ANTENNA STRUCTURE OF PORTABLE RADIO

Abstract: A slide lever (6) is provided to a cabinet (2) of portable radio equipment, and an antenna (3) formed by nickel elastic alloy is held by a holding member (5). Alower portion of the antenna engages with an engaging portion (61) of slide lever (6), and by sliding slide lever (6), the lower portion of antenna (3) is bent at engaging portion (61) such that the entire antenna is inclined in a vertical direction by a desired angle, thereby reducing loss due to nonconformity of polarization with respect to an antenna of a base station.

Description: Technical Field The present invention relates to an antenna structure for portable radio equipment, and more specifically, to an antenna structure for portable radio equipment that allows inclining an antenna to a desired angle in order to improve sensitivity of the portable radio equipment. In particular, the invention relates to an antenna structure according to the preamble of claim 1. Background Art Existing types of transmitting/receiving antennas of portable radio equipment include a whip antenna mounted in a longitudinal direction of a cabinet and a helical antenna. The most often adopted antenna for portable radio equipment currently commercially available in Japan is a whip and helical antenna having a structure that operates as a whip antenna when pulled out and in that, when retracted, a helical antenna operates that is provided on a tip of the whip antenna with an insulating material intervening therebetween. In addition, an inverted F antenna or the like is built into the cabinet as an antenna for reception diversity. In general, one factor that degrades antenna characteristic is antenna efficiency determined by an effective radiation area owing to the physical size and the structure of the antenna. Moreover, there is loss due to impedance mismatch with a radio unit and loss due to nonconformity of polarization plane and directivity in relation to an antenna that is a target of communication. Since the environment in which an antenna on mobile equipment of mobile communications such as portable radio equipment is installed or held constantly changes, directivity and plane of polarization vary constantly. An antenna of a base station that communicates with portable radio equipment through transmission and reception is configured with vertical polarization as the main polarization. Transmission waves from a transmitting/receiving antenna of the base station are repeatedly reflected and diffracted by various structures such as buildings before they arrive at a receiving antenna of portable radio equipment. Vertical polarization, however, is generally known to be dominant as the main polarization of the waves arriving at portable radio equipment from the base station. In the reception characteristic of the transmitting/receiving antenna of the base station, it is obvious from the reversibility of the transmission/reception characteristic of the antenna that the greater the vertical polarization component in the waves arriving from portable radio equipment, the higher the gain of the antenna becomes. Whip antennas and the like formed on portable radio equipment have radiation patterns of various forms depending on an electrical length of an antenna element and a dimension of the cabinet. When the portable radio equipment is provided such that it stands upright, the main polarization is known to become vertical polarization in relation to the ground. Thus, during a call on portable radio equipment (often used with an inclination of about 60° from the direction of the zenith) or when the portable radio equipment is placed horizontally on a desk and the like, nonconformity in the direction of main polarization becomes significant between the antenna formed on the portable radio equipment and the antenna of the base station that has vertical polarization in relation to the ground, and the gain of the antenna is disadvantageously degraded. Figs. 6A and 6B are diagrams related to the description of polarization loss when portable radio equipment is inclined. As shown in Fig. 6A, E indicates an electric field level of vertical polarization and E indicates an electric field level of horizontal polarization when portable radio equipment 1 is erected vertically. As shown in Fig. 6B, when portable radio equipment 1 is inclined by 60°, the electric field level of vertical polarization becomes E' and the electric field level of horizontal polarization becomes E', producing a polarization loss as indicated by the following expression: Polarization loss = 20 log 10 (E/E')dB In order to reduce such polarization loss, conventionally, techniques are proposed of providing a metal joint portion, for example, in order to mechanically incline the antenna alone, for instance, in JP-A-8-274 525, JP-A-6-260 959 and JP-A-5-055 817. An antenna structure according to the preamble of claim 1 is known from EP-A-0 652 646. In the conventional antenna structure, an antenna mast is rotatably coupled to a housing via a pivot pin for rotation about an axis. A weight is coupled to the one end of the antenna mast so that an inclining effect is achieved by gravitation. Hence, when the housing is not in an upright or vertical position, the weight is operating on the antenna mast in order to maintain it in a substantially vertical orientation. Moreover, the mechanisms, described above in connection with conventional devices, may disadvantageously involve an increase in the number of parts and may easily break when such a portable radio equipment is dropped. Disclosure of the Invention Thus, the object underlying the present invention is to provide an antenna structure for a portable radio equipment which can be formed with a small number of parts, allows inclining of the antenna to a desired angle and is adapted to reduce loss due to non-conformity of polarization. According to the invention, the object is solved by an antenna structure comprising the features of claim 1. Advantageous further developments of the antenna structure according to the invention are specified in the subclaims. The antenna structure according to the invention provides the advantage that the antenna can be adjusted in its inclination to a desired angle in order to obtain the highest possible sensitivity. According to a further development of the antenna structure according to the invention, the antenna has a vertical polarization and the inclining portion is adapted to incline a polarization plane of the antenna to a direction vertical to the ground. In one specific embodiment of the antenna structure according to the invention the inclining portion includes a sliding member whose tip is adapted to engage a lower portion of the antenna within the cabinet and which slides to incline the antenna. In another specific embodiment of the antenna structure according to the invention the inclining portion includes a stopping member whose upper end is adapted to engagingly stop against the antenna outside the cabinet and which inclines the antenna. In another specific embodiment of the antenna structure according to the invention the inclining portion includes a disc member having a groove that is cut away departing from a center, and a lower portion of the antenna is adapted to be inserted in the groove of the disc member, and a rotation member is adapted to rotate to incline the antenna. According to a further development of the antenna structure according to the invention, the antenna has vertical polarization plane during a call and a length of N times λ/2, wherein N is an integer, when it is inclined to a desired direction vertical to the ground. Brief Description of the Drawings Fig. 1 is a conceptual diagram of the present invention. Figs. 2A and 2B are diagrams showing an antenna structure of portable radio equipment according to one embodiment of the present invention. Figs. 3A to 3C are diagrams showing an antenna structure according to a second embodiment of the present invention. Figs. 4A and 4B are diagrams showing an antenna structure according to a third embodiment of the present invention. Figs. 5A and 5B are diagrams showing a further embodiment of the present invention. Figs. 6A and 6B are diagrams related to the description of polarization loss when portable radio equipment is inclined. Best Modes for Carrying Out the Invention Fig. 1 is a conceptual diagram of the present invention. In the present invention, an antenna that can be flexibly bent is provided to a cabinet of portable radio equipment 1 such that an electric field level E of vertical polarization and an electric field level E of horizontal polarization when the portable radio equipment 1 is erected are made substantially equal to an electric field level E' of vertical polarization and an electric field level E' of horizontal polarization when the portable radio equipment 1 is inclined, for instance, by 60° in use during a call, thereby reducing polarization loss. Fig. 2A is a diagram of an antenna structure of portable radio equipment according to one embodiment of the present invention viewed from the rear side, and Fig. 2B is a diagram of the portable radio equipment provided with a slide lever for inclining the antenna, viewed from the front. An antenna 3 shown in Figs. 2A and 2B utilizes nickel elastic alloy, for instance, and is flexible to any desired angle. A helical antenna 4 is provided in an upper portion of the antenna 3, a lower portion of the antenna 3 is held by a holding portion 5 as shown in Fig. 2A, and a slide lever 6 is provided above the holding portion 5. An engaging portion 61 for engaging with the antenna 3 is formed in a backside of the slide lever 6. Slide lever 6 is configured such that it is slidable in a horizontal direction along a groove not shown. When the slide lever 6 slides to a central position, the antenna 3 stands upright in relation to the cabinet 2, and the antenna 3 can be inclined to any desired angle by sliding the slide lever 6 to the right or to the left. As described above, according to this embodiment, an elastic antenna 3 can be inclined by a desired angle by merely sliding the slide lever 6. Thus, if a caller notices the poor sensitivity during a call, the caller may manipulate the slide lever 6 to determine an angle of inclination of the antenna 3 such that an angle with highest sensitivity can be obtained. Moreover, since it is only required that the antenna 3 be formed with elastic alloy and that the slide lever 6 be provided, the number of parts can be reduced, and because of a complex mechanical structure, there is little risk of antenna 1 being broken even when dropped by mistake. Figs. 3A to 3C are diagrams showing an antenna structure according to the second embodiment of the present invention. In the embodiment shown in Figs. 3A to 3C, a stopping member 7 that is slidable up and down is provided on an upper portion of a cabinet 2. Here, an antenna 3 is formed by nickel elastic alloy as in the embodiment of Figs. 2A and 2B. Thus, the antenna 3 is flexible to any given angle, and a tip of the stopping member 7 engagingly stops against the antenna 3 such that the stopping member 7 may be moved up and down to incline the antenna 3 to any desired angle. Therefore, this embodiment also allows adjustment of the angle of inclination of the antenna 3 such that sensitivity is maximized while a caller has portable radio equipment tilted in use during a call. Figs. 4A and 4B are diagrams showing an antenna structure according to the third embodiment of the present invention. An antenna 3 is made of nickel elastic alloy, and has its lower portion held by a holding portion 5, and has a disk member 8 provided on its upper portion. A groove 71 that is cut away and departing from a center is formed in the disk member 8, and the antenna 3 is inserted in the groove 71. A portion of a peripheral surface of the disk member 8 protrudes from a cabinet 2, and when a caller touches that portion with a finger to rotate the rotation member 8, antenna 3 slidably moves along the groove 71 since the groove 71 departs from a center, and the angle of inclination of the antenna 3 changes. When storing the antenna 3 within the cabinet 2, the rotation member 8 is rotated so as to locate the antenna 3 in the center of the groove 71, and thus, the antenna 3 is received in the cabinet 2. Figs. 5A and 5B are diagrams showing a further embodiment of the present invention. Specifically, Fig. 5A shows a λ/4 type antenna, while Fig. 5B shows a λ/2 type antenna. While the added length of a length of an antenna 3 and a length in a longitudinal direction of a cabinet 2 is selected to be λ/4 in the λ/4 type antenna shown in Fig. 5A, the length of the antenna 3 alone is selected to be λ/2 for the λ/2 type antenna shown in Fig. 5B. Thus, in the λ/2 type antenna, a current closes in the vicinity of a portion where the antenna 3 and the cabinet 2 are joined so that a current hardly flows through the cabinet 2 and the current flows through the antenna 3 alone. Consequently, a greater reduction effect of polarization loss upon inclining of the antenna 3 can be achieved. Therefore, in each of the above-described embodiments, it is desirable to select N times λ/2 (N is an integer) such as λ/2, λ, 3/2 • λ for the antenna 3. This is based on the fact that a frequency band used for a portable telephone in recent years is as high as 2 GHz and one wavelength is 15 cm, and that, at λ/2, an antenna at 7.5 cm can be resonated. As described above, according to the present invention, an antenna can be provided with flexibility by using an elastic alloy as a conductor for the antenna, for instance, and the antenna can be bent during a call such that it is inclined in a direction vertical to the ground, thereby reducing loss due to nonconformity of polarization with respect to an antenna of a base station. In addition, according to the present invention, no mechanism for inclining the antenna provided to the antenna itself is required so that the antenna should not be broken when dropped, and a lighter weight can be achieved since the number of parts is small. In particular, the present invention can be applied effectively to an antenna that resonates at N times λ/2. The embodiments of the present invention were described above in detail with reference to the drawings. The present invention, however, is not limited to the embodiments, and is subject to various modifications and alterations within the scope of the concept of the present invention.

Claims: An antenna structure mounted on a cabinet (2) of a portable radio equipment for inclining the antenna to reduce polarization loss, comprising: a rod shaped antenna (3) mounted to the cabinet (2) and an inclining portion (6, 7, 8) provided on the cabinet (2) for inclining the rod shaped antenna (3), characterized in that the rod shaped antenna (3) is made of a conductor of an elastic alloy and flexibly bendable; and in that the inclining portion (6, 7, 8) is movably adapted to act on the elastic rod shaped antenna (3) so as to flexibly bend the antenna (3) into the desired inclination. The antenna structure according to claim 1, characterized in that the antenna (3) has a vertical polarization, and in that the inclining portion (6, 7, 8) is adapted to incline a polarization plane of the antenna (3) to a direction vertical to the ground. The antenna structure according to claim 1 or 2, characterized in that the inclining portion (6, 7, 8) includes a sliding member (6) whose tip is adapted to engage a lower portion of the antenna (3) within the cabinet (2) and which slides to incline the antenna (3). The antenna structure according to claim 1 or 2, characterized in that the inclining portion (6, 7, 8) includes a stopping member (7) whose upper end is adapted to engagingly stop against the antenna (3) outside the cabinet (2) and which inclines the antenna (3). The antenna structure according to claim 1 or 2, characterized in that the inclining portion (6, 7, 8) includes a disk member (8) having a groove (71) that is cut away departing from a center, and in that a lower portion of the antenna (3) is adapted to be inserted in the groove (71) of the disk member (8) and a rotation member is adapted to rotate to incline the antenna (3). The antenna structure according to any of claims 1 to 5, characterized in that the antenna (3) has a vertical polarization plane during a call and a length of N times λ/2 (N is an integer) when it is inclined to a desired direction vertical to the ground.

Inventors: FUKASAWA TORU, IMANISHI Y, OHMINE HIROYUKI, SHOJI HIDEAKI, FUKASAWA, TORU, IMANISHI, Y., OHMINE, HIROYUKI, SHOJI, HIDEAKI, FUKASAWA, Toru, Mitsubishi Denki Kabushiki Kaisha, IMANISHI, Y., Mitsubishi Denki Kabushiki Kaisha, OHMINE, Hiroyuki,Mitsubishi Denki Kabushiki Kaisha, SHOJI, Hideaki, Mitsubishi Denki Kabushiki Kaisha
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 2000
Main classification: H01Q1
IPC codes: H01Q3, H01Q1