Title: Plane antenna and method for manufacturing the same
Abstract: A method for manufacturing a plane antenna that coats dielectric with conductor and forms a pattern free of the conductor on a surface of the dielectric which is otherwise coated with conductor includes the step of molding the dielectric and the pattern through injection molding using a mold that has the pattern.
Patent Number: 6,897,823 Issued on 05/24/2005 to Iida, et al.
| Inventors:
|
Iida; Tamotsu (Ibaraki, JP);
Koyama; Eiji (Ibaraki, JP)
|
| Assignee:
|
Hitachi Maxell, Ltd. (Osaka, JP)
|
| Appl. No.:
|
207991 |
| Filed:
|
July 31, 2002 |
Foreign Application Priority Data
| Jul 31, 2002[JP] | 2001-231193 |
| Current U.S. Class: |
343/770; 343/700MS |
| Intern'l Class: |
H01G 013/10 |
| Field of Search: |
343/770,700. MS,873,846,702
29/600
|
References Cited [Referenced By]
U.S. Patent Documents
| 5266961 | Nov., 1993 | Milroy.
| |
| 6006419 | Dec., 1999 | Vandendolder et al.
| |
| 6147660 | Nov., 2000 | Elliott.
| |
| 6150982 | Nov., 2000 | Bergstedt et al.
| |
| 6486852 | Nov., 2002 | Hirose et al.
| |
| 6531983 | Mar., 2003 | Hirose et al.
| |
| Foreign Patent Documents |
| 56-32807 | Apr., 1981 | JP.
| |
| 3-157004 | Jul., 1991 | JP.
| |
| 3-171802 | Jul., 1991 | JP.
| |
| 5-283931 | Oct., 1993 | JP.
| |
| 6-77723 | Mar., 1994 | JP.
| |
| 06-140830 | May., 1994 | JP.
| |
| 6-164234 | Jun., 1994 | JP.
| |
| 08-325440 | Dec., 1996 | JP.
| |
| 09-041137 | Feb., 1997 | JP.
| |
| 9-275310 | Oct., 1997 | JP.
| |
| 2000/-228603 | Aug., 2000 | JP.
| |
| 2000/-312111 | Nov., 2000 | JP.
| |
| 2001/-143531 | May., 2001 | JP.
| |
Primary Examiner: Vannucci; James
Attorney, Agent or Firm: Birch, Stewart, Kolasch & Birch, LLP
Claims
1. A method for manufacturing a plane antenna that coats dielectric with conductor
and forms a pattern free of the conductor using a surface of the dielectric which
is otherwise coated with conductor and is made of material having a coefficient
of water absorption of 0.01% or less, said method comprising the step of:
molding the dielectric to form the pattern therein through injection molding
using a mold that includes the pattern,
forming a first conductor film on the dielectric formed by said molding step,
using electroless plating, evaporation or sputtering; and
forming a second conductor film on the dielectric on which the first conductor
film has been formed by said step of forming a first conductor film.
2. A method according to claim 1, wherein the second conductor film is formed
by electroplating, and the step of forming the second conductor film includes controlling
a film thickness of the second conductor film formed by the electroplating.
3. A method according to claim 1, wherein the pattern has a concave shape, and
the step of forming the first conductor film uses evaporation or sputtering, and
includes the step of arranging a patterned surface oblique to an ejection direction
of a material of the conductor in the evaporation or sputtering.
4. A method according to claim 3, wherein the step of forming the second conductor
film uses evaporation or sputtering of aluminum.
5. A plane antenna comprising a plate dielectric and a conductor that coats a
surface of the dielectric, the plate antenna forming a resonant slot of a predetermined
pattern at a predetermined position uncovered with the conductor,
wherein the dielectric is made of a material having a coefficient of water absorption
of 0.01% or less, and has a convex section forming the pattern at the predetermined
position,
wherein the conductor is arranged approximately as high as the dielectric around
the dielectric having the convex section and forms a convex section together with
the dielectric having the convex section; and
wherein said plane antenna serves as a high frequency wave array antenna for
use with 50 GHz or higher.
6. A plane antenna comprising a plate dielectric and a conductor that coats a
surface of the dielectric, the plate antenna forming a resonant slot of a predetermined
pattern at a predetermined position on the dielectric uncovered with the conductor,
wherein the dielectric is made of material having a coefficient of water absorption
of 0.01% or less, and has a convex section forming the pattern at the predetermined
position,
wherein the conductor is arranged approximately as high as the dielectric around
the dielectric having the convex section, and forms a convex section together with
the dielectric having the convex section, and
wherein d≦h≦λg/10 is satisfied where d is a thickness of
the conductor at a location other than the predetermined position, λg is
a wavelength of an electric wave, and h is a height of the dielectric having the
convex section.
7. A plane antenna according to claim 6, wherein the wave has a frequency of
50 GHz or higher.
8. A plane antenna comprising a plate dielectric and a conductor that coats a
surface of the dielectric, the plate antenna forming a resonant slot of a predetermined
pattern at a predetermined position on the dielectric uncovered with the conductor,
wherein the dielectric is made of material having a coefficient of water absorption
of 0.01% or less, and has a convex section forming the pattern at the predetermined
position,
wherein the conductor is arranged approximately as high as the dielectric around
the dielectric having the convex section, and forms a convex section together with
the dielectric having the convex section, and
wherein 25 μm≦h≦250 μm is satisfied where h is a height
of the dielectric having the convex section.
Description
BACKGROUND OF THE INVENTION
The present invention relates antennas and methods for manufacturing the same,
and more particularly to a method for manufacturing a slot pattern in an antenna.
The present invention is suitable for a plane antenna for use with a frequency
band of 50 GHz or higher in a wave guiding space.
The recent highly information-oriented society has universally utilized radio
communication systems, and drastically developed them particularly in the microwave
and millimeter wave ranges that may transmit large information content. A plane
antenna is a suitable input/output ("I/O") device for short-wavelength radio system
among these communication systems, and is expected applicable to many fields including
radio LANs and automobile collision prevention radars. The antenna size should
correspond to a wavelength of an electric or electromagnetic wave, and should be
required smaller as the I/O device for shorter wavelengths. Thereby, the fine process
has been required for the recent antenna to maintain its size accuracy.
Conventional antennas include, for example, a dielectric antenna disclosed
in Japanese Laid-Open Patent Application No. 56-32807 and a continuous stub antenna
disclosed in Japanese Laid-Open Patent Application No. 6-77723.
However, it has become difficult to for conventional manufacturing methods
to precisely and cost-efficiently provide plane antennas. The conventional methods
rely upon the etching technology to form, for example, a slot pattern and patch
pattern in an antenna, and the fine process drastically affects antenna characteristics.
However, the etching technology cannot precisely produce the pattern disadvantageously.
In particular, the size accuracy in the millimeter wave range requires 1% or higher
of the wavelength and, for example, several tens of micrometers for 50 GHz. When
a multiplicity of resonant slots and patch patterns are arrayed, stricter size
accuracy control is required to maintain directivity. For this demand it is conceivable
to apply the fine processing technology that has been usually used for the LSI
fabrications, but this technology cannot provide inexpensive antennas.
The conventional plane antenna has formed a slot, for example, using etching.
As shown in sectional view of a pattern in FIG. 14A, the conventional plane antenna
300 coats conductor
320 on plate dielectric
310, and forms
a slot at a portion (or a concave) uncoated by the conductor
320. Here,
FIG. 14A is a schematic, partially sectional view near a surface of the conventional
plane antenna. As shown, the conductor
320 defines the slot
330.
However, the conductor
320 erodes, as shown in FIG. 14B, when water
340
is collected in the concave
330 and, as indicated by broken lines, deteriorates
and turns into the conductor
320A as shown in FIG.
14C. As it is
understood from a comparison between an arrow between the broken lines and an arrow
between the solid lines, an interval of the slot
330 changes and the plane
antenna
300 varies its property. Here, FIG. 14B is a schematic sectional
view showing that the water
340 is collected in the slot
330 shown
in FIG. 14A, and FIG. 14C is a schematic sectional view of changing widths of the
slot
330 in the plane antenna
300 as a result of FIG.
14B.
The antenna disclosed in Japanese Patent Application No. 56-32807 has, as shown
in FIG.
6(
d), a flat conductor around a slot, thereby easily collecting
water and resulting in erosion of the slot. As a result, the slot width varies
as discussed above. The antenna disclosed in Japanese Laid-Open Patent Application
No. 6-77723 is a continuous cross stub device that has a long slot extending in
one direction without the resonant slot. The stub device may maintain the antenna
property even when the slot partially erodes in its longitudinal direction and
the slot interval changes in one part, because the slot interval in other parts
does not change. Therefore, this stub device is relatively corrosion resistant.
However, another and separate countermeasures should be taken for such an antenna
that is required to be corrosion resistant in a slot's longitudinal direction,
such as a plane antenna having a resonant slot.
BRIEF SUMMARY OF THE INVENTION
In order to solve the above disadvantages, it is a general object of the present
invention to provide a novel and useful plane antenna and a method for manufacturing
the same.
More specifically, it is an exemplary object of the present invention to provide
an inexpensive plane antenna that has good size accuracy and productivity, and
a method for manufacturing the same.
Another exemplary object of the present invention is to provide a plane antenna
that may maintain its property under environmental changes over time, such as corrosion,
and a method for manufacturing the same.
In order to achieve the above objects, a method of one aspect of the present
invention
for manufacturing a plane antenna that coats dielectric with conductor and forms
a pattern free of the conductor on a surface of the dielectric which is otherwise
coated with conductor includes the step of molding the dielectric and the pattern
through injection molding using a mold that has the pattern. This manufacturing
method uses the injection molding to simultaneously mold the pattern free of the
conductor together with the dielectric, and forms the pattern integrated with the
dielectric with accuracy of micron order. This pattern may serve, for example,
as a slot or patch in the plane antenna, and realize an accurately manufactured
small antenna suitable for short wavelengths. In addition, the injection molding
for producing the dielectric would enable the antenna to be inexpensively mass-produced
once a mold is prepared for the dielectric having the predetermined pattern. The
predetermined pattern formed by the molding step may have a convex or concave section,
and the region coated with the conductor may have a convex or concave section.
The method may further include the steps of forming the conductor on the dielectric
formed by the molding step, and removing the conductor from the portion patterned.
These steps enable the pattern (i.e., slot or patch) to serve as an electric antenna
pattern after forming the conductor on the molded dielectric, and removing the
conductor from the patterned portion.
The method may further include the steps of forming a first conductor film on
the dielectric formed by the molding step, using electroless plating, evaporation
or sputtering, and forming a second conductor film on the dielectric on which the
first conductor film has been formed by the forming step. This manufacturing method
may form a conductor film on the molded dielectric. As an example, the second conductor
film may be formed by electroplating, and the step of forming the second conductor
film may control a film thickness of the second conductor film formed by the electroplating.
The film thickness of the second conductor is controllable such that the second
conductor has an appropriate thickness suited to meet the skin effect as the electromagnetic
property. When the pattern has a concave shape, the step of forming the first conductor
film may use evaporation or sputtering, and include the step of arranging a patterned
surface oblique to an ejection direction of a material of the conductor in the
evaporation or sputtering. Thereby, when the pattern has a concave section from
which the conductor is hard to be removed, the conductor is prevented from forming
a film when the conductor film is formed. The step of forming the second conductor
film may use, for example, evaporation or sputtering of aluminum, copper, silver,
nickel, etc.
When the predetermined pattern has a concave section, the method may further
include the steps of embedding a predetermined material into the predetermined
pattern of the dielectric formed by the forming step, forming the conductor in
the dielectric into which the predetermined material has been embedded, removing
the predetermined material from the predetermined pattern so as to peel off the
conductor from the predetermined pattern. Similar to the above, this manufacturing
method may form the conductor on the dielectric so as not to form the conductor
on the predetermined pattern having the concave section as an electric pattern.
The predetermined material may be solid at the room temperature, and have such
property that it vaporizes and expands when heated above the room temperature,
and the step of peeling off has the step of heating the dielectric on which the
conductor has been formed. This step heats the dielectric into which the predetermined
material has been embedded and on which the conductor has been formed. As a result,
the predetermined material swells and peels off the conductor film formed in the
predetermined step. For example, the predetermined material is petrolatum.
A plane antenna of another aspect of the present invention is manufactured by
the
above method. This plane antenna exhibits the operations similar to those of the
above manufacturing method. The instant invention may be also directed to the plane
antenna manufactured by the above method.
A plane antenna of another aspect of the present invention includes a plate dielectric
and a conductor that coats a surface of the dielectric, the plate antenna forming
a resonant slot of a predetermined pattern at a predetermined position uncovered
with the conductor, wherein the dielectric has a convex section at the predetermined
position, and wherein the conductor is arranged approximately as high as the dielectric
around the dielectric having the convex section and forms a convex section together
with the dielectric having the convex section. This plane antenna does not easily
erode, because the conductor is approximately level with the dielectric at the
resonant slot, and the resonant does not usually collect water due to the convex
section. As a result, the plane antenna has good weather resistance and maintains
stable property for a long time.
Alternatively, the dielectric has a convex section at the predetermined
position, and the conductor is arranged around and adhered to the dielectric having
the convex section, and forms a convex section together with the dielectric having
the convex section. The plane antenna maintains water resistance and stable property
due to adherence. A plasma process would enhance the adherence between the dielectric
and the conductor.
Alternatively, the dielectric is made of a water repellent material
and has a convex section at the predetermined position, wherein the conductor is
arranged around the dielectric having the convex section forms a convex section
together with the dielectric having the convex section. This plane antenna may
enhance the water resistance and corrosion resistance due to the water repellent
material (such as resin having a low dielectric constant). The resin having a low
dielectric constant does not generally have a hydrophilic polar group in a molecule,
and is hydrophobic due to the small saturation moisture absorption. It is not porous
and thus more water repellent than inorganic materials, such as alumina. Concrete
materials include fluorocarbon resin such as ethylene-tetrafluoroethylene copolymer,
aromatic series resin, such as polystylene, and polyolefine resin, such as polypropylene,
polyethylene, polymethylpentene, and norbornene. Hydrocarbon resin is particularly
preferable for cost and processing purposes. A filler and fiber sheet, such as
silicon dioxide, may be blended for adjustment of a coefficient of thermal expansion.
Dimethanonaphthalene resin is preferable for use with high frequency of 50 GHz
or higher.
The dielectric may be made of a material having a coefficient of water absorption
of 0.01% or less, and have a convex section at the predetermined position, wherein
the conductor is arranged around the dielectric having the convex section, and
forms a convex section together with the dielectric having the convex section.
This plane antenna is made of the material having a coefficient of water absorption
of 0.01% or less, and may enhance the water resistance and corrosion resistance.
The dielectric may be made of a material having a coefficient of thermal expansion
of 7×10
-5 or less, and has a convex section at the predetermined
position, wherein the conductor is arranged around the dielectric having the convex
section forms a convex section together with the dielectric having the convex section.
This plane antenna is made of the material having a coefficient of thermal expansion
of 7×10
-5 or less, and may enhance the water resistance and corrosion resistance.
The dielectric may have a pillar shape with a convex section at the predetermined
position, wherein the conductor is arranged around the dielectric having the convex
section, and forms a convex section together with the dielectric having the convex
section. Even when the conductor near the antenna slot erodes, the pillar-shaped
convex dielectric (having the approximately constant sectional area) may maintain
the slot shape and thus stable property for a long time.
A plane antenna of another aspect of the present invention includes a plate dielectric
and a conductor that coats a surface of the dielectric, the plate antenna forming
a resonant slot of a predetermined pattern at a predetermined position on the dielectric
uncovered with the conductor, wherein the plane antenna serves as an array antenna
that two-dimensionally arranges a multiplicity of isolated convexes for forming
the predetermined pattern at the predetermined position on the dielectric. This
plane antenna may maintain a shape and size of each pattern, and positional relationship
among the patterns. Therefore, the plane antenna does not easily cause positional
offsets among its predetermined patterns, and may maintain the antenna property
irrespective of environmental changes. This plane antenna is suitable especially
for as an array antenna for use with high frequency of 50 GHz or higher.
A plane antenna of still another aspect of the present invention includes a plate
dielectric and a conductor that coats a surface of the dielectric, the plate antenna
forming a resonant slot of a predetermined pattern at a predetermined position
on the dielectric uncovered with the conductor, wherein the dielectric has a first
surface and a second surface opposite to the first surface, wherein the first surface
forms a multiplicity of predetermined patterns each having a convex section at
the predetermined position on the dielectric, and wherein the second surface forms
and coats with the conductor a pattern around a center which corresponds to a center
of the multiplicity of predetermined patterns, a tip of the pattern in the second
surface being free of the conductor and exposing as a gate for an electromagnetic
signal the dielectric. Preferably, the pattern formed in the second surface has
a concave or convex section for feeder matching. This plane antenna accords centers
between two patterns with each other, fixes a distance from the feeding center
to the radiation pattern, and controls a difference of relative phases among array
antenna elements, maintaining tie stable property. In particular, when the convex
or concave feeder would be able to realize impedance matching between the feeder
and antenna patterns using this shape.
A plane antenna of another aspect of the present invention includes a plate dielectric
and a multiplicity of patterned, conductor coated concave portions two-dimensionally
arranged on a surface of the dielectric, no conductor coated film being provided
except for the concave portions and thus the dielectric exposing and forming a
resonant patch so that the plane antenna may serve as an array antenna. This plane
antenna may flatten the conductor coated concave surface, fill the low moisture
absorptive resin in the concave, and maintain the stable property under environmental changes.
A plane antenna of another aspect of the present invention includes a plate dielectric
and a conductor that coats a surface of the dielectric, the plate antenna forming
a resonant slot of a predetermined pattern at a predetermined position on the dielectric
uncovered with the conductor, wherein the dielectric has a convex section at the
predetermined position, wherein the conductor is arranged approximately as high
as the dielectric around the dielectric having the convex section, and forms a
convex section together with the dielectric having the convex section, and wherein
d≦h≦λg/10 is satisfied where d is a thickness of the conductor
at a location other than the predetermined position, λg is a wavelength of
an electric wave, and h is a height of the dielectric having the convex section.
The height h equal to or less than λg/10 would limit a phase offset of the
electromagnetic wave emitted from the convex, and provide the antenna property
with sharp directivity. The convex is higher than the thickness d of the coating
conductor so that it may not become a concave. When the frequency of the electric
wave is within a band of 50 GHz or higher, for example, the plane antenna may set
the thickness of the coating conductor to be 3 μm fully taking the electromagnetic
skin effect into consideration.
A plane antenna of another aspect of the present invention includes a plate dielectric
and a conductor that coats a surface of the dielectric, the plate antenna forming
a resonant slot of a predetermined pattern at a predetermined position on the dielectric
uncovered with the conductor, wherein the dielectric has a convex section at the
predetermined position, wherein the conductor is arranged approximately level with
the dielectric around the dielectric having the convex section, and forms a convex
section together with the dielectric having the convex section, and wherein 25
μm≦h≦250 μm is satisfied where h is a height of the dielectric
having the convex section. This plain antenna indicates h in the absolute value
in the millimeter range, and exhibits similar operations as the above plane antenna.
Alternatively, the dielectric has a first surface and a second surface
opposite to the first surface, wherein the first surface forms as a radiation array
pattern the predetermined pattern of a convex section at the predetermined position
on the dielectric, and wherein the second surface forms a feeder of another pattern
having a center that offsets from a portion within λ/50 which corresponds
to a center of the radiation array patterns. This plane antenna forms an array,
and restrains the phase offset of the radiation electromagnetic wave from each
antenna element on the convex surface (i.e., a resonant slot) within a permissible
range by taking a distance from the feeding center into consideration. This would
properly adjust the radiation pattern for the entire antenna, which is formed by
synthesizing these radiation electromagnetic waves, and provide the antenna with
sharp directivity.
A plane antenna of still another aspect of the present invention includes a plate
dielectric and a conductor that coats a surface of the dielectric, the plate antenna
forming a resonant slot of a predetermined pattern at a predetermined position
on the dielectric uncovered with the conductor, wherein the dielectric has a first
surface and a second surface opposite to the first surface, wherein the first surface
forms the predetermined pattern of a convex section at the predetermined position
on the dielectric, and wherein the second surface forms a feeder of a convex section.
This plane antenna provides the feeder to a concave or convex base that forms the
antenna radiation part, realizing the impedance matching between the antenna radiation
part and feeder, and thus enhancing the antenna efficiency. The integrated molding
with the dielectric would make the manufacture efficient.
A method of another aspect of the present invention for manufacturing a plane
antenna
comprising a plate dielectric and a conductor that coats a surface of the dielectric,
the plate antenna forming a resonant slot or patch pattern of a predetermined pattern
at a predetermined position on the dielectric uncovered with the conductor includes
the steps of filling, hardening, and molding a material of the dielectric in a
mold having an uneven part corresponding to the resonant slot or patch pattern
so that the predetermined pattern may be defined as the convex section of the dielectric,
coating the surface of the dielectric with the conductor, and molding the resonant
slot or patch pattern by removing the dielectric and the conductor at the predetermined
position. This method may establish all the slot sizes, and a positional relationship
among the antenna elements and feeder with accuracy.
Other objects and further features of the present invention will become readily
apparent from the following description of preferred embodiments with reference
to accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic perspective view of one surface of a plane antenna according
to the present invention.
FIG. 2 is a schematic perspective view of another surface of the plane antenna
shown in FIG. 1
FIG. 3 is a schematic sectional view of the plane antenna shown in FIG. 1.
FIG. 4 is a partially enlarged perspective view of a base encircled as a V-shaped
area by a solid line in FIG. 1.
FIG. 5 is a flowchart for explaining a method for manufacturing the antenna
shown in FIG. 1.
FIG. 6 is a detailed view of step 1000 shown in FIG. 5.
FIG. 7 is a detailed view of step 1005 shown in FIG. 5.
FIG. 8 is a detailed view of step 1010 shown in FIG. 5.
FIG. 9A is a schematic perspective view corresponding to FIG. 4 before a conductor
film is peeled off. FIG. 9B is a schematic perspective view corresponding to FIG.
4 after the conductor film is peeled off.
FIG. 10A is a schematic perspective view of an emitting surface of an antenna
manufactured by the manufacturing method shown in FIG. 5. FIG. 10B is a
schematic perspective view of the rear surface of the antenna shown in FIG. 10A.
FIG. 11 is a flowchart showing another method for manufacturing the antenna
according to the present invention.
FIG. 12 is a flowchart showing still another method for manufacturing the antenna
according to the present invention.
FIG. 13A is a plane view of a patch antenna of one embodiment according to the
present invention. FIG. 13B is a plane view of a patch antenna of another embodiment
according to the present invention. FIG. 13C is a sectional view of FIG. 13A.
FIG. 13C is a sectional view of FIG. 13B. FIG. 13E is a sectional view of
a patch antenna of still another embodiment according to the present invention.
FIG. 14 is a schematic, partial enlarged section for explaining disadvantages
of the prior art plane antenna.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to the accompanying drawings, a description will now be given
of an optical disc
100 of the present invention. In each figure of the accompanying
drawings, the same reference numeral denotes the same element and a description
thereof will be omitted. Here, FIG. 1 is a schematic perspective view of a front
surface of a plane antenna
100. FIG. 2 is a schematic perspective view of
a rear surface of a plane antenna
100. FIG. 3A is a schematic sectional
view of the plane antenna
100. FIG. 3B is a partially enlarged sectional
view of the plane antenna
100. The plane antenna
100 includes a base
110 made of plate dielectric, and a conductor (film)
120 for coating
the surface of the base
110, and forms one or more resonant slots of a predetermined
pattern at predetermined positions on the base
110, uncovered with the conductor
120.
As shown in FIG. 3A, the plane antenna
100 includes the base
110
and the conductor film
120, and the conductor
120 is formed with
a predetermined thickness on the base
110 with taking the skin effect into
consideration. The plane antenna
100 does not form the conductor
120
at predetermined areas (i.e., slot patterns
114 and feeding slot pattern
116, which will be described later), and serve as an antenna when these
areas are formed as one or more slots. FIGS. 1 through 3 exaggerate and partially
omit slot patterns
114 and feeding slot pattern
116 in order to assist
understanding of the plane antenna
100.
The plane antenna
100 exemplarily includes a disc shape with a diameter
of 30 to 50 mm and a thickness of 1 mm, and is implemented as a small radial slot
antenna. However, the inventive plane antenna
100 is not limited to this
type, and applicable to any antenna of any size, such as a patch antenna and a
micro strip antenna, only if it has a dielectric area free of the conductor on
the conductor coated surface
106. The small plane antenna
100 may
be manufactured with high accuracy.
The base
110 has a predetermined thickness, which thickness serves as
a wave-guide path and thus a feeder circuit for each slot. The base
110
has a base body
112, plural slot patterns
114, and a feeding slot
pattern
116. The instant specification defines as a conductor coated surface
106 a portion forming the conductor film
120 except for the slot
patterns
114 of the base
110 and the feeding slot pattern
116.
As shown in FIGS. 1-3, the plane antenna
100 forms the convex slot patterns
114 at a front surface (emitting surface)
102 side, and the convex,
feeding slot pattern
116 at a rear surface (feed surface)
104 side,
and both patterns
114 and
116 are integrated with the base
110.
Alternatively, the feeding slot pattern
116 may be formed as
a concave shape. As shown in FIGS. 1 and 2, the base
110 has different patterns
(i.e., slot patterns
114 and feeding slot pattern
116) between the
front and rear surfaces (i.e., the emitting surface
102 and electric power
surface
104). As discussed in a manufacturing method, the alignment is needed
between the front and rear patterns (i.e., slot patterns
114 and feeding
slot pattern
116). Therefore, the base
110 may separately mold a
front pattern molded base (i.e., a base having the slot patterns
114), and
a rear pattern molded base (i.e., a base having the feeding slot pattern
116),
and then stick both bases together so as to integrate them with each other. Of
course, the base
110 may be manufactured as a base that is integrated with
the front and rear patterns (i.e., slot patterns
114 and feeding slot pattern
116).
The base
110 is integrated with the slot patterns
114 in place
free of the conductor film
120 on the conductor coated surface
106,
and the feeding slot pattern
116. The instant embodiment uses the injection
molding to mold the base
110 integrated with the slot patterns
114
and feeding slot pattern
116, and makes the base
110 of resin, such
as plastic that is a low dielectric plate material with an operational band. As
discussed, the slot patterns
114 forms a slot of the plane antenna, but
the injection molding may mold the slot patterns
114 and feeding slot pattern
116 with sub-micron accuracy. For example, the injection molding molds pits
on an optical disc (for example, a DVD) having a width of 0.3 μm, a length
of 0.4 μm, a depth of 0.04 μm with accuracy. Application of the accurate
molding technology to the method of manufacturing the inventive base
110
would be able to make a slot for the antenna
100 with accuracy, in particular,
for the small antenna
100 suitable for the short wavelengths. Once a mold
for manufacturing the base
110 including the slot patterns
114 and
feeding slot pattern
116 is manufactured, the antenna
100 may become
mass-produced inexpensively.
The slot pattern
114 is a pattern that serves as a slot of the antenna
100 and located at a region free of the conductor film
120. As shown
in FIG. 4, the slot patterns
114 form an array of multiple patterns. Such
an array antenna should maintain a size and shape of each array, and a positional
relationship among patterns with accuracy. Here, the injection molding forms the
slot pattern
114 integrated with the base
110 with accuracy, as discussed,
and maintain desired directivity of the antenna
100. As discussed later,
the slot
114 has such a convex shape that the resonant slot
114 may
maintain its shape, and secures the conductor coated film
120, properly
preventing relative positional offsets irrespective of environmental conditions
including the thermal expansion, contraction, and their iterations. Therefore,
the antenna
100 may maintain the stable antenna property irrespective of
environmental changes, such as heat, cold, and moisture absorption. Such an array
antenna may be act for a high-frequency array antenna for use with, for example,
50 GHz or higher. A change of an interval in the array antenna becomes 4.2×10
-3
where the dielectric base has a coefficient of expansion of 7×10
-5
(/° C.) and, for example, the temperature range is -10° C. to +50°
C. The wavelength λg in the dielectric is 3.8 mm where the dielectric constant
is 2.5 and the frequency is 50 GHz, and the element interval in the array antenna
is calculated to be 0.001 λg as a ratio to the wavelength in the dielectric
due to the thermal expansion/contraction. Considering that the size accuracy between
the antenna elements is maintained within 0.01 λg, an array antenna having
a length of about 10 wavelengths may be configured. This corresponds to an antenna
element of about 78 antenna elements maximum, and allows the directivity and gain
to be freely designed.
Each slot pattern
114 includes a pair of patterns
114a and
114b in this embodiment, and the slot patterns
114 are formed
spirally or concentrically on the base body
112. Here, FIG. 4 is a partially
enlarged perspective view of the base
110 showing a V-shaped area encircled
by solid lines in FIG.
1. The shape of the slot patterns
114 shown
in FIG. 4 is exemplary, and the slot pattern
114 serves as a slot of the
antenna
100. The spiral and concentric shapes provides the antenna
100
with different properties.
The patterns
114a and
114b are required to have size
accuracy of at least 1% of a wavelength in the millimeter wave range. For example,
50 GHz requires the accuracy of scores of micrometers. As discussed, the pattern
shape appears as a difference in depth in the optical disc molding, and this should
be expressed as an existence or non-existence of the conductor in the antenna
100.
For example, the slot antenna makes an opening by removing the conductor from the
patterned portion, while the patch antenna leaves the conductor on the patterned
portion. A difference in depth is very small such as about 0.03 μm to 0.07
μm in an optical disc. It is practically difficult to distinguish the existence
and non-existence of the conductor by the difference in depth. It is noted that
the present embodiment forms the patterns
114a and
114b
so that their heights should be from several micrometers to scores of micrometers.
As a result, the difference in height may distinguish the existence and non-existence
of the conductor. The higher patterns
114a and
114b are
required as the conductor film
120 formed on the base
110 becomes thicker.
As shown in FIG. 3B, the dielectric base
110 has a convex section at each
resonant slot
114. The conductor
120 is arranged around the slot
114, and approximately as high as or level with the slot
114 (so
that it forms one flat surface). The conductor
120 has a convex section
with a dielectric having the convex section. In the prior art example shown in
FIG. 14, the slot
330 collects water
340, changes the size of the
slot
330 due to erosion, and cannot maintain the predetermined antenna property
for a long time. On the other hand, the plane antenna
100 of this embodiment
arranges the slot
114 level with or approximately as high as the conductor
120. The conductor
120 does not form the concave, and both the conductor
120 and the dielectric form a convex shape. Therefore, water is not collected
in the slot
114 and thus the slot
114 is less affected by erosion.
In this way, the conductor
120 may be rendered as high as the dielectric
near the slot
114
As shown in FIG. 3B, d≦h≦λg/10 is preferably met where d
is
a thickness of the conductor
120 at a location other than the slot
114,
λg is a wavelength of an electric wave that propagates the dielectric, and
h is a height of the slot
114. The height h of λg/10 or smaller would
limit phase offsets among waves emitted from the slot patterns
114, and
provide the antenna property with sharp directivity. The convex is higher than
the thickness d of the coating conductor so that it may not become a concave for
the above reason. Such a plane antenna is especially suitable in the frequency
band of 50 GHz or higher of the electric wave. The conductor
120 may have
such a thickness d as 3 μm. The range for the height h in the absolute value
in the millimeter range may be expressed as 25 μm≦h≦250 μm.
λo=300/f and λg=λo (√εr) where λo (mm) is
a wavelength in the vacuum, f (GHz) is a frequency, λg (mm) is a wavelength
in the dielectric, and εr is a dielectric constant of the dielectric. Tables
1 and 2 summarize a range of materials suitable for the antenna
100.
| |
f (GHz) |
λo (mm) |
λg (mm) |
λg/10 (μm) |
| |
|
| |
50 |
6 |
4.2 |
420 |
| |
60 |
5 |
3.5 |
350 |
| |
75 |
4 |
2.8 |
280 |
| |
|
| |
f (GHz) |
λo (mm) |
λg (mm) |
λg/10 (λm) |
| |
|
| |
50 |
6 |
3.5 |
350 |
| |
60 |
5 |
2.9 |
290 |
| |
75 |
4 |
2.3 |
230 |
| |
|
As discussed, the minimum value of the height h is determined by the film thickness
d of the conductor
120 by considering the electromagnetic skin effect of
the conductor film thickness d in the working frequency. The skin effect is a phenomenon
in which the current density of current flowing through the conductor film
120
concentrates on the surface of the conductor film
120, and thus the small
thickness does not always lead to the small resistance in the high frequency. A
thickness in which the current density becomes 1/e (0.37 times) as large as that
of the conductor surface is referred to as the skin depth, and this value becomes
small in inverse proportion to the square root of the frequency. When the conductor
film
120 is made of copper, the skin depth is 0.6 μm at 12 GHz and
is 0.3 μm at 50 GHz, while the surface resistance is 29 Ω at 12 GHz
and is 58 Ω at 50 GHz. Influence of the skin effect should be considered,
and ten times as large as the skin depth should be contemplated for a range that
mostly propagate the current. In other words, unless the conductor film thickness
d maintains at least 3.0 μm at 50 GHz so as to reduce the skin resistance,
the transmission loss lowers the antenna's radiant efficiency. The height of the
convex is a height measured from the dielectric flat portion, i.e., a height from
the bottom of the conductor film
120, and the value should be larger than
the thickness d of the conductor film
120. The height that is set to be
one-tenth or smaller of the wavelength in the dielectric would not form a resonance
circuit in a height direction of the convex, and limit dispersions among radiation
phases to be at least λ/10 or smaller.
In the slot
114, the conductor
120 is arranged around and adhered
to the dielectric having the convex section. The plane antenna
100 maintains
water resistance and stable property due to this adherence. Preferably, a plasma
process is conducted for the dielectric to enhance the adherence between the dielectric
and the conductor.
The instant embodiment makes the dielectric for forming the slot
114 of
a water repellent material. This plane antenna may enhance the water resistance
and corrosion resistance due to the water repellent material (such as resin having
a low dielectric constant). The resin having a low dielectric constant does not
generally have a hydrophilic polar group in a molecule, and is hydrophobic due
to the small saturation moisture absorption. It is not porous and thus more water
repellent than inorganic materials, such as alumina. Concrete materials include
fluorocarbon resin such as ethylene-tetrafluoroethylene copolymer, aromatic series
resin, such as polystyrene, and polyolefine resin, such as polypropylene, polyethylene,
polymethylpentene, and norbornene. Hydrocarbon resin is particularly preferable
when cost and process are considered. A filler and fiber sheet, such as silicon
dioxide, may be blended for adjustment of a coefficient of thermal expansion. For
use with high frequency of 50 GHz or higher, dimethanonaphthalene resin is preferable.
The dielectric may be made of a material having a coefficient of water absorption
of 0.01% or less. Thereby, the antenna
100 may enhance the water resistance
and corrosion resistance. That material may include polyolefine resin, such as
polypropylene, polyethylene, polymethylpentene, and norbornene.
The dielectric may be made of a material having a coefficient of thermal expansion
of 7×10
-5 or less. Thereby, the antenna
100 and may enhance
the water resistance and corrosion resistance. Such a material may, for example,
include dimethanonaphthalene resin.
As shown in FIGS. 3A an
3B, the dielectric preferably has a pillar shape
in the slot
114. As shown in FIG. 3C, even when the slot
114 erodes,
the pillar shape having the approximately constant sectional area may maintain
the slot shape and thus stable property for a long time.
The feeding pattern
116 is a pattern for serving as a feeding slot of
the antenna
100 and for forming an area free of the conductor film
120.
The feeding pattern
116 is, for example, cylindrical-shaped, and formed
at a center of the base body
112. When the feeding slot pattern
116
as a feeding slot cannot supply power to a center of the antenna
100, the
radiation power pattern has biased property. Therefore, the feeding pattern
116
is provided at a center of the spiral pattern of the slots
114 with accuracy.
The feeding pattern
116 has a convex section in this embodiment. The convex
feeder integrated with the plate would provide sufficient impedance matching at
the supply side of the antenna, improving the antenna efficiency. It is integrated
with the dielectric and thus efficiently manufactured through the integration molding.
A difference between a center of the slot patterns
114 and a center of
the
feeder is preferably within λ/50. This plane antenna forms an array, and
restraint the phase offset of radiation electromagnetic waves from the resonant
slot patterns
114 within a permissible range. This would properly adjust
the radiation pattern, which is formed by synthesizing these radiation electromagnetic waves.
Alternatively, the pattern
116 having a convex section may
serve as an entrance/exit for electric waves. The pattern
116 accords centers
of patterns
114, prevents relative positional offsets between front and
rear patterns irrespective of environmental conditions including the thermal expansion,
contraction, and their iterations, and maintain the stable property. Preferably,
the pattern
116 may be concave, but is preferably be convex section for
impedance matching using the convex.
The conductor film
120 is a conductor portion provided on the base
110,
and has a predetermined thickness so that the conductor coated surface
106
on the base
110 is not affected by the skin effect. The conductor material
generally includes copper, silver and nickel, but the conductor film
120
may have a multilayer structure of the conductor if necessary. Although not shown,
the conductor film
120 directly formed on the base
110 is (a first
conductor) build without electricity, for example, by electroless plating, sputtering,
and evaporation, and made of chrome, nickel, copper, silver, gold, etc. The conductor
that coats next is (a second conductor) composed of most part of the conductor
film
120 formed by electroplating. This conductor is different in current
density, electrolyte temperature density, and electric property. As discussed,
a thickness of the conductor film
120 or second conductor is controlled
by the current value or plating time to avoid the skin effect. Using this layer
as a coat layer, a boundary layer with the dielectric for flowing much current
may be made of a layer of silver and copper, while a layer located far from the
dielectric may apply such a material as gold and nickel taking cost, acid resistance,
etc. into consideration.
The plane antenna
100 may coat the conductor film
120 with resin
to protect the conductor film
120, which serves as a protective layer of
the antenna
100 (although not shown here). Such a protective layer attempts
to protect from rust and flaw, and needs to serve as dustproof solution, for example,
in installing the antenna
100 without using such a cover material as radome.
Although the coat layer should be made of a material of small dielectric loss for
the electric property of the antenna
100, UV hardening resin is also applicable.
The plane antenna may be a patch antenna for resonating with a pattern in response
to feeding to a pattern. A description will be given of the patch antenna of the
instant embodiment with reference to FIG.
13. Here, FIGS. 13A and 13B are
plane views of patch antennas, respectively. As shown in FIG. 13A, the patch antenna
100A includes plate dielectric
110A, and conductor (coated layer)
120A, and feeder
140A. As shown in FIG. 13B, the patch antenna
10B
is the same as the patch antenna
100a except it uses the feeder
140B
instead of the feeder
140A. The patch antennas
100A and
100B
two-dimensionally arrange a multiplicity of convexes, on a surface of the plate
dielectric
110A, for forming the predetermined pattern. Each convex on the
dielectric
110A surface has the conductor coated film
120A, and an
area other than the convexes is free of conductor coated film
120, exposing
the dielectric
110A and forming a patch antenna that serves as an array
antenna. FIG. 13C is a sectional view of the patch antenna
100A, while FIG.
13D is a sectional view of the patch antenna
100B. As shown in FIGS. 13C
and 13D, the patch antenna
100A and
100B may have a flat surface,
and overcome the disadvantageous water collection etc., in a manner similar to
FIG.
3B. As shown in FIG. 13E, the low hygroscopic resin may be filled when
a thickness of the convex is larger than the conductor thickness.
A description will now be given of a manufacturing method of the above antenna
100, with reference to FIGS. 5 to
9. Here, FIG. 5 is a flowchart
for explaining a method for manufacturing the antenna
100 shown in FIG.
1. FIG. 6 is a detailed view of step
1000 shown in FIG.
5.
FIG. 7 is a detailed view of step
1005 shown in FIG.
5. FIG. 8 is
a detailed view of step
1010 shown in FIG.
5. FIG. 9A is a schematic
perspective view corresponding to FIG. 4 before the conductor film
120 is
peeled off. FIG. 9B is a schematic perspective view corresponding to FIG. 4 after
the conductor film
120 is peeled off FIG. 10A is a schematic perspective
view of the emitting surface
102 of the antenna
100 manufactured
by the manufacturing method shown in FIG.
5. FIG. 10B is a schematic perspective
view of the rear surface
104 of the antenna
100 shown in FIG.
10A.
FIGS. 9 and 10 exemplarily show a portion painted in black in which the conductor
film
120 is formed in order to clarify the existence and non-existence of
the conductor film
120. Although the instant embodiment manufactures the
plane antenna
100 by the injection molding, the present invention does not
eliminate the presswork.
As discussed, step
1000 makes a mold for molding the base
110 having
the slot patterns
114 and feeding pattern
116 in order to mold the
base
110 of the antenna
100 using injection molding. The step
1000
forms two molds for the emitting surface
102 side and feeder surface
104
side of the base
110. For example, an upper mold forms concave/convex part
including a concave portion corresponding to the resonance slot patterns
114
at its cavity side.
First, a master M is prepared (see FIG. 6A) onto which the resist is applied
in order to describe the step
1000 in detail. The master uses one having
a flat glass surface, onto which exposure resist R is, in turn, applied (see FIG.
6B). Then, the master, on which the resist has been applied, is exposed
through a patterned mask "m" using the exposure apparatus (see FIG.
6C).
The patterned mask "m" indicates the slot patterns
114 or feeding slot pattern
116 that has been designed by a CAD, and preferably successfully simulated.
FIG. 6C shows the patterned mask "m" forming the slot patterns
114 for the
emitting surface
102.
After the exposure (see FIG.
6D), the m
