Antenna device

Abstract: An antenna device comprises a first antenna capable of moving between a storage position where the first antenna is contained within an equipment housing and an extended position where the first antenna is pulled out of the device housing for receiving and/or transmitting a signal. A second antenna is attached to the tip of the first antenna for receiving and/or transmitting a signal when the first antenna assumes the storage position. The rotator rotates the first antenna with respect to the device housing in the extended position.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention generally relates to antenna devices for use in electronic devices such as portable radio communication devices. Description of the Prior Art: Antenna devices are generally required for electronic devices for receiving and transmitting radio signals. When a user carries such an electronic device, an antenna device is preferably contained within equipment housing because the antenna device should be protected from any damage during carriage. Japanese Patent Laid-open No. 7-86819, for instance, discloses an antenna device capable of transmitting and receiving signals from when either within or out of the equipment housing. The antenna device comprises a pole-shaped first antenna which moves axially between a storage position where the first antenna is contained within the equipment housing, and an extended position where the first antenna is pulled out of the equipment housing. The antenna device is capable of transmitting and receiving signals with a second antenna which is attached to the tip of the first antenna so as to protrude from the equipment housing while the first antenna assumes a storage position. A conventional antenna device is adapted to adjust the extent of the first antenna outside of the equipment housing in the extended position. The direction of the first antenna, however, cannot be adjusted. SUMMARY OF THE INVENTION An object of the present invention is thus to provide an improved antenna device. An antenna device according to the invention is provided by the device according to claim 1. Further developments of this antenna device are given in the dependent claims. The antenna device includes: a first antenna capable of moving between a storage position where the first antenna is contained within an equipment housing and an extended position where the first antenna is pulled out of the equipment housing for receiving and/or transmitting a signal. A second antenna is attached to a tip of the first antenna for receiving and/or transmitting a signal when the first antenna assumes the storage position. Rotation means capable of rotating the first antenna in the extended position with respect to the equipment housing is also included. The rotation means comprises a conductive shaft attached to the equipment housing; a rotator rotating about the conductive shaft; and a through hole formed in the rotator, said through hole supporting the second antenna when the first antenna assumes the storage position and the first antenna when the first antenna assumes the extended position. A signal feeder is provided in the through hole for contacting the second antenna when the through hole supports the second antenna and for contacting the first antenna when the through hole supports the first antenna, so that the signal is supplied to the first and second antennas through the signal feeder. The signal feeder can commonly supply a signal to the first and second antennas, thereby leading to a facilitated structure. If the first and second antennas are connected to each other via an insulator, irradiation of a signal from the first antenna can be prevented even when the first antenna is contained within the equipment-housing. On the other hand, the first and second antennas may be directly connected to each other so that the mechanical strength can be improved in a connection between the first and second antennas. At least one of the first and second antennas may comprise either a helical antenna or a meander line antenna for reducing the height of the antenna. Further, the first antenna may comprise either a linear antenna or a planar antenna for reducing antenna thickness. If the first and second antennas are set to have electrical length of a quarter wavelength, it is possible to omit a matching circuit. The electrical length may be in a range of a quarter to half wavelength. Additionally, if the electrical length becomes longer over a half wavelength, the directivity can be improved in the horizontal direction. The first antenna may rotate in a plane perpendicular to a surface of the equipment housing. The first antenna may also rotate in a plane inclined with respect to a surface of the equipment housing by an angle less than or equal to 90 degrees so that the tip of the antenna comes closer to the equipment housing. The first antenna may rotate in a range of 180 degrees. The antenna device may further comprise a withdrawal prevention piece for preventing the first antenna from withdrawing from the extended position when the first antenna is rotated with respect to the equipment housing. The withdrawal prevention piece serves to reliably maintain an electrical connection between the first antenna and the signal feeder. The antenna device may further comprise a click mechanism for temporarily holding the rotation means when the withdrawal prevention piece prevents the first antenna from withdrawing from the extended position. The reliable electrical connection can be further enhanced. BRIEF DESCRIPTION OF THE DRAWINGS The above and the other objects, features and advantages will be further apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings wherein: Fig. 1 is a perspective view of a portable information terminal employing an antenna device according to a first embodiment of the present invention; Fig. 2 is a perspective view of the portable information terminal illustrating an extended position of the antenna assembly; Fig. 3 is a perspective view of the portable information terminal illustrating rotation of the antenna assembly; Fig. 4 illustrates a portable information terminal in use; Fig. 5 is an enlarged sectional view of the antenna device in the extended position; Fig. 6 is an enlarged sectional view of the antenna device in the storage position; Fig. 7 is a partial sectional view of a rotator from the above; Fig. 8 is a sectional view along the line 8-8 in Fig. 7; Fig. 9 illustrates variations in radiation pattern depending on electrical length; Fig. 10 schematically illustrates a wire grid model; Fig. 11 illustrates an antenna device according to a second embodiment of the present invention; Fig. 12 illustrates an antenna device according to a third embodiment of the present invention; Fig. 13 is a perspective view of a portable information terminal employing an antenna device according to a fourth embodiment of the present invention; Fig. 14 illustrates the portable information terminal in use; Figs. 15 and 16 illustrate a rotation extent of the antenna assembly; Fig. 17 illustrates a modified example of an antenna assembly; Fig. 18 illustrates another modified example of an antenna assembly; Fig. 19 illustrates still another modified example of an antenna assembly; Fig. 20 illustrates an antenna device according to a fifth embodiment of the present invention; Fig. 21 illustrates a fixed position of the rotator; Fig. 22 illustrates a click mechanism for the rotator; and Figs. 23 to 25 illustrate a modified example of the fifth embodiment; DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 illustrates a portable information terminal or PDA 10 employing an antenna device according to a first embodiment of the present invention. The portable information terminalf 10 can function as a cellular phone. A user may input speech via a microphone 11 and hear voice via a speaker 12. A user can make a call using dial keys displayed on an LCD (liquid crystal display) 13 or input various information into the portable information terminal 10 via icons displayed on the LCD 13. An antenna assembly 14 operates both in a storage position where the antenna assembly 14 is contained within a housing 15 as shown in Fig. 1 and in an extended position where the antenna assembly 14 is pulled out of the housing 15 as shown in Fig. 2. The antenna assembly 14 can rotate within a plane inclined by 45 degrees to the Y-Z axes reference plane PL of the portable information terminal 10 at the extended position as shown in Fig. 3. Accordingly, when placing the portable information terminal 10 on a horizontal plane, a standing position of the antenna assembly 14 allows a high antenna gain to a vertical polarization from an antenna of a base station. The antenna assembly 14 comprises a whip antenna 20 with the electrical length of a half wavelength as a first antenna made from metallic material such as stainless steel, and a helical antenna.21 with the electrical length of a half wavelength as a second antenna attached to the tip of the whip antenna 20. The whip antenna 20 and the helical antenna 21 are insulated from each other by an insulator 22. The helical antenna 21 comprises a spiral metallic wire 23 and a synthetic resin body 24 in which the wire 23 is embedded. The synthetic resin body 24 serves to hold the shape of the wire 23. A high-frequency signal is supplied to the antenna assembly 14 from a high-frequency signal source 25 via a matching circuit 26. The antenna assembly 14 at the extended position, as shown in Fig. 5, receives a signal with the whip antenna 20 through a first electrical feeder 27 which is attached to the base end of the whip antenna 20. The antenna assembly 14 at the storage position, as shown in Fig. 6, receives a signal with the helical antenna through a second electrical feeder 28 which is formed at the base end of the helical antenna 21. Referring to Figs. 7 and 8, the antenna assembly 14 is supported for rotation on a housing wall 31 with a synthetic resin rotator 30. The rotator 30 is attached to the housing wall 31 through a metallic shaft 32. A fix nut 33 is inserted between the flange of the metallic shaft 32 and the inner surface of the housing wall 31. A through hole 34 is formed in the rotator 30 for receiving the antenna assembly 14 in a direction perpendicular to the rotation axis of the rotator 30. A spring member 35 is disposed within the through hole 34 serving as a signal feeder. When the antenna assembly 14 assumes the extended position, the first electrical feeder 27 is held by the elasticity of the spring member 35 so that a signal is supplied to the whip antenna 20 through the shaft 32 and the spring member 35 from the high-frequency signal source 25. When the antenna assembly 14 assumes the storage position, the second electrical feeder 28 is held by the elasticity of the spring member 35 so that a signal is supplied to the helical antenna 20 through the shaft 32 and the spring member 35 from the high-frequency signal source 25. It should be noted that the flange of the first electrical feeder 27 serves to prevent the antenna assembly from completely withdrawing from the rotator 30. The operation of the antenna device will next be described. When the antenna assembly 14 is completely pulled out to the extended position as shown in Fig. 5, the first electrical feeder 27 of the whip antenna 20 enters the through hole 34 so that the first electrical feeder 27 is held by the spring member 35. A high-frequency signal is fed to the whip antenna 20 from the high-frequency signal source 25 through the first electrical feeder 27, the shaft 32, and the matching circuit 26. The whip antenna 20 protruding from the housing 15 irradiates radio waves. The insulator 22 serves to prevent the helical antenna 21 from receiving a high-frequency signal. When the antenna assembly 14 is pushed into the storage position as shown in Fig. 6, the second electrical feeder 28 of the helical antenna 21 is held by the spring member 35. A high-frequency signal is fed to the helical antenna 21 from the high-frequency signal source 25 through the second electrical feeder 28, the shaft 32, and the matching circuit 26. The helical antenna 21 protruding from the housing 15 irradiates radio waves. The insulator 22 likewise serves to prevent the whip antenna 20 from receiving a high-frequency signal. As described above, the first embodiment allows the helical antenna 21 to efficiently transmit and/or receive a signal having electrical length of a half wavelength, even when the whip antenna 20 is contained in the housing 15. In addition, the whip antenna 20 does not receive high-frequency signals in the storage position, so that radio waves are not irradiated from the whip antenna 20 within the housing 15. Electronic parts within the housing 15 operate reliably. Placing the portable information terminal on a desk or the like may facilitate an input operation to the LCD 13 on the front surface of the portable information terminal 10. Raising the whip antenna 20 allows the antenna's polarization plane to match that of radio waves from a base station, thereby achieving a high antenna gain. Further, since the first embodiment allows the antenna assembly 14 to rotate in a plane inclined by 45 degrees from the X-Y axes reference plane PL as shown in Fig. 3, input operations are not hindered, as may be caused by excessive approach of the antenna assembly 14 to the portable information terminal 10. The electrical length of the whip and helical antennas 20, 21 may be set at a quarter, instead of a half, wavelength. The electrical length of a quarter wavelength allows an impedance of the antenna device to approach 50 ohms, which allows omission of the matching circuit 26. Specifically, assume that a whip antenna having electrical length L=1/4λ, 3/8λ and 1/2λ irradiate radio waves having wavelength λ=348.6mm. The irradiation patterns of Fig. 9 are illustrated by simulation of the moment method using the wire grid model as shown in Fig. 10. It is apparent that a larger electrical length improves directivity in the horizontal direction. The results have proved that the electrical length of a whip antenna may be set at a half wavelength for emphasizing a directivity in the horizontal direction, while being set at a quarter wavelength for omitting a matching circuit. Larger electrical length, over a half wavelength, further allows improved directivity in the horizontal direction. Fig. 11 illustrates an antenna device according to a second embodiment of the present invention. The second embodiment is characterized in that the spring member 35 holds both the whip and helical antennas 20, 21 when the whip antenna 20 assumes the storage position. The whip and helical antennas 20, 21 both receive a common external force even when the rotator 30 accidentally rotates, so that stress is not concentrated on the insulator 22, thereby protecting a relatively weak connection between the whip and helical antennas 20, 21. The strength of the antenna assembly 14 can be enhanced accordingly. For instance, a constant diameter for the whip antenna 20, the insulator 22, and the second electrical feeder 28 as shown in Fig. 11 enables the spring member 35 to simultaneously hold the whip and helical antennas 20, 21. It should be noted that the same reference numerals are attached to elements having the same function as those of the first embodiment. Fig. 12 illustrates an antenna device according to the third embodiment of the present invention. The third embodiment is characterized in that the whip and helical antennas 20, 21 are electrically connected to each other. As shown in Fig. 12, the first electrical feeder 27 of the whip antenna 20 is electrically connected to an impedance control circuit 41 through a metallic contact spring 40 when the antenna assembly 14 assumes the storage position. The same reference numerals are attached to elements having the same function as those of the first and second embodiments. The third embodiment allows the whip and helical antennas 20, 21 to receive a high-frequency signal through the first electrical feeder 27, the spring member 35, the shaft 32, and the matching circuit 26 when the antenna assembly 14 assumes the extended position. The matching circuit 26 has a constant which is set to match a combined impedance of the whip and helical antennas 20, 21. When the antenna assembly 14 is in the storage position, the whip and helical antennas 20, 21 receive a high-frequency signal through the second feeder 28, the spring member 35, the shaft 32, and the matching circuit 26. Contact of the first electrical feeder 27 with the contact spring 40 enables the impedance control circuit 41 to match only the impedance of the helical antenna 21. Accordingly, irradiation efficiency cannot be reduced. Further, a connection between the whip and helical antennas 20, 21 can be strengthened or enhanced in the antenna assembly 14 due to direct connection between the whip and helical antennas 20, 21. Fig. 13 illustrates an antenna device according to a fourth embodiment. The fourth embodiment is characterized in that the antenna assembly 14 can rotate within a plane perpendicular to the X-Y axes reference plane PL of the portable information terminal 10 at the extended position. When the portable information terminal 10 is placed on a desk or the like, as shown in Fig. 14, antenna efficiency can further be improved with respect to vertical polarization. In addition, the antenna assembly 14 can rotate in a range of 180 degrees as shown in Figs. 15 and 16, so that the antenna device can be freely positioned. The identical reference numerals are attached to the elements having the same function as those in the previous embodiments. The previous embodiments generally employs an antenna assembly 14 comprising a whip antenna 20 as a first antenna and a helical antenna 21 as a second antenna. A planar antenna 44 and a meander line antenna 45 can be employed as shown in Fig. 17 in place of the respective whip and helical antennas. In this case, a meander line antenna 46 may be combined in place of the planar antenna 44, as shown in Fig. 18, and a helical antenna 47 may be combined in place of the planar antenna as shown in Fig. 19. The meander line antennas 45, 46 comprise a meander line wire formed on or embedded in a non-conductive panel member. The helical antenna 47 comprises a wire spirally wound around a non-conductive pole member. Employment of the planar antenna 44 or the meander line antennas 45, 46 enables an antenna assembly 14 to be reduced in thickness. Employment of the meander line antennas 45, 46 and the helical antenna 47 enables the reduction in height of the antenna assembly 14. Further, since the planar antenna 44 and a plate member of the meander line antennas 45, 46 are arranged along a plane on which the antenna assembly 14 moves, they have strength along such a plane so that rotating force applied to the antenna assembly 14 is smoothly transmitted to the rotator 30. In Figs. 17 to 19, the first antenna likewise receives a signal through the first electrical feeder 27 while the second antenna likewise receives a signal through the second electrical feeder 28. Fig. 20 illustrates an antenna device according to a fifth embodiment of the present invention. The fifth embodiment is characterized in that the antenna device further comprises a withdrawal prevention piece for preventing the first antenna from withdrawing from the extended position when the first antenna rotates relative to the housing. The identical reference numerals are attached to the elements having the same function as those in the previous embodiments. The withdrawal prevention piece 50 is integrally formed in the housing wall 31 so as to include a prevention surface 51 of a shape corresponding to the peripheral shape of the rotator 30. The antenna assembly 14 can displace between the extended position and the storage position at a reference position of the rotator 30 as shown in Fig. 20. When the antenna assembly 14 is pulled out in the withdrawal direction X1 until it is mostly removed from the storage hole 52 of the housing wall 31, the rotator 30 is brought into a rotatable state. When the antenna assembly 14 is pulled out to the extended position and rotated by means of the rotator 30, as shown in Fig. 21, the prevention surface 51 is opposed to the exit of the through hole 34 of the rotator 30. It is thus possible to prevent the first electrical feeder 27 of the whip antenna 20 from being completely removed out of the rotator 30, whereby electrical connection would be disconnected. A click mechanism 53 may be provided between the withdrawal prevention piece 50 and the rotator 30 for temporarily holding the rotator 30. The click mechanism 53 comprises a guide slot 54 carved on the periphery of the rotator 30, and a ball 55 provided to the withdrawal prevention piece 50 for moving along the guide slot 54, as shown in Fig. 22. When the rotator 30 assumes the reference position, the ball 55 fits into a first recess 56 so that the rotator 30 is held at the reference position by the spring 57 biasing the ball 55. When the rotator 30 starts rotating in the direction X2, the ball 55 enters the guide slot 54 against the biasing force from the spring 57 so as to move along the guide slot 54. When the rotator 30 reaches a fixed position as shown in Fig. 21, the ball 55 fits into a second recess 58 so that the rotator 30 is held at the position by the biasing force from the spring 57. The antenna assembly 14 is prevented from moving when it assumes certain positions. As shown in Figs. 23 to 25, the withdrawal prevention piece 50 may be formed separately from the housing wall 31. The withdrawal prevention piece 50 projects from a planar receiving member 60 which receives the bottom of the rotator 30. Although the receiving member 60 is disposed around the shaft 32, the receiving member 60 is prevented from rotating about the shaft 32 by a rotation blocking mechanism 61 comprising a recess and a projection. The rotator 30 includes a notch 62 for receiving the withdrawal prevention piece 50 in the extent the withdrawal displaces. The movement of the rotator 30 is thus not hindered by the withdrawal prevention piece 50. Moreover, the contact of the withdrawal prevention piece 50 with opposite end surfaces of the notch 62 defines an extent of rotation of the rotator 30. The identical reference numerals are attached to elements having the same function as those shown in Figs. 20 to 22.

Claims: An antenna device comprising: a first antenna (20) capable of moving between a storage position where the first antenna (20) is contained within an equipment housing (15) and an extended position where the first antenna (20) is pulled out of the equipment housing (15) for receiving and/or transmitting a signal; a second antenna (21) attached to a tip of the first antenna (20) for receiving and/or transmitting a signal when the first antenna (20) assumes the storage position; a rotator (30) rotating about a conductive shaft (32) attached to the equipment housing, the rotator (30) being capable of rotating the first antenna (20) in the extended position with respect to the equipment housing (15); a through hole (34) formed in the rotator (30), and said through hole (34) supporting the second antenna (21) when the first antenna (20) assumes the storage position and supporting the first antenna (20) when the first antenna (20) assumes the extended position; and wherein a signal feeder (35) is provided in the through hole (34) for contacting the second antenna (21) when the through hole (34) supports the second antenna (21) and for contacting the first antenna (20) when the through hole (34) supports the first antenna (20), a signal being supplied to the first and second antennas (20, 21) through the signal feeder (35). An antenna device as defined in claim 1, wherein the first and second antennas (20, 21) are connected to each other via an insulator (22). An antenna device as defined in claim 1, wherein the first and second antennas (20, 21) are directly connected to each other. An antenna device as defined in any of claims 1 to 3, wherein at least one of the first and second antennas (20, 21) comprises either a helical antenna (21, 47) or a meander line antenna (45, 46). An antenna device as defined in any of claims 1 to 3, wherein the first antenna (20) comprises either a linear antenna (20) or a planar antenna (44). An antenna device as defined in any of claims 1 to 5, wherein the first and second antennas (20, 21) are set to have electrical lengths of a quarter wavelength. An antenna device as defined in any of claims 1 to 5, wherein the first and second antennas (20, 21) are set to have electrical lengths in a range of a quarter wavelength to a half wavelength. An antenna device as defined in any of claims 1 to 5, wherein the first and second antennas (20, 21) are set to have electrical lengths of longer than a half wavelength. An antenna device as defined in any of claims 1 to 8, wherein the first antenna (20) rotates in a plane perpendicular to a surface of the equipment housing (PL). An antenna device as defined in any of claims 1 to 8, wherein the first antenna (20) rotates in a plane inclined with respect to a surface of the equipment housing (PL) by an angle less than or equal to 90 degrees. An antenna device as defined in any of claims 1 to 10, wherein the first antenna (14) rotates in a range of 180 degrees. An antenna device as defined in any of claims 1 to 11, further comprising a withdrawal prevention piece (50) for preventing the first antenna (20) from withdrawing from the extended position when the first antenna (20) is rotated with respect to the equipment housing (15). An antenna device as defined in claim 12, further comprising a click mechanism (53) for temporarily holding the rotation means (30) when the withdrawal prevention piece (50) prevents the first antenna (20) from withdrawing from the extended position.

Inventors: ENDO TSUTOMU, MATSUMOTO WATARU, TAKEMOTO MAKOTO, ENDO, TSUTOMU, MATSUMOTO, WATARU, TAKEMOTO, MAKOTO, Endo, Tsutomu, Mitsubishi Denki K.K., Matsumoto, Wataru, Mitsubishi Denki K.K., Takemoto, Makoto, Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1996
Main classification: H01Q1
IPC codes: H01Q1, H01Q21