Patent Publication Number: US-6906675-B2

Title: Multi-band antenna apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-126425, filed Apr. 26, 2002, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a multi-band antenna apparatus for transmitting and receiving in a plurality of frequency bands by one antenna. 
   2. Description of the Related Art 
   It is planned in a near future to realize an emergency information system called Telematics system in Japan. This system operates as follows. If an automobile accident occurs, for example, the accident is detected. The vehicle position is automatically calculated by receiving a radio wave from a global positioning system (GPS). On the basis of the calculated information of the vehicle position, it is automatically noticed by a mobile phone. 
   Telematics system requires, for the ease of installation of the apparatus in an automobile, a multi-band antenna integrally combining an antenna for receiving GPS waves in a band of, for example, about 1.6 GHz, and an antenna for transmitting and receiving radio waves for mobile phone in a band of 880 MHz. 
   BRIEF SUMMARY OF THE INVENTION 
   According to an aspect of the present invention, there is provided a multi-band antenna apparatus high in antenna efficiency in a wide band, and easy in setting of desired frequency band. 
   A multi-band antenna apparatus according to an aspect of the invention is characterized by comprising: a first conductor and a second conductor arranged at a specific interval; and a feeder which feeds power to the first conductor and second conductor, wherein the first conductor is divided by at least one slit. 
   In a frequency band higher than a specific frequency, by feeding power by parasitic method by using the slit, the plurality of antenna elements can be coupled to function as one antenna element. Accordingly, by adjusting the width and interval of the slit, the antenna efficiency is enhanced in a wide band, and it is easy to set the desired frequency band. 
   Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiment of the invention, and together with the general description given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the invention. 
       FIG. 1  is a diagram showing a configuration of dipole antenna of bowtie type according to an embodiment of the invention; 
     FIG.  2 A and  FIG. 2B  are views showing examples of results of measurement of VSWR in a range including two frequency bands in the same embodiment; and 
       FIG. 3  is a diagram showing a configuration of another example of a dipole antenna of bowtie type of the same embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of the invention applied in an antenna apparatus of Telematics system is described below while referring to the accompanying drawings. 
     FIG. 1  is a diagram showing a configuration of application in a dipole antenna of bowtie type (hereinafter called bowtie antenna)  20 . 
   In  FIG. 1 , shorter bottoms of trapezoidal hot-side element  21  and ground-side element  22  are formed face to face on an antenna substrate (not shown) by a copper foil printing pattern or the like. By feeding power to the opposing positions from power feeder  24 , the bowtie antenna  20  is configured. 
   At the hot-side element  21 , in particular, a slit  23  with a specific width of, for example, 0.2 mm is formed at a position of a distance L 12  from the power feed position. As a result, the hot-side element  21  is divided into a first antenna element  21   a  and a second antenna element  21   b.    
   The specific configuration will be described. 
   The position of the distance L 12  from the power feed position is adjusted to a quarter wavelength of GPS wave in 1.6 GHz band, so that the second antenna element  21   b  functions as a GPS receiving antenna. 
   On the other hand, a distance L 11  from the power feed position to an end point not close to the first antenna element  21   a  and second antenna element  21   b  is adjusted to a quarter wavelength of mobile phone wave of 880 MHz band, so that the first antenna element  21   a  and second antenna element  21   b  function as antennas for transmitting and receiving waves of the mobile phone. 
   In this case, the slit  23  feeds power between the first antenna element  21   a  and the second antenna element  21   b  by a parasitic method, and couples the antenna elements  21   a  and  21   b  to function as one antenna element. 
   In this way, by feeding power between the hot-side element  21  and the ground-side element  22  formed by interposing the slit  23  between the antenna elements  21   a  and  21   b  with the power feeder  24 , a two-band antenna can be realized for the mobile phone antenna by the first antenna element  21   a  and second antenna element  21   b , and for the GPS receiving antenna by the second antenna element  21   b  only. 
   In such configuration, results of measurement of VSWR (voltage stationary wave ratio) are shown in FIG.  2 A and FIG.  2 B. 
     FIG. 2A  shows results of measurement in a range of 790 MHz to 1090 MHz including the mobile phone frequency band by the first antenna element  21   a  and second antenna element  21   b  by way of the slit  23 . 
     FIG. 2B  shows results of measurement in a range of 1.5 GHz to 2.1 GHz including the GPS frequency band by the second antenna element  21   b  only. 
   In the range including the mobile phone frequency band shown in  FIG. 2A , the VSWR of 2.0 or less is obtained from a low frequency band of 790 MHz up to about 930 MHz, and it is understood to be sufficiently practicable. 
   On the other hand, in the range including the GPS frequency band shown in  FIG. 2B , the VSWR is 2.0 or less in the entire range, and the antenna efficiency is very high, and it is proved that the supplied electric power can be utilized efficiently. 
   Thus, in the bowtie antenna apparatus, by adjusting the shape of the antenna elements  21   a ,  21   b  and the width and interval of the slit, the antenna efficiency becomes higher in a wider band, and the intended frequency band can be set easily. 
   The width of the slit  23  has been verified to function favorably as parasitic power feeder at the interval of 0.1 mm to 0.3 mm. However, the appropriate interval and width vary with the shape of the antenna element or frequency band. 
   It has been proved by measurement that the slit  23  is small in loss and effective in parasitic current feed in a frequency band generally higher than decimeter waves (300 MHz to 3 GHz). 
   The above-mentioned embodiment is an antenna apparatus for Telematics system, realizing a two-band antenna for the GPS wave receiving antenna in 1.6 GHz band, and the mobile phone wave transmitting and receiving band in 880 MHz band, but the invention is not limited to the present embodiment, but three-band or more multi-band antenna apparatus can be easily configured. 
     FIG. 3  is a diagram showing a configuration of a bowtie antenna  20 ′ for three-band frequency. In  FIG. 3 , shorter bottoms of trapezoidal hot-side element  21 ′ and ground-side element  22 ′ are formed face to face on an antenna substrate (not shown) by a copper foil printing pattern or the like. By feeding power to the opposing positions from power feeder  24 ′, the bowtie antenna  20 ′ is configured. 
   At the hot-side element  21 ′, slits  25  and  26  with a specific width of, for example, 0.2 mm are formed at two points, that is, a position at a distance L 23  from the power feed position and at a position at a distance L 22 . As a result, the hot-side element  21 ′ is divided into a first antenna element  21   c , a second antenna element  21   d , and a third antenna elements  21   e.    
   In this case, as similar to the above-mentioned embodiment, the distance L 23  from the power feed position to the slit  26  is adjusted to a quarter wavelength of third frequency band f 23 , so that the third antenna element  21   e  alone functions as a antenna for transmitting and receiving waves of the third frequency band f 23 . 
   On the other hand, the distance L 22  from the power feed position to the slit  25  is adjusted to a quarter wavelength of second frequency band f 22 , so that the second antenna element  21   d  and third antenna element  21   e  function as antennas for transmitting and receiving waves of the second frequency band f 22 . 
   Moreover, the distance L 21  from the power feed position to an end side of the second antenna element  21   d  not contacting with the first antenna element  21   c  is adjusted to a quarter wavelength of the first frequency band f 21 , so that the first to third antenna elements  21   c  to  21   e  are bound together across the slits  25 ,  26  so as to function as an antenna for transmitting and receiving waves of the first frequency band f 21 . 
   The antenna type is not limited to the print type dipole antenna, but it can be applied in antennas of various element configurations. 
   It is not limited to the above-mentioned embodiment, the invention may be modified and embodied in several modes within the scope of the invention. 
   Further, the present embodiments includes various stages of inventions, and various inventions may be devised by properly combining the disclosed a plurality of constituent requirements. For example, if certain constituent requirements are deleted from the entire constituent requirements of the embodiment, the configuration deleting such constituent requirements may be devised as an invention as far as at least one of the problems to be solved by the invention can be solved and at least one of the effects of the invention is obtained. 
   According to the embodiment of the invention, in a higher frequency band than a specific frequency, by parasitic power feed by using the slit, the plurality of antenna elements can be coupled to function as one antenna element. Hence, by adjusting the width or interval of the slit, the antenna efficiency is high in a wide band, and the intended frequency band can be set easily. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.