Portable radio apparatus

Abstract: A small portable radio apparatus has a casing having a curvedly bulging side edge surface. An antenna member (20) disposed in the casing has first and second conductive plates (21, 23) having a slot groove at an outer peripheral position of a circuit board, and a short-circuiting portion for short-circuiting the conductive plates with each other cover the slot groove. A tuning capacitor element is connected to the first and second conductive plates at a position opposite to a position where the short-circuiting portion is provided. The first and second conductive plates respectively have opening portions at rears thereof which face the circuit board, and side portions which bulge slantingly toward outer peripheral edges thereof.

Description: The present invention relates to a portable radio apparatus for use as, for example, a pager, and more particularly, to a structure of a slot antenna member in a casing thereof. Conventional portable radio apparatus employ a ferrite antenna, a small loop antenna, a plate-shaped loop antenna or the like. The reception efficiency of such an antenna is determined by the ratio of the wavelength used to the antenna length. Thus, a portable radio apparatus which employs a loop antenna must be used at high frequencies. To allow the portable radio apparatus to be used in, for example, the VHF band, the aperture area of the loop antenna must be increased, thus making a small size of the portable radio apparatus difficult. When n is the antenna efficiency, y rad is the radiation resistance and y loss is the antenna resistance, n is expressed by the following equation: n = y rad / ( y rad + y loss ) The radiation resistance y rad is in proportion to the square of the aperture area of a loop antenna. The antenna resistance y loss is in proportion to the antenna length, and is inverse proportion to the surface area of an antenna member. Thus, to achieve a reduction in the aperture area of an antenna member and an increase in the antenna efficiency n at the same time, the surface area of the antenna member must be increased, that is, restrictions are imposed on the shape of an antenna member, resulting in an increase in the width of the antenna member. If a wide loop antenna is accommodated in a casing having a curvedly bulging side surface, useless space is generated within the casing. In an antenna having a wide surface area, proposed in, for example, JP-B-1-34414, the surface of the loop antenna parallel to the aperture surface forms a vertical thick surface. Thus, it is apparent that accommodation of such a loop antenna in the above-described casing generates useless space therein. In small portable radio apparatus, a circuit board must be disposed near an antenna because the space in the casing is limited. In such a layout, the loop antenna is influenced by an electronic circuit on the circuit board, deteriorating the sensitivity thereof. Particularly, if a direct conversion type radio apparatus circuit is employed, since the frequency of a local oscillation signal is almost equal to the reception frequency, the local oscillation signal and the noise occurring in the local oscillation signal interfere with radio transmission and reception between that radio apparatus and other radio apparatus. In order to eliminate such a problem in a small portable radio apparatus which employs a loop antenna, the antenna must be disposed at a position separated from the local oscillator circuit, or an effective shielding structure must be provided to suppress an electromagnetic radiation from the local oscillator circuit. Thus, the use of a loop antenna precludes a reduction in the size of the portable radio apparatus. The present inventors have proposed the use of a slot antenna in a portable radio apparatus, such as a pager. However, even with a slot antenna, it is difficult to achieve a reduction in the size of the portable radio apparatus. That is, if, as shown in Fig. 21(a), a slot antenna member 90 has a structure in which a circuit board 94 is sandwiched between two conductive plates 92 and 93 having a slot groove 91 formed between their outer peripheral portions, too large a space (slot groove) is generated between the conductive plates 92 and 93. Further, if the slot antenna member 90 is accommodated in a radio apparatus casing 95 having a curvedly bulging side end surface 951, useless space S is generated within the casing 95. Furthermore, as shown in Fig. 21(b), in a slot antenna member 90 in which two conductive plates 92 and 93 are laid one on top of the other in such a manner that a slot groove 91 is formed between outer peripheral portions thereof, the slot antenna member 90 receives noise from a circuit board 94 superimposed on the conductive plates, thus reducing the sensitivity thereof. GB-A-2 217 131 discloses a portable radio apparatus comprising a circuit board constituting a radio apparatus circuit and a loop antenna member including first and second conductive plates arranged so as to accommodate said circuit board in between. The conductive plates are substantially flat plates forming at the same time top and bottom plate of the apparatus' casing. The two conductive plates are fixed to the top and bottom, respectively, of a frame forming the periphery of the casing and keeping the two conductive plates spaced apart from each other. A side portion of the casing, namely the frame has a rounded shape at a position radially outside of the conductive plates. In view of the aforementioned problems of conventional radio apparatus, an object of the present invention is to provide a portable radio apparatus employing a slot antenna member having an improved shape which avoids generation of useless space within a casing having a curvedly bulging side end surface when the slot antenna member is accommodated in the casing, so as to enable a reduction in the size thereof compared to the size of conventional portable radio apparatus. Another object of the present invention is to provide a portable radio apparatus having an internal structure which is less influenced by the noise generated from a circuit board so as to enable the circuit board to be located near an antenna member and thereby enable a reduction in the size thereof compared to the size of conventional portable radio apparatus. These objects are achieved with a portable radio apparatus as claimed in claim 1. Preferred embodiments of the invention are subject-matter of the dependent claims. In a first embodiment of the portable radio apparatus according to the present invention, the radio apparatus casing has a side portion which bulges toward an outer periphery thereof, and the first and second conductive plates, constituting the slot antenna member, have side portions which bulge toward outer peripheral edges thereof and form a slot groove. Portable radio apparatus must be small in size because they are put in a pocket and carried around, and at the same time, must have a good design and comfortable texture. Hence, in this invention, the radio apparatus casing has a side portion which becomes thinner toward an outer periphery thereof so as to enhance design and texture. Further, since the slot antenna member has the bulging side portions, it can be disposed along the inner surface of the radio apparatus casing, thus eliminating useless space within the radio apparatus casing. As a result, a reduction in the size of the portable radio apparatus can be achieved. In a another embodiment the radio apparatus casing has a substantially spherical shape and two semi-spherical conductive plates are employed for the slot antenna member are thereby to achieve substantially the same effects as with the first embodiment. Embodiments of the present invention will now be described with reference to the accompanying drawings. In each of the following embodiments, an antenna member is accommodated in a casing to constitute a casing-incorporated portable apparatus, such as a pager. Fig. 1(a) is a perspective view of a first embodiment of a radio apparatus according to the present invention; Fig. 1(b) is a side elevational view of the radio apparatus of Fig. 1(a); Fig. 1(c) is a plan view of a radio apparatus having a curled cord on a casing; Fig. 1(d) illustrates a state wherein the radio apparatus of Fig. 1(c) is hung from a human body; Fig. 2 is an exploded perspective view of the radio apparatus of Fig. 1(a); Fig. 3(a) is a plan view of the antenna member shown in Fig. 2; Fig. 3(b) is a front view of the antenna member of Fig. 2; Fig. 3(c) is a left side view of the antenna member of Fig. 2; Fig. 3(d) is a right side view of the antenna member of Fig. 2; Fig. 4 is an expansion plan view of the antenna member shown in Fig. 2; Fig. 5 is a section taken along the line X-X' of Fig. 1; Fig. 6 is a section taken along the line Y-Y' of Fig. 1; Fig. 7 is an equivalent circuit diagram of the antenna member shown in Fig. 2; Figs. 8(a) and 8(b) are block diagrams of a direct conversion type radio apparatus circuit; Fig. 9 is a graphic representation of comparison between the reception sensitivity of a radio apparatus employing the slot antenna according to the first embodiment of the present invention and the reception sensitivity of a radio apparatus employing a conventional slot antenna; Fig. 10 is a graphic representation of comparison between the reception sensitivity of a radio apparatus having a local oscillator layout structure according to the first embodiment of the present invention and the reception sensitivity of a radio apparatus having a local oscillator layout structure according to a comparative example; Fig. 11 is a graphic representation of comparison between the reception sensitivities of a radio apparatus in which the antenna member according to the first embodiment of the present invention is disposed, when the radio apparatus is and is not put on a human body, respectively; Fig. 12 is a graphic representation of comparison between the reception sensitivity of a radio apparatus in which the antenna member according to the first embodiment of the present invention is disposed when put on a human body and the reception sensitivity of a super-heterodyne radio apparatus employing a conventional loop antenna when put on a human body; Fig. 13 is a perspective view of an antenna member incorporated in a second embodiment of the radio apparatus according to the present invention; Fig. 14 is a section taken along a line corresponding to the line X-X' of Fig. 1 in the radio apparatus shown in Fig. 13; Fig. 15 is a section taken along a line corresponding to the line Y-Y' of Fig. 1 in the radio apparatus shown in Fig. 13; Fig. 16(a) is a plan view of the antenna member shown in Fig. 13; Fig. 16(b) is a front view of the antenna member shown in Fig. 13; Fig. 16(c) is a right side view of the antenna member of Fig. 13; Fig. 17 is a perspective view of a third embodiment of a radio apparatus according to the present invention; Fig. 18(a) is an expansion plan view of the antenna member incorporated in the radio apparatus shown in Fig. 17; Fig. 18(b) is a perspective view of the antenna member of Fig. 17; Fig. 18(c) is a bottom plan view of the antenna member of Fig. 17; Fig. 18(d) is a side view of the antenna member of Fig. 17; Fig. 19 is a vertical cross-sectional view of the radio apparatus of Fig. 17; Fig. 20 is a perspective view of a radio apparatus according to another embodiment of the present invention; Fig. 21(a) illustrates a radio apparatus employing a conventional slot antenna; and Fig. 21(b) illustrates a radio apparatus employing another conventional slot antenna. First embodiment Fig. 1(a) is a perspective view illustrating an external view of a first embodiment of a portable radio apparatus according to the present invention. Fig. 1(b) is a side elevational view of the radio apparatus of Fig. 1(a). In Figs. 1(a) and 1(b), the radio apparatus 10 employs a casing 13 which is formed by placing an upper casing member 11 on a lower casing member 12. The casing 13 has an elliptical form when viewed from above. The casing 13 has a side portion 130 which curvedly bulges toward an outer periphery thereof. Thus, design of the radio apparatus 10 is improved and the user can readily put the radio apparatus 10 in the pocket or take it out from the pocket. The reception contents are displayed on a liquid crystal display panel 14 on the upper surface of the casing 13 so that the user can check them through a protective lens 140 incorporated in the upper casing member 11. Below the liquid crystal display panel 14 are disposed two operation buttons 151 and 152. In order to indicate, to the user, a side of the radio apparatus 10 which should be up or down when the user puts the radio apparatus 10 in a pocket and carries it around, an arrow mark 16 is provided on the upper casing member 11. The radio apparatus 10 is internally constructed such that it exhibits the maximum sensitivity when carried around with the mark 16 up or down. As shown in Fig. 1(c), a curled cord 74 may be provided at a position near the mark 16 in place of the mark 16 so that the user can hang the radio apparatus 10 in the manner shown in Fig. 1 (d) with the portion of the apparatus provided with the curled cord 74 up. Thus, the user can carry the radio apparatus 10 around with a particular portion thereof up or down so that the radio apparatus 10 is directed in a direction which ensures the highest sensitivity when carried around. In the radio apparatus 10 having the above-described shape, a slot antenna is accommodated in the casing 13, which has a shape that matches the internal shape of the casing 13 and which is not readily affected by an electronic circuit. The structure of this slot antenna will be described below with reference to Figs. 2 to 4. Fig. 2 is an exploded perspective view of the first embodiment of the radio apparatus according to the present invention. Fig. 3(a) is a plan view of the antenna member. Fig. 3(b) is a front view of the antenna member. Fig. 3(c) is a left side elevational view of the antenna member. Fig. 3(d) is a right side elevational view of the antenna member. Fig. 4 is an expansion plan view of the antenna member. In Fig. 2, the antenna member 20 (a slot antenna member) is accommodated between the upper casing member 11 and the lower casing member 12. The antenna member 20 has a shape which matches the shape of the interior of the upper and lower casing members 11 and 12. That is, the entire shape of the antenna member 20 is hexagonal, as shown in Fig. 3(a), and the antenna member 20 has a side portion 200 which slantingly bulges toward the outer peripheral edge thereof, as shown in Figs. 3(b) to 3(d). The antenna member 20 includes a first conductive plate 21 constituting an upper half portion, a second conductive plate 23 which is positioned opposite to the first conductive plate 21 in such a manner that a slot groove is formed between their outer peripheries, and a short-circuiting portion 24 for electrically short-circuiting the first and second conductive plates 21 and 23. The first and second conductive plates 21 and 23 have square opening portions 210 and 230 on their surfaces, respectively. In the antenna member 20, the first and second conductive plates 21 and 23 and the short-circuiting portion 24 are formed as one unit, as shown in Fig. 4. The antenna member 20 shown in Fig. 3 is obtained from the structure shown in Fig. 4 through folding one of the conductive plates back onto the other by bending at a coupling portion 241 between the short-circuiting portion 24 and the first conductive plate 21 and a coupling portion 242 between the short-circuiting portion 24 and the second conductive plate 23. At that time, the side portion 200 of the antenna member 20 is constituted by side portions 215 and 235 which respectively bulge slantingly toward outer peripheral edges thereof in the first and second conductive plates 21 and 23. Fig. 5 is a section taken along the line X-X' of Fig. 1. Fig. 6 is a section taken along the line Y-Y' of Fig. 1. When the radio apparatus 10 is to be manufactured using the antenna member 20 having the above-described structure, the antenna member 20, a circuit board 30 constituting a radio apparatus circuit, the liquid crystal display panel 14, an electric cell 33 and so on are accommodated in the casing 13, as shown in Figs. 5 and 6. As shown in Figs. 5 and 6, since the antenna member 20 has the bulging side portion 200, it is disposed within the casing 13 along the inner surfaces of the upper and lower casing members 11 and 12, thus substantially eliminating useless space within the side portion 130 of the casing 13. The circuit board 30 constituting the radio apparatus circuit is sandwiched between the first and second conductive plates 21 and 23. The slot groove 22 of the antenna member 20 is located on the outer peripheral portion of the circuit board 30. On the front side of the circuit board 30 is located the opening portion 210 of the first conductive plate 21. Thus, the user can see the data displayed by the liquid crystal display panel 14 through the opening portion 210. On the rear side of the circuit board 30 is located the opening portion 230 of the second conductive plate 23. Thus, the user can replace the button type electric cell 33, serving as a power source of the radio apparatus 10, with a new one through the opening portion 230 by removing a rear lid 125 of the lower casing member 12. At a position on the side of the X' direction with respect to the circuit board 30, the short-circuiting portion 24 extends over the slot groove 22 to electrically short-circuit the first and second conductive plates 21 and 23. On the X direction side of the circuit board 30 is mounted a tuning capacitor element 301 which is electrically connected to both the first and second conductive plates 21 and 23 through terminals 302 and 303, respectively. The connecting position of the tuning capacitor element 301 is opposite to the short-circuiting position of the first and second conductive plates 21 and 23 by the short-circuit portion 24, as shown in Fig. 7 which is an equivalent circuit diagram of the antenna member 20. The tuning capacitor element 301 enables the antenna member 20 to be tuned at a high antenna gain even if the length of the slot groove 22 is shorter than the length corresponding to half the used wavelength (λ/2). Thus, locating the tuning capacitor element 301 at a central position in the longitudinal direction of the slot groove 22, i.e., at a position remotest from the short-circuiting portion 24, is the most effective. The vicinity of the connecting position of the tuning capacitor element 301 with the antenna member 20 constitutes a high impedance portion of the antenna member 20 from which electromagnetic waves are radiated. Thus, when the user carries the radio apparatus 10 around, he or she puts the radio apparatus 10 in a pocket with the connecting position between the tuning capacitor element 301 and the antenna member 20 up or down so as to obtain the highest sensitivity. The direction in which the radio apparatus 10 should be directed during use may be indicated by the arrow mark 16 on the upper casing member 11 and/or the cord 74 as mentioned before. In this embodiment, the radio apparatus circuit is a direct conversion type circuit. Fig. 8(a) is a block diagram of such a radio apparatus circuit. In Fig. 8(a), an RF amplifier 340 (high-frequency amplifying circuit) receiving the signal from the antenna member 20, a mixer 341, a local oscillator 342 (local oscillator circuit), a low-pass filter 343, a detector 344, a decoder 345 and a CPU 346 constitute the radio apparatus circuit. Unlike a single super-heterodyne type radio apparatus circuit, conversion into an intermediate frequency cannot be performed. That is, in the direct conversion type radio apparatus circuit, since the tuning frequency matches the oscillation frequency of the local oscillator 342, the local oscillation signal of the local oscillator 342 readily supplies the antenna member 20, suppressing a received signal or interfering with other radio apparatus. Further, the operation clock of a booster circuit (which will be explained later) is supplied through a power line as noise which is superimposed to the local oscillation signal. If the frequency of the operation clock, which generally ranges from ten plus several kHz to several MHz, is very low and if the C/N ratio of the clock oscillation is not good, the side band noise of the operation clock is supplied from the antenna member 20, passes through the RF circuit and the mixer circuit, and is then converted into base-band noise in the direct conversion detector circuit output, thus reducing the S/N ratio of a received useful signal. To avoid such a deficiency, in the direct conversion type radio apparatus circuit, the antenna member 20 and the local oscillator 342 should be disposed at positions separated from each other. However, in a small radio apparatus 10, such as that of this embodiment, it is generally impossible to obtain such a layout. Further, it is also necessary to provide means for avoiding mixture of the side band noise of the operation clock of the booster circuit into the antenna member. Hence, in this embodiment, the local oscillator 342 is mounted on the front side of the circuit board 30 at a position deviating from the center of the antenna member 20 in the X' direction, i.e., at a position close to the short-circuiting portion 24, in a state wherein it is placed in a shielding box, as shown in Fig. 5, so that the local oscillator 342 can be located at a position where it does not readily influence the antenna member 20. Accordingly, the local oscillator 342 is at a position remote from the connecting position between the tuning capacitor element 301 and the antenna member 20 (which is the highest impedance portion in the antenna member 20) where the antenna member 20 is least influenced by the noise from the local oscillator 342. On the front side of the circuit board 30 is also mounted a digital IC 347 functioning as the decoder 345 and the CPU 346, and so on. However, an influence of the digital IC 347 on the antenna member 20 is relatively small, and there is thus no limitation on the position of the digital IC 347. Regarding the problem involving the occurrence of the side band noise of the operation clock of the booster circuit in the local oscillation signal, mixture of the side band noise into the antenna member 20 can be eliminated when the above-described layout is employed. If the operation clock is set in the stop-band of the low-pass filter and if the clock oscillator is a crystal oscillator, such mixture can be more reliably eliminated. Fig. 8(b) is a block diagram of the radio apparatus circuit with power source lines. The electric cell 348 is a dry cell or air cell of 1.5 volts or below. A voltage of 2 volts or above is necessary to operate a direct conversion IC 349. Hence, the voltage of the electric cell 348 is boosted by a DC/DC converter 352. A voltage boosting method is the charge pumping method by a reactance element. A crystal oscillator 350 is used as a reference signal source used to store and discharge electric charges. The crystal oscillator, having a frequency ranging from 32.768 kHz to 76,8 kHz, is also used as a reference signal for clock operation or data demodulation in the CPU. The amount of attenuation by the low-pass filter 343 at 32.768 kHz is 90 dB or above. This, together with a high Q of the crystal oscillator 350, can sufficiently attenuate the operation clock and the side band noise. In the structure shown in Fig. 8(b), the local oscillator 342 is separate, and the mixer 341 is within the IC. In this structure, a signal line 351 is an exposed printed pattern on the board or the like. The signal intensity on the signal line 351 at a 50 Ω terminal is between -10 dBm and-20 dBm, and the impedance of the signal line 351 is several kΩ. Thus, an externally radiating level is very high, and radiation takes place in upward and downward directions of the signal line 351. Particularly, in a small and thin radio apparatus having a structure in which the signal line 351 is covered by a loop antenna, the local oscillator circuit 342 radiates intense radiations. The present inventors measured and found that the radiated electric field level at the input terminal of the RF amplifier 340 is 110 dBµV. The minimum reception electric field level of the radio apparatus 10 is between 10 dBµV and 15 dBµV. Thus, the reception signal wave is distorted and suppressed at either the RF amplifier 340 or the mixer 341 due to disturbance by an electric wave discharged by that radio apparatus and higher by 100 dB than the reception electric field level. Further, the level of side band noise occurring in the oscillation signal increases in proportion to the electric field level, and appears as base-band noise, deteriorating the S/N ratio of the reception signal wave. This embodiment assures good performance even in a portable radio apparatus having the above-described circuit configuration. In the structure shown in Fig. 8(b), since the antenna member 20 and the above-described layout are employed, the radiated electric field level at the input terminal of the RF amplifier 340 reduces to 80 dBµV. Thus, the reception signal wave is not suppressed and the side band noise level is reduced, thus increasing the S/N ratio. The same effect can be obtained in a structure other than the structure shown in Fig. 8(b) if the local oscillator 342 and the mixer 341 are formed as a shielded single unit so that the output signal of this unit can be a base-band signal and if the low-pass filter 343 and the detector 344 are provided on separate ICs. If a power supply circuit or a reception circuit electrically connected to the antenna member 20 is a balanced circuit, the RF amplifier 340 is connected to both the first and second conductive plates 21 and 23 over the slot groove 22. If the power supply circuit or the reception circuit is an unbalanced circuit, the RF amplifier 340 is connected to either the first conductive plate 21 or the second conductive plate 23. In the present embodiment which employs such an unbalanced power supply, the local oscillator 342, which is a noise generation source, is mounted on the front side of the circuit board 30 so that the noise from the local oscillator 342 can be extracted through the opening portion 210 of the first conductive plate 21, and the RF amplifier 340 is connected to the second conductive plate 23 through a connector 304 while a ground potential is applied to the first conductive plate 21 through a connector 305, as shown in Fig. 6, so as to reduce an influence of the noise from the local oscillator 342. Hereon, the connecting position (power supplying point) of the RF amplifier 340 to the second conductive plate 23 is shifted from the connecting position of the tuning capacitor element 301 which indicates the highest impedance in order to simplify impedance matching between the antenna member 20 and the RF amplifier 340. The connecting position between the RF amplifier 340 and the antenna member 20 and the position of the local oscillator 342 are shown in Fig. 7. In the radio apparatus 10 arranged in the manner described above, since a slot antenna is used as the antenna member 20, a magnetic field component is detected. Further, the radio apparatus 10 is suitable for use as a pager, because the antenna gain increases due to the image effect of a human body when the radio apparatus 10 is placed in a chest pocket. In the radio apparatus 10, the side portion 200 of the antenna member 20 slantingly bulges toward an outer periphery thereof so that it matches the shape of the side portion 130 of the casing 13 which curvedly bulges toward an outer periphery thereof. Thus, the antenna member 20 can be packed in the casing 13 along the inner surface of the side portion 130 of the casing 13, eliminating useless space within the casing 13. Consequently, a relatively small size of the radio apparatus 10 can be achieved while a high degree of freedom is assured in the design of the radio apparatus 10. Furthermore, since the antenna member 20 has the opening portions 210 and 230, the noise generated from the circuit board 30 escapes from the opening portions 210 and 230, that is, the noise does not readily supply the antenna member 20. It is possible to dispose the liquid crystal display panel 14 utilizing the opening portion 210. Further, in this embodiment, since the local oscillator 342 is disposed near a low impedance position on the antenna member 20, the noise generated from the local oscillator 342 does not readily supply the antenna member 20. Thus, in a direct conversion type radio apparatus 10, even if the local oscillator 342 is disposed near the antenna member 20, an influence of the noise generated by the local oscillator 342 can be reduced. As a result, the relatively small size can be achieved while a high sensitivity is maintained. In the case of a slot antenna structure disclosed in JP-A-60-239106, the above-described effect cannot be obtained if the structure excluding the antenna is the same as that of this invention. Also, it is difficult to obtain the design shown in Fig. 1. In this embodiment, a dielectric material (glass-epoxy resin) may be filled in the slot groove 22 of the antenna member 20. In such an antenna member 20, a reception signal is apparently shortened in proportion to the square root of a dielectric constant of the dielectric material filled in the slot groove 22. This is equivalent to the effective length of the antenna member 20 being extended. In such a state, even if the antenna member 20 is small and thin, signals having long wavelengths can be received. In contrast, if the wavelengths of the signals are the same, the antenna member 20 (the radio apparatus 10) can be made even smaller and thinner. Whereas in the preferred embodiment the local oscillator 342, which is the major noise generation source, is shown to be disposed at a position deviating from the central portion of the antenna member 20 toward the short-circuiting portion 24 in order to suppress an influence from the electronic parts mounted on the circuit board 30, it is desirable that other noise generation sources be also disposed at positions deviating toward the short-circuiting portion 24. Furthermore, in a case where the circuit board 30 is relatively small, the circuit board 30 itself may be disposed at a position deviating from the central portion of the antenna member 20 toward the short-circuiting portion 24. The reception sensitivity of the radio apparatus 10 will now be described with reference to Figs. 9 to 12. In Fig. 9, a bearing characteristic 101 indicates the reception sensitivity of a portable radio apparatus in free space (not influenced by a human body etc.) which employs a slot antenna shown in Fig. 7 in which the conductive plates 21 and 23 are formed vertically, and a bearing characteristic 100 indicates the reception sensitivity of a portable radio apparatus in free space which employs the antenna member 20 according to the present embodiment in which the conductive plates 21 and 23 form the side portion 200, a shown in Fig. 2(b). In both cases, the entire length of the antenna member 20 is 150 mm, and the reception frequency is 280 MHz. In the bearing characteristic 100, the best value is 14 dBµV/m, which is better by 3 dB to 4 dB than the best value of the bearing characteristic 101. If such an improvement is to be obtained with a conventional loop antenna, the opening area must be correspondingly large, thus precluding a small size of the radio apparatus. In contrast, in this embodiment, since a previously useless space S shown in Fig. 21 can be utilized effectively, excellent characteristics can be obtained while a reduction in the size can be achieved. In Fig. 10, a bearing characteristic 100 indicates the reception sensitivity of a portable radio apparatus according to the present invention in free space, in which the local oscillator 342 is disposed at a position deviating from the center of the antenna member 20 in the X' direction, as shown in Fig. 5, and a bearing characteristic 102 indicates the reception sensitivity of a portable radio apparatus in free space, in which the local oscillator 342 deviates in the opposite direction to the X' direction. The difference between the bearing characteristics 100 and 102 is about 10 dB. This indicates that the reception sensitivity is affected by the layout. In a slot antenna, the vicinity of the short-circuiting portion 24 has the lowest impedance. Thus, even if noise is radiated from the local oscillator 342 from that vicinity, the level of noise which supplies the antenna member 20 is small. In Fig. 11, bearing characteristics 103 and 100 indicate the reception sensitivity of a radio apparatus 10 in which the antenna member 20 is put on a human body and not put on a human body, respectively. How the radio apparatus 10 is put on the human body is illustrated in Fig. 1(d). When the portable radio apparatus is put on the front of a human body, the sensitivity is improved by about 4 dB. This indicates that the antenna member 20 according to this embodiment detected the magnetic field component, like a loop antenna. In Fig. 12, a bearing characteristic 103 indicates the reception sensitivity of the radio apparatus 10 according to the present embodiment which employs the antenna member 20, when the radio apparatus 10 is put on a human body, and a bearing characteristic 104 indicates the reception sensitivity of a conventional super-heterodyne type portable radio apparatus which employs a loop antenna, when the radio apparatus is put on a human body. In these portable radio apparatus, the reception sensitivity was almost the same, namely 10 dBµV/m. In the super-heterodyne type radio apparatus, the frequency of a local oscillation signal differs from the reception frequency by, for example, 455 kHz or 10 MHz. Thus, an influence of a local oscillation signal on its and other radio apparatus can be eliminated, and the bearing characteristics 104 can thus be readily obtained, even if the loop antenna is used. In the direct conversion type radio apparatus according to the present embodiment, since the antenna member 20 is optimally disposed, the above-described problem can be solved, a radio apparatus can be designed in the manner shown in Fig. 1, and characteristics equivalent to those of a conventional super-heterodyne type radio apparatus can be obtained. Second embodiment Whereas the first embodiment is structured such that the side portion 200 of the antenna member 20 slantingly bulges toward an outer periphery thereof so that it matches the shape of the side portion 130 of the casing 13 which curvedly bulges toward an outer periphery thereof, a second embodiment is constructed such that a side portion 400 of an antenna member 40 (slot antenna member) curvedly bulges toward an outer periphery thereof in the same manner as the casing 13 having the same shape as that of the first embodiment, as shown in Fig. 13. In that case, the side portion 400 of the antenna member 40 is closely attached to the inner surface of the side portion 130 of the casing 13, as shown in Figs. 14 and 15, and thus there is substantially no space between the antenna member 40 and the casing 13. In a portable radio apparatus 10a employing the antenna member 40, the circuit board 30 constituting the radio apparatus circuit, and the display panel 14 are disposed within the casing 13. The display panel 14 is disposed on the front side of the circuit board 30. As shown in Figs. 16(a) to 16(c), the antenna member 40 includes first and second conductive plates 41 and 43 which sandwich the circuit board 30 and constitute a slot groove 42 outside the periphery of the circuit board 30, and a short-circuiting portion 44 for electrically short-circuiting the first and second conductive plates 41 and 43. The side portion 400 of the antenna member 40 is constituted by side portions 415 and 435 of the first and second conductive plates 41 and 43 which curvedly bulge toward outer peripheral edges thereof. The first and second conductive plates 41 and 43 have opening portions 410 and 430, respectively, at positions corresponding to the two sides of the circuit board 30. The other structure of this embodiment is the same as that of the first embodiment, the description thereof being, therefore, omitted. The radio apparatus 10a arranged in the manner described above has the same effects as those of the first embodiment. That is, since the antenna member 20 is a slot antenna, the magnetic field component is detected. Further, when the radio apparatus 10a is put in a chest pocket, the antenna gain is increased due to the image effect of the human body. Further, in the radio apparatus 10a, since the side portion 400 of the antenna member 40 curvedly bulges toward an outer periphery thereof so that it matches the shape of the side portion 130 of the casing 13 which curvedly bulges toward an outer periphery thereof, there is no useless space on the inner side of the side portion 130 of the casing 13. Thus, a high degree of freedom can be obtained in designing of the radio apparatus 10, while a reduction in the size thereof can be achieved. Third embodiment Fig. 17 is a perspective view illustrating the external shape of a portable radio apparatus according to a third embodiment. Fig. 18(a) is a development view of an antenna member employed in the third embodiment. Fig. 18(b) is a perspective view of the antenna member. Fig. 18(c) is a bottom plan view of the antenna member. Fig. 18(d) is a side elevational view of the antenna member. In the radio apparatus 50 shown in Fig. 17, a casing 53 has a substantially spherical shape, and a liquid crystal display panel 54 with a protective lens is disposed at a position corresponding to a pole of that spherical shape. Operation buttons 551 and 552 are disposed at the side of the liquid crystal display panel 54. The arrow mark 56 is provided on the casing 53 to indicate that the radio apparatus 50 should be put in a pocket and carried around with this side up (a cord like cord 74 of Fig. 1 may be used instead or in addition). When the radio apparatus 50 is carried around with the side marked by the mark 56 up, the sensitivity of the radio apparatus 50 becomes maximum. As shown in Figs. 18(a) to 18(c), such a spherical radio apparatus 50 accommodates an antenna member (slot antenna member) 60 formed by superimposing substantially semi-spherical first and second conductive plates 61 and 63 one on top of the other in such a manner that a slot groove 62 is provided therebetween. The first conductive plate 61 is electrically short-circuited to the second conductive plate 63 through the short-circuiting portion 64. As schematically illustrated in Fig. 18(d), the tuning capacitor element 301 is connected to both the first and second conductive plates 61 and 63 at a position opposite to that where the short-circuiting portion 64 is provided. The first conductive plate 61 has an opening portion 610 at a portion thereof corresponding to one pole of the spherical form. Fig. 19 is a vertical cross-sectional view of the radio apparatus 50. The liquid crystal display panel 14 with the protective lens 140 is disposed at the opening portion 610 of the first conductive plate 61. An opening portion 630 is formed at a portion of the second conductive plate 63 corresponding to the other pole so that the user can replace the electric cell 33 with a new one through the opening portion 630 by opening a rear lid 525. In this embodiment, since the interior of the antenna member 60 is relatively wide, the circuit board 30 is disposed within the antenna member 60 as a circuit block. However, since the radio apparatus circuit constituted by the circuit board 30 is the direct conversion type, the local oscillator is disposed in the same manner as in the previous embodiments at a position deviating from the central portion of the antenna member 60 toward the short-circuiting portion 64 so that the noise generated by the local oscillator does not supply the antenna member 60. The circuit board 30 itself may be disposed at a position deviating from the center of the antenna member 60 toward the short-circuiting portion 64. The other structure of this embodiment is the same as that of the first embodiment. The radio apparatus 50 arranged in the manner described above has the same effects as those of the previous embodiments. That is, since the antenna member 60 is a slot antenna, the magnetic field component is detected. Further, when carried around in a chest pocket, the antenna gain is increased due to the image effect of the human body. Furthermore, in the radio apparatus 50, the spherical antenna member 60 is formed by semi-spherical first and second conductive plates 61 and 63 so that it matches the spherical shape of the casing 53, and such an antenna member 60 is accommodated in the casing 53. Accordingly, there is no useless space within the casing 53, and consequently, a high degree of freedom can be obtained in designing the radio apparatus 50, and a reduction in the size thereof can be achieved. Other embodiments Fig. 20 illustrates a portable radio apparatus 70 as a modification of the first and second embodiments. The radio apparatus 70 has shape in which a recessed portion 71 is formed at one side thereof while a bulging portion 72 is formed on the other side. This facilitates the user's holding of the radio apparatus 70. A side portion 73 bulges toward an outer periphery thereof, and a slot antenna member, such as that employed in the first or second embodiment in which the side portion thereof bulges toward an outer periphery thereof, is used, although not shown, so as to achieve reduction in the entire size of the radio apparatus 70. Such a radio apparatus 70 has advantages in that it has a good design and in that it allows the user to feel with hands the direction in which the radio apparatus 70 is directed in a pocket. Further, when the radio apparatus 70 is hung using a curled cord 74, as shown in Fig. 1(d), the antenna gain can be increased. Further, the radio apparatus 70 enables the user to carry it handily as if the user is wearing an accessory. As will be understood from the foregoing description, in the portable radio apparatus provided in one aspect of the present invention, the casing has the side portion which bulges toward an outer periphery thereof, and the first and second conductive plates, constituting the slot antenna member, have the side portions which bulge toward outer peripheral edges thereof and form the slot groove therein. In another aspect of the present invention, the casing has a substantially spherical form, and the first and second conductive plates, constituting the slot antenna member accommodated in the casing, have a substantially semi-spherical external shape. Thus, in the present invention, since the shape of the slot antenna matches the shape of the casing, there is no useless space in the casing, thus reducing the size of the portable radio apparatus. The first and second conductive plates have an opening portion at an area which faces the circuit board. Thus, the noise generated from the electronic parts mounted on the circuit board can be released from the opening portions, thereby increasing the sensitivity of the radio apparatus. Since the circuit board, which is the noise generating source, or the local oscillator mounted on the circuit board is disposed at a position deviating from the central portion of the antenna member toward the short-circuiting portion, the noise generation source can be separated from the high impedance portion of the antenna member. In this structure, since a noise signal does not readily supply the antenna member, even if the direct conversion method is employed, transmission or reception of the portable radio apparatus and other radio apparatuses is not interfered. Particularly, in a structure in which an orthogonal transform mixer circuit and the base-band signal detecting circuit are in the same IC and in which the local oscillator and the mixer circuit are connected to each other through a printed circuit pattern, although a radiation level of the oscillated signal is high, an influence of that radiation can be eliminated. This effect can be increased when the operation clock of the booster circuit, which can be the cause of the side band noise which occurs in the oscillated signal, is set in the stop-band (no-pass band) of the low-pass filter of the direct conversion detecting circuit and when a crystal oscillator is used as the clock source. Further, the high-frequency amplifying circuit of the radio apparatus circuit is preferably electrically connected to the conductive plate located on the side of the circuit board which is opposite to the side thereof where the local oscillator circuit of the radio apparatus circuit is provided, to reduce an influence of the noise from the local oscillator circuit. A dielectric material may be filled in the slot groove, whereby the reception wavelength is apparently shortened, enabling a small antenna to receive signals of long wavelengths.

Claims: A portable radio apparatus comprising: a circuit board (30) constituting a radio apparatus circuit, and a slot antenna member (20; 40; 60) including first and second conductive plates (21, 23; 41, 43; 61, 63) arranged so as to accommodate said circuit board in between and to define a slot groove (22; 42; 62) at an outer peripheral portion of said circuit board, said conductive plates being short-circuited over said slot groove by a short-circuiting portion (24; 44; 64), and a casing (13; 53) accommodating said circuit board and said slot antenna member, characterized in that at least a side portion (130) of said casing has a rounded shape and said first and second conductive plates are formed to substantially match the rounded shape of the casing. The apparatus according to claim 1, wherein said casing (13) has a side portion (130) which bulges toward an outer periphery thereof and said first and second conductive plates (21, 23; 41, 43) have side portions (200; 400) which bulge in such a manner that a distance between said conductive plates decreases toward outer peripheral edges thereof, said first and second conductive plates being disposed in such a manner that they sandwich said circuit board (30). The apparatus according to claim 2, wherein said side portions (200) of said first and second conductive plates (21, 23) bulge slantingly toward the outer peripheral edges thereof. The apparatus according to claim 2, wherein said side portions (400) of said first and second conductive plates (41, 43) bulge curvedly toward the outer peripheral edges thereof. The apparatus according to claim 1, wherein said casing (53) has a substantially spherical external shape and said first and second conductive plates (61, 63) each have a substantially semi-spherical external shape, said first and second conductive plates being disposed such that they accommodate said circuit board (30) therein. The apparatus according any one of the preceding claims, further comprising a tuning capacitor element (301) electrically connected to said first and second conductive plates (21, 23; 41, 43; 61, 63) at a position opposite to a position where said short-circuiting portion (24; 44; 64) is formed. The apparatus according to any one of the preceding claims, wherein said first and second conductive plates (21, 23; 41, 43; 61, 63) each have an opening portion (219, 230; 610, 630) at an area facing said circuit board (30). The apparatus according to any one of the preceding claims, wherein said circuit board (30) is disposed at a position deviating from a central portion of said slot antenna (20; 40; 60) toward said short-circuiting portion (24; 44; 64). The apparatus according to any one of the preceding claims, wherein said radio apparatus circuit is a direct conversion type circuit, a local oscillator circuit (342) thereof being located at a position deviating from a central portion of said antenna member (20; 40; 60) toward said short-circuiting portion (24; 44; 64). The apparatus according to any one of the preceding claims, wherein said radio apparatus circuit is a direct conversion type circuit, a high-frequency amplifying circuit (340) thereof being electrically connected to that one of said conductive plates (21, 23; 41, 43; 61, 63) located on a side of said circuit board (30) which is opposite to a side thereof where a local oscillator circuit (342) of said radio apparatus circuit is provided. The apparatus according to claim 9 or 10, wherein in said direct conversion type radio apparatus circuit, an orthogonal transform mixer circuit and a base-band signal detecting circuit are disposed in the same integrated circuit. The apparatus according to claim 9, 10 or 11, wherein said direct conversion type radio apparatus circuit is driven by via a booster circuit (352) for boosting an electric cell voltage, the operation frequency of said booster circuit being set in a stop-band of a base-band signal filtering circuit (343) included in said radio apparatus circuit. The apparatus according to claim 12, wherein said operation frequency is set by a crystal oscillator (350). The apparatus according to any one of the preceding claims, wherein said slot groove (22; 42; 62) is filled with a dielectric material. The apparatus according to any one of the preceding claims in combination with claim 6, further having indicating means (16, 74) provided on the outside of said casing (13; 53) at a position corresponding to the position of either the connecting position between said first and second conductive plates (21, 23; 41, 43; 61, 63) by said tuning capacitor element (301) or said short-circuiting portion (24; 44; 64). The apparatus according to claim 15, wherein said indicating means comprises a curled cord (74) fixed at said position to the casing.

Inventors: HAMA NORIO, HAMA, NORIO, Hama, Norio, c/o Seiko Epson Corporation
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1995
Main classification: H01Q13
IPC codes: H01Q1, H04B1, H01Q13