Antenna device

An antenna device capable of securing the space for disposing a conductor element easily in view of the trend of downsizing, without the need of a step for the conductance with other electric devices. An antenna feeder part comes in contact with a feeding spring at the time of contraction so that a helical part can function as an antenna as well as a conductor element is provided elongating along an antenna storage part in the space in the housing for capacitive coupling with the antenna feeder part so that the antenna gain is improved by the conductor element. Therefore, even when the radiation of the helical part is restrained by the influence of a human head part, in particular, of an earlobe, since the conductor element is the radiation source, it is easy to secure the space as well as a step for the conductance with other electric devices is not required, and restraint of the radiation by the human head part can be alleviated for the antenna device as a whole so that the antenna gain can be improved.

BACKGROUND OF THE INVENTION
 The present invention relates to an antenna device, in particular, it
 relates to one capable of having good communication even in the case the
 antenna characteristic is deteriorated due to the influence of a human
 body on the antenna.
 Japanese Patent Application 10-160026, which was filed by the present
 inventor, discloses "antenna devices comprising a fixed (retractable)
 antenna provided with a shield case in a housing, comprising a conductor
 element conductive with the shield case inside the housing so that the
 antenna gain is improved by the conductor element". Among them, an antenna
 device comprising a fixed antenna provided with a shield case inside a
 housing will be explained with reference to FIGS. 5A and 5B.
 The antenna device shown in FIGS. 5A and 5B are a partial view of the part
 in the vicinity of the antenna device of a portable radio terminal device,
 such as PHS. FIG. 5A is a plan view of the rear side of the portable radio
 terminal device, and FIG. 5B is a side view thereof. In FIGS. 5A and 5B,
 the antenna device comprises a fixed antenna having a helical part 11
 provided with an helical antenna element functioning as a radiation
 element in an antenna cover, and a connection part 12 provided in a
 housing 14, to be connected with the helical antenna element of the
 helical element part, a high frequency feeder part having a matching
 circuit part 16 provided in the housing 14, to be connected via a feeder
 piece 15 to be a feeding point 13 of the antenna, and a radio circuit part
 20 to be connected with the matching circuit part 16, a shield case 19 for
 shielding a radiated unnecessary electromagnetic wave, and a conductor
 element 17 to be connected with the shield case at a contact part 18.
 The conductor element 17 provided inside the housing 14 is connected with
 the ground of the radio circuit part 20 via the contact part 18 and the
 shield case 19 such that the ground electric current dispersed in the
 shield case 19 and the radio circuit part 20 is gathered so as to serve as
 a radiation element.
 The matching circuit part 16 matches the impedance between the radio
 circuit part 20 and a radiation element comprising the helical element
 part 11 and the conductor element 15 for transmitting the electric power
 from the radio circuit part 20 to the radiation element without
 reflection.
 The conductor element 17 has a comb teeth-like shape, with one of the comb
 teeth bent such that the connection part 12 of the fixed antenna is
 accommodated in the bent part. The radio circuit part 20 is disposed in
 the shield case 19.
 As mentioned above, the antenna device of the prior application provided
 with a conductor element conductive with the shield case inside the
 housing for improving the antenna gain by the conductor element gave rise
 to a problem in that a step for the conductance with other electric
 devices is required as well as it is difficult to secure the space for
 accommodating the conductor element in view of the trend of downsizing of
 the device.
 SUMMARY OF THE INVENTION
 Accordingly, an object of the invention is to provide an antenna device
 capable of securing the space for accommodating a conductor element in
 view of the trend of downsizing of the device, without requiring the step
 for the conductance with other electric devices (antenna, shield case).
 In order to solve the problems, in the invention, an antenna feeder part
 comes in contact with a feeding spring at the time of contraction so that
 a helical part can function as an antenna as well as a conductor element
 is provided elongating along an antenna storage part in the space in the
 housing for capacitive coupling with the antenna feeder part so that the
 antenna gain is improved by the conductor element.
 Accordingly, even when the radiation of the helical part is restrained by
 the influence of a human head part, in particular, of an earlobe, since
 the conductor element is the radiation source, it is easy to secure the
 space as well as a step for the conductance with other electric devices is
 not required, and restraint of the radiation by the human head part can be
 alleviated for the antenna device as a whole so that the antenna gain can
 be improved.
 Since a first aspect of the invention is an antenna device comprising a
 retractable antenna provided with a shield case in a housing, wherein an
 antenna feeder part comes in contact with a feeding spring at the time of
 contraction so that a helical part can function as an antenna as well as a
 conductor element is provided elongating along an antenna storage part in
 the space in the housing for capacitive coupling with the antenna feeder
 part so that the antenna gain is improved by the conductor element, it is
 advantageous in that it is easy to secure the space as well as a step for
 the conductance with other electric devices is not required, and restraint
 of the radiation by the human head part can be alleviated for the antenna
 device as a whole so that the antenna gain can be improved.
 Moreover, since a second aspect of the invention is the antenna device
 according to the first aspect, wherein the conductor element is disposed
 with a three-dimensional shape along the antenna storage part for allowing
 further capacitive coupling with the antenna feeder part, it is
 advantageous in that it is easy to secure the space as well as a step for
 the conductance with other electric devices is not required, and restraint
 of the radiation by the human head part can be alleviated for the antenna
 device as a whole so that the antenna gain can be improved.
 Furthermore, since a third aspect of the invention is an antenna device
 comprising a fixed antenna provided with a shield case in a housing,
 wherein an antenna feeder part contacts with a feeding spring so that a
 helical part can function as an antenna as well as a conductor element is
 provided elongating along a prolongation of the antenna feeder part in the
 space in the housing for capacitive coupling with the antenna feeder part
 so that the antenna gain is improved by the conductor element, it is
 advantageous in that it is easy to secure the space as well as a step for
 the conductance with other electric devices is not required, and restraint
 of the radiation by the human head part can be alleviated for the antenna
 device as a whole so that the antenna gain can be improved.
 Moreover, since a fourth aspect of the invention is the antenna device
 according to the third aspect, wherein the conductor element is disposed
 with a three-dimensional shape along the antenna storage part for allowing
 further capacitive coupling with the antenna feeder part, it is
 advantageous in that it is easy to secure the space as well as a step for
 the conductance with other electric devices is not required, and restraint
 of the radiation by the human head part can be alleviated for the antenna
 device as a whole so that the antenna gain can be improved.
 Furthermore, since a fifth aspect of the invention is portable radio
 terminal device comprising the antenna device according to the first
 aspect or the third aspect, it is advantageous in that the antenna gain
 can be improved in the portable radio terminal device.
 Moreover, since a sixth aspect of the invention is a portable radio phone
 device comprising the antenna device according to the first aspect or the
 third aspect, it is advantageous in that the antenna gain can be improved
 in the portable radio phone device.

DETAILED DESCRIPTION OF THE INVENTION
 Hereinafter an embodiment of the invention will be explained with reference
 to FIGS. 1 to 3.
 FIGS. 1A and 1B are diagrams showing the configuration of an antenna device
 of the invention. An entire view of the portable radio terminal device is
 not provided here, but only the part in the vicinity of the antenna device
 will be explained.
 FIGS. 1A and 1B show the part in the vicinity of the antenna device in a
 portable radio terminal device, such as a PHS. FIG. 1A is a side view of
 the portable radio terminal device, and FIG. 1B is a plan view of the
 portable radio terminal device viewed from the front side. In FIGS. 1A and
 1B, the antenna device comprises a retractable antenna having a helical
 part 1 with a helical antenna element in an antenna cover and a feeder
 part 2 provided in a housing 7, to be connected with the helical antenna
 element of the helical part, a radio circuit substrate 6 disposed in the
 housing 7, to be connected via a feeding spring 3 to be the feeding point
 of the antenna, a matching circuit part 10 for transmitting the electric
 power of a radio circuit part provided in the radio circuit substrate 6 to
 the antenna via the feeding spring 3 without reflection, a shield case 4
 for shielding an unnecessary electromagnetic wave radiated from the radio
 circuit part provided in the radio circuit substrate 6, and a conductor
 element 5 elongating along the antenna storage part.
 The conductor element 5 is for capacitive coupling with the antenna feeder
 part 2 in the space inside the housing 7 so as to serve as a radiation
 element by the electric current to be excited by the capacitive coupling.
 Moreover, the conductor element 5 is disposed with a three-dimensional
 shape along the antenna storage part for allowing further capacitive
 coupling with the antenna feeder part.
 FIG. 2 is an exploded perspective view of principal components of the
 antenna device according to the embodiment of the invention. The principal
 components of the antenna device, that is, the retractable antenna
 comprising the helical part 1, the feeder part 2, a detaching part 8 and a
 whipping part 9, the shield case 4, and the conductor element 5 disposed
 with a three-dimensional shape along the antenna storage part for allowing
 further capacitive coupling with the antenna feeder part are shown
 disassembled and separated with respect to the housing 7. The arrow
 applied on each component shows the position at which the component is to
 be disposed.
 FIGS. 3A and 3B are graphs for comparing the antenna device according to
 the embodiment of the invention and a conventional antenna device in a
 vertical polarization component and a horizontal polarization component of
 the radiation field strength in a 360 degree horizontal plane radiated
 from a portable radio terminal device with the portable circuit part in
 the transmitting state and the portable radio terminal device radiating an
 electromagnetic wave from the antenna disposed adjacent to a human head
 part in the state the same as having the conversation, and measured by a
 receiving antenna provided at a distance 3 m away.
 It is observed that the radiation from the helical part 1 is slight due to
 the influence by the human head part in the case without the conductor
 element shown in FIG. 3B.
 On the other hand, in the case the conductor element is provided as shown
 in FIG. 3A, it is observed that the radiation amount is increased owing to
 the radiation from the conductor element 5 in addition to that of the
 helical part 1. That is, by the comparison between FIGS. 3A and 3B, it is
 learned that the present invention has achieved the improvement as much as
 about 10 dBd.
 FIG. 4A is a diagram showing the measured field strength distribution in
 the vicinity of the antenna at the time of radiating the power
 (electromagnetic wave) from the antenna with the antenna comprising the
 conductor element of the invention stored in the antenna device in the
 transmission state. On the other hand, FIG. 4B is a diagram showing the
 measured field strength distribution in the vicinity of the antenna at the
 time of radiating the power (electromagnetic wave) from the antenna with
 the antenna stored in the conventional antenna device without the
 conductor element in the transmission state.
 As shown in FIGS. 4A and 4B, in the case of the antenna device of the
 invention, the field strength spreads to the conductor element 5 so that
 it is leaned that the conductor element 5 serves as the radiation source
 whereas the field strength of the conventional antenna device without the
 conductor element is concentrated in the helical part.
 Accordingly, it is apparent that by providing the conductor element 5,
 influence by the human head can be alleviated owing to the radiation from
 the conductor element 5 even when radiation from the helical part is
 restrained due to the approach of the human head so that the effect of
 improving the antenna characteristic is provided.
 Although the case of a retractable antenna has been explained in the
 embodiment of the invention described above, it is not limited thereto,
 but it is easily understood by those skilled in the art that the invention
 is applied to fixed antennas used in a portable radio phone device to
 operate in the same manner as the retractable antenna at the time of
 contraction. Although a helical element commonly used is presented as the
 radiation element of the retractable antenna, it is not limited thereto
 but the invention is effective for other radiation elements. Moreover, the
 conductor element can be disposed two-dimensionally with the effect the
 same as the case of being disposed three-dimensionally as long as the
 space is sufficient. Furthermore, the conductor element is bent for saving
 the entire conductor length, and thus it is. not always needed to be bent
 as long as a sufficient space is secured.
 As heretofore mentioned, since the invention is an antenna device
 comprising a retractable antenna provided with a shield case in a housing,
 wherein an antenna feeder part comes in contact with a feeding spring at
 the time of contraction so that a helical part can function as an antenna
 as well as a conductor element is provided elongating along an antenna
 storage part in the space in the housing for capacitive coupling with the
 antenna feeder part so that the antenna gain is improved by the conductor
 element, even when the radiation of the helical part is restrained by the
 influence of a human head part, in particular, of an earlobe, since the
 conductor element is the radiation source, it is easy to secure the space
 as well as a step for the conductance with other electric devices is not
 required, and restraint of the radiation by the human head part can be
 alleviated for the antenna device as a whole so that the effect of
 improving the antenna gain can be achieved.