Antenna device

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an antenna device of a compact, thin design having wideband frequency characteristics.

2. Description of the Related Art

Recently, mobile satellite communications, using a mobile means (e.g. an airplane, a ship or a car) and a communication satellite, have come into wide use. With the spread of the mobile satellite communications, there has now been a stronger demand for a compact, high-performance antenna. As is well known, in order to achieve a compact antenna design, there has been proposed a meandering-type antenna in which a radiation element of the antenna comprises a wire-like conductor formed or bent into a meandering configuration. One example of such antenna is disclosed in JP-A-6-90108.

Generally, the frequency bandwidth of a conventional antenna is about several % in terms of the specific band, and when the length of a radiation element was reduced so as to achieve a compact design, a problem was occurred that the band was further narrowed. When the transmitting band and the receiving band were larger than the specific band thereof, a problem was occurred that a plurality of antennas for transmitting and receiving purposes were required.

FIGS. 13A

to

13

B are a plan view showing the construction of a conventional antenna,

FIGS. 13B and 13C

are views showing the installation of the conventional antenna, and

FIG. 13D

is a graph showing resonance characteristics of the conventional antenna. The resonance frequency of the conventional antenna is a single resonance, and therefore the conventional antenna can not deal with a plurality of frequency bands (that is, the frequency band between 137.0 MHz and 138.0 MHz for a down-line and the frequency band between 148.0 MHz and 150.05 MHz for an up-line) assigned to a mobile satellite communication system which effects a ground-satellite-ground data communication using a satellite orbiting in a low orbit. Namely, the resonance frequency fr is determined by the length L of a radiation element, and this has resulted in a problem that the resonance occurred only for the single frequency.

In the installation of the antenna on a mobile means such as a vehicle, it is desirable that the antenna should have a low posture (reduced antenna height) in order to reduce the wind pressure, acting on the antenna open surface, and also to prevent damage to the antenna upon contact with other objects. Particularly, when the antenna is installed on a container, the antenna height is about 0.5 m as a result of the stacking of the containers even if the above ¼-wavelength grounded-type antenna is used, and therefore the installation of the antenna is impossible. If the conventional antenna, shown in

FIG. 13A

, is mounted vertically on the vehicle body as shown in

FIG. 13B

, in addition to the above bandwidth problem, further problems concerning the reduction of the wind pressure and the damage to the antenna upon contact with other object will be occurred. If the antenna is mounted horizontally on the vehicle body as shown in

FIG. 13C

, the impedance is lowered as the antenna approaches an electrically-conductive panel or plate of the vehicle body, and also the resonance frequency is shifted, so that the impedance matching between the antenna and the feeder line is adversely affected, which has resulted in a problem that the transmitting and receiving operation can not be operated.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an antenna device which can deal with more frequencies, and has a compact design and a low posture, and is hardly influenced by a box-like metal body such as a vehicle body.

In order to achieve the object of present invention an antenna device of the present invention comprising radiation elements, feed means for feeding electric power to the radiation elements, a ground plate, and a cover member covering the radiation elements and the feed means, which is mounted on metal cubic and using short circuit between ground plate and metal cubic, wherein a value, obtained by dividing the distance (H) between the radiation elements and the ground plate by a wavelength (Λ), is 1÷250≦HΛ≦1÷80, and preferably 1÷200≦H÷Λ1÷100.

With this construction, an overall loss of the antenna can be suppressed while suppressing the decrease of the antenna impedance, and therefore there can be provided the antenna device of high reliability which can positively operate under a wide range conditions of use.

The plurality of radiation elements and the feed equipment are formed on a common antenna board, and therefore as compared with the case where such elements are formed on separate boards, the antenna construction can be simplified, and the productivity can be enhanced, and besides the compact, thin design of the antenna can be achieved. Furthermore, since the different line lengths are provided, a plurality of wavelengths can be transmitted and received.

Particularly, by setting the line length to about 25% of the corresponding wavelength, the optimum transmitting and receiving operation becomes possible corresponding to wavelength, and also the polarization characteristics of the antenna can be enhanced.

Electric power is fed to the plurality of radiation elements through the single feed equipment, and therefore the area of the antenna board, which is occupied by the feed equipment can be reduced, then the antenna board size can be reduced. Besides, since the power is fed to the plurality of radiation elements through the common feed equipment, the power can be fed to the plurality of radiation elements under the same condition, and therefore there can be provided the antenna of high reliability having excellent antenna characteristics each frequency to which the plurality of radiation elements correspond, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a perspective view of an antenna according to a first embodiment of the invention;

FIG. 2

is a perspective view of the antenna according to the first embodiment of the invention;

FIG. 3

is a plan view showing the construction of radiation elements formed on an antenna board in the first embodiment of the invention;

FIG. 4

is a plan view showing the construction of radiation elements formed on an antenna board in a second embodiment of the invention;

FIG. 5

is a plan view showing the construction of radiation elements formed on the antenna board in the first embodiment of the invention;

FIGS. 6A and 6B

are plan views showing the construction of radiation elements formed on the antenna board in the first embodiment of the invention;

FIG. 7

is a perspective view showing the construction of an antenna according to a third embodiment of the invention;

FIG. 8

is a view showing the installation of the antenna on a car in the third embodiment of the invention;

FIG. 9

is an enlarged view showing an antenna-mounting portion in the third embodiment;

FIG. 10

is a graph showing the correlation with the distance between pole plates and an antenna loss in the third embodiment;

FIG. 11A

is a plan view of an antenna and

FIG. 11B

is a graph showing resonance characteristics of an antenna according to the first embodiment of the invention;

FIGS. 12A and 12B

are graphs showing a current distribution in the antenna according to the first embodiment of the invention;

FIG. 13A

is a plan view of the construction of a conventional antenna;

FIG. 13B

is a view showing the installation of the conventional antenna;

FIG. 13C

is a view showing the installation of the conventional antenna;

FIG. 13D

is a graph showing resonance characteristics of the conventional antenna;

FIGS. 14A and 14B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 15A and 15B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 16A and 16B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 17A and 17B

are plan views showing the construction of radiation elements formed in an antenna board In the invention;

FIGS. 18A and 18B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 19A and 19B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 20A and 20B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 21A and 21B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 22A and 22B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 23A and 23B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 24A and 24B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 25A and 25B

are plan views showing the construction of radiation elements formed in an antenna board in the invention;

FIGS. 26A and 26B

are plan view showing the construction of radiation elements formed in an antenna board in the invention;

FIG. 27

is a perspective view showing the construction of an antenna according to a fourth embodiment of the invention;

FIG. 28

is a perspective view showing the construction of radiation elements In the fourth embodiment;

FIG. 29

is a perspective view showing the construction of radiation elements in the fourth embodiment;

FIG. 30

is a diagram showing characteristics of the radiation elements in the fourth embodiment;

FIGS. 31A and 31B

are illustrations showing a current distribution In the antenna of the fourth embodiment;

FIG. 32

is a perspective view showing the construction of an antenna according to the fourth embodiment;

FIGS. 33A and 33B

are plan views showing the construction of radiation elements in a fifth embodiment of the invention;

FIGS. 34A and 34B

are plan views showing the construction of radiation elements in the fifth embodiment;

FIG. 35

is a diagram showing the relation between radiation power and frequencies in the fifth embodiment;

FIG. 36

is a perspective view showing the construction of a feed portion in the fourth embodiment of the invention;

FIG. 37

is an enlarged view showing the feed portion in the fourth embodiment;

FIG. 38

is a perspective view showing the grounding of the radiation elements in the fourth embodiment; and

FIG. 39

is a perspective view showing the construction of the antenna device of the fourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below.

First Embodiment

A first embodiment of an antenna device of the present invention will now be described with reference to the drawings.

FIG. 1

is a perspective view of the first embodiment of the antenna of the invention, and

FIG. 2

is a perspective view of the antenna of the first embodiment of the antenna of the invention.

FIG. 3

is a plan view showing the construction of a radiation element formed on an antenna board in the first embodiment of the invention.

In

FIG. 1

, the antenna board

1

comprises of a dielectric material, and has a thickness t. The antenna board

1

usually comprises a printed circuit board or a PET film board. Various elements are formed and mounted on the antenna board

1

, and these elements will be described below.

Radiation elements

2

a

,

2

b

,

2

c

and

2

d

are formed on one or both sides of the antenna board

1

by etching, photolithography, sputtering or other method. In this embodiment, in order that a plurality of wavelengths can be transmitted and received, one pair of radiation elements corresponds to one wavelength, and the radiation element pair

2

e

, constituted by the radiation elements

2

a

and

2

b

corresponds to a short wavelength (λg

1

), and the radiation element pair

2

f

, constituted by the radiation elements

2

c

and

2

d

, corresponds to a long wavelength (λg

2

).

The radiation elements

2

a

and

2

b

are formed substantially symmetrically in a longitudinal direction a of teh antenna board

1

, and similarly the radiation elements

2

c

and

2

d

are formed substantially symmetrically in the longitudinal direction a of the antenna board

1

. The radiation element pair

2

e

and the radiation element pair

2

f

are arranged generally symmetrically each other in a transverse direction b of the antenna board

1

.

The radiation element

2

a

and the radiation element

2

c

are connected together in the vicinity of the center of the antenna board

1

, and the radiation element

2

b

and the radiation element

2

d

are connected together in the vicinity of the center of the antenna board

1

being independent of the radiation elements

2

a

and

2

c.

Each of the radiation elements

2

a

,

2

b

,

2

c

and

2

d

is formed by a meandering lind being bent regularly into such a meandering configuration wherein a line width w≈λ/100˜λ/400, an element interval d≈λ/100˜λ/200, and an element width l≈/10˜λ/20. The radiation element

2

a

and the radiation element

2

b

, constituting the radiation element part

2

e

, have substantially the same line length, and also the radiation element

2

c

and the radiation element

2

d

, constituting the radiation element pair

2

f

, have substantially the same line length.

On the other hand, the radiation elements, constituting one of the radiation element pairs, are different in line length from the radiation elements constituting the other radiation element pair (for example, the radiation element

2

a

is different in line length from the radiation element

2

c

). More specifically, each of the radiation elements

2

a

and

2

b

, constituting the radiation element pair

2

e

, has the length L

1

(L

1

≈(λg

1

)/4), and each of the radiation elements

2

c

and

2

d

, constituting the radiation element pair

2

f

, has the length L

2

(L

2

≈(λg

2

)/4).

The radiation elements, corresponding to different wavelengths, are thus formed on the common board, and therefore as compared with the case where such radiation elements are formed on separate boards, the antenna construction can be simplified, and the productivity can be enhanced, besides the compact, thin design of the antenna can be achieved. Furthermore, since the different line lengths are provided, a plurality of wavelengths can be transmitted and received. Particularly, by setting the line length to about 25% of the corresponding wavelength, the optimum transmitting and receiving operation can be achieved for each corresponding wavelength, and also the polarization characteristics of the antenna can be enhanced.

The arrangement of the radiation elements

2

a

2

b

,

2

c

and

2

d

are not limited to that of this embodiment. Various arrangements of radiation elements

2

a

,

2

b

,

2

c

and

2

d

are shown in

FIGS. 14A

to

26

B.

FIGS. 14A

to

26

B are plan views showing the constructions of the radiation elements formed on the antenna board of the invention.

In the arrangements shown in

FIGS. 14A and 15B

, the antenna width is constant, and the element widths are the same. In the arrangement shown in

FIG. 14A

, the configuration of the radiation elements is symmetrical in a right-left direction, and is asymmetrical in a upward-downward direction, and power is fed right and left. Thus, the lengths of the elements are different at those ends which are the opposite sides of the feed portion, and merely with this construction, radio waves with different wavelengths can be transmitted and received, and therefore the design of the radiation elements is easy. Besides, since the power is fed in the right and left directions, the radiation elements with different lengths can be brought into the same power-fed condition, and therefore the difference in antenna characteristics due to the difference of the power-fed condition can be suppressed to a minimum.

In the arrangement shown in

FIG. 14B

, the configuration of the radiation elements is symmetrical in the center, and is asymmetrical in an upward-downward direction, and power is fed right and left.

In the arrangement shown in

FIG. 15A

, the configuration of the radiation elements is symmetrical in a right-left direction, and is asymmetrical in an upward-downward direction, and power is fed upward and downward. In this case, the power is fed upward and downward, and therefore the radiation elements, which correspond to the same wavelength, can be brought into the same power-fed condition, and therefore a variation in antenna characteristics on the antenna board, which would be caused by the radiation elements corresponding to the same frequency, can be suppressed to a minimum.

In the arrangement shown in

FIG. 15A

, the configuration of the radiation elements is symmetrical in the center, and is asymmetrical in an upward-downward direction, and power is fed upward and downward. With this arrangement, the substantial element lengths can be increased, and therefore the width of the antenna device in its longitudinal direction can be shortened.

In the arrangements shown in

FIGS. 16A

,

16

B,

17

A and

17

B, the antenna width is constant, and the element widths are different. In

FIG. 16A

, the configuration of the radiation elements is symmetrical in a right-left direction, and is asymmetrical in an upward-downward direction, and power is fed right and left. In

FIG. 16B

, the configuration of the radiation elements is symmetrical in the center, and is asymmetrical in an upward-downward direction, and power is fed right and left. In

FIG. 17A

, the configuration of the radiation elements is symmetrical in a right-left direction, and is asymmetrical in an upward-downward direction, and power is fed upward and downward. In

FIG. 17B

, the configuration of the radiation elements is symmetrical in the center, and is asymmetrical in an upward-downward direction, and power is fed upward and downward.

In the arrangements shown in

FIGS. 18A

,

18

B,

19

A and

19

B, the antenna width is different, and the element widths are different. In

FIG. 18A

, the configuration of the radiation elements is symmetrical in a right-left direction, and is asymmetrical in an upward-downward direction, and power is fed right and left. In

FIG. 18B

, the configuration of the radiation elements is symmetrical in the center, and is asymmetrical in an upward-downward direction, and power is fed right and left. In

FIG. 19A

, the configuration of the radiation elements is symmetrical in a right-left direction, and is asymmetrical in an upward-downward direction, and power is fed upward and downward. In

FIG. 19B

, the configuration of the radiation elements is symmetrical in the center, and is asymmetrical in an upward-downward direction, and power is fed upward and downward.

The arrangements, shown in

FIGS. 20A

,

20

B,

21

A, and

21

B, differ from those of

FIGS. 14A

to

15

B in a ground plate being provided.

The arrangements, shown in

FIGS. 22A

,

22

B,

23

A and

23

B, differ from those of

FIGS. 16A

to

17

B in a ground plate being provided.

The arrangements, shown in

FIGS. 24A

,

24

B,

25

A and

25

B, differ from those of

FIGS. 18A and 19B

in a ground plate being provided.

In the arrangement shown in

FIG. 26A

, the antenna width is constant, and the element widths are the same, and four pairs of radiation elements (four radiation element pairs) are used, and these are arranged in a rotation symmetry manner to form an array. With this arrangement, the antenna device, capable of dealing with three or more frequencies, can be achieved with the simple construction. Also, the plurality of radiation element pairs can correspond to the same frequency, and therefore the antenna characteristics are enhanced, and if the directions of the radiation elements differ from one another, the antenna device having the wider receiving range can be realized.

In the arrangement shown in

FIG. 26B

, the antenna width is constant, and the element widths are the same, and each radiation element pair is arranged in a rotation asymmetrical manner, and further a ground plate is provided.

The feed portion

3

serve to feed high-frequency power to the radiation elements

2

, and is formed on that side (surface) of the antenna board

1

, having the radiation elements formed thereon, or the back side thereof, the feed portion

3

being disposed in the vicinity of the center of the antenna board

1

. In this embodiment, the feed portion

3

a

of the antenna board

1

is formed in the vicinity of the point of junction between the radiation elements

2

a

and

2

c

connected together, and feeds power to the radiation element s

2

a

and

2

c

. The feed portion

3

b

is formed in the vicinity of the point of junction between the radiation elements

2

b

and

2

d

connected together, and feeds power to the radiation elements

2

b

and

2

d.

A matching circuit

4

and a transmission line

5

both serve to efficiently feed the predetermined high-frequency power to the feed portion

3

. A coaxial cable or a micro-strip line can be use d as the transmission line

5

.

The feed equipment is constituted by the transmission line

5

. the matching circuit

4

and the feed portion

3

.

Thus, the power is fed to the plurality of radiation elements

2

a

,

2

b

,

2

c

and

2

d

through the single feed equipment comprising the transmission line

5

, the matching circuit

4

and the feed portion

3

. With this construction, the power can be fed to the plurality of radiation elements

2

through the single feed equipment, and therefore the area of the antenna board

1

, occupied by the feed equipment, can be reduced, and therefore the size of the antenna board

1

size can be reduced. Besides, since the power is fed both to the radiation element pair

2

e

and the radiation element pair

2

f

through the common feed equipment, the power can be fed to the radiation element pairs

2

e

and

2

f

under the same condition, and therefore the antenna of high reliability having excellent antenna characteristics can be provided both for the frequencies f

1

and f

2

to which the radiation element pairs

2

e

and

2

f

correspond, respectively.

Besides, since the single transmission line

5

connected to the antenna board

1

is provided, the construction of the antenna can be simplified compared with the case where one transmission line is provided for each radiation element pair, and therefore the productivity of the antenna can be enhanced. Furthermore, the number of lead-in through holes, extending to the exterior of the antenna, can be reduced, and therefore the intrusion of water and foreign substances through the lead-in holes can be suppressed to a minimum, and therefore the malfunction of the antenna due to these factors can be suppressed, and the antenna with high reliability can be achieved.

The radiation elements

2

, the feed portion

3

and the matching circuit

4

may be formed on the same side (surface) of the antenna board

1

, or the radiation elements

2

may be formed on one side of the antenna board

1

while the feed portion

3

and the matching circuit

4

may be formed on the other side thereof. If the radiation elements

2

, the feed portion

3

and the matching circuit

4

are formed on the same side of the antenna board, the construction of the antenna board

1

can be simplified, and therefore the steps of processing and forming the antenna board

1

can be shortened, so that the productivity of the antenna board

1

can be enhanced. Besides, various circuits to be formed on the antenna board

1

can be simultaneously formed thereon, and therefore the productivity can be enhanced as well.

Furthermore, one radiation element pair

2

e

may be formed on one side of the antenna board while the other radiation element pair

2

f

may be formed on the other side thereof. With this construction, the distance between the radiation element pair

2

e

and the ground plate

6

and the distance between the radiation element pair

2

f

and the ground plate

6

are different from each other by an amount corresponding to the thickness t of the antenna board

1

, and therefore in the case where the antenna characteristics required respectively for these radiation element pairs are different, the characteristics required respectively for the radiation element pairs can be optimized.

If the radiation elements

2

, the feed portion

3

and the matching circuit

4

are formed on the same side of the antenna board

1

, it is preferred that the radiation elements

2

and so on formed on the antenna board, should face the ground plate

6

, that is, should be directed to the inner side of the antenna device. With this construction, the overall thickness of the antenna device can be reduced.

The ground plate

6

is made of a metal conductor such as aluminum, stainless steel or a plated copper.

A gap

9

, with the height h, is formed between

5

the antenna board

1

and the ground plate

6

. A dielectric plate may be inserted into the gap

9

over the entire area thereof, or several support members or means (not shown) may be provided in the gap

9

to support between them. If the gap

9

is formed by the use of the support means, the gap

9

is filled with the air.

The operation of the antenna of the above construction will now be described.

High-frequency power, fed through the transmission line

5

. is supplied to the radiation elements

2

a

,

2

b

,

2

c

and

2

d

via the matching circuit

4

. In this case, the dimensions of various portions of the radiation elements

2

a

and

2

b

, as well as the dimensions of various portions of the radiation elements

2

c

and

2

d

, are suitably selected, and by doing so, the radiation elements can radiate radio waves into the air with desired resonance frequency. Here, if the length of the radiation elements

2

a

and

2

b

is represented by L

1

, the length of the radiation elements

2

c

and

2

d

is represented by L

2

, the dielectric constant of the dielectric material, constituting the antenna board

1

, is represented by ∈1, the thickness of the antenna board

1

is represented by t, the dielectric constant of the gap

9

between the antenna board I and the ground plate

6

is represented by ∈2, and the velocity of light is represented by C, the resonance frequencies f

1

and f

2

of the antenna are expressed by the following formulas:

f

1

≈C/

2

L

1

{square root over (∈)} (Formula 3)

f

2

≈C/

2

L

1

{square root over (∈)} (Formula 4)

However, the following formula is established, and a plurality of resonance characteristics (two cycles in the case), as shown in

FIGS. 11A and 11B

, are obtained:

∈≈(∈

1

×∈

2

(t+h))/(∈

1

×h+∈

2

×t) (5)

FIGS. 11A and 11B

are graphs showing the resonance characteristics of the antenna of the first embodiment of the invention.

The current distribution in the antenna, obtained in this case, will be described with reference to

FIGS. 12A and 12B

.

FIGS. 12A and 12B

are views showing the current distribution in the antenna of the first embodiment of the invention. For the sake of simplicity, only the radiation element pair

2

f

is shown in

FIGS. 12A and 12B

.

As shown in the drawings, the element line length L

1

of each of the radiation elements

2

c

and

2

d

is set to about ¼ length of a respective one of the two line wavelengths λg

1

corresponding to the desired frequency f

1

, and by doing so, the current is distributed generally sinusoidally in the antenna in such a manner that the amplitude becomes maximum in the vicinity of the feed portion

3

at the desired frequency f

1

while the amplitude becomes minimum at the distal end portions of the radiation elements

2

a

and

2

b

. As indicated by arrows (→) in the drawings, the two parallel lines, extending obliquely in an upward-downward direction on the sheet of the drawings, are opposite to each other with respect to the direction of flow of the current, and vertically-polarized waves due to this current cancel each other, and therefore the radiation of the vertically-polarized waves in a vertical direction on the drawing sheet can be almost eliminated. The two parallel lines, extending in the right-left direction on the sheet of the drawings, are the same with respect to the direction of flow of the current, and horizontally-polarized waves due to this current are radiated in a horizontal direction on the drawing sheet. Therefore, the antenna which has excellent polarization-identifying characteristics, and has a compact size can be provided.

As shown in

FIG. 5

, an inductance device, comprising an air-core coil or a micro-strip line, can be provided at the distal end of each of the radiation elements

2

.

FIG. 5

is a plan view showing the construction of the radiation elements formed on the antenna board in the first embodiment of the invention.

With this construction, the effective length of the antenna is increased in an equivalent manner, and therefore the current amplitude (which contributes to radiation of the waves), flowing through the two parallel lines of the radiation element, extending in the main polarization direction, that is, in the right-left direction on the sheet is increased, and therefore the efficiency of the antenna is enhanced by the increased amplitude of the current.

As shown in

FIGS. 6A and 6B

, a construction in which a plurality of antennas are formed on one antenna board, using a plurality of radiation element pairs

2

e

, a plurality of radiation element pairs

2

f

and one feed equipment is possible.

FIGS. 6A and 6B

are plan views showing the construction of the radiation elements formed on the antenna board in the first embodiment of the invention.

In this embodiment, the ground plate

6

is provided beneath the antenna. However, if there is no need to provide the ground plate

6

in the vicinity of the antenna board

1

, the antenna can be formed by the antenna board

1

, having the radiation elements

2

, the feed portion

3

and the matching circuit

4

formed thereon, and the transmission line

5

, as shown in FIG.

2

. In this case, the antenna can be further reduced in thickness, and can be further simplified in construction. Therefore, the antenna can be installed in a narrow space, and the productivity of the antenna device can be enhanced.

Second Embodiment

A further preferred arrangement of radiation elements

2

will be described. This construction is the same construction as the first embodiment except for the arrangement of the radiation elements.

FIG. 4

is a plan view showing the construction of the radiation elements formed on an antenna board in the second embodiment of the invention. As shown in

FIG. 4

, in this embodiment, the radiation element width W

1

of two parallel lines of radiation elements

2

, extending in a main polarization direction, that is, in a right-left direction on the drawing sheet, is larger than the radiation element width W

2

of those portions of the radiation elements extending in a polarization direction perpendicular to the main polarization direction, that is, in a vertical direction on the drawing sheet. Generally, when a transmission line, such as a micro-strip line, is provided on an upper surface of a ground plate, the larger the line width of the radiation element

2

is, the larger the amount of radio waves radiated from this transmission line, is, if the distance h between the ground plate

6

and the radiation element

2

is constant. In contrast, the smaller the line width of the radiation element

2

is, the smaller the amount of the radiated radio waves is. Therefore, the radiation element width W

1

of the two parallel lines, extending in the main polarization direction, that is, in the right-left direction on the drawing sheet, is increased, and the radiation line width W

2

of those portions of the radiation elements, extending in the polarization direction perpendicular to the main polarization direction, that is, in the vertical direction on the drawing sheet, is made smaller than the width W

1

. By doing so, the radiation of the horizontally-polarized waves in the direction, parallel to the drawing sheet, can be further increased while more efficiently suppressing the radiation of the vertically-polarized waves (which cancel each other) in the vertical direction on the drawing sheet. Therefore, the gain of the necessary horizontally-polarized waves can be increased while reducing a radiation loss due to the unnecessary vertically-polarized waves, thereby greatly enhancing the efficiency of the antenna can be realized.

Third Embodiment

Next, a third embodiment of the present invention will be described with reference to the drawings.

FIG. 7

is a perspective view showing the construction of an antenna of the third embodiment of the invention, and those members identical to those of the first embodiment will be designated by identical reference numbers, respectively.

In the antenna of this embodiment, an antenna board

1

, on which radiation elements

2

, a feed portion

3

and a matching circuit

4

are formed, and a ground plate

6

are basically similar in construction to those of the first embodiment, respectively.

Spacers

10

are made of an elastic material such as rubber or a resin, and are interposed, as support ,members, between the antenna board

1

and the ground plate

6

to keep the gap between the antenna board

1

and the ground plate

6

accurately to a height h. Preferably, the spacers

10

are mounted respectively on those portions of the antenna board

1

on which the radiation elements

2

are not formed. With this arrangement, a change in dielectric constant of the gap between the ground plate

6

and the antenna board

1

, which affects the antenna characteristics, can be kept to the minimum.

Although not shown in the drawing, in order that the mounting positions can be easily recognized, mounting recesses are preferably formed in at least one of the ground plate

6

and the antenna board

1

, and the spacers

10

are fitted in these recesses, respectively. With this construction, the spacers

10

, when mounted, will not be disposed out of position, and therefore a change of the antenna characteristics, resulting from the mounting of the spacer

10

on that portion of the antenna board

1

on which the radiation element

2

is formed, hardly occurs. As a result, the antenna of high reliability can be achieved.

An arrangement may be used in which projections are formed on at least one of the ground plate

6

and the antenna board

1

while recesses for fitting respectively on these projections are formed in the spacers

10

, respectively. Alternatively, an arrangement may be used in which through holes are formed through at least one of the ground plate

6

and the antenna board

1

, and the spacers

10

are fixed by screws passing respectively through these through holes.

In this embodiment, in addition to the spacers

10

provided only between the antenna board

1

and the ground plate

6

, spacers may be further provided between the ground plate

6

and a radome

11

. In this case, preferably, the spacers, provided between the antenna board

1

and the ground plate

6

, are larger in height than the spacers provided between the ground plate

6

and the radome

11

, and with this construction the antenna board

1

is spaced farther from the ground plate

6

, and this enhances the antenna characteristics.

If the additional spacers are not used, it is preferred for the same reason that the antenna board

1

should be disposed closer to the radome

11

than to the ground plate

6

.

Preferably, the elasticity of the spacer is different depending on whether the spacer is held in contact with the obverse surface or the reverse surface of the antenna board

1

. More specifically, the spacer, held in contact with that surface of the antenna board

1

having the radiation elements

2

formed thereon, has higher elasticity, and the spacer, held in contact with that surface of the antenna board

1

having no radiation element

2

formed thereon, has lower elasticity. With this construction, when the antenna board

1

is displaced out of position by vibrations or the like, the possibility of damaging the radiation elements

2

by the spacers is lowered.

In the case where the antenna board

1

is held in direct contact with the radome

11

, it is preferred for the same reason that that surface of the antenna board

1

, having the radiation elements

2

formed thereon, should face the ground plate

6

.

The radome

11

is provided to cover the antenna board

1

having various circuits and so on formed thereon, and preferably the radome

11

is made of a material (e.g. a resin) having weather resistance. The antenna board

1

, the spacers

10

and so on are covered with the radome

11

and the ground plate

6

, and the radome

11

and the ground plate

6

are bonded together by a bonding material, or fixed together by bolts or the like. Preferably, the boundary portion between the radome

11

and the ground plate

6

is sealed against water or moisture by a waterproof seal member or an O-ring, and by doing so, the intrusion of water into the inside of the antenna is prevented, thereby preventing the degradation of the antenna characteristics and the malfunction of the antenna.

More preferably, the inside of the antenna is completely sealed, and inert gas, such as dry air or nitrogen gas, is sealed in the inside of the antenna. With this construction, dew condensation, developing within the antenna which may be used in a weather-beaten condition, can be suppressed, and therefore the degradation of the antenna characteristics and the -malfunction of the antenna due to such condensation can be prevented.

Mounting holes

12

are formed through end portions of the ground plate

6

, and the ground plate

6

of the antenna can be mounted directly on a box-like metal body of a vehicle or a container through the mounting holes

12

. With this construction, the antenna device of this embodiment can be mounted or installed directly on the mounting body or structure, with the ground plate

6

serving as the bottom surface. Therefore, the height of the antenna device from the installation surface is smaller as compared with the case where the antenna device is installed with using an antenna-mounting member.

In this embodiment, although the mounting holes are arranged only in the transverse direction of the antenna, the mounting holes may be formed and arranged only in the longitudinal direction, or may be formed and arranged in the transverse and longitudinal directions in surrounding of the antenna device.

If the ground plate

6

of the antenna and the box-like metal box (i.e., the mounting object) are bonded together by an electrically-conductive bonding material, the mounting holes

12

do not need to be provided.

Next, the mounting of the antenna board

1

will a be described. In this embodiment, the antenna board

1

is pressed against the inner surface of the radome

11

by the spacers

10

, provided between the antenna board

1

and the ground plate

6

, and therefore is fixed. In this case, the spacers

10

have a certain degree of elasticity, and the inner surface of the radome

11

is disposed substantially parallel to the ground plate

6

after the assembling of the antenna is completed. The antenna board

1

and the spacers

10

are beforehand located at their respective predetermined positions relative to the ground plate

6

, and in this condition the radome

11

is mounted on the ground plate

6

. By doing so, the mounting and fixing of the spacers

10

relative to the antenna board

1

and the ground plate

6

, as well as the fixing of the antenna board

1

relative to the ground plate

6

, can be effected, and therefore the antenna of high productivity can be provided in which the number of the antenna-assembling and mounting steps can be reduced. Since the antenna board

1

is pressed against the radome

11

, the antenna board

1

can have the good flatness with the simple construction, and therefore the distance between the antenna board

1

and the ground plate

6

, which particularly exerts a great influence on the antenna characteristics, can be made substantially constant. Therefore, there can be achieved the antenna which has the excellent antenna characteristics and productivity, and can deal with a plurality of frequencies.

For fixing the radome

11

and the ground plate

6

together, mounting holes are formed in those portions of the radome

11

aligned respectively with the mounting holes

12

, and common mounting members are used. Alternatively, mounting holes are formed in the radome

11

, and mounting portions are formed on those portions of the ground plate

6

aligned respectively with these mounting holes in the radome

11

, and the fixing is effected using fixing members such as screws. In the case where the mounting portions are formed on the ground plate

6

, it is preferred that projections or convex portions, projecting toward the outer surface of the antenna, should not be formed. With this construction, the height of the antenna device can be lowered, and also the flatness of the ground plate

6

, serving as the mounting surface for mounting on the antenna-mounting object, can be secured. Therefore, there can be achieved the antenna device in which the mounting operation is easy, and which has the good stability.

The installation of the antenna of the above construction on the mounting object (particularly on a vehicle (truck)) will be described with reference to the drawings.

FIG. 8

is a side-elevational view showing the installation of the antenna of the third embodiment on the vehicle, and

FIG. 9

is an enlarged view showing an antenna-mounting portion in the third embodiment of the invention.

Reference number

13

denotes a vehicle body (mounting object), and the above-mentioned antenna

14

is installed on a box-like metal body

13

a

of the upper part of the vehicle body

13

. More specifically, through holes

13

b

are formed respectively through the box-like metal body

13

a

aligned respectively with the mounting holes

12

in the antenna

14

, and a bolt

15

a

of fixing means

15

is passed through the aligned mounting hole

12

and through hole

13

, and the bolt is tightened using a nut

15

b

threaded on the distal end of the bolt, thus mounting the antenna

14

on the vehicle body

13

.

In this case, preferably, the ground plate

6

of the antenna

14

is held in direct contact with the box-like metal body

13

a

of the car body

13

. This will be described below. In many cases, the antenna

14

of this embodiment is mounted on the mounting surface of a box-like metal body of a car or a container (mounting object) in parallel relation thereto. Generally, when an antenna is mounted in close proximity to a box-like metal body (mounting object) of a car or a container, the characteristics of the antenna are often adversely affected even if the antenna is beforehand so adjusted that the antenna characteristics become optimum at a predetermined frequency. The reason is that the antenna impedance is influenced by the box-like metal body, on which the antenna is mounted, and is decreased, so that the loss increases because of the mismatching with an impedance of a feeder.

In order to prevent such antenna characteristics change, the ground plate

6

of the antenna

14

is exposed, and is adapted to be in direct contact with the box-like metal body

13

a

of the vehicle body

13

. With this construction, the ground plate

6

of the antenna

14

and the box-like metal body

13

a

can be kept at the same potential. and therefore a change of the antenna characteristics due to the influence of the box-like metal body

13

a

can be almost eliminated. The ground plate

6

of the antenna

14

and the box-like metal body

13

a

need only to be held in electrical contact with each other, and therefore the ground plate

6

and the box-like metal body

13

a

may be bonded together by an electrically conductive bonding material, instead of using the fixing means

15

. In this case, the installation of the antenna

14

on the vehicle body

13

can be effected easily, besides here is no need to provide the mounting holes

12

in the round plate

6

. Therefore, the construction of the round plate

6

can be simplified, and the antenna can be achieved which has high productivity and a low-cost design, and can be used easily.

Although not shown in the drawing, a cushioning member may be provided between the antenna

14

and the vehicle body

13

. In this case, an impact due to vibrations, developing during the movement of the car or the container (on which the antenna

14

is installed), is not reached the antenna

14

directly, and therefore the antenna

14

is not damaged by such impact, then the reliability of the antenna

14

can be enhanced.

Preferably, the fixing means

15

is made of metal in order that the ground plate

6

and the box-like metal body

13

a

can be positively held in electrical contact with each other. This is effective particularly where the cushioning member is interposed between the antenna

14

and the vehicle body

13

and where the antenna

14

and the vehicle body

13

are not held in direct contact with each other.

Reference number

16

denotes fixing means-assisting member. Preferably, the fixing means-assisting member

16

has a ring-shape, and is made of a material (e.g. rubber) which has a waterproof property so as to prevent the intrusion of water into the inside of the mounting object through the fixing means

15

, and has a certain degree of elasticity. Such fixing means-assisting member

16

effectively suppresses the intrusion of water. Specifically, a washer, made of rubber, can be used as the fixing means-assisting member.

Next, the thickness of the antenna

14

to be mounted on the box-like metal body

13

a

will be studied.

FIG. 10

is a graph showing the correlation between the distance between the radiation elements and the ground plate and a loss of the antenna in the third embodiment of the invention.

In an antenna in which the distance between the antenna board

1

and the ground plate

6

is close as in the antenna of this embodiment, a copper loss (loss due to a heat loss of the copper element, which is indicated by B in

FIG. 10

) is in inverse proportion to the distance H (hereinafter, the distance H) between the ground plate

6

and the radiation elements

2

provided the width of the radiation element

2

is constant, and the loss decreases with the increase of the distance H. A radiation loss (loss due to radiation, which is indicated by A in FIG.

10

), is in proportion to the distance H between the radiation elements

2

and the ground plate

6

provided the width of the radiation element

2

is constant, and the loss increases with the increase of the distance H. Usually, the receiving sensitivity of the antenna greatly varies, depending external factors, though it somewhat varies, depending on the intensity of the target radio waves and the corresponding frequency. Therefore, in order that the antenna can be kept in a usable condition under any circumstances, it is necessary that the internal loss (the sum of the copper loss and the radiation loss; A+B in

FIG. 10

) should be kept to the minimum. Generally, the allowable internal loss is not more than 1 dB, and particularly when transmitting and receiving weak radio waves in a satellite communication or the like, the allowable internal loss is not more than 0.5 dB. In view of this, the distance H is as follows; 1÷250≦H÷λ≦1÷80, and preferably 1÷200≦H÷λ≦1÷100 (where λ represents a wavelength), the good antenna efficiency can be obtained, and therefore the antenna of high reliability can be provided which can positively operate under a wide range of conditions of use.

For example, in a mobile satellite communication system which effects a ground-satellite-ground data communication using a satellite orbiting in a low orbit, assume that this antenna

14

is used in Obcomb communication to which the frequency band between 137.0 MHz and 138.0 MHz for a down-line and the frequency band between 148.0 MHz and 150.05 MHz for an up-line are assigned in WARC' 92 (Meeting of World Radio communication Association, 1992). The range of variation of the wavelength (λ) is 2000≦λ≦2190 (mm), and therefore good antenna characteristics can be achieved at all wavelength bands In the range in which the range of obtained with the shortest wavelength (λ=2000), overlaps the range H obtained with the longest wavelength (λ=2190). This range is 8.76≦H≦25 (mm), and preferably 10.95≦H≦20 (mm).

If the distance H is in the above range, the sum of the radiation loss and the copper loss is suppressed to the minimum, and therefore the antenna can be achieved which has a small loss and good antenna characteristics as a whole. Besides, the thickness of the antenna

14

is very small, and therefore the antenna can be easily installed on a container or the like designed to be used in a stacked condition. More specifically, when freight containers are stacked together, a gap, formed between the containers, is 1 to 2 inches at the largest, and when the antenna

14

is used for Obcomb communication, the antenna

14

can be easily formed into a thickness within this range. Therefore, the antenna can be achieved which being mounted on the container, enables the stacking of the containers. Besides, by short-circuiting the ground plate

6

and the box-like metal body of the container together, the change of antenna impedance can be suppressed to the minimum even when the container is stacked on the antenna

14

, and therefore the antenna can be achieved which has good antenna characteristics even in a stacked condition.

Fourth Embodiment

Next, a fourth embodiment of the invention will be described with reference to the drawings.

FIG. 27

is a perspective view showing the construction of an antenna of the fourth embodiment, and

FIGS. 28 and 29

are perspective views showing the construction of radiation elements in the fourth embodiment.

In

FIG. 27

, an antenna board

20

is usually made of a dielectric material, and comprises a printed circuit board, a PET film board or the like having a conductor layer formed on one or both sides thereof, and radiation elements

21

and

22

with different electrical lengths are formed on these boards by etching method. With respect to the electrical length of the radiation elements

21

and

22

, the line lengths L

21

and L

22

of the radiation elements

21

and

22

may be different from each other while their line widths W are the same, as shown in FIG.

28

. Alternatively, the line widths W

1

and W

2

of the radiation elements may be different from each other while their line lengths are the same, as shown in FIG.

29

. In either case, preferably, the element line length of each of the radiation elements is set to about ¼ of a respective one of a plurality of line wavelengths λg

1

, λg

2

, . . . λgn corresponding to a plurality of desired frequencies f

1

, f

2

, . . . fn.

A transmission line

24

is connected to an end

21

a

of the radiation element

21

, and a transmission line

25

is connected to an end

22

a

of the radiation element

22

. The transmission line

24

connects the radiation element

21

to a ground point

26

grounded to a ground plate

23

disposed substantially parallel to the radiation elements

21

and

22

, and the transmission line

25

connects the radiation element

22

to a ground point

27

grounded to the ground plate

23

. Preferably, the transmission lines

24

and

25

are connected respectively to central portions of the ends

21

a

and

22

a

since this enhances antenna characteristics. The ground plate

23

may be provided on that side of the antenna board

20

facing the opposite side thereof having the radiation elements

21

and

22

formed, or the ground plate

23

may be provided separately in substantially parallel relation to the antenna board

20

.

A transmission line

28

is connected at a feed point F

1

to the transmission line

24

, and a transmission line

29

is connected at a feed point F

2

to the transmission line

25

. The transmission lines

28

and

29

are respectively connected to a common transmission line

30

(extending from the ground plate

23

) through a feed portion

31

, and feed high-frequency power in a matched manner to the radiation elements

21

and

22

via the feed points F

1

and F

2

through transmission lines

24

and

25

. Although the transmission line

30

is disposed i-substantially vertically relative to both of the ground plate

23

and the antenna board

20

, the transmission line

30

and the feed portion

31

may be both formed on the antenna board

20

.

The distance L

1

between the ground point

26

and the feed point F

1

is different from the distance L

2

between the ground point

27

and the feed point F

2

, and by doing so, the impedance matching can be accurately achieved, and therefore the antenna device can be provided in which the resonance frequency is not shifted in the radiation elements

21

and

22

, and which can shared between two wavelengths.

If the lengths of the transmission lines

27

and

28

are different from each other, the feed phase can be adjusted more easily.

Coaxial cables, micro-strip transmission lines or the like can be used as the transmission lines

24

,

25

,

28

,

29

and

30

.

In this embodiment, although only one feed portion

31

is provided, two separate feed portions may also be possible.

In this embodiment, although only two radiation elements are provided, more than two radiation elements can be of course provided.

The radiation elements

21

and

22

may be formed into a meandering line as shown in

FIG. 32

, or may be formed into any other suitable configuration. With the construction of the radiation elements

21

and

22

shown in

FIG. 27

, the dimension of each of the radiation elements

21

and

22

in the transverse direction can be reduced, and therefore the size of the antenna can be reduced, and therefore the antenna device, having a narrow, elongate configuration, can be achieved. With the construction of the radiation elements

21

and

22

shown in

FIG. 32

, the length of the radiation elements

21

and

22

in the longitudinal direction can be reduced, and therefore there can be achieved the antenna device of a compact design having a smaller projected area.

As shown in

FIG. 36

(which is a perspective view showing the construction of a feed portion of the invention), a construction may be possible in which a coaxial feeder cable

36

, connected to the transmission line

31

, is provided between the ground plate

23

and the antenna board

20

in substantially parallel relation thereto. With this construction, the antenna can have a thinner design as compared with the case where a connector is exposed at the reverse surface of the ground plate

23

.

As shown in

FIG. 37

(which is an enlarged, perspective view showing a feed portion of the invention), a metal member of an integral construction may be provided which includes braid-clamping portions

37

for clamping a braid of a coaxial feeder cable

36

, and ground line portions

38

for grounding the radiation elements

21

and

22

via transmission lines

24

and

25

. This metal member may be electrically connected to the ground plate by soldering or welding. In this construction, the structural portion, having the braid-clamping portions

37

(which receive the braid of the coaxial cable

36

therebetween, and are deformed by a tool (e.g. pliers) to hold this cable therebetween), is formed integrally with the ground line portions

38

for grounding the radiation elements

21

and

22

to the ground board

23

each of the ground line portions

38

having a soldering projection formed at its upper end. Therefore, the number of the component parts is reduced, and the assembling process is simplified, thus enhancing the productivity, besides the reliability is enhanced since the number of the connected and processed portions is reduced.

As shown in

FIG. 38

(which is a perspective view showing a grounded form of radiation elements in the invention), a construction may be provided in which a plurality of ground points

26

and

27

are grounded to the ground plate

23

by a wall

39

made of electrically-conductive metal. With this construction, the area of grounding is increased, and the electrical operation which is stable for noises can be effected, besides the mechanical strength of the structure increases.

As shown in

FIG. 39

(which is a perspective view showing the construction of an antenna device of the invention), a construction may be provided in which the plurality of radiation elements

21

and

22

are formed on the common antenna board

20

, and a gap between the antenna board

20

and the ground plate

23

is maintained by spacers

40

made of a resin or the like. Owing to the provision of the spacers

40

, the gap between the antenna board

20

and the ground plate

23

can be kept to a predetermined height, and the antenna device having stable antenna characteristics can be provided. In this construction, although the spacers

40

are provided in spaced relation to one another, a single board, made of a dielectric material, may be inserted in the gap.

The operation of the antenna of the above construction will be described.

The high-frequency power, supplied via the transmission line

31

, is supplied to the radiation elements

21

and

22

via the feed portion

30

, the transmission lines

28

and

29

, the feed points F

1

and F

2

, the transmission lines

24

and

25

and the ends

21

a

and

22

a

of the radiation elements

21

and

22

. By setting the distance L

1

between the ground point

26

and the feed point F

1

and the distance L

2

between the ground point

27

and the feed point F

2

to different desired lengths, respectively, the power can be fed in a matched manner so that the desired impedance can be obtained. By suitably selecting the dimension of the each portion of the radiation elements

21

and

22

, the radiation elements

21

and

22

radiate radio waves into the air at the desired resonance frequencies f

1

and f

2

. In this case, as shown in

FIG. 27

, if the electrical length of the radiation element

21

is represented by Le

1

, and the electrical length of the radiation element

22

is represented by Le

2

, the following formulas are provided:

Le

1

≈C/

4

f

1

(Formula 1)

Le

2

≈C/

4

f

2

(Formula 2)

A plurality of resonance characteristics are obtained (two cycles in the case) as shown in

FIG. 30

(which is a diagram showing the characteristics of the radiation elements in the fourth embodiment of the invention).

The current distribution I in the antenna of the above construction will be described with reference to

FIGS. 31A and 31B

.

FIGS. 31A and 31B

are views showing the current distribution in the antenna of the fourth embodiment of the invention. As shown in

FIG. 31A

, the electrical length Le

1

, Le

2

of each of the radiation elements

21

and

22

is set to about ¼ of a respective one of the two line wavelengths λg

1

and λg

2

corresponding to the desired frequencies f

1

and f

2

, and by doing so, the current is distributed generally half sinusoidally in the antenna in such a manner that the amplitude is the maximum in the vicinity of the central portion of the feed portion at the desired frequencies f

1

and f

2

while the amplitude is the minimum at the distal end portions of the radiation elements. As indicated by arrows (→) in the drawings, the direction of the current, flowing in a horizontal direction on the drawing sheet, is horizontal, and horizontally-polarized radio waves due to this current are radiated. In this case, the potential of the voltage distribution V is the minimum at the ground point, and is the maximum at the free end of the radiation element, as shown in FIG.

31

(

b

). Therefore, the impedance Z at the feed point F is expressed by the following formula:

Z=V÷I (Formula 3)

Here, the gap between the ground plate and the radiation elements is represented by h. As shown in

FIG. 31B

, by adjusting the distance between the ground point G and the feed point F, that is, by varying L, the values of the voltage distribution V and current distribution I are varied at that point (position) in accordance with the change of L. Namely, the impedance Z. representing the ratio of the voltage distribution V to the current distribution I, can also be adjusted by varying the distance L between the ground point G and the feed point F. As shown in

FIG. 27

, in the case where the resonance occurs at the two frequencies f

1

and f

2

, the impedance Z

1

, Z

2

can be adjusted for each of the frequencies f

1

and f

2

by adjusting the distance L

1

between the ground point G and the feed point F

1

and the distance L

2

between the ground point G and the feed point F

2

for each of the frequencies f

1

and f

2

. Therefore, the matching with the impedance Z

0

of the feeder, such as a coaxial cable, can be achieved.

Fifth Embodiment

Next, a fifth embodiment of the invention will be described with reference to the drawings. Those portions of the antenna device of this embodiment, which are not described, are almost similar to those of the fourth embodiment.

FIGS. 33A and 33B

are plan view showing the construction of radiation elements of the fifth embodiment, and the radiation elements in these Figures are different only in configuration. As shown in

FIGS. 33A and 33B

, impedance devices

34

and

35

are provided at free end portions

32

and

33

of the radiation elements

21

and

22

, respectively, and by setting these impedance values to desired values, respectively, the voltage standing wave ratio (VSWR) in a wide-band pattern can be obtained as indicated by a line b in FIG.

30

. The desired results can be obtained if the impedance device is provided at one of the radiation elements. With this construction, even if slight variations are developed in the mass-produced antennas, the antenna characteristics can be kept within the predetermined range, and the antenna device, which is less liable to be defective during production, can be achieved. Besides, the antenna device of high reliability can be achieved in which the degradation of the antenna characteristics is extremely low even when snow, rain, dirt and so on deposits on the surface of the antenna device.

As shown in

FIGS. 34A and 34B

(which are plan views showing the construction of radiation elements of the invention), the impedance devices

34

and

35

are provided in the vicinity of feed points F

1

and F

2

at one or both sides, and by doing so, similar effects can be obtained. More specifically, generally, in the vicinity of the feed points F

1

and F

2

, the value of the voltage distribution V is small, and the value of the current distribution I is large, and the impedance Z, representing the ratio of the voltage distribution V and the current distribution I, decreases (usually, several tens Ω, from Z≈5 to 75Ω). Therefore, the impedance devices

34

and

35

are provided in the vicinity of the feed points F

1

and F

2

, and their impedance values are set to desired values, respectively, and by doing so, the VSWR in a wide-band pattern can be obtained. Besides, by setting the values of the impedance devices

34

and

35

to desired values, respectively, the radiation power can be varied arbitrarily. For example, a solid line a in

FIG. 35

(which shows the relation between the radiation power and the frequency in the invention) represents the radiation power obtained when the impedance devices

34

and

35

are substantially the same in impedance device ratio, and a broken line B represents the radiation power obtained when the impedance devices

34

and

35

are not equal in impedance device ratio. Thus, in accordance with the demand of the radio system, the radiation power at the frequencies f

1

and f

2

, that is, the antenna gain, can be adjusted. Besides, using the above constructions in combination, the antenna device can be provided which has a wider band and adjustable in antenna gain.

Number	Name	Date
4464663	Lalezari et al.	Aug 1984
4849765	Marko	Jul 1989
4987424	Tamura et al.	Jan 1991
5936583	Sekine et al.	Aug 1999

Number	Date	Country
0777293A1	Jun 1997	EP
0690108	Mar 1994	JP
WO9627219	Sep 1996	WO

Antenna device

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Date Filed

Date Issued

Inventors

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Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (4)

Foreign Referenced Citations (3)

Non-Patent Literature Citations (5)

Entry
European Search Report dated Mar. 1, 2000.
Patent Abstract of Japan, JP 05 291 825 A, Nov. 5, 1993.
Patent Abstract of Japan, JP 11 251 825 A, Sep. 17, 1999.
European Search Report dated Nov. 5, 1999.
Patent Abstract of Japan, JP 05 291 825, Nov. 5, 1993.