Antenna system for portable radio apparatus

Abstract: An antenna for a portable radio apparatus has a first antenna construction (12) connected to the casing (11) of the apparatus and a second antenna construction (18) affixed to a base plate or earth plate (17) which is incorporated in the casing. The first antenna construction (12) has a movable joint (14) which allows the first antenna construction (12) to move between a first position where it is regarded as forming a part of the contour of the casing (11) and a second position where it is protruded from the contour and regarded as being located in free space. The second antenna construction (18) corrects the matching state of the first antenna construction (12) such that adequate antenna radiation characteristics are set up in the first position. Optimal antenna characteristics are, therefore, achievable when the first antenna construction is in any one of the first and second positions.

Description: BACKGROUND OF THE INVENTION The present invention relates to an antenna system and, more particularly, to an antenna system for a portable radio telephone or similar portable radio apparatus. With a portable radio apparatus such as a portable radio telephone, it is desirable from the portability standpoint that when transmission or reception is not effected or is effected at low levels, a regular antenna be received in the casing of the apparatus to reduce the overall dimensions of the apparatus. An implementation for receiving the antenna as mentioned has been proposed in various forms in the past, as follows. Specifically, the antenna may be bodily removed from the portable radio apparatus to allow the apparatus to be carried in a smaller configuration. This, however, brings about a problem that mounting and dismounting the antenna is troublesome, and a problem that the antenna physically separated from the apparatus can easily be lost. Moreover, the radio apparatus is practically unable to transmit or receive a radio signal without the antenna. The antenna may be provided with a foldable structure to reduce the length of the radio apparatus. A drawback with the foldable antenna scheme is that, in the folded position, the radiation characteristics of the antenna are effected by a shield structure and a printed circuit board which are usually incorporated in a radio apparatus, obstructing adequate transmission and reception. In addition, the antenna exposed to the outside at all times is not desirable for cosmetic reasons. Another implementation heretofore proposed is such that when the radio equipment is not operated or is operated at low levels, the regular antenna is retracted into the casing of the apparatus and switched to a built-in or internal antenna. This approach, however, is not practicable without resorting to two independent antennas and a switch for switching them over. This, coupled with the fact that a mechanism for interlocking the antenna switching operations is indispensable, results in the need for substantial space, impeding the miniaturization of such a radio apparatus. Further, the extra switch aggravates the high-frequency losses of signals. The radio apparatus with this antenna switching scheme would be complicated in structure and, therefore, expensive. A telescopic antenna is another scheme for enhancing the portability of a portable radio apparatus. This type of antenna is telescoped into the casing, of the apparatus when a small antenna gain suffices. A telescopic antenna, however, lacks sufficient mechanical strength since the diameter thereof is extremely small at the tip. Such an antenna also requires an extra space for its accommodation in the casing of the apparatus, thus obstructing the miniaturization of the apparatus. Further, the radiation characteristics of the antenna are critically degraded when the antenna is telescopically retracted. In the specification of United States Patent No. 4,860,024, which was published on August 22 1989, there was proposed a portable radio telephone with a main antenna element which can be accommodated within a casing and an auxiliary antenna element electrically connected to the main antenna element when the main antenna element is in the casing. In Vol 9 No. 258 (E-350)(1981) October 16 1985 and Japanese Patent No. 60/107903 in the name of Zeneraru Research OBU Erekutoronitsukusu K.K. which was published on June 13 1985, there was proposed a radio equipment with an extendable rod antenna so arranged that in its retracted condition, its outer sleeve was coupled electrostatically to a grounded part of the receiver to increase the effective capacitance of the antenna. Features of the present invention are the provision of an antenna for a portable radio apparatus which miniaturizes and enhances the portability of the apparatus without being removed from the apparatus, which preserves desirable radiation characteristics thereof even when brought to an easy-to-carry position, and which has an attractive appearance. An antenna system for a portable radio apparatus which will be described below has a base plate or earth plate incorporated in the casing of the apparatus, a first antenna construction having an antenna element thereinside, and a second antenna construction. The first antenna construction has a movable joint which allows it to move between a first position where it forms a part of the contour of the apparatus and a second position where it protrudes from the contour of the apparatus. When the first antenna construction is in the first position, the second antenna construction corrects the antenna radiation characteristics and matching characteristics of the antenna. The second antenna construction is affixed to the earth plate inside the casing. The following description and drawings disclose, by means of an example, the invention which is characterised in the appended claims, whose terms determine the extent of protection conferred hereby. In the drawings:- Figs. 1(a) and 1(b) are perspective views each showing a portable radio apparatus embodying the present invention in a particular position; Fig. 2 is a block diagram schematically showing circuitry incorporated in the radio apparatus of Figs. 1(a) and 1(b); Fig. 3 is a fragmentary perspective view showing an antenna portion of the embodiment in detail; Fig. 4(a) and 4(b) are charts representative of antenna radiation characteristics particular to the embodiment; Fig. 5(a) and 5(b) are perspective views each showing an alternative embodiment of the present invention in a particular position; and Fig. 6 is a fragmentary perspective view showing an antenna portion of the alternative embodiment in detail. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. 1(a) and 1(b) and 2, a portable radio apparatus embodying the present invention is shown which includes a casing 11. A first antenna construction 12 is mechanically connected to the casing 11 and constitutes a major element of the antenna of the apparatus. The first antenna construction 12 has an antenna element 13 which is the main element of an antenna reflector, and a movable joint 14 which serves as a part of the antenna reflector as well. Incorporated in the casing 11 are a transmitter-receiver 15, an antenna feeder 16 interconnecting the transmitter-receiver 15 and the movable joint 14, a base plate or ground (earth) plate 17, and a second antenna construction 18. Generally, the transmitter-receiver 15 has an antenna duplexer 19, a transmitting portion 20, a receiving portion 21, and a control portion 22 for controlling the transmitting and receiving portions 20 and 21. The radio apparatus may further include a power supply portion and a dialling unit, not shown. In this embodiment, the first antenna construction 12 is movable between two different positions, i.e., a first position where the first antenna construction 12 is formed as a part of the contour of a casing 11 (Fig. 1(a)) and a second position where it is protruded from the casing 11 (Fig. 1(b)). As shown in Fig. 1(a), the first antenna construction 12 forms a part of the contour of the radio apparatus which is mainly defined by the casing 11. Assume that the antenna element 13 is positioned close to the earth plate 17 which is incorporated in the casing 11 and has ground potential as shown in Fig. 1(a), and that the second antenna construction 18 is absent. Then, the antenna characteristics of the radio apparatus such as the antenna gain and radiation impedance would be changed and degraded, compared to the characteristics under the condition wherein the antenna element 13 is regarded as existing in free space. The second antenna construction 18 serves to correct such antenna characteristics which would otherwise be degraded. Affixed to the earth plate 17, the second antenna construction 18 is so positioned, shaped and dimensioned as to implement adequate correction, which will be described in detail. As shown in Fig. 1 (b), the first antenna construction 12 may be rotated by the movable joint 14 to the second position where it protrudes from the contour of the casing 11. The joint 14 is of the type having a rotatable shaft, as well known in the art. While Fig. 1(b) does not show the internal arrangement of the casing 11 for clarity, it shows a specific configuration of the antenna element 13 which is disposed in the first antenna construction 12. Specifically, the antenna element 13 is provided with a helical whip structure implemented with a metallic wire. In the second position shown in Fig. 1(b), the antenna element 13 and the antenna construction 18 are spaced apart from each other and, therefore, electrically sparingly coupled with each other. It follows that the antenna characteristics of the radio apparatus are substantially determined by the characteristics of the antenna element 13. In the condition shown in Fig. 1(b), the antenna characteristics may be determined with no regard to the characteristics of the second antenna construction 18. Fig. 3 shows in detail the first and second antenna constructions 12 and 18 determining the major characteristics of the antenna, and the earth plate 17. As shown, the antenna construction has the antenna element 13 implemented with a metallic wire, a cover 23 made of a plastic or similar dielectric substance for protecting the antenna element 13, and the movable joint 14. The casing 11 made of a plastic or similar substance is so configured and positioned as to isolate the first antenna construction 12 from the earth plate 17 and the second antenna construction 18. The antenna feeder 16 is electrically connected at one end to the movable joint 14 and at the other end to the duplexer 19, Fig. 2. The movable joint 14 is made of a metal and electrically connects the antenna element and feeder 13 and 16. The movable joint 14 also mechanically fixes the casing 11 and the first antenna construction 18. The developed length of the helical antenna element 13 is substantially one-fourth of the wavelength of the frequency used. Adjustment is made such that substantially optimal antenna characteristics are set up when the first antenna construction 12 is positioned as shown in Fig. 1(b). It is to be noted that the influence of the casing 11 and cover 23 on the antenna characteristics is negligible so long as they have a minimum of losses and are thin. On the other hand, when the antenna construction 12 is laid down to the position shown in Fig. 1(a), the antenna characteristics are noticeably effected. Specifically, should the second antenna construction 18 be absent, the first antenna gain would be reduced by more than 20 dB, compared to that in free space. This may be accounted for by the radiation impedance which, as the antenna element 13 approaches the earth plate 17, decreases due to the resultant increase in the capacitance between the element 13 and the plate 17. The second antenna construction 18 comprises a metallic wire which is electrically connected to the earth plate 17 at one end thereof. The second antenna construction 18 is shaped, dimensioned and positioned in consideration of a necessary frequency and the band thereof, such that the first antenna construction 12 is adequately matched. For example, the second antenna construction 18 may be provided with a rectangular ring-like configuration and located in close proximity to the open end of the antenna element 13. This ring-like configuration is successful in reducing the distance between the earth plate 17 and the first antenna construction 12 and thereby the overall dimensions of the radio apparatus. The second antenna construction 18 may be affixed to the earth plate 17 by a fixing member made of a plastic, for example. In such a configuration, the second antenna construction 18 plays the role of an inductance element and, therefore, compensates for a, capacitance component ascribable to the position of the first antenna construction 12 close to the earth plate 17. It will be noted that the structure and electric characteristics of the second antenna construction 18 described above are only illustrative and may be selected in matching relation to the characteristics of the first antenna construction 12 and required antenna characteristics. Further, the earth plate 17 may be configured such that a part thereof forms a structural element of the first antenna construction 12. Figs. 4(a) and 4(b) are representative of the results of specific measurements associated with the positions shown in Figs. 1(a) and 1(b), respectively. As shown, when the frequency was 962 MHz, the average gain Gav was measured to be -4.8 dBd (dBd: antenna gain normalized by dipole antenna gain) in the position of Fig. 1(a) and -3.5 dBd in the position of Fig. 1(b). With the illustrative embodiment, therefore, it is possible to suppress the decrease in antenna gain to 1.3 dB even when the first antenna construction 12 is brought to the position where it is regarded as forming a part of the contour of the radio apparatus. Referring to Figs. 5(a) and 5(b), an alternative embodiment of the present invention will be described. This embodiment also has a first antenna construction 51 which is movable between two different positions, i.e., a first position where it is nested in a casing 52 (Fig. 5(a)) and a second position where it is protruded from the casing 52 (Fig. 5(b)). In the illustrative embodiment, the first antenna construction 51 bas thereinside an antenna element 53 having a flat plate-like configuration. A sliding mechanism 54 which per se is conventional is used to allow the antenna construction to move between the two positions as mentioned above. The first antenna construction 51 and a second antenna construction 55 which determine the major characteristics of the antenna of the radio apparatus are shown in Fig. 6 in detail, together with a base plate or earth plate 56. As shown, the antenna construction 51 has an antenna element 53, a cover 57 made of a plastic for protecting the antenna element 53, and one part of the slide mechanism 54. The casing 52 isolates the second antenna construction 55 and earth plate 56 from the first antenna construction 51. An antenna feeder 58 is connected in the neighborhood of a side of the flat antenna element 53. The total length of the sides of the antenna element 53 is selected to be substantially one-half of the wavelength of the frequency used. The second antenna construction 55 is mechanically affixed and electrically connected to the earth plate 56 at a position which is substantially one-fourth of the wavelength as measured from the side of the antenna element 53 which is closest to the position where the antenna feeder 58 is connected. More specifically, this position corresponds to the open end of the flat antenna and allows antenna matching to be set up most easily. The second antenna construction 55, like the antenna construction 18 shown in Fig. 1, is implemented with a ring-like metallic wire which constitutes an inductance element. Again, as the antenna element 53 is moved toward the earth plate 56, the resulting capacitance component is compensated for by the second antenna construction 55. This is successful in preventing the antenna gain of the antenna of the radio equipment from being lowered. It will be understood that, although the invention has been described, by way of example, with reference to particular embodiments, variations and modifications thereof, as well as other embodiments may be made within the scope of the protection afforded by the appended claims.

Claims: An antenna system for a portable radio apparatus, including an earth plate (17) mounted in a casing (11) of the radio apparatus, a first antenna construction (12) having an antenna element (13) accommodated therein and extendable from the apparatus, and a second antenna construction (18) inside the casing (11), characterised in that there is provided a movable joint (14) for allowing the first antenna construction (12) to move between a first position in which the first antenna construction (12) forms a part of the contour of the casing (11) and a second position in which the first antenna construction (12) protrudes from the contour of the casing (11) and in that the second antenna construction (18) is affixed to the earth plate (17) and magneto-electrically coupled to the first antenna construction (12) to constitute a single antenna together with the first antenna construction (12) at least when the first antenna construction is in the first position, the second antenna construction (18) correcting an antenna radiation characteristic of the first antenna construction (12) when the first antenna construction (12) is in the first position. An antenna system as claimed in claim 1, wherein, when the first antenna construction (12) is in the first position, the second antenna construction (18) is located in close proximity to an open end of an antenna element (13) of the first antenna construction (12). An antenna system as claimed in either claim 1, or claim 2 wherein the antenna element (13) is a helical whip type antenna element. An antenna system as claimed in any one of the preceding claims wherein the earth plate (17) is flat and is configured such that a part thereof forms a structural element of the first antenna construction (12). An antenna system as claimed in any one of the preceding claims, wherein the second antenna construction (18) includes a ring-like metal wire. An antenna system as claimed in any one of the preceding claims, wherein the movable joint (14) allows the first antenna construction (12) to rotate about one of its ends. An antenna system as claimed in any one of claims 1 to 5, wherein the movable joint (14) allows the first antenna construction (12) to slide on the casing (11) .

Inventors: ONO TAKAO, TAMURA YOSHIHARU, ONO, TAKAO, TAMURA, YOSHIHARU
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1990
Main classification: H01Q1
IPC codes: H04B1, H01Q1