought down to a ground plate as shown in FIG.
6
B. Of course, in this state, the four-phase helical antenna
12
has a gain in a vertical direction (in a direction perpendicular to the axial direction of the four-phase helical antenna
12
).
In addition, inasmuch as the above-mentioned predetermined angle θ is equal to about 30 degrees, if the antenna unit
10
is fixed on a horizontal place of a car, the antenna unit
10
is operable as a stick-shaped GPS antenna having directivity with the maximum gain in a direction at an angle of elevation of about 60 degrees.
As described above, inasmuch as the four-phase helical antenna having the axial direction in parallel with the principal surface
11
a
of the circuit board
12
is used as the antenna element
12
in this embodiment of the present invention, the antenna unit
10
can receive a GPS signal from a GPS satellite having a low angle of elevation although the antenna unit
10
is fixed or mounted on the car with an inclined state to the horizontal plane. Accordingly, it is possible to use the antenna unit
10
with the antenna unit
10
put on an inclined glass surface such as a rear window or a front window of the car. In addition, putting the antenna unit
10
on the glass surface may be carried out by using, for example, double-sided tape.
While this invention has thus far been described in conjunction with a preferred embodiment thereof, it will readily be possible for those skilled in the art to put this invention into practice in various other manners. For example, although the above-mentioned embodiment has been described only a case where the antenna unit is applicable to the GPS receiver, uses for the antenna unit is not limited to this. In addition, although the four-phase helical antenna is used as the helical antenna in the above-mentioned embodiment, the helical antenna is not restricted to this.
Claims
- 1. An antenna unit comprising:a circuit board on which circuit elements are mounted, said circuit board having a principal surface; and an antenna element mounted on the principal surface of said circuit board and connected to said circuit elements, wherein said antenna element comprises a four-phase helical antenna having an axial direction which extends in a direction substantially parallel with the principal surface of said circuit board, and wherein said four-phase helical antenna receives circular polarization and comprises a cylindrical member made of an insulator and four antenna leads wound around an outer peripheral surface of said cylindrical member in a helix fashion.
- 2. An antenna unit as claimed in claim 1, wherein said circuit elements include a low-noise amplifier (LNA) circuit.
- 3. An antenna unit comprising:a circuit board having a principal surface and a back surface opposite to the principal surface; circuit elements arranged on the back surface of said circuit board; an antenna element mounted on the principal surface of said circuit board and connected to said circuit elements, said antenna element comprising a four-phase helical antenna having an axial direction which extends in a direction substantially parallel to the principal surface of said circuit board; and a shield cover, added to the back surface of said circuit board so as to cover said circuit elements, for shielding said circuit elements, wherein said four-phase helical antenna receives circular polarization and comprises a cylindrical member made of an insulator and four antenna leads wound around an outer peripheral surface of said cylindrical member in a helix fashion.
- 4. An antenna unit as claimed in claim 3, wherein said circuit elements include a low-noise amplifier (LNA) circuit.
- 5. An antenna unit comprising:a circuit board having a principal surface and a back surface opposite to the principal surface; circuit elements arranged on the back surface of said circuit board; an antenna element mounted on the principal surface of said circuit board and connected to said circuit elements, said antenna element comprising a four-phase helical antenna having an axial direction which extends in a direction substantially parallel to the principal surface of said circuit board; a shield cover, added to the back surface of said circuit board so as to cover said circuit elements, for shielding said circuit elements; and an output cable connected to said circuit elements inside said shield cover, said output cable being pulled out of said shield cover, wherein said four-phase helical antenna receives circular polarization and comprises a cylindrical member made of an insulator and four antenna leads wound around an outer peripheral surface of said cylindrical member in a helix fashion.
- 6. An antenna unit as claimed in claim 5, wherein said circuit elements include a low-noise amplifier (LNA) circuit.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2000-271074 |
Sep 2000 |
JP |
|
US Referenced Citations (3)
Number |
Name |
Date |
Kind |
5691726 |
Nichols et al. |
Nov 1997 |
A |
6271803 |
Watanabe et al. |
Aug 2001 |
B1 |
6342869 |
Edvardsson et al. |
Jan 2002 |
B1 |
Foreign Referenced Citations (1)
Number |
Date |
Country |
9-236650 |
Sep 1997 |
JP |