Antenna apparatus and communication apparatus using the antenna apparatus

Abstract: An antenna apparatus (20) has improved gain, and its characteristics are barely affected by changes in the external environment in which it used, such as when it is placed close to a ground conductor. A surface-mount antenna (5) and a monopole antenna (23) are fed by a single feeding point, and the direction of an open end of the surface-mount antenna (5), taking a ground end of a radiation electrode (11) as a reference, runs opposite to the direction of the open end (23b) of the monopole antenna (23), taking the feeding terminal (23a) as a reference.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna apparatus and a communication apparatus using the antenna apparatus, and more particularly relates to an antenna apparatus used in a mobile communication apparatus, and a communication apparatus using the antenna apparatus. 2. Description of the Related Art Recently, amid advances in high-performance mobile telephones such as PHS, there are demands to provide a mobile communication apparatus wherein an antenna mounted thereon has even higher performance characteristics, such as high gain and a capability to be miniturized. FIG. 6 shows a conventional antenna apparatus mounted on a mobile communication apparatus. In FIG. 6, an antenna apparatus 1 comprises a ground electrode 3 provided on one major surface 2a of a mount substrate 2, the corner of the major surface 2a having a removed portion 3a, a supply wire 4 provided in the removed portion 3a, and a surface-mount antenna 5 mounted thereabove. Then, the supply wire 4 is connected to a supply terminal (not shown in the diagram) of the surface-mount antenna 5, and also to a signal source 6 provided on the mount substrate 2. FIG. 7 shows the surface-mount antenna 5 in more detail. The surface-mount antenna 5 has the basic constitution of that disclosed in Japan Unexamined Patent Publication No. 10-13139 corresponding to EP 0 814 535 A2. In FIG. 7, the surface-mount antenna 5 comprises several electrodes provided on the surface of a rectangular substrate 10, which comprises an insulating dielectric such as ceramic or resin. Firstly, a strip-shaped radiation electrode 11 is provided extending from the other major surface 10b of the substrate 10, across one end face 10d, and returning once again to the other major surface 10b. One end of the radiation electrode 11 is an open end 11a, and the other end connects to a first ground terminal 12, which extends from an end face 10c of the substrate 10 to a first major surface 10a thereof. Furthermore, a feeding electrode 13 is isolated from the radiation electrode 11 and is provided on a second major surface 10b of the substrate 10. One end of the feeding electrode 13 connects to a feeder terminal 14, which extends from the end face 10c of the substrate 10 to the first major surface 10a thereof. Similarly, a ground electrode 15 is provided on the other major surface 10b of the substrate 10 near the open end 11a of the radiation electrode 11. One end of the ground electrode 15 is connected to a second ground terminal 16, which extends from the end face 10c of the substrate 10 to the first major surface 10a. Furthermore, terminals for securing 17 and 18 are provided on the first major surface 10a of the substrate 10, and connect to the radiation electrode 11. When the surface-mount antenna 5 is mounted on a mount substrate (not shown in the diagram), the five electrodes comprising the first and second ground terminals 12 and 16, the feeder terminal 14, and the terminal for securing 17 and 18, are connected by soldering to ground electrodes, supply lines, and electrodes for securing on the mount substrate side. Therefore, the five electrodes are represented as terminals in order to distinguish them from these other electrodes. In a surface-mount antenna 5 having such a constitution, when a high-frequency signal is input to the feeder terminal 14, the high-frequency signal is transmitted to the radiation electrode 11 via a capacitance created between the open end 11a of the radiation electrode 11 and the feeding electrode 13. The radiation electrode 11 is made to resonate by the inductance component of the radiation electrode 11 itself, and by the capacitance formed between the open end 11a of the radiation electrode 11 and the feeding electrode 13. The surface-mount antenna 5 functions as an antenna by radiating a portion of the resonance energy into space as electric waves. At this point, since one end of the radiation electrode 11 is an open end 11a, and the other end is a grounded end, the resonance is approximately one-quarter wavelength. A current 19 flowing to the radiation electrode 11 (i.e. the current flowing to the surface-mount antenna 5) flows from the grounded end of the radiation electrode 11 (more specifically, the first ground terminal 12) toward the open end 11a. As a result, magnetic field components of the electric waves radiated from the surface-mount antenna 5, and the electric waves received by the surface-mount antenna 5, vibrate mainly in the direction of the z axis of the coordinates shown in FIG. 7. The electrodes and terminals of the surface-mount antenna 5 are provided separately from each other, but it is not absolutely necessary for them to be separated by some kind of clear boundary. The electrodes and the terminals may acceptably be provided together. In the antenna apparatus 1 shown in FIG. 6, when the current 19 flows to the surface-mount antenna 5, an image current 7 which is 180 degrees out of phase with the current 19 flows mainly to the ground electrode 3. However, when the antenna apparatus 1 is used, the mount substrate 2 is covered by a case of plastic, metal, or the like. The case is often left in such places as on a shelf, or in a bag. When placed on a shelf or in a bag, the case often comes into close contact with conductive objects comprising metal and the like, and such objects function more or less like ground conductors. This leads to a problem that, depending on the external environment in which this type of antenna apparatus 1 is used, the ground conductors in close proximity thereto alter the direction and position of the flow of the image current 7 of the current 19 flowing to the surface-mount antenna 5, affecting the characteristics of the antenna apparatus 1 such as its gain and directivity. EP 0 523 867 A2 discloses an antenna assembly comprising an elongate radiating element moveable between a retracted position and an extended position and a substantially planar radiating element transversely extending to the elongate element. The elongate element extends through an aperture in the planar element. A pair of concentric conductors provide coaxial feed to the radiating elements and the elongate element is slidably mounted within the inner conductor in the retracted position, the elongate element forming part of the coaxial feed to the planar element and is, itself, rendered inoperative as a radiator. SUMMARY OF THE INVENTION To overcome the above described problems, preferred embodiments of the present invention provide an antenna apparatus having higher gain and characteristics which are largely unaffected by the external environment in which the antenna apparatus is used, and a communication apparatus using the antenna apparatus. One preferred embodiment of the present invention provides an antenna apparatus comprising a strip-shaped radiation electrode having one open end and one grounded end, a surface-mount antenna comprising a feeding electrode isolated from the radiation electrode, and a monopole antenna disposed in the vicinity of the surface-mount antenna. The radiation electrode, the surface-mount antenna, and the monopole antenna are provided on the surface of a base comprising an insulator. In addition, the surface-mount antenna and the monopole antenna are fed from a single feeding point, and the direction of the open end of the surface-mount antenna, taking a ground end of the radiation electrode as a reference, runs opposite to the direction of the open end of the monopole antenna, taking the feeding point as a reference. Preferably, the electrical length of the monopole antenna is between one-eighth and one-quarter of the wavelength of the frequency used by the antenna apparatus. Furthermore, a communication apparatus of the present invention uses any of the antenna apparatuss described above. According to such a constitution, the gain of the antenna apparatus of the present invention can be improved. Further, changes in the characteristics of the antenna apparatus, which are caused by the place where it is positioned, can be reduced. Furthermore, the communication apparatus of the present invention can achieve better characteristics. BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are diagrams showing an embodiment of the antenna apparatus of the present invention; FIGS. 2A to 2F are diagrams showing reflection loss and directivity of the antenna apparatus of the present invention; FIG. 3 is a diagram showing the relationship between electrical length and maximum gain of a monopole antenna of the antenna apparatus of the present invention; FIGS. 4A and 4B are diagrams showing another embodiment of the antenna apparatus of the present invention; FIG. 5 is a perspective view of an embodiment of a communication apparatus of the present invention; FIG. 6 is a diagram showing a conventional antenna apparatus; and FIG. 7 is a perspective view of a surface-mount antenna used in the antenna apparatus of FIG. 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A and 1B show an embodiment of the antenna apparatus of the present invention. Here, 1A is a view from a first major surface 2a of a mount substrate 2, and FIG. 1B is a view from a second major surface 2b of the mount substrate 2. In FIGS. 1A and 1B, portions identical to those in FIG. 6 and FIG. 7 are represented by the same reference numerals, and further explanation thereof is omitted. In the antenna apparatus 20 shown in FIGS. 1A and 1B, a ground electrode 21 is provided on the second major surface 2b of the mount substrate 2, a feeder wire 22 is provided in a removed portion 21a of the ground electrode 21 at the corner of the second major surface 2b of the mount substrate 2, and a monopole antenna 23 is mounted thereon. A feeder end 23a of the monopole antenna 23 connects to the feeder wire 22. A feeder wire 4 is provided on the first major surface 2a of the mount substrate 2, and is connected by a through hole 24 to the feeder wire 22 provided on the second major surface 2b of the mount substrate 2. Here, since the feeder wire 4 is connected to a signal source 6, the surface-mount antenna 5 and the monopole antenna 23 are both supplied by the same feeder point. Furthermore, the surface-mount antenna 5 and the monopole antenna 23 are provided so that the direction of the open end 11a of the radiation electrode 11, taking as a reference the grounded end of the radiation electrode 11 of the surface-mount antenna 5, is opposite to the direction of the open end 23b of the monopole antenna 23, taking as a reference the feeder end 23a. In the antenna apparatus 20 of such a constitution, when a current 19 flows to the surface-mount antenna 5, a current 25 also flows to the monopole antenna 23 which is fed simultaneously. Then, since the surface-mount antenna 5 is fed via a capacitance formed between the feeding electrode 13 and the open end 11a of the radiation electrode 11, and the monopole antenna 23 is fed directly at its feeder end 23a, the currents flowing to the surface-mount antenna 5 and the monopole antenna 23 are in reverse phase to each other. Taking the surface-mount antenna 5 as a reference, the image current of the current 19 flowing to the surface-mount antenna 5 has the same direction and phase as the current 25 flowing to the monopole antenna 23. Consequently, most of the image current of the current 25 flowing to the surface-mount antenna 5 flows to the monopole antenna 23, and not to the ground electrode 3. Conversely, taking the monopole antenna 23 as a reference, when operating in devices, the image current of the monopole antenna 23, which ought to flow to the ground electrode 21, has the same direction and phase as the current 19 flowing to the surface-mount antenna 5. As a consequence, most of the image current of the current 25 flowing to the monopole antenna 23 flows to the surface-mount antenna 5, and not to the ground electrode 21. In this way, most of the image current of the current 19 flowing to the surface-mount antenna 5 and the image current of the current 25 flowing to the monopole antenna 23 do not flow to the ground electrode 21 or the ground electrode 3 of the mount substrate 2. As a result, even when the antenna apparatus 20 is covered with a case of plastic or the like and used in a variety of external environments, there is no change in the position and direction of the flow of the image current of the current fed to the surface-mount antenna 5 and the monopole antenna 23, whereby the problem of changes in the characteristics of the antenna apparatus 20 is almost completely eliminated. FIGS. 2A to 2F show directivity of gain and reflection loss of the antenna apparatus 20 of the present invention, in comparison with an antenna apparatus wherein only the monopole antenna is mounted, and an antenna apparatus wherein only the surface-mount antenna is mounted. Here, FIG. 2A shows reflection loss of the antenna apparatus when only the monopole antenna is mounted, FIG. 2B shows directivity of gain in the same antenna apparatus, FIG. 2C shows reflection loss of the antenna apparatus when only the surface-mount antenna is mounted, FIG. 2D shows directivity of gain in the same antenna apparatus, FIG. 2E shows reflection loss of the antenna apparatus 20 of the present invention, and FIG. 2F shows directivity of gain in the same. In FIGS. 2A, 2C, and 2E, symbols BW1, BW2, and BW3 represent bandwidths (frequency bandwidths in which reflection loss is below -9.5 dB) of the antenna apparatus. As can be understood from FIGS. 2A to 2F, the bandwidth of the antenna apparatus of the present invention does not have the overall balance achieved when only the monopole antenna is mounted, but a wider bandwidth is achieved than when only the surface-mount antenna is mounted, especially on the high frequency side. Furthermore, as regards directivity, the null points which appear near 0 degrees and 180 degrees when only the monopole antenna is mounted can be compensated by the directivity of the surface-mount antenna, and thereby eliminated. Moreover, although the average gain of the antenna apparatus of the present invention is -3.19 dBd, this being between the average values when only the monopole antenna is mounted (-3.00 dBd) and when only the surface-mount antenna is mounted (-3.65 dBd), the maximum value of gain in the antenna apparatus of the present invention is 3.01 dBd, which exceeds the maximum values of the other cases (1.21 dBd and 2.38 dBd respectively). In this way, by combining the surface-mount antenna and the monopole antenna, supplying them from a single feeding point, and arranging them so that the direction from the grounded end of the radiation electrode of the surface-mount antenna to the open end thereof is opposite to the direction from the feeding point of the monopole antenna to the open end, it is possible to improve the bandwidth and the gain of both antennas. FIG. 3 shows changes in the maximum gain when the electrical length of the monopole antenna 23 of the antenna apparatus 20 is changed. Here, a reference line r represents the maximum gain of the antenna apparatus 20 when only the surface-mount antenna 5 is mounted. According to FIG. 3, when the electrical length of the monopole antenna 23 is one-eighth of the wavelength to one-quarter of the wavelength, the maximum gain exceeds the reference line r. As a consequence, in the antenna apparatus 20 of the present invention, by setting the electrical length of the monopole antenna 23 to between one-eighth and one-quarter of the wavelength, higher gain can be achieved than when only the surface-mount antenna 5 is mounted. FIGS. 4A and 4B show another embodiment of the antenna apparatus of the present invention. In FIGS. 4A and 4B, since the view from the first major surface 2a of the mount substrate 2 is the same as FIG. 1, only a view from the second major surface 2b of the mount substrate 2 is shown. Furthermore, portions identical to those in FIG. 1 are represented by the same reference numerals, and further explanation thereof is omitted. In FIGS. 4A and 4B, a monopole antenna 31 of the fs antenna apparatus 30 is able to rotate 180 degrees around an axis of rotation 32. Here, FIG. 4A shows the monopole antenna 31 protruding from the mount substrate 2 (i.e. the case), and FIG. 4B shows the monopole antenna 31 stored in the mount substrate 2 (i.e. the case). When the monopole antenna 31 is protruding, the feeder end 31a of the monopole antenna 31 connects to the feeder wire 22. According to this constitution, the monopole antenna 31 of the antenna apparatus 30 does not function when it is stored (on standby in the case of a mobile telephone), and only the surface-mount antenna 5 functions as an antenna apparatus. Then, when the monopole antenna 31 is pulled out to the protruding position (when making a call in the case of a mobile telephone), the antenna apparatus 30 functions as an antenna apparatus combining the monopole antenna 31 and the surface-mount antenna 5. When the surface-mount antenna 5 and the monopole antenna 31 are combined in this way to form the antenna apparatus 30, since the monopole antenna 31 is stored when for instance the mobile telephone is on standby, the monopole antenna 31 will suffer no damage even if the antenna apparatus 30 is dropped or mishandled. The monopole antenna can be stored by methods other than rotation, such as extension, folding, etc. In the embodiments described above, the base of the surface-mount antenna 5 comprises an insulating dielectric such as ceramic or resin, but a magnetic body having similar insulating characteristics may be used instead. Furthermore, the monopole antenna is not restricted to the rectangular antenna shown in FIGS. 1A and 1B, and FIGS. 4A and 4B. A monopole antenna of another shape may be used, such as a helical antenna comprising a radiation conductor twisted into a spiral, or an antenna combining a rectangular antenna with a helical antenna. FIG. 5 shows an embodiment of a communication apparatus which uses the antenna apparatus 20 of the present invention. In FIG. 5, the communication apparatus 40 comprises the antenna apparatus 20 provided in a case 41. A feeder wire 4 is provided on the mount substrate 2 of the antenna apparatus 20, and is connected to a transmitter 43 and a receiver 44 via a switch 42, similarly provided on the mount substrate 2. By using the antenna apparatus 20 to form the communication apparatus 40 in this way, the bandwidth of the communication apparatus 40 can be widened, and its gain can be increased. Furthermore, since most of the image current of current flowing to the monopole antenna 23 and to the surface-mount antenna 5 mounted on the antenna apparatus 20 does not flow to the case 41 of the communication apparatus 40 or to the ground electrode 3 of the mount substrate 2, the antenna characteristics are not affected by changes in the external environment which the communication apparatus 40 is used in. According to the antenna apparatus of the present invention, a strip-shaped radiation electrode having an open end and a grounded end, a surface-mount antenna comprising a feeding electrode isolated from said radiation electrode, and a monopole antenna, are fed from a single feeding point, and are provided on a surface of a base comprising an insulator so that the direction of the open end of the surface-mount antenna, taking the ground end of the radiation electrode as a reference, runs opposite to the direction of the open end of the monopole antenna, taking the feeding point as a reference. As a result, the image current of the current flowing to the surface-mount antenna can flow to the monopole antenna, and the image current of the current flowing to the monopole antenna can flow to the surface-mount antenna, so that most of the image current flows to the ground electrode. Consequently, it is possible to prevent the characteristics of the antenna apparatus from being affected by changes in the external environment in which it is used. Furthermore, the bandwidth and gain of the antenna apparatus can both be improved. Furthermore, by setting the electrical length of the monopole antenna to between one-eighth and one-quarter of the wavelength, the gain of the antenna apparatus can be increased to more than when only the surface-mount antenna is mounted. Moreover, when the antenna apparatus of the present invention is used in a communication apparatus, the bandwidth of the communication apparatus is wider, and gain is improved. Furthermore, it is possible to prevent the characteristics of the communication apparatus from being affected by changes in the external environment in which it is used.

Claims: An antenna apparatus comprising: a strip-shaped radiation electrode (11) having one open end and (11a) one grounded end; a surface-mount antenna (5) comprising a feeding electrode isolated from said radiation electrode (11), characterized in that : a monopole antenna (23) is disposed in the vicinity of said surface-mount antenna (5); the radiation electrode (11), the surface-mount antenna (5), and the monopole antenna (23) being provided on a surface (2a) of a base (2) comprising an insulator; and said surface-mount antenna (5) and said monopole antenna (23) being fed from a single feeding point, and the direction of said open end (11a) of said surface-mount antenna (5), taking a ground end of the radiation electrode (11) as a reference, being opposite to the direction of the open end (23b) of the monopole antenna (23), taking the feeding point as a reference. The antenna apparatus according to Claim 1, wherein the electrical length of said monopole antenna (23) is between one-eighth and one-quarter of the wavelength of the frequency used. A communication apparatus including the antenna apparatus according to Claim 1 or 2.

Inventors: KAWAHATA KAZUNARI, KURITA JUNICHI, NAGUMO SHOJI, OKADA KEN, YUASA ATSUYUKI, KAWAHATA, KAZUNARI, KURITA,JUNICHI, NAGUMO,SHOJI, OKADA, KEN, YUASA, ATSUYUKI, Kawahata, Kazunari, c/o (A170) Int. Prop. Depart., Kurita,Junichi c/o (A170) Int. Prop. Department, Nagumo,Shoji c/o (A170) Int. Prop. Department, Okada, Ken, c/o (A170) Int. Prop. Department, Yuasa, Atsuyuki, c/o (A170) Int. Prop. Department
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1999
Main classification: H01Q1
IPC codes: H01Q21, H01Q1