Surface mounting antenna and communication apparatus using the same antenna

Abstract: A surface mounting antenna in which non-contact excitation can be achieved via a capacitor, and easy impedance matching can be provided even when the antenna is downsized. A communication apparatus loaded with the above antenna is also disclosed. A radiation electrode (2; 2a; 2b; 2c) is disposed on the obverse surface of a substrate (1). A ground electrode (3) is formed on substantially the overall area of the reverse surface of the substrate (1). The radiation electrode (2; 2a; 2b; 2c) is connected at one end to the ground electrode (3) via a first end surface of the substrate (1), and extends at the other end to the portion adjacent to a second end surface opposedly facing the first end surface so as to form a free end. An excitation electrode (4; 4a) is disposed to face the forward end of the free end of the radiation electrode across a gap g and to extend from the obverse surface of the substrate (1) to the reverse surface via the second end surface of the substrate (1).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface mounting antenna for use in mobile communication apparatus, such as cellular mobile telephones and radio Local Area Networks (LAN). The invention also relates to a communication apparatus using the above type of antenna. 2. Description of the Related Art A typical surface mounting antenna of the prior art, in particular, a 1/4-type surface-mounting patch antenna, is shown in Fig. 7. A radiation electrode 10 is disposed at the central portion of the obverse surface of a dielectric substrate 8, and a ground electrode 9 is provided on the overall reverse surface of the substrate 8. The radiation electrode 10 is connected to the ground electrode 9 via a plurality of short-circuit pins 11 located at one edge of the radiation electrode 10. A feeding pin 12 is further disposed adjacent to the short-circuit pins 11. However, the 1/4-type surface-mounting patch antenna of the above known type encounters the following problem. In a downsized antenna of this type, the feeding pin 12 is placed in proximity to the short-circuit pins 11, thus making it difficult to provide impedance matching due to an inductance of the feeding pin 12, and also causing a variation in the resonant frequency. Further, the sensitivity of a communication apparatus loaded with the above known type of surface-mounting patch antenna is decreased because of a deviation of the resonant frequency. EP 0 332 139 A2 discloses a wide band antenna for mobile communications which has a ground plate with a flat surface. On the ground plate a L-shaped radiator plate is attached which has one leg arranged parallel to the ground plate and another leg positioned perpendicular to the ground plate. The radiator plate has a narrow gap between the lower end of the vertical leg and the upper surface of the ground plate. A sub-radiator element formed by a L-shaped plate is mounted on the ground plate at a position in close proximity to the radiator plate at free ends of the radiator plate and of the sub-radiator element having a given distance. EP 0 621 653 A2 relates to a surface-mountable antenna unit which includes a dielectric substrate having a rectangular plane shape which is provided on a side surface or a bottom surface with a ground electrode. A radiator is provided with a radiating part having a substantially rectangular plane shape and is fixed to the dielectric substrate such that the radiator is opposed to a top surface of the dielectric substrate. A feed part is provided on a side surface of the substrate. EP 0 637 094 A1 relates to an antenna for mobile communication which comprises a first metal plate having a slit, a second plate opposed to the first metal plate, and electrically connected to the first metal plate. Two metal foils connected to the second metal plate, and a cable for supplying feed signals to the first metal plate and the second metal plate are provided. The cable includes a first conductor connected to the first metal plate by a capacitor and a second conductor connected to the second metal plate. EP 0 383 292 A2 relates to an electronic circuit device which comprises a printed circuit board having a first surface on which a circuit pattern is formed on which components are mounted and a second surface on which a ground plane is formed, a coupling stop being formed in part of the circular pattern, and a plane antenna having an antenna element formed on one surface of the dielectric substrate. The printed circuit board and the plane antenna are unified such that the second surface of the printed circuit board and the other surface of the dielectric substrate are opposed to each other and the coupling stop is placed in position to be coupled to the antenna element. It is an object of the present invention to provide a surface mounting antenna in which non-contact excitation can be performed via a capacitor, an ease of impedance matching can be provided even when the antenna is down sized. It is also an object to provide a communication apparatus using the above type of antenna. These objects are achieved by a surface mounting antenna according to claim 1, and by a communication apparatus according to claim 8. According to the surface mounting antenna disclosed in any of the above-described aspects of the present invention, the radiation electrode may be partially or completely bent in the form of a U-shape or a meandering shape. The present invention also provides a communication apparatus loaded with the surface mounting antenna disclosed in any one of the aspects of the present invention. In this manner, according to the present invention, a gap is provided between the free end of the radiation electrode and the forward end of the excitation electrode, so that the two elements can be electromagnetically coupled to each other via a capacitor formed in the gap. Thus, non-contact excitation can be achieved, and also, easy impedance matching can be provided. This gap can be formed on the main surface or on the side surface of the substrate so as to increase the flexibility of the design of the antenna, thereby enhancing easy control and adjustments of the gap. Further, the radiation electrode may be lengthened by forming it in a U-shape or a meandering shape, thereby making it possible to further downsize the antenna. A communication apparatus loaded with the above type of surface mounting antenna is advantageous because only the shortest minimal wiring is required to connect the antenna to a high-frequency circuit mounted on the circuit board of the apparatus that processes signals input from and output to the antenna, and also because variations in the frequency caused when the antenna is mounted on the apparatus can be reduced. Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a surface mounting antenna according to a first embodiment of the present invention; Fig. 2 is a perspective view of a surface mounting antenna according to a second embodiment of the present invention; Fig. 3 is a perspective view of a surface mounting antenna according to a third embodiment of the present invention; Fig. 4 is a perspective view of a surface mounting antenna according to a fourth embodiment of the present invention; Fig. 5 is a diagram of an electrical equivalent circuit of the respective embodiments shown in Figs. 1 through 4; Fig. 6 is a perspective view of a communication apparatus of the present invention; and Fig. 7 is a perspective view of a conventional surface mounting antenna. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Embodiments of the present invention will now be described with reference to the drawings. Referring to Fig. 1 illustrating a first embodiment of the present invention, a rectangular substrate generally indicated by 1 formed of a dielectric material, such as ceramics, resin or the like, or a magnetic material, has a stripline radiation electrode 2 having an approximately 1/4-length on the surface of the substrate 1. This radiation electrode 2 extends at one end to the portion adjacent to a first edge 1b of the substrate 1 so as to form a free end and is connected at the other end to a ground electrode 3 formed on the reverse surface of the substrate 1 via an side surface 1a opposedly facing the first edge of the substrate 1. An excitation electrode 4 is disposed adjacent to the first edge of the substrate 1, facing the radiation electrode 2 across a gap. This electrode 4 extends from side surface 1b opposedly facing the above-described side surface 1a to the reverse surface of the substrate 1 and is electrically insulated from the ground electrode 3 by virtue of the material of the substrate 1. The excitation electrode 4 and the radiation electrode 2 are electromagnetically coupled to each other due to a capacitor generated in the gap g. The electrical equivalent circuit at the resonant frequency of the substrate 1 constructed as described above can be indicated, such as shown in Fig. 5. More specifically, a high-frequency signal f, a capacitor C formed in the gap g, and an inductor L and a radiation resistor R generated due to the radiation electrode 2 are connected in series to each other via ground. The high-frequency signal f applied to the excitation electrode 4 is electromagnetically coupled to the radiation electrode 2 because of the capacitor C generated in the gap g, thereby radiating as radio waves. An explanation will now be given of a second embodiment of the present invention with reference to Fig. 2. The second embodiment differs from the first embodiment in that the free end of the radiation electrode 2a having an approximately 1/4-length is extended to the side surface 1b opposedly facing the end surface 1a, and a gap g is thus formed between the free end of the electrode 2a and the excitation electrode 4a on the side surface 1b. With this arrangement, frequency adjustments can be easily made by varying the size of the gap g. The other constructions are similar to those of the first embodiment. The same and corresponding elements as those explained in the first embodiment are designated by like reference numerals and an explanation thereof will thus be omitted. The electrical equivalent circuit of this antenna can also be indicated as shown in Fig. 5, as in the previous embodiment. A third embodiment of the present invention will now be described with reference to Fig. 3. The third embodiment is different from the first embodiment in that the radiation electrode 2b having an approximately 1/4-length is lengthened by bending it in the form of a meandering shape. The resulting antenna can thus cope with lower frequencies with the same chip size as the first embodiment. This makes it possible to downsize the chip size at the same frequency as the first embodiment employed. The other constructions are similar to those of the first embodiment. The same and corresponding elements as those described in the first embodiment are indicated by like reference numerals, and an explanation thereof will thus be omitted. The electrical equivalent circuit of this antenna can also be designated as illustrated in Fig. 5, as in the first embodiment. An explanation will now be given of a fourth embodiment of the present invention while referring to Fig. 4. This embodiment differs from the first embodiment in that the radiation electrode 2c having an approximately 1/4-length is formed in a U shape, and the connecting portion between the radiation electrode 2c and the ground electrode 3 is placed on the same side surface 1b on which the excitation electrode 4 is disposed. In this embodiment, as well as in the third embodiment, the radiation electrode 2c is lengthened in the U shape, thereby making it possible to downsize the chip. The other constructions are similar to those of the first embodiment. The same and corresponding elements as those described in the first embodiment are designated by like reference numerals, and an explanation thereof will thus be omitted. The electrical equivalent circuit of this antenna can also be indicated as shown in Fig. 5, as in the first embodiment. In the foregoing embodiments, the connecting portion between the radiation electrode and the ground electrode is formed on the same end surface on which the excitation electrode is disposed or on the opposedly-facing side surface. Alternatively, the connecting portion and the excitation electrode may be formed on end surfaces adjacent to each other. Fig. 6 illustrates the surface mounting antenna described in the above-described embodiments being mounted on a communication apparatus. A surface mounting antenna 5 is mounted on a printed circuit board (or its sub board) 7 of a communication apparatus 6 by soldering the ground electrode and the excitation electrode thereto. As will be clearly understood from the foregoing description, the present invention offers the following advantages. A gap is provided between a free end of the radiation electrode and the excitation electrode, and the two elements are electromagnetically coupled to each other via a capacitor formed in this gap, thereby achieving non-contact excitation. Even when the chip antenna is downsized, impedance matching can be easily provided due to the absence of a feeding pin. The above-described gap can be formed on the main surface or on the side surface or at the edge of the substrate so as to increase the flexibility of the design of the antenna, thereby enhancing easy control and adjustments of the gap. Further, the radiation electrode may be lengthened by forming it in the U or meandering shape, thereby enabling the antenna itself to be downsized. A communication apparatus loaded with the above type of surface mounting antenna is advantageous because only the shortest minimal wiring is required to connect the antenna to a high-frequency circuit mounted on the circuit board of the apparatus that processes signals input from and output to the antenna, and also because variations in the frequency caused when the antenna is mounted on the apparatus can be reduced.

Claims: A surface mounting antenna comprising: a substrate (1) of rectangular form having first and second main surfaces and side surfaces connecting the main surfaces; a ground electrode (3) disposed on substantially the overall area of the first main surface of said substrate (1); a radiation electrode (2; 2a; 2b; 2c) having a free end and being disposed on the second main surface of said substrate (1) and connected to said ground electrode (3); and an excitation electrode (4; 4a) disposed on a side surface of said substrate (1) and having a forward end; characterized in that said radiation electrode (2; 2a; 2b; 2c) is a stripline radiation electrode and has a 1/4 wavelength on the second main surface of said substrate (1); a gap (g) is formed between the free end of said radiation electrode (2; 2a; 2b; 2c) and the forward end of said excitation electrode (4; 4a); and said excitation electrode (4; 4a) and said radiation electrode (2; 2a; 2b; 2c) are electromagnetically coupled to each other through a capacitor generated in said gap (g). A surface mounting antenna according to claim 1, wherein said stripline radiation electrode (2; 2a; 2b; 2c) is positioned at a first end adjacent to an edge of said substrate (1) so as to form said free end and connected at a second end to said ground electrode (3); and said excitation electrode (4; 4a) is disposed near said edge of said substrate (1), facing said free end of said radiation electrode (2; 2a; 2b; 2c) across said gap (g). A surface mounting antenna according to claim 1, wherein said stripline radiation electrode (2a) extends at a first end to a first side surface of said substrate to form said free end and is connected at a second end to said ground electrode (3); and said excitation electrode (4a) is disposed on said first side surface, facing said free end of said radiation electrode (2a) across said gap (g). A surface mounting antenna according to claim 1 or 2, wherein the gap (g) is disposed on the second main surface. A surface mounting antenna according to claim 1 or 2, wherein the gap (g) is disposed on a side surface of the substrate (1). A surface mounting antenna according to one of claims 1 to 5, wherein said radiation electrode (2b; 2c) is at least partly bent in the form of one of a U-shape and a meandering shape. A surface mounting antenna according to claim 2, wherein the side surface comprises one of a first side surface and a second side surface opposedly facing the first side surface. A communication apparatus comprising a surface mounting antenna according to any of claims 1 to 7.

Inventors: KAWAHATA KAZUNARI, KAWAHATA, KAZUNARI
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1996
Main classification: H01Q9
IPC codes: H01Q1, H01Q13, H01Q9