Foldable portable cellular phone

Abstract: A foldable compact cellular phone has two planar antennas (13A, 13B) inside. Spacing between the two antennas (13A, 13B), each of which is in a respective one of a pair of housings (11A, 11B), is equal to or greater than a width of a hand palm when the phone is open and held in the hand. The two antennas (13A, 13B) are planar inverse F-type antennas or patch antennas, and impedance around each of the two antennas (13A, 13B) is measured. Based on the measurement, that one of the two antennas (13A, 13B) which has a preferred transmission characteristic is selected and used.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention generally relates to a compact cellular phone having a pair of housings formed in an approximate flat shape and being foldably connected by using a hinge. Description of the Related Art As shown in FIG.1A, in a configuration of a conventional cellular phone, a whip antenna 14 has a 1/4 wave length or 1/2 wave length and is on a housing 15. The whip antenna 14 can be retracted into the housing 15. A coil antenna 16.is wound around dielectrics provided at a top end of the whip antenna 14. When the whip antenna 14 is retracted into the housing 15, the coil antenna 16 remains outside the housing 15 and serves as an antenna for a transmission instead of the whip antenna 14. In addition, a planar inverse F-type antenna (not shown) is provided inside the housing 15. Thus, a diversity antenna system is made up of the whip antenna 14, the coil antenna 16 and the planar inverse F-type antenna, whereby a phasing caused by multiplex wave can be prevented and a preferable transmission feature can be maintained. Alternatively, instead of using the whip antenna 14 and the coil antenna 16, as shown in FIG.1A, a cellular phone may include the planar inverse F-type antenna (not shown) or a planar antenna 17 such as a patch antenna inside a housing 18 as shown in FIG.2A. Since the cellular phone generally contacts a human head in use, a radio wave emitted from the antenna 14, 16, or 17 is partially blocked by the human head which causes transmission quality to be degraded. Particularly, the whip antenna 14 or the coil antenna 16 has an isotropic directivity in a surface perpendicular to an axis of the whip antenna 14 or the coil antenna 16 as shown in FIG.1B. Thus, the radio wave is transmitted toward the body, and transmission efficiency deteriorates due to blocking of the radio wave by the head. As a result, the transmission quality is remarkably degraded. On the other hand, in a surface perpendicular to the planar antenna 17 such as the planar inverse F-type antenna (not shown) or the patch antenna shown in FIG.2A, the planar antenna 17 has a directivity having a greater gain in a direction opposite to a ground board, as shown in FIG.2B, and a small amount of radio wave transmits to a side of the human head. Thus, a deterioration of the transmission quality affected by the human head can be reduced. However, in a waiting state, the planar antenna 17 having the directivity of the great gain on only one side of the ground board has problems in sending or receiving the radio wave between the planar antenna 17 and a base station (not shown) located at an opposite side to a direction in which the planar antenna 17 has a greater directivity. Also, in a case of using the planar antenna 17 alone, when the planar antenna 17 is covered with a hand holding the cellular phone, the transmission effect is remarkably degraded, and then a degraded transmission quality can disconnect a transmission. In order to suppress degradation of antenna characteristics by the head and realize a stable transmission, Japanese Laid-open Patent Application No. Hei 11-220418 discloses an "Outer Antenna Device for Cellular Phone" in which a technology is disclosed to mount the outer antenna at a bottom surface of the cellular phone. However, since another device for the outer antenna is mounted outside the cellular phone, it is cumbersome to handle the entire cellular phone and a device shape becomes large-sized. Patent Abstracts of Japan, Vol. 1999, No. 12, 29 October 1999 (JP 11-177485, NEC Saitama Ltd., 2 July 1999) discloses a folded portable telephone set having an antenna on each of upper and lower cases and being provided with an antenna changeover switch for changing reception from one antenna to the other antenna when a busy signal is detected. US Patent 4,992,799 discloses an antenna arrangement for a portable communication device, the antenna arrangement being on first and second members hinged together and defining a single loop antenna when the members are in a closed state and an antenna on each member when the members are in an opened state. WO 00/35124 discloses a mobile communication device having two antennas and means for automatically selecting which one of the antennas to use depending a suitable radiation pattern for a particular environment. EP 0 871 236 A2 discloses an antenna arrangement for two-way radio communication having two housings foldably connected and having a planar antenna in one of the housings such that a communicative surface of the antenna is directed outwardly on the phone when the phone is in a closed state. US 5 486 836 discloses a foldable phone in which the antennas are operated in diversity. SUMMARY OF THE INVENTION In view of the above, it is a general object of the preferred embodiments of the present invention to provide a compact cellular phone in which the above-mentioned problems are eliminated. A more specific object of the preferred embodiments of the present invention is to provide a compact cellular phone which is less influenced by presence of a head or hand, and which always maintains a preferred transmission quality in both a waiting state and a transmitting state. According to the present invention, there is provided a compact cellular phone as set out in claim 1. A preferable mode is one in which each antenna is in a respective interior of a respective one of the pair of housings and, when the phone is in the closed state, are at an outermost position in the respective housing interior. Another preferable mode is one in which the antennas are two planar inverse F-type antennas or two patch antennas. With configurations of the above aspect, in the waiting state in which the compact cellular phone is closed, the cellular phone has directivities at both sides. Thus, it is possible to improve the transmission characteristics between the base station and the compact cellular phone. In addition, in the communication state in which the compact cellular phone is opened and receives from and send to the base station, the directivities of the planar antennas 13A and 13B oppositely direct to a side of the human body. Thus, the influence of absorbing the radio wave into the human body hardly occurs and then it is possible tomaintain the preferred transmission characteristics. Furthermore, it possible to eliminate the influence by the human hand holding the compact cellular phone by using at least one of the planar antennas 13A and 13B. Therefore, the preferred transmission.characteristics can be maintained. BRIEF DESCRIPTION OF THE DRAWINGS Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- FIG.1A is a diagram showing a conventional cellular phone using a whip antenna and Fig.1B is a diagram showing a directivity of the whip antenna in the conventional cellular phone shown in FIG.1A; FIG.2A is a diagram showing another conventional cellular phone using a planar antenna and Fig.2B is a diagram showing a directivity of the planar antenna in the conventional cellular phone shown in FIG.2A; FIG.3A is a side elevational view of a compact cellular phone in a closed state, according to an example of the present invention and FIG.3B is a rear elevational view of the compact cellular phone in the closed state, according to the example of the present invention; FIG.4A is a side elevational view of the compact cellular phone in an open state, according to the example of the present invention and FIG.4B is a rear elevational view of the compact cellular phone in the open state, according to the example of the present invention; FIG.5A is a side elevational view of the compact cellular phone in the closed state, according to the example of the present invention and FIG.5B is a diagram showing characteristics of directivities of planar antennas in the closed state, according to the example of the present invention; FIG.6A is a side elevational view of the compact cellular phone in the open state, according to the example of the present invention and FIG.6B is a diagram showing characteristics of directivities of the planar antennas in the open state, according to the example of the present invention; and, FIGS.7A, 7B, and 7C are diagrams showing various usage of the compact cellular phone in a communication state, according to the example of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Best modes for carrying out the present invention will be described in further detail using an embodiment and an example with reference to the accompanying drawings. Embodiment A compact cellular phone has a foldable configuration and two planar antennas having outward directivities are provided inside two housings in the foldable configuration, respectively. In addition, in a waiting state in which the compact cellular phone is closed and used, both of the two planar antennas or at least one of the two planar antennas is used to transmit. In a communication state in which the compact cellular phone is opened and used, one planar antenna having the better transmission condition between the two planar antennas is selected and used. A space provided between the two planar antennas provided to the compact cellular phone is at least equal to or greater than a palm width (of a human hand) in an open state in which the compact cellular phone is open. Also, a planar inverse F-type antenna or a patch antenna can be used as the planar antenna. For each of the two planar antennas, an impedance change is detected and also a physical quantity of a reflective wave caused by the impedance change on an electric-power transmission medium provided inside the compact cellular phone is detected. With the above embodiment, the two planar antennas can realize wider directivities and the transmission characteristics between the compact cellular phone and a base station is improved more than a case of using a single planar antenna. Also, it is possible to obtain the transmission quality which maintains better quality than a conventional whip antenna or coil antenna. Moreover, in the communication state in which the compact cellular phone is open and used, since the two planar antennas have higher sensitivities outward only (opposite to a human head side, the human head less influences the two planar antennas. In addition, an impedance evaluation selects one of the two planar antennas, which one planar antenna is not covered with the palm of the human hand. Thus, it is possible to prevent an attenuation caused by the palm of the human hand. Consequently, it is possible to obtain a preferred transmission quality in both of the waiting state and the communication state. Example The example of the present invention will now be described with figures. Figures 3A and 3B and FIGS.4A and 4B show schematic outside views of a compact cellular phone according to the example of the present invention. FIG.3A is a side elevational view of the compact cellular phone in a closed state, according to the example of the present invention and FIG.3B is a rear elevational view of the compact cellular phone in the closed state, according to the example of the present invention. FIG.4A is a side elevational view of the compact cellular phone in an open state, according to the example of the present invention and FIG.4B is a rear elevational view of the compact cellular phone in the open state, according to the example of the present invention. It should be noted that detailed parts that are not directly related to the present invention are not shown in figures and an explanation thereof is omitted. A configuration of the compact cellular phone according to the example of the present invention is mostly similar to the conventional cellular phone which is foldable. A pair of housings 11A and 11B formed in an approximate flat shape is foldably connected by using a hinge 12, so that the compact cellular phone is foldable. Each of the housings 11A and 11B are made up of synthetic resin and formed in a similar rectangular board shape. Similar to the conventional cellular phone, for example, a speaker and a display part are appropriately provided to the housing 11A and an operating part such as ten-key pad and a microphone are provided to the housing 11B. These components are well-known and not illustrated; therefore, an explanation thereof is omitted. In the example, planar antennas 13A and 13B having outward directivities are provided inside the pair of the housings 11A and 11B. That is, the planar antenna 13A is arranged inside the housing 11A so that a highly sensitive surface of the planar antenna 13A is directed outward when the compact cellular phone is closed, and also the planar antenna 3B is arranged inside the housing 11B so that a highly sensitive surface of the planar antenna 13B is directed outward when the compact cellular phone is closed. In the open state (see FIG.4A and FIG.4B), an interval L between the planar antennas 13A and 13B is provided so as to be equal to or greater than the palm width. In the closed state, the planar antennas 13A and 13B are arranged outer most (closest to a outside surface) of the compact cellular phone (see FIG.3A). The planar inverse F-type antennas are applied to the planar antennas 13A and 13B. Such planar inverse F-type antenna is well-known. For example, the Japanese Laid-open Application No. HEI 2-13842 discloses the planar inverse F-type antenna. Alternatively, conventional patch antennas can be used as the planar antennas 13A and 13B. Theses antennas above have radiation characteristics having non-directivity in a surface direction on one side. Directivities of antennas of the compact cellular phone will be now described according to the example of the present invention. FIG.5A is a side elevational view of the compact cellular phone in the closed state, according to the example of the present invention and FIG.5B is a diagram showing characteristics of directivities of the planar antennas 13A and 13B in the closed state, according to the example of the present invention. FIG. 6A is a side elevational view of the compact cellular phone in the open state, according to the example of the present invention and FIG.6B is a diagram showing characteristics of directivities of the planar antennas 13A and 13B in the open state, according to the example of the present invention. In the closed state in which the compact cellular phone according to the example is closed (see FIG. 5A), the planar antennas 13A and 13B have directivities as shown in FIG.5B and can send and receive at both sides of the compact cellular phone. Accordingly, one of the planar antennas 13A and 13B, which one planar antenna maintains preferred transmission between a base station (not shown) and the compact cellular phone, is selected and used. Since the planar antennas 13A and 13B are arranged outer most inside the housings 11A and 11B, it is possible to reduce an influence of a metal board to the planar antenna 13A or 13B even if the compact cellular phone is placed on the metal board or the like. On the other hand, in the opened state in which the compact cellular phone is open as shown in FIG.6A, the planar antennas 13A and 13B have directivities towards a single direction opposite to a human body. Thus, an influence by the human body absorbing the radio wave becomes smaller and the preferred transmission characteristics can be maintained. Moreover, in a radio wave absorption by the human hand holding the compact cellular phone, as shown in FIGS.7A, 7B, and 7C, at least one of the planar antennas 13A and 13B is not covered with the human hand. Therefore, it is possible to obtain the preferred transmission characteristics by one of the planar antennas 13A and 13B, which one planar antenna 13A or 13B is not covered with the human hand. For example, when a user holds an upper part of the compact cellular phone (see FIG.7A), since the planar antenna 13B being a lower part of the compact cellular phone is not covered with the human hand, the preferred transmission characteristics can be maintained by the planar antenna 13B. On the other hand, when the user holds the lower part of the compact cellular phone (see FIG.7B), similarly, since the planar antenna 13A being the upper part of the compact cellular phone is not covered with the human hand, the preferred transmission characteristics can be maintained by the planar antenna 13A. When the user holds a center part of the compact cellular phone, both of the planar antennas 13A and 13B are not covered with the human hand. Furthermore, the user holds the housing 11B of the compact cellular phone to use because of operating buttons located at the housing 11B while the user watches at a display part such as a liquid crystal display provided inside the housing 11A of the compact cellular phone. Even in this case, the preferred transmission characteristics can be maintained because the planar antenna 13A of the housing 11A is not covered with the human hand. The following method can be applied to select one of the planar antennas 13A and 13B, which is not covered with the human hand. In a case in which the human hand covers one of the planar antennas 13A and 13B, an input impedance changes at a side of the planar antenna 13A or 13B covered by a hand. Thus, by detecting and evaluating the impedance change and the physical quantity of the reflective wave, resulting from the impedance change on the electric-power transmission path provided inside the compact cellular phone, it can be determined whether or not the planars 13A and 13B are influenced by the presence of the hand. Also, it can be determined whether or not the degree of influence is significant. Therefore, it is possible to select that one of the planar antennas 13A and 13B that is less influenced by the presence of the hand during communication. While the present invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation, and that changes may be made to the invention without departing from its scope as defined by the appended claims. Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features. Reference numerals appearing in the claims are by way of illustration only and should be disregarded when interpreting the scope of the claims. The text of the abstract filed herewith is repeated here as part of the specification. A foldable compact cellular phone has two planar antennas inside. Spacing between the two antennas, each of which is in a respective one of a pair of housings, is equal to or greater than a width of a hand palm when the phone is open and held in the hand. The two antennas are planar inverse F-type antennas or patch antennas, and impedance around each of the two antennas is measured. Based on the measurement, that one of the two antennas which has a preferred transmission characteristic is selected and used.

Claims: A compact cellular phone having a pair of housings (11A, 11B) having approximately the same length, each of approximately flat shape, the housings being foldably connected by a hinge (12) such that the phone may assume either an opened state or a closed state, the compact cellular phone also having two planar antennas (13A, 13B), each of the housings being provided inside with a respective one of the antennas such that a communicative surface of each antenna is directed outwardly on the phone when the phone is in the closed state, characterized by : when the phone is in the closed waiting state, one or both of the two antennas (13A, 13B) is used for sending and receiving, and when the phone is in an opened communication state, whichever one of the two antennas (13A, 13B) is in the better transmission state is used for sending and receiving; and by means for detecting and evaluating a change of the input impedance of said antennas and a physical quantity of a reflective wave resulting from said impedance change on an electric-power transmission path inside the phone, to determine which one of the two antennas (13A, 13B) is in the better transmission state. The compact cellular phone according to claim 1 or 2, wherein the two antennas (13A, 13B) are each in a respective interior of a respective one of the pair of housings (11A, 11B) and, when the phone is in the closed state, are at an outermost position in the respective housing interior. The compact cellular phone according to any one of claims 1 or 2, wherein the antennas (13A, 13B) are two planar inverse F-type antennas or two patch antennas.

Inventors: HANKUI EIJI, KURIYAMA TOSHIHIDE, HANKUI, EIJI, KURIYAMA, TOSHIHIDE
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 2001
Main classification: H01Q1
IPC codes: H04B7, H01Q13, H01Q1, H01Q3, H01Q9, H04M1, H04B1