Patent Publication Number: US-7215293-B2

Title: High-gain loop antenna

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to an antenna, and more specifically to a high-gain loop antenna. 
   BACKGROUND OF THE INVENTION 
   Along with the cost decrease for establishment of wireless local area network (LAN), there is no computer maker who doesn&#39;t try introducing the wireless LAN equipments, for example a wireless net card, into a notebook computer, however a difficult job for antenna design due to the limited space inside the notebook computer. 
   A U.S. Pat. No. 6,344,823 “Structure of an antenna and method for manufacturing the same” has disclosed a planar inverted F antenna for use in wireless LAN, which is more advantageous than an average single-pole antenna in build-in allocation and convenience for application. 
   Another U.S. Pat. No. 6,724,348 “Computer with an embedded antenna” has disclosed a planar inverted F antenna for notebook computer by using an LCD as an allocation environment. However, as the radiant gain of a usual planar inverted F antenna is about 2 dBi, the valid transmission range is decreased owing to the space complexity. 
   A loop antenna is generally applied for high frequency (HF) communication, but rarely used in small communication equipments because of its high input impedance. A U.S. Pat. No. 6,236,368 “Loop antenna assembly for telecommunication devices” has introduced the concept for using loop antenna in small communication equipments, however, in which a defect is that an operating frequency in the range of 0.05–0.3 wavelength is reserved between a loop antenna and a ground plane. 
   Another U.S. Pat. No. 6,525,694 “High gain printed loop antenna” has disclosed a tip for solving matching problems by means of feeding a web design, however, which is rather overcomplicated in operating two extra loop circuits in parallel, and has a relatively longer reserved distance about 0.11–0.16 times the wavelength of operating frequency. 
   Yet, another U.S. Pat. No. 6,697,025 “Antenna apparatus” has disclosed an antenna, which can be folded into a rectangle, is placed in a portable receiver element. This antenna is workable near the ground. However, the radiation element must be folded several times, and the antenna must be grounded or a matching element must be adopted, alternatively. 
   SUMMARY OF THE INVENTION 
   The present invention provides a high-gain loop antenna. The high-gain loop antenna mainly comprises a conductor ground plane, a feeding signal line, a radiation element, and a dielectric element. The radiation element includes a matching element and a conductor loop. The dielectric element is allocated between the conductor ground plane and the radiation element. 
   The feeding signal line is provided for feeding signals. The matching element is connected to the feeding signal line and the conductor loop, so as to achieve the resistance impedance between the matching element and the conductor loop. The conductor loop is used to actuate the operation mode of the antenna, when the current flows onto the radiation element. This not only allows that the radiation directivity pattern is maximal on the horizontal plane, but also simplifies the fabrication of the antenna. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  shows a structural view of a first embodiment of the high-gain loop antenna according to the present invention. 
       FIG. 1B  shows an example of the electrical connection of the elements in the first embodiment of the present invention. 
       FIGS. 2A–2C  are three examples showing the relative space structure of two matching sections of the present invention. 
       FIG. 3  shows a structural view of a second embodiment of the present invention. 
       FIG. 4  shows that the conductor loop and the dielectric element are protrudent at an edge of the conductor ground plane. 
       FIG. 5  shows that the conductor loop and the dielectric element are inwardly shrunk at the edge of the conductor ground plane. 
       FIG. 6  shows the result of the radiation pattern measurement when the first embodiment of the present invention is operated at 2450 MHz. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1A  shows a structural view of a first embodiment of the high-gain loop antenna according to the present invention. Referring to  FIG. 1A , the high-gain loop antenna  100  comprises a conductor ground plane  110 , a feeding signal line  120 , a radiation element  130 , and a dielectric element  140 . The feeding signal line  120  is provided for feeding signals, including a feeding signal positive end  121  and a feeding signal negative end  122  as shown in  FIG. 1B . The radiation element  130  includes a matching element  131  and a conductor loop  133 . The matching element  131  includes a first matching section  1311  and a second matching section  1312 . The feeding signal line  120  is electrically connected the matching element  131 , and the matching element is electrically connected to the conductor loop. The dielectric element  140  is allocated between the conductor ground plane  110  and the radiation element  130 . 
     FIG. 1B  shows an example of the electrical connection of the elements in the first embodiment. Referring to  FIG. 1B , the feeding signal line  120  has two ends,  121  and  122  respectively. Every matching section has two ends. The first matching section  1311  includes a first end  1311   a  and a second end  1311   b ; similarly, the second matching section  1312  includes a first end  1312   a  and a second end  1312   b . The first end  1311   a  of the first matching section  1311  is electrically connected to one end  121  of the feeding signal line  120 , while the first end  1312   a  of the second matching section  1312  is electrically connected to the other end  122  of the feeding signal line  120 . 
   The conductor loop  133 , which functions to actuate the operating mode of antenna while the current flows onto the radiation element, has two ends including a first end  133   a  and a second end  133   b . The first end  133   a  of the conductor loop is electrically connected to the second end  1311   b  of the first matching section; while the second end  133   b  of the conductor loop is electrically connected to the second end  1312   b  of the second matching section. 
   The input impedance of the conductor loop  133  may be changed by adjusting the length of the matching element  131  or adjusting the length between the first matching section  1311  and the second matching section  1312  according to this invention, and whereby it is possible to cut down the distance to be reserved between the conductor loop  133  and the conductor ground plane  110  in antenna. For instance, the distance between the conductor loop  133  and the conductor ground plane  110  could be shorter than 0.045 λ (wavelength) of the operating frequency under the condition of a center operating frequency at 2.4 GHz. Besides, the center operating frequency of antenna may be changed by adjusting length of the outer diameter of the conductor loop  133 . 
   From the above mentioned embodiment, this invention is merited as the following. (a) It is able to operate at frequency 2.4 GHz when the height of antenna is shorter than 0.045 λ, and moreover, as no connection to the ground plane is needed, industrial applications are rather convenient. (b) No parallel connection for two loops and two matching elements is necessary for obtaining a low profile of antenna. (c) No extra impedance matching circuit is required, the antenna is thus simple to fabricate. 
   According to this invention, the conductor ground plane may be a screen of a liquid crystal display (LCD) according to this invention. The first and the second matching sections may be parallel or intersected, and the length thereof may be equal or unequal.  FIG. 2  shows examples of three possible space structures formed by those two matching sections.  FIG. 2   a  shows two matching sections  201  in parallel with equal lengths;  FIG. 2   b  shows an included angle smaller than 30° nipped by two matching sections  202 ; and  FIG. 2   c  shows two matching sections  203  in different lengths. 
     FIG. 3  shows a structural view of a second embodiment of the present invention, in which, different from the first embodiment, a conductor ground plane  310  is bent into an L-shape. 
   In the first embodiment, the conductor loop  133  of the radiation element  130  for the antenna  100  is right at an edge of the conductor ground plane  110 . According to the embodiment of this invention, the conductor loop and the dielectric element may be protrudent or inwardly shrunk at an edge of the conductor ground plane, as illustrated in  FIG. 4  and  FIG. 5  respectively. Referring to  FIG. 4 , the conductor loop  433  of the radiation element  430  for the antenna  400  is protrudent at an edge of the conductor ground plane  110 . Referring to  FIG. 5 , the conductor loop  533  of the radiation element  530  for the antenna  500  is inwardly shrunk at an edge of the conductor ground plane  110 . 
     FIG. 6  shows the results of the antenna radiation pattern measurement of the first embodiment. Wherein the maximal measurement is 4.2 dBi, as indicated by an arrow, thereby, greatly extending the range for receiving signals. In addition, the angle range for receiving signals can be reached up to 135° (i.e. 180°–315°) for 3 dB beam width (i.e. 1.2 dBi–4.2 dBi), as shown in the  FIG. 6 . 
   The radiating element in the embodiment of the invention can be fabricated by using a metal-cutting technique or a conductor-formation process on a printed or flexible circuit board. In conclusion, the reserved distance between the radiating element and the conductor ground plane is short. Thereby, it is applicable to small-size communication devices. 
   Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.