JP3618267B2 - Antenna device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an antenna device that can be reduced in size, for example, an antenna device that can be used for a small communication device such as a mobile phone or a PHS (Personal Handy Phone).
[0002]
[Prior art]
In recent years, there has been an increase in communication devices in which a radio and an antenna are integrated. Examples of this type of communication device include portable wireless devices such as PHS and mobile phones, and small wireless base stations. The antenna of this type of communication device is required to have a characteristic close to omnidirectionality.
[0003]
In addition, portable radios need to be resistant to destruction when dropped, and base stations need to be resistant to damage caused by natural disasters such as wind and rain, so the radio and antenna are integrated. It is desirable to do.
[0004]
However, it is known that when the wireless device and the antenna are integrated, the radiation pattern from the antenna changes under the influence of electromagnetic waves emitted from the housing of the wireless device.
[0005]
This cause will be briefly described below. The casing of the radio is made of a conductor, and also serves as a ground and shield for the built-in radio circuit. Since this casing is also grounded for the antenna, there is a problem that high-frequency current fed to the antenna flows into the casing, and radio waves are emitted from the casing as described above. In particular, in the case of a built-in antenna, since the amount of radiation from the antenna is small, it is strongly influenced by the wireless device casing.
[0006]
In order to reduce these effects, a proposal has been made to use a dipole antenna (Japanese Patent Laid-Open No. 61-205004). This is because a dipole antenna is an antenna that does not require a ground, so that it is not necessary to directly connect the antenna to a casing that is a ground, and leakage of high-frequency current to the casing can be suppressed.
[0007]
However, the dipole antenna also has a problem that it is actually difficult to realize. The reason is that if the dipole antenna is disposed close to the casing, the impedance of the antenna becomes very low and matching with the feeder line cannot be achieved.
[0008]
As a technique for solving such a problem, Japanese Patent Application Laid-Open No. 61-205004 discloses a feeding circuit having a folded structure for matching. However, in practice, it is difficult to make a folded structure.
[0009]
FIG. 13 is a perspective view showing a schematic configuration of a power feeding circuit disclosed in Japanese Patent Application Laid-Open No. 61-205004. As can be seen from the reference numeral 5 in FIG. 13, it is necessary to perform balanced feeding (parallel two lines) from the feeding point to the antenna. However, in general, radio equipment feeds in an unbalanced state (for example, coaxial feeding or microstrip line). Therefore, a balance-unbalance conversion (balun) must be provided. In the conventional example, this balun is omitted.
[0010]
Even when balanced feeding is not performed, antenna characteristics change due to the influence of the feeding line if the feeding line is easily arranged. This is because the dipole antenna itself is a balanced element, so a balanced / unbalanced conversion (balun) is required at the feed point, and unnecessary current leaks from the antenna feed point to the feed line. This is because the radiation characteristics of the antenna change.
[0011]
As described above, when the dipole antenna is used, there is a problem that a balun having a relatively large structure is required for the power feeding circuit.
[0012]
In general, a balun has a quarter wavelength length. For example, a linear element having a length of a quarter wavelength is arranged in parallel to the outer conductor of the coaxial line that is the feeder line, and one end thereof is short-circuited to the outer conductor. Thereby, since it can be set as a high impedance when the short circuit end is seen from the open end, the leakage of the unnecessary current to an outer conductor can be prevented.
[0013]
However, in principle, a length of about a quarter wavelength is required, and the size of the balun becomes very large depending on the frequency used. This makes it difficult to reduce the size of the antenna and the entire radio.
[0014]
The above problem can also occur in the case where a diversity antenna is configured by attaching a plurality of antennas to a housing.
[0015]
The present invention has been made in view of the above points, and an object of the present invention is to provide an antenna device that can be miniaturized and can easily obtain a desired radiation pattern.
[0016]
[Problems to be solved by the invention]
[0017]
In order to solve the above-described problems, the present invention provides a casing, a first linear element having one end connected to the end of the casing, and a second end connected to the other end of the first linear element. And second and third linear elements arranged in directions different from each other by approximately 180 degrees and having different lengths, and the sum of the electrical lengths of the second and third linear elements is transmitted. An absolute multiple of a half wavelength of the frequency of the radio wave or the received radio wave, and the electrical length of the first linear element is the absolute value of the difference between the electrical lengths of the second and third linear elements. Less than half.
[0018]
In the invention of claim 1, the sum of the electrical lengths of the second and third linear elements is an integral multiple of a half wavelength of the radiation frequency of the radio wave, and the electrical length of the first linear elements is Since the absolute value of the difference between the electrical lengths of the second and third linear elements is less than half, each linear element can be resonated only in a desired resonance mode. Therefore, radio waves having a desired frequency can be transmitted or received. Here, the electrical length is the wavelength length of the frequency at which the element resonates. In general, the electrical length is shortened by bending or the like, and is increased by bringing a dielectric or the like closer.
[0019]
In the invention of claim 2, since the second and third linear elements are arranged close to the surface of the casing, the size of the entire antenna device can be reduced.
[0020]
In the invention of claim 3, since two sets of antennas are arranged in parallel, a space diversity antenna can be configured, the reception sensitivity can be improved, and the radio wave state changes rapidly with time (for example, Even during mobile communication, stable communication is possible by suppressing changes in radio wave conditions.
[0021]
In the invention of claim 4, since the two sets of antennas are arranged so as not to see through each other, the electromagnetic coupling between the antennas can be reduced.
[0022]
In the invention of claim 5, since the two sets of antennas are arranged in directions different by about 90 degrees, signals having low correlation with each other can be received efficiently. Therefore, the correlation of the received signals can be lowered without increasing the distance between the antennas.
[0023]
In the invention of claim 6, in order to arrange the two antennas in directions different from each other by about 90 degrees, and to arrange the antennas so as not to see each other, in addition to the effect of the invention of claim 4, electromagnetic waves between the antennas The boundary coupling can be reduced.
[0024]
In the invention of claim 7, a fourth antenna comprising a fourth linear element is provided separately from the first antenna comprising the first to third linear elements, and both antennas are arranged in parallel. Therefore, the combined gain of both antennas can be obtained, and the sensitivity is improved.
[0025]
In the invention of claim 8, a fourth antenna comprising a fourth linear element is provided separately from the first antenna comprising the first to third linear elements, and the two antennas differ by approximately 90 degrees. Since they are arranged in the direction, a polarization diversity antenna can be configured, and signals having low correlation with each other can be received efficiently.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an antenna device according to the present invention will be specifically described with reference to the drawings.
[0027]
(First embodiment)
FIG. 1 is a perspective view of a first embodiment of an antenna device according to the present invention. The antenna device of FIG. 1 includes a linear element (first linear element) 102 connected to one end side of a housing 101 and a linear element (second and third elements) connected to one end of the linear element 102. (Linear element) 103 and 104, and a feeding point 105 is provided between the housing and the linear element 102.
[0028]
The linear elements 103 and 104 are arranged in directions different by about 180 degrees with a connection point with the linear element 102 as a boundary. More specifically, the linear elements 102 to 104 are arranged in a T shape, and the linear elements 102 and 103 constituting the T-shaped horizontal bar are arranged so as to be substantially parallel to one side of the housing 101. ing. Further, the sum of the lengths of the linear elements 103 and 104 is set to be an integral multiple of a half wavelength of the frequency of the transmission radio wave or the reception radio wave.
[0029]
The housing 101 is made of a conductor such as aluminum, and is omitted in FIG. The shielding of the wireless circuit is also performed by the casing 101 itself.
[0030]
A T-shaped monopole antenna is conventionally known as an antenna similar to the antenna device of FIG. In this type of monopole antenna, the lengths of the two linear elements constituting the T-shaped horizontal bar are made substantially equal to each other and used as a quarter-wave low profile antenna. Conventionally, it has been common to use radio wave radiation from a T-shaped vertical bar.
[0031]
On the other hand, the antenna apparatus of FIG. 1 utilizes the radiation of radio waves from the T-shaped horizontal bar portions (linear elements 103 and 104). In this embodiment, as shown in FIG. 2, the lengths A, B, and C of the linear elements 102, 103, and 104 are set so as to satisfy the relationship of the expression (1).
[0032]
2 × A <| BC | (1)
Hereinafter, the reason for setting the length of each linear element so as to satisfy the relationship of the expression (1) will be described. The antenna device of FIG. 1 has three resonance modes m1, m2, and m3. FIG. 3A is a diagram for explaining an outline of the resonance modes m1 to m3, and FIG. 3B is a diagram illustrating a vibration state of each of the resonance modes m1 to m3.
[0033]
The resonance mode m1 is a resonance mode of a desired half-wave dipole antenna. When viewed from the feeding point 105, the resonance mode m1 is a parallel resonance mode in an equivalent circuit of L and C. In the case of FIG. 3, the current at the feeding point 105 is minimized during resonance.
[0034]
The resonance modes m2 and m3 are resonance modes of an undesired quarter-wave monopole antenna, which is a series resonance mode in an equivalent circuit of L and C. In the resonance modes m2 and m3, the current at the feeding point 105 is maximized during resonance.
[0035]
The resonance mode m1, which is a desired mode, is a parallel resonance mode that resonates at a frequency between the resonance frequencies m2 and m3 by separating the series resonance of the resonance modes m2 and m3. For this reason, in order to perform resonance in the resonance mode m1, the resonance frequency of each mode needs to satisfy the relationship of the following formula (2) or (3).
[0036]
Resonance frequency of resonance mode m2 <resonance frequency of resonance mode m1 <resonance frequency of resonance mode m3 (2)
Resonance frequency of resonance mode m3 <resonance frequency of resonance mode m1 <resonance frequency of resonance mode m2 (3)
Here, assuming that the resonance wavelengths of the respective resonance modes are λ1, λ2, and λ3, the resonance wavelengths respectively use the lengths A to C of the linear elements 102 to 104,
In the resonance mode m1, λ1 = 2 × (B + C)
When the resonance mode is m2, λ2 = 4 × (B + A)
When the resonance mode is m3, λ3 = 4 × (C + A)
Can be expressed.
[0037]
For example, assuming that the length B of the linear element 2 is shorter than the length C of the linear element 3,
λ2 <λ1 <λ3
Since it is a condition that
4 × (B + A) <2 × (B + C) <4 × (C + A) (4)
It becomes. (4) If the formula is arranged with A,
(B−C) <2 × A <(C−B)
It becomes. Where A takes a positive value and B is longer than C.
2 × A <| BC |. . . . . . . . . (1)
It becomes.
[0038]
In the formula (1), each antenna element needs to consider the electrical length. Here, the electrical length is the wavelength length of the frequency at which the element resonates. The quarter-wave monopole antenna of the resonance modes m2 and m3 is bent at the junction with the linear element 102, so that its electrical length is several percent of the actual physical length. It is known to shrink. That is, in order for a bent element to resonate at the same frequency as a straight element, it is necessary to increase the physical length.
[0039]
The half-wave monopole antenna in the resonance mode m1 is similarly shrunk. However, unlike the quarter-wave monopole antenna, the quarter-wave antenna is not affected by the bent portion in the vicinity of the feeding point 105. The shrinkage effect becomes smaller.
[0040]
For example, when the shrinkage effect is relatively strong in the resonance modes m2 and 3, the above-described equation (4) is expressed by the following equation (5) when the shrinkage rate of the resonance modes m2 and 3 is α. become.
[0041]
4 × α × (B + A) <2 × (B + C) <4 × α × (C + A) (5)
When formula (5) is modified, formula (6) is obtained.
[0042]
B + (1-2 × α) × C <2 × α × A <C + (1-2 × α) × B (6)
Here, the value of α may be determined according to the structure of each of the linear elements 102 to 104. Further, since the impedance changes depending on the lengths B and C of the linear elements 103 and 104 in FIG. 1, it is possible to match the feeding point 105 by adjusting the lengths B and C.
[0043]
Further, the antenna device of FIG. 1 has a feature that unnecessary current leakage to the housing 101 is small. The reason for this will be described below.
[0044]
Since the antenna apparatus of FIG. 1 operates by parallel resonance, the current flowing through the feeding point 105 is smaller than the current flowing through the linear elements 103 and 104. Therefore, the amount of current leaking from the feeding point 105 to the housing 101 is smaller than that of the series resonance antenna. For this reason, the unnecessary radiation from the housing | casing 101 is suppressed and the influence on the radiation | emission characteristic of an antenna becomes small.
[0045]
4 is a diagram showing antenna characteristics of the antenna device of FIG. 1, FIG. 4 (a) is a diagram showing the relationship between frequency and mismatch loss indicating the amount of gain degradation, and FIG. 4 (b) is a Smith chart diagram. 4 (c) is a diagram showing radiation patterns of vertical polarization and horizontal polarization, and FIG. 4 (d) is a diagram for explaining the coordinates of FIG. 4 (c).
[0046]
In FIG. 4, the length A of the linear element 102 is 0.026λ (λ is an operating frequency), the length B of the linear element 103 is 0.221λ, and the length C of the linear element 104 is 0.279λ. An example of the case is shown. In this case, the relationship of the above-described expression (1) is satisfied.
[0047]
As can be seen from FIG. 4A, the mismatch loss at the resonance frequency f0 of the resonance mode m1 is sufficiently small. Further, as can be seen from the Smith chart of FIG. 4B, the impedance characteristic changes so as to draw a loop centering on 50 ohms, and it can be seen that matching with the feeder line is achieved over a relatively wide band. .
[0048]
Further, as can be seen from the radiation pattern of FIG. 4C, it can be seen that the radiation pattern spreads uniformly along the outer circumferential circle, and is a non-directional pattern that is a characteristic of the dipole antenna itself. In addition, since the vertical polarization is small, it can be seen that unnecessary radiation from the housing 101 is also small.
[0049]
FIG. 5 is a diagram showing the relationship between the frequency and the antenna gain of this embodiment. As shown, the antenna gain at the resonance frequency f1 of the resonance mode m1 is large, and the antenna gain at the resonance frequencies f2 and f3 of the resonance modes m2 and m3 is sufficiently small. That is, by setting the lengths A, B, and C of the linear elements 102 to 104 so as to satisfy the relationship of the above-described expression (1), radio waves can be radiated at the resonance frequency of the resonance mode m1.
[0050]
As described above, the antenna according to the present embodiment has a relatively simple configuration, but suppresses the influence from other parts close to the antenna, which has been a problem in the past, and realizes an operation as a dipole antenna. I understand that.
[0051]
Further, according to the experiment by the present applicant, the length A of the linear element 102 is left as it is, the length B of the linear element 103 is 0.234λ, and the length C of the linear element 104 is 0.266λ. However, it has been found that the operation of the antenna exhibits the desired characteristics. Further, as a result of calculating the shrinkage rate from the values of the first resonance point (resonance mode m2) and the third resonance point (resonance mode m3), it was found that the shrinkage rate α was 0.95. Since these parameters satisfy the relationship of the expression (6), resonance in the desired resonance mode m1 is performed, and an antenna radiation pattern with less influence of unnecessary radiation from the housing 101 can be obtained.
[0052]
(Second Embodiment)
In the second embodiment, two sets of antennas having the same structure as that of the first embodiment are provided.
[0053]
FIG. 6 is a perspective view of a second embodiment of the antenna device according to the present invention. In the antenna device of FIG. 6, two sets of antennas having the same structure as that of FIG. 1 are arranged substantially in parallel. Each antenna (first and second antennas) 11 and 12 is composed of T-shaped linear elements 102 to 104 as in FIG. 1, and between the linear element 102 and the housing 101. A feeding point 105 is provided. These two sets of antennas 11 and 12 constitute a diversity antenna.
[0054]
In FIG. 6, the linear elements 102 and 103 of the antennas 11 and 12 are arranged in parallel, and the antenna elements are arranged at a distance in the same plane. With such a configuration, it can be operated as a space diversity antenna.
[0055]
Space diversity is a method that places multiple antennas at a distance and selects or synthesizes the signals received by each antenna to improve reception sensitivity. In particular, mobile communications in which radio wave conditions change rapidly over time. Is widely used as a method for performing stable communication while suppressing changes in radio wave conditions.
[0056]
It is desirable that the antennas constituting the diversity have a low correlation between signals received by the respective antennas. In space diversity, the correlation between signals can be lowered by making the distance between antennas sufficiently wide.
[0057]
More specifically, it is desirable to arrange the two antennas 11 and 12 at least half a wavelength apart. For that purpose, it is necessary to make the size of the housing 101 more than a half wavelength.
[0058]
In the configuration of FIG. 6, when the distance between the antennas is about half a wavelength, electromagnetic coupling occurs between the antennas, and the directivity of the antennas changes. The correlation of the received signal can be lowered also by the change in the directivity of the antenna. Thereby, the improvement of the diversity effect can be expected.
[0059]
FIG. 7 is a perspective view showing an example in which two sets of antennas 11 and 12 are arranged back to back. By arranging the antennas as shown in FIG. 7, the antennas do not exist in line of sight, and the electromagnetic coupling between the antennas can be reduced. Therefore, electromagnetic field coupling that causes a change in antenna characteristics can be suppressed, and an unnecessary change in antenna characteristics can be eliminated. Whether the two sets of antennas 11 and 12 are arranged as shown in FIG. 6 or as shown in FIG. 7 may be selected according to the system specifications.
[0060]
FIG. 8 is a diagram illustrating an example in which antennas 11 and 12 are connected to two opposing surfaces of the housing 101, respectively. With the configuration as shown in FIG. 8, the distance between the two antennas 11 and 12 can be increased, and the diversity effect can be improved. Further, since the antennas do not exist within the line of sight, the electromagnetic coupling between the antennas can be reduced.
[0061]
(Third embodiment)
In the third embodiment, two sets of antennas are arranged in directions different from each other by approximately 90 degrees.
[0062]
FIG. 9 is a perspective view of an antenna device according to a third embodiment of the present invention. The antenna device of FIG. 9 has two sets of antennas 11 and 12 having the same structure as that of FIG. 1 arranged in directions different from each other by approximately 90 degrees. Each antenna 11, 12 is composed of T-shaped linear elements 102 to 104 as in FIG. 1, and a feeding point 105 is provided between the linear element 102 and the housing 101. These two sets of antennas 11 and 12 constitute a polarization diversity antenna.
[0063]
In an actual outdoor radio wave environment, it is known that the correlation between vertically polarized waves and horizontally polarized waves is very low. Therefore, by arranging the antenna elements in directions different by about 90 degrees as shown in FIG. 9, it becomes possible to receive signals having low correlation with each other.
[0064]
The antenna of FIG. 9 has an advantage that the correlation of received signals can be lowered without increasing the distance between the antennas. Accordingly, the size of the housing 101 can be reduced by the amount that the distance between the antennas can be shortened.
[0065]
FIG. 10 shows a modification of FIG. 9 in which two sets of antennas 11 and 12 are arranged back to back. By arranging them back to back, coupling between antennas can be reduced, and unnecessary characteristic fluctuations can be suppressed.
[0066]
Also in the case of FIG. 10, similarly to FIG. 9, even if the distance between the antennas is shortened, the correlation of the received signals can be lowered.
[0067]
(Fourth embodiment)
In the fourth embodiment, an antenna composed of linear elements is provided separately from an antenna composed of three linear elements.
[0068]
FIG. 11 is a block diagram of a fourth embodiment of the antenna device according to the present invention. The antenna device of FIG. 11 includes an antenna 13 including a linear element (fourth linear element) 106 protruding from the housing 101, separately from the antenna 11 having the same structure as that of FIG. 1.
[0069]
First, the case where an array antenna is comprised by these antennas 11 and 13 is demonstrated. In FIG. 11, the linear elements 106 constituting the antenna 13 are arranged substantially parallel to the linear elements 102 and 103 constituting the antenna, and both antennas are arranged as close as possible.
[0070]
By supplying power so that both antennas 11 and 13 are in phase with each other, the combined gain of both antennas 11 and 13 can be improved. In this case, the linear element 106 may have a half wavelength.
[0071]
In the conventional case, it is necessary to configure the linear element to have a two-stage structure and protrude from the housing 101. However, in this embodiment, a gain equivalent to that can be obtained with a half length.
[0072]
These antennas 11 and 13 can also be used as diversity antennas. In this case, the linear element 106 may be about a half wavelength or a quarter wavelength.
[0073]
FIG. 12 is a modification of FIG. 11 and is a perspective view showing an example of a polarization diversity antenna in which two antennas 11 and 13 are arranged in directions different from each other by approximately 90 degrees. The linear element 106 in FIG. 12 is configured to supply power at the center thereof, and has a length of approximately half a wavelength. Thereby, the radiation of the radio wave from the linear element 106 becomes the same as that of the dipole antenna.
[0074]
You may comprise combining each antenna demonstrated by the 1st-4th embodiment mentioned above arbitrarily. For example, FIG. 6 and FIG. 9 may be combined to provide three or more antennas, and some of the antennas may be arranged in parallel and the rest may be arranged at approximately 90 degrees. Moreover, you may combine the antenna 13 demonstrated in FIG.11 and FIG.12 with these antennas. Thus, there are no particular restrictions on the number or arrangement of antennas.
[0075]
In each of the embodiments described above, an example in which the rectangular housing 101 is used has been described, but the shape of the housing 101 is not particularly limited.
[0076]
【The invention's effect】
As described above in detail, according to the present invention, the sum of the electrical lengths of the second and third linear elements is an integral multiple of a half wavelength of the radiation frequency of the radio wave, and the first linear Since the electrical length of the element is less than half of the absolute value of the difference between the electrical lengths of the second and third linear elements, unnecessary frequency components are suppressed, and radio waves having a desired frequency can be transmitted. Can be radiated. In addition, unnecessary radiation from the feeder line can be prevented, and the antenna device can be downsized. Furthermore, a radiation pattern close to omnidirectional can be obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view of an antenna device according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining the length of each linear element.
FIG. 3A is a diagram for explaining an outline of resonance modes m1 to m3, and FIG. 3B is a diagram illustrating a vibration state of each resonance mode m1 to m3.
4 is a diagram showing antenna characteristics of the antenna device of FIG. 1. FIG.
FIG. 5 is a diagram illustrating a relationship between a frequency and an antenna gain according to the present embodiment.
FIG. 6 is a perspective view of a second embodiment of an antenna device according to the present invention.
FIG. 7 is a perspective view showing an example in which two antennas are arranged back to back.
FIG. 8 is a diagram showing an example in which antennas are connected to two opposite surfaces of a housing.
FIG. 9 is a perspective view of a third embodiment of an antenna device according to the present invention.
FIG. 10 is a diagram showing an example in which two sets of antennas are arranged back to back with each other.
FIG. 11 is a block diagram of a fourth embodiment of an antenna device according to the present invention.
FIG. 12 is a perspective view showing an example of a polarization diversity antenna in which two antennas are arranged in directions different from each other by approximately 90 degrees.
FIG. 13 is a perspective view illustrating a schematic configuration of a power feeding circuit disclosed in Japanese Patent Application Laid-Open No. 61-205004.
[Explanation of symbols]
11-13 Antenna 101 Cases 102-104, 106 Linear element 105 Feed point

Claims (8)

A housing,
A first linear element having one end connected to an end of the housing;
Second and third linear elements respectively connected to the other ends of the first linear elements, arranged in directions different from each other by approximately 180 degrees and having different lengths ;
The sum of the electrical lengths of the second and third linear elements is an integral multiple of a half wavelength of the frequency of the transmission radio wave or reception radio wave, and the electrical length of the first linear element is the first An antenna device, wherein the antenna device is less than half the absolute value of the difference in electrical length between the second and third linear elements. The antenna device according to claim 1, wherein the second and third linear elements are arranged close to the surface of the casing. A plurality of antennas comprising the first, second and third linear elements;
3. The antenna device according to claim 1, wherein the second and third linear elements of each antenna are arranged in parallel with each other for at least two sets of these antennas. The antenna apparatus according to claim 3, wherein at least two sets of antennas having the second and third linear elements arranged in parallel are arranged so as not to be seen through each other. A plurality of antennas comprising the first, second and third linear elements;
3. The antenna device according to claim 1, wherein the second and third linear elements of each antenna are arranged in directions different from each other by approximately 90 degrees with respect to at least two sets of these antennas. 6. The antenna device according to claim 5, wherein at least two sets of antennas having the second and third linear elements arranged in directions different from each other by approximately 90 degrees are arranged so as not to be seen through each other. . Separately from the first antenna consisting of the first, second and third linear elements, a second antenna consisting of a fourth linear element protruding from the housing is provided,
The antenna apparatus according to claim 1 or 2, wherein the first and second antennas are arranged in parallel to each other. Separately from the first antenna consisting of the first, second and third linear elements, a second antenna consisting of a fourth linear element protruding from the housing is provided.
3. The antenna device according to claim 1, wherein the first and second antennas are arranged in directions different from each other by approximately 90 degrees.

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