Wrist-Type Wireless Instrument and Antenna Apparatus

1. Field of the Invention

This invention relates to a wrist-type wireless instrument in which an antenna body, unitarily formed with a wrist band, functions as a slot antenna and, in particular, to an antenna apparatus for attaining an improvement in terms of antenna gain.

2. Description Of Related Art

FIG. 1 shows the structure of an antenna body 1, which is an example of the wrist-type wireless instrument in which an antenna body, unitarily formed with a wrist band, functions as a slot antenna. A strip-shaped conductive plate 2 is fastened to a wrist band, and a narrow slot 3 is formed so as to extend along the length dimension of the wrist band, thereby dividing the conductive plate 2 into two sections 2a and 2b. In FIG. 1, the wireless instrument is shown in the state in which it is placed on a person's wrist, i.e., the conductive plate 2 is looped. A capacitive element 4 is electrically connected across the sections 2a and 2b of the conductive plate 2. By appropriately adjusting the capacitance value of this capacitive element 4, it is possible for the antenna to be tuned to a desired frequency. It is desirable that the capacitive element 4 be electrically connected approximately in the central portion with respect to the length dimension of the conductive plate 2 because in this portion the current distribution can be well balanced and a large antenna gain can be obtained. Feeders 5a and 5b, connected to the conductive plate sections 2a and 2b respectively, are connected to a wireless instrument circuit section (not shown).

FIG. 2 shows the radiation pattern of this antenna. The drawing shows the vertical polarization component in the X-Y plane, which is normalized in maximum antenna gain. The radiation is maximum in the direction of the X-axis, which corresponds to the loading direction of the capacitive element 4. This fact indicates that the antenna is functioning as a slot antenna.

However, in this slot antenna for wrist-type wireless instrument, which is unitarily formed with the wrist band, the antenna is restricted to rather small dimensions, so that it is rather difficult to obtain a sufficient level of antenna gain. Thus, with the conventional antenna, it has been difficult to maintain a satisfactory radio communication quality.

The present invention has been made with a view toward solving the above problem. It is an object of the present invention to provide an improved antenna structure for a wrist-type wireless instrument or antenna apparatus of the type in which an antenna body, formed unitarily with the wrist band, functions as a slot antenna, wherein the space inside the wireless instrument casing is effectively utilized, thereby providing a simple structure which helps to obtain an antenna gain larger than that in the prior art.

To solve the above problem, the present invention provides a wrist-type wireless instrument that includes a casing containing a circuit board; a wrist band connected to either side of the casing; and a conductive plate having a slot and provided in the casing and in the wrist band, wherein a capacitive element is loaded across conductive sections of a conductive plate that are defined by a slot, wherein the circuit board is arranged on the inner side of a loop for wrist wear that is formed by the casing and the wrist band, and wherein the capacitive element is arranged approximately at the center of the circuit board.

More specifically, it is desirable that the wrist band be comprised of two (first and second) wrist band members that are respectively joined to each side of the casing. It is also desirable that the conductive plate be comprised of two (first and second) conductive plates and two electric paths provided in the casing, the two electric paths and the two conductive plates being respectively provided for the two wrist band members, a slot being formed in each conductive plate so as to extend longitudinally from the end edge of the casing to which the associated wrist band member is joined, thereby dividing each conductive plate into first and second sections.

Additionally, it is desirable that, on the casing side, the ends of the respective first sections of the first and second conductive plates be electrically connected to each other through one of the two electrical paths, the ends of the respective second sections of the first and second conductive plates being electrically connected to each other through the other of the two electrical paths, with the capacitive element being loaded between the two electric paths.

Further, it is desirable that the capacitive element be arranged between a display element for displaying information of the wrist-type wireless instrument and the circuit board. Alternatively, the capacitive element may be surface-mounted on the circuit board.

Further, it is possible for the capacitive element to be comprised of two varactor diodes that are connected in series.

Embodiments of the present invention are described hereafter, with reference to the drawings, in which:

FIG. 1 illustrates the construction of a conventional, prior art wrist-type wireless instrument antenna apparatus;

FIG. 2 is a graph showing the radiation directivity characteristic of a conventional, prior art wrist-type wireless instrument antenna apparatus;

FIG. 3 illustrates the construction of a wrist-type wireless instrument antenna apparatus according to the present invention;

FIG. 4 illustrates the operational principle of the wrist-type wireless instrument antenna apparatus shown in FIG. 1;

FIGS. 5(a) and 5(b) are diagrams illustrating antenna characteristics, which depend on the position and arrangement of the capacitive element, of which FIG. 5(a) is a plan view of a wrist-type wireless instrument antenna apparatus and FIG. 5(b) is a side view thereof;

FIGS. 6(a) and 6(b) are diagrams illustrating the operation of the present invention (the antenna characteristic depending on the position of arrangement and the capacitive element), of which portion 6(a) is a plan view of a wrist-type wireless instrument antenna apparatus according to the present invention and FIG. 6(b) is a side view thereof;

FIG. 7 is a schematic perspective view of a wrist-type wireless instrument equipped with a wrist-type wireless instrument antenna apparatus according an embodiment of the present invention;

FIGS. 8(a) and 8(b) are diagrams showing a wrist-type wireless instrument antenna apparatus according an embodiment of the present invention, of which FIG. 8(a) is a cutaway top view showing the structure of a near-casing portion thereof and FIG. 8(b) is a cutaway side view thereof;

FIG. 9 is a cutaway top view showing the structure of a near-casing portion of a wrist-type wireless instrument that is equipped with a wrist-type wireless instrument antenna apparatus according to another embodiment of the present invention which is near the casing thereof;

FIGS. 10(a) and 10(b) are diagrams showing still another embodiment of a wrist-type wireless instrument antenna apparatus according to the present invention, of which FIG. 10(a) is a cutaway top view showing the structure of a near-casing portion thereof and FIG. 10(b) is a cutaway side view thereof; and

FIG. 11 is a circuit diagram illustrating a wrist-type wireless instrument antenna apparatus according an embodiment of the present invention.

The operation of the antenna apparatus of the present invention will now be described. First, the operation of a wrist-type antenna apparatus will be described.

FIG. 4 shows the operational principle of a wrist-type-wireless instrument antenna apparatus. A slot antenna is a magnetic-field-detection type antenna, whose vertical-polarization magnetic field component 10 is in the horizontal direction, as shown in the drawing. In this condition, the directions of electric current flowing through the conductive plate are as indicated at 12. Here, the conductive plate 11 is shown in a diagrammatic form, with a capacitive element 13 being loaded thereon. These two directions of current are in the same phase when seen in the direction of the Y-axis, representing an appearance as if two loop antennas are connected in parallel. When the conductive plate 11 is thus looped, the direction of current of the slot antenna and that of the loop antenna coincide with each other, so that the antenna apparatus is functioning not only as a slot antenna but also as a loop antenna. The two are combined together to make it possible to obtain a relatively large antenna gain.

As shown in FIG. 3, in the antenna apparatus of the present invention, a conductive plate 7 and a capacitive element 6, loaded on the central portion with respect to the longitudinal direction of the conductive plate 7, are arranged on the outer side of a circuit board 8 (conversely, the circuit board 8 is arranged on the inner side of the loop formed by the conductive plate 7), and the capacitive element 6 is situated approximately at the center of the circuit board 8. The reason for this arrangement is to effectively utilize the circuit board 8, which is a conductive plate, as an antenna reflector, thereby attaining an increase in antenna gain. Further, the conductive plate 7 and the circuit board 8 are connected together through feeders 9a and 9b.

To obtain a larger antenna gain, according to the present invention, the circuit board of a wrist-type wireless instrument is utilized as the reflector of a slot antenna. The effect of this arrangement will be described below.

In FIGS. 5 and 6, a capacitive element 14, a wireless instrument circuit board 15, and a part of a conductive plate 16 are arranged inside a wireless instrument casing 17.

FIG. 5(a) is a plan view of the antenna apparatus, and FIG. 5(b) is a side view thereof. When, as shown in FIG. 5(a) and FIG. 5(b), the capacitive element 14, which is in the central portion with respect to the longitudinal dimension of the conductive plate 16, is arranged so as to be situated at an end of the circuit board 15, an electromagnetic wave 18 that is reflected by the circuit board 15 is radiated in a direction inclined with respect to the frontal direction of the antenna, so that the effect of the slot antenna as the reflector is diminished. Moreover, as shown in FIG. 5(b), the effective opening area of a slot 19 (the shaded portion in FIG. 5(b)) is reduced, so that the characteristic of the apparatus as a loop antenna deteriorates, resulting in a reduction in antenna gain.

Similarly, FIG. 6(a) is a plan view of an antenna apparatus, and FIG. 6(b) is a side view thereof. Since the structure shown is similar to that of FIGS. 5(a) and 5(b), the components which correspond to those of FIG. 5(a) and 5(b) are indicated by the same reference numerals. When, as shown in FIG. 6(a) and FIG. 6(b), the capacitive element 14, which is in the central portion with respect to the longitudinal dimension of the conductive plate 16, is arranged so as to be situated at the center the circuit board 15, the electromagnetic wave 18, reflected by the circuit board 15, is radiated in the frontal direction of the antenna, so that the effect of the slot antenna as a reflector is maximum. Further, as shown in FIG. 6(b), which is a side view of FIG. 6(a), the reduction in the effective opening area of the slot 19 (the shaded portion in FIG. 6(b)) is restrained to a minimum, so that there is practically no deterioration in the characteristic of the apparatus as a loop antenna, resulting in a maximum antenna gain. The effect of the reflector in the optimum antenna-apparatus construction as shown in FIGS. 6(a) and 6(b) is such that an improved antenna gain of approximately 2 or 3 dB can be obtained.

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 7 is a schematic perspective view of a wrist-type wireless instrument (an antenna apparatus for wrist-type wireless instrument) according to an embodiment of the present invention. In the drawing, the wrist-type wireless instrument comprises: a casing 20 containing a wireless instrument circuit; and first and second band members 21a and 21b respectively connected to each longitudinal end of the casing 20. A band clasp 22 is attached to the other end of the first band member 21a, and a plurality of clasp holes 23 capable of being mechanically engaged with the band clasp 22 are formed in the second band member 21b.

A metal conductive plate 24 is fastened to the first and second band members 21a and 21b, a slot 25 being longitudinally formed in the conductive plate 24. The conductive plate 24 is arranged on the inner side of the first and second band members 21a and 21b. When the band members 21a and 21b are formed of a synthetic resin, such as urethane or silicone resin, it is possible for the band members 21a and 21b and the conductive plate 24 to be formed integrally. When the band members 21a and 21b are formed of leather, the conductive plate 24 is sewed in between the outer and inner sheets of leather.

A capacitive element 26, which comprises, for example, a variable capacitor, is loaded on the conductive plate 24, at a position which is in the central portion with respect to the longitudinal dimension of the conductive plate 24 and which is between the two sections, defined by the slot 25, of the conductive plate 24. By appropriately adjusting the capacitance value of this capacitive element 26, it is possible to tune the antenna apparatus to a desired frequency. If the wireless instrument only uses a single frequency, a fixed or semi-fixed capacitor suffices for the capacitive element 23.

FIG. 8(a) is a cutaway top view showing the structure of a near-casing portion of an embodiment of a wrist-type wireless instrument (an antenna apparatus for wireless instrument) according to the present invention; and FIG. 8(b) is a cutaway side view of the same. In FIG. 8(a) and FIG. 8(b), conductive plates 28a and 28b, which are respectively fixed to first and second band members 27a and 27b, have slots 29a and 29b, respectively, extending from their ends on the side of a wireless instrument casing 30 to thereby divide each of the first and second conductive plates 28a and 29b into first and second divided sections. The respective first divided sections of the conductive plates 28a and 28b are connected to each other through one of two electrical paths consisting of conductive plates 31 and 32 provided in the wireless instrument casing 30. Similarly, the respective second divisional sections of the conductive plates 28a and 28b are connected to each other through the other electrical path. The conductive plates 31 and 32, which may be metal plates, may also comprise flexible copper tapes covered with polyamide or the like. The connections between the conductive plates 28a and 28b and the conductive plates 31 and 32 are effected through conductive connections such as spring contact, soldering, or screwing.

In this embodiment, the conductive plate is divided into band and case sections. Of course it is also possible for the conductive plate to be formed as an integral piece as indicated in FIG. 7. However, the divided structure is advantageous in that the assembly of the casing section and that of the band section can be separately conducted, which increases the freedom in the production of the wrist-type wireless instrument.

A capacitive element 33, which includes a variable capacitor or the like, is connected to the conductive plates 31 and 32, and is situated approximately in the central portion with respect to the longitudinal dimension of the antenna body inclusive of the conductive plates 28a and 28b. The capacitive element 33 is arranged in the space between a display device 34, which includes, for example, a liquid crystal device, for indicating information of the wrist-type wireless instrument, and a circuit board 35, and situated substantially at the center of the circuit board 35. The circuit board 35 is a glass-epoxy-type or the like, multi-layered double-sided circuit board, having a printing pattern on either side. In its inner layer, the circuit board 35 has a power source and a grounding pattern.

The display device 34 is connected to the circuit board 35 through conductive connectors 36a and 36b. An integrated circuit (IC) 37 is arranged on the upper side of the circuit board 35. An IC 39, which is connected to the conductive plates 31 and 32 through feeders (not shown), and a battery 40 are arranged on the lower side of the circuit board 35. The casing 30 has a back cover 41, the material of which may be synthetic resin to reduce cost. However, when it is made of a metal, the effect of the antenna reflector is enhanced. Further, a metal cover has the effect of shielding against noise components generated from the wireless instrument circuit, so that a further improvement is achieved in terms of antenna gain.

In the construction described above, the capacitive element 33 is arranged in the space between the display device 34 and the circuit board 35, so that the space can be effectively utilized and the thickness of the wireless instrument body can be reduced. Further, since the circuit board 35 can be utilized most effectively as the antenna reflector, it is possible to obtain a larger antenna gain.

FIG. 9 is a cutaway top view, showing the portion near the casing, of a wrist-type wireless instrument (an antenna apparatus for wrist-type wireless instrument) according to another embodiment of the present invention. The wrist-type wireless instrument (the antenna apparatus for wrist-type wireless instrument) of this embodiment is a modification of that shown in FIG. 8, and has substantially the same construction as the latter, so the corresponding components are indicated by the same reference numerals.

In FIG. 9, the capacitive element 34 is arranged between the display device 34 and the circuit board 35 but situated at a position shifted two-dimensionally such that it does not overlap the IC 37 (this position also is regarded to be substantially the center of the circuit board 35). Therefore, it is possible to reduce the gap between the display device 34 and the circuit board 35, so that a further reduction in the thickness of the wireless instrument casing 30 can be realized. In this construction also, the circuit board 35 can function as an antenna reflector, so that a large antenna gain can be obtained.

FIG. 10(a) is a cutaway top view, showing the portion near the casing, of a wrist-type wireless instrument (an antenna apparatus for wrist-type wireless instrument) according to still another embodiment of the present invention, and FIG. 10(b) is a cutaway side view of the apparatus. The wrist-type wireless instrument (the antenna apparatus for wrist-type wireless instrument) of this embodiment also has substantially the same construction as that shown in FIG. 8, so the corresponding components are indicated by the same reference numerals.

In FIGS. 10(a) and 10(b), the conductive plates 28a and 28b, fixed to the first and second band members 27a and 27b, respectively, have slots 29a and 29b formed so as to extend longitudinally from the end edges on the side of the wireless instrument casing 30. Thus, each of the conductive plates 28a and 28b is separated into first and second divided sections by the slots 29a and 29b, respectively. Their respective first divided sections are connected to each other through a conductive plate 31 provided in the wireless instrument casing 30. Similarly, their respective second divided sections are connected to each other through a conductive plate 32, which is also provided in the wireless instrument casing 30. The capacitive element 33, consisting of a variable capacitor or the like, is connected to the conductive plates 31 and 32 and situated substantially in the central portion with respect to the length dimension of the antenna inclusive of the conductive plates 28a and 28b. Further, the capacitive element 33 is surface-mounted on the circuit board 35, at a position below the display device 34, including a liquid crystal panel or the like for displaying information of the wrist-type wireless instrument, and is positioned substantially at the center of the circuit board 35. The display device 34 is connected to the circuit board 35 through conductive connectors 36a and 36b. Arranged on the upper side of the circuit board 35 are ICs 37 and 38. On the lower side of the circuit board 35, an IC 39, which is connected to the connective plates 31 and 32 through feeders (not shown), and a battery 40 are arranged.

In the construction of this embodiment, the IC is comprised of two chips, and the capacitive element 33 is surface-mounted on the circuit board 35, so that it is possible to further reduce the gap between the display device 34 and the circuit board 35, thereby attaining a further reduction in the thickness of the casing body 30. Further, since the circuit board 35 can be utilized most effectively as an antenna reflector, the effect of providing a large antenna gain can be obtained as in the above-described embodiment.

FIG. 11 is a circuit diagram illustrating an embodiment of the wire-type-wireless instrument antenna apparatus of the present invention. The capacitive element, which is loaded across two divisional sections of a connective plate 42, defined by a slot 43, includes two varactor diodes 44a and 44b that are connected in series. The respective cathode terminals of the varactor diodes 44a and 44b are connected to each other, and further connected to a wireless instrument circuit 46, formed on the circuit board, through a signal line 47. The respective anode terminals of the varactor diodes 44a and 44b are connected to the connective plate 42, at central positions 45a and 45b with respect to the length dimension of the plate. The anode terminal of one of the varactor diodes 44a and 44b is connected to the wireless instrument circuit 46 through a signal line 48. The anode/cathode combination in the connection of the varactor diodes 44a and 44b is interchangeable. The wireless instrument circuit 46 is connected to feeding points 49a and 49b at appropriate positions on the connective plate 42 through feeders 50a and 50b. By appropriately adjusting the positions of these feeding points 49a and 49b, it is possible to change the antenna input impedance, thereby making it possible to achieve an optimum impedance matching with the wireless instrument circuit 46.

With the above arrangement, it is possible, in this wrist-type wireless instrument antenna apparatus, to use the varactor diodes 44a and 44b in a simple structure, and, by varying the voltages of the two signal lines 48 and 49 by the wireless instrument circuit 46, to change the tuning frequency of the antenna. Thus, it is possible to realize an automatic electronic tuning like that in a synthesizer system, so that a plurality of frequencies may be used.

As described above, the wrist-type wireless instrument and antenna apparatus of the present invention provide the following advantages. The limited space in the wrist-type wireless instrument can be effectively used, so that it is possible to realize a reduction in the thickness of the casing. Further, due to the structure which allows the circuit board to be used most effectively as a antenna reflector, it is possible to attain a still larger antenna gain.

Also, by the conductive plate being divided into band and casing sections, a substantial improvement in the producibility of the wrist-type wireless instrument is attained.

Additionally, it is possible to realize a further reduction in the thickness of the casing. Further, the operation of mounting the capacitive element is facilitated.

Also, a circuit is provided in which the capacitive element can be easily formed of varactor diodes, so that it is possible to change the tuning frequency when automatic electronic tuning is to be performed.

While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.