Patent Publication Number: US-8125404-B2

Title: Monopole antenna with high gain and wide bandwidth

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a monopole antenna, and more particularly to a monopole antenna with a spiral structural benefited with increased gain. 
     2. Description of the Prior Art 
     Wireless communication devices, such as cellular phones, notebook computers, electronic appliances, and the like, are normally equipped with an antenna that serves as a medium for transmission and reception of electromagnetic signals, such as date, audio, image, and so on. The antenna can be built outside or inside of the devices. Usually, an external antenna is not easily interfered by inner components of the electrical device and can be easily adjusted by user for achieving desired operating performance. Either a monopole antenna or a dipole antenna is a kind of traditional external antenna. The length of a radiating element of a traditional monopole antenna substantially equals to ½ wavelength (λ). While, when used in long distance transmission/reception, general monopole antenna generally has weak gain and undesired operating performance. 
     Taiwanese Patent No. 560706, issued to Chen on Nov. 1, 2003, disclosed a hybrid antenna comprising a dipole antenna, a helical antenna, and a rod antenna all of which connect to one another in series. The complex antenna improves the gain of the antenna and the communication distance of the antenna is fairly increased. However, the connection area between the dipole antenna and the inner conductor of the feeding line does not have any additional protection. Thus, not only will the connecting area be easily broken, but will also be easily oxidized. Taiwanese Patent No. I276251, issued to Wong et al. on Feb. 1, 2006, discloses a monopole antenna attached on a printed circuit board and having high gain. However, the monopole antenna failed to work in a wide bandwith. 
     Hence, in this art, a monopole antenna to overcome the above-mentioned disadvantages of the prior art should be provided. 
     BRIEF SUMMARY OF THE INVENTION 
     A primary object, therefore, of the present invention is to provide a monopole antenna having high gain, wide bandwidth and while with compact size. 
     In order to implement the above object, the monopole antenna made in accordance with the present invention comprises a base board having a first side and a second side, a grounding element attached on the first side of the base board, a coupling element attached on the first side of the base board and being spaced apart from the grounding element and a radiating element connected to the coupling element and exposed out the base board. 
     Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of a preferred embodiment when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a preferred embodiment of a monopole antenna in according with the present invention; 
         FIG. 2  is a partly exploded, perspective view of  FIG. 1 ; 
         FIG. 3  is an exploded view of  FIG. 1 ; 
         FIG. 4  is an exploded view similar to  FIG. 3 , but viewed from another angle; and 
         FIG. 5  is a test chart recording for the monopole antenna of  FIG. 1 , showing Voltage Standing Wave Ratio (VSWR) as a function of WLAN frequency. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to a preferred embodiment of the present invention. 
     Reference to  FIGS. 1 to 4 , a monopole antenna assembly made in according with a preferred embodiment of the present invention is shown. The monopole antenna assembly  100  is intended for being attached to an electric device, such as access points (AP), mobile phones, notebooks et al., and extending out the electric device for transmitting wireless signals. The monopole antenna assembly  100  comprises a monopole antenna  80  and a fastening element  70  for securely fixing the monopole antenna  80  on the electrical device. 
     The monopole antenna  80  includes a base board  10 , a radiating element  20 , a grounding element  31  attached on the base board  10  and separated from the radiating element  20 , a coupling element  30  attached on the base board  10  and electrically connected to the radiating element  20 , and a feeding line  60 . 
     The radiating element  20  includes a straight first radiating portion  21  with a first end  210  and a second end  212 , a spiral second radiating portion  23  extending from the second end  212  of the first radiating portion  21 , and a straight second radiating portion  25  extending from the second radiating portion  23 . The first radiating portion  21  and the third radiating portion  25  are respectively connected to the two opposite ends of the second radiating portion  23 . 
     The coupling element  30  and the grounding element  31  are respectively arranged on the base board  10  and the coupling element  30  is spaced apart from the grounding element  31 . The coupling element  30  is substantially equal to a quarter of λ of the monopole antenna&#39;s working frequency and includes a first fixing portion  40  and a second fixing portion  42  respectively arranged on the two ends of the coupling element  30 . The radiating element  20  is electrically connected to the coupling element  30  by the first radiating portion  21  being attached on the first and second fixing portions  40 ,  42  of the coupling element  30 . The first end  210  of the first radiating portion is connected to the first fixing portion  40  and the middle of the first radiating portion  21  connected to the second fixing portions  42 . 
     The grounding element  31  is substantially of U-shaped and includes a first side arm  310 , a second side arm  314  and a connecting arm  312  connecting the first side arm  310  and the second side arm  314 . The length of both the first arm  310  and the second side arm  314  is substantially equal to a quarter of λ. A grounding point  44  is substantially defined on the middle of the connecting arm  312 . The grounding element  31  is attached on the base board  10  with the connecting arm  312  being attached on the middle of the base board  10  and the first side arm  310  and the second side arm  314  respectively extending along the two sides of the base board  10 . In this preferred embodiment, the base board  10 , the grounding element  31 , and the coupling element  40  are formed by a printed circuit board. While in other alternative embodiments, the grounding element  31  and the coupling element  40  can be made from a metal patch and be plastered on the insulative base board  10 . 
     The feeding line  60  has an inner conductor  61  soldered to the fixing portion  42  of the coupling element  30 , an outer conductor  63  soldered to the connecting arm  314  of the grounding element  31  on the grounding point  44 , and an outer insulative stratum  65  cover the outer conductor  63 . The base board  10  has a third fixing portion  46  on one end thereof opposite to the first fixing portion  40  and the outer insulative stratum  65  of the feeding line  60  is attached on the third fixing portion  46  for securely fixing the feeding line  60  on the base board  10 . In this embodiment, the inner conductor  61 , the first end  210  of the first radiating portion  21 , and the outer conductor  62  are further securely fixed on their corresponding fixing portions  40 ,  42 ,  46  by glue. 
     The fastening element  70  is substantially of cylindrical shape and the base board  10  is inserted into the fastening element  70  for being fixed in the fastening element  70 . The fastening element  70  includes a receiving slot  73  and a pair of pins  79  respectively arranged in the two sides of the receiving slot  73 . The base board  10  includes a pair of gaps  101  respectively arranged on the two sides thereof and corresponding to the pins  79  in the receiving slot  73 , so as to the base board  10  is received in the fastening element  70  along the receiving slot  73  and the pins  79  are inserted into the gaps  101 . The fastening element  70  fixes the monopole antenna  80  and can be assembled on the electrical device. 
     In this embodiment, the distance between the coupling element  40  and the grounding element  30  is equal to 2 mm and the coupling element  40  is used to match the impedance of the monopole antenna  80  to the feeding impedance. Thus, reference to  FIG. 5 , the monopole antenna  80  works at 2.35-2.58 GHz frequency band, and has a bandwidth over 200 MHz. 
     While the foregoing description includes details which will enable those skilled in the art to practice the invention, it should be recognized that the description is illustrative in nature and that many modifications and variations thereof will be apparent to those skilled in the art having the benefit of these teachings. It is accordingly intended that the invention herein be defined solely by the claims appended hereto and that the claims be interpreted as broadly as permitted by the prior art.