Patent Publication Number: US-6667716-B2

Title: Planar inverted F-type antenna

Description:
FIELD OF THE INVENTION 
     The present invention relates to a planar inverted F-type antenna and more particularly to an improved planar inverted F-type antenna for increasing operative bandwidth and enhancing signal quality. 
     BACKGROUND OF THE INVENTION 
     The rapid innovation and development of wireless communication technology have created a wide range of communication products in recent years. Among them, mobile communication products that integrate  3 C technologies and communication modules are the mainstream of the market these days. These products include notebook computers, PDA, Palm, etc. They can couple with communication modules to link LAN (Local Area Network), to transmit and receive e-mail, and to receive instant information (such as news, stocks quotations and so on) for sharing resources and information. The planar inverted F-type antennas are known to have the advantages of compact size and light weight, thus have been widely adopted as built-in antennas in the mobile communication products. 
     Referring to FIG. 1 for a conventional planar inverted F-type antenna, the antenna includes a metal ground plane  10 , a flat metal plate  12 , a short circuit leg  14  and a feeding leg  16 . The metal ground plane  10  is substantially parallel with the flat metal plate  12  and has a feeding metal bore  15 . The short circuit leg  14  and the feeding leg  16  are located respectively on one side of the flat metal plate  12 . The short circuit leg  14  connects the metal ground plane  10 . The feeding leg  16  passes through the feeding metal bore  15  to connect a matching circuit (not shown in the drawing) for generating matching impedance. The flat metal plate  12  is a rectangular thin metal sheet having one side connected with the short circuit leg  14  to form a short circuit end and another side formed an open circuit end. The distance between the short circuit end and the open circuit end is preferably a quarter of wavelengths. 
     As the current on the flat metal plate  12  adopting conventional techniques has a constant length, the transmitting and receiving signals through the antenna also have constant frequency. As a result, the operative bandwidth is limited, and thus applications of the antenna are restricted. 
     Moreover, the feeding leg  16  adopting conventional technique is located at one side of the flat metal plate  12 . Because the antenna is not a symmetrical structure, hence it cannot generate symmetrical radiation field in the horizontal direction. As a result, signal transmission and receiving quality of the antenna is definitely not satisfactory. 
     Therefore, producers of the planar inverted F-type antenna have devoted a lot of research and development efforts to improve the operating bandwidth and enhance the transmission quality. 
     SUMMARY OF THE INVENTION 
     The primary object of the invention is to provide an improved planar inverted F-type antenna for increasing operating bandwidth of the antenna. 
     Another object of the invention is to provide an improved planar inverted F-type antenna for enhancing signal quality of the antenna while transmitting and receiving data. 
     A further object of the invention is to provide an improved planar inverted F-type antenna design that is simpler to fabricate and is adaptable for mass production. 
     The improved planar inverted F-type antenna of the invention has a feeding leg of the antenna soldered to a center location of a flat metal plate that has two symmetrical sides thereof. A supplying current is fed at the center such that left and right symmetrical radiation fields can be generated from the antenna structure plate. As a result, signal quality for data transmitting and receiving of the present invention is better than that of an antenna adopting the conventional techniques. Moreover, the invention offers various shapes of the flat metal plate to change the feeding current route distance so as to increase operative bandwidth. In addition, the invention provides a novel fabrication method to make the feeding leg and forms an inverted U-shaped slit structure at a selected location in the center of the flat metal plate. The middle portion of the metal slit structure is bent downwards to form a feeding leg for passing through the feeding metal bore to replace soldering for making the feeding leg. The antenna thus can be integrally made of a single metal element and may be adaptable for mass production. 
     The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic perspective view of a conventional planar inverted-F type antenna; 
     FIG. 2A is a schematic view of a first embodiment of the invention 
     FIG. 2B is a schematic view of a second embodiment of the invention; 
     FIG. 3 is a schematic view of a third embodiment of the invention; 
     FIG. 4 is a schematic view of a fourth embodiment of the invention; and 
     FIG. 5 is a schematic view of a fifth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention aims at providing an improved planar inverted F-type antenna that has a more symmetrical radiation field to improve transmitting and receiving signal quality, has a wider operative bandwidth for receiving and transmitting more signals of different frequencies, and is integrally made to streamline fabrication process for mass production. Details of the invention will be elaborated as follows. 
     Referring to FIG. 2A for a first embodiment of the invention, the antenna consists of a metal ground plane  20 , a trapezoid flat metal plate  22  in parallel with the metal ground plane  20 , a grounded short circuit leg  24 , a feeding leg  26 , and a metal bore  25  formed on the metal ground plane  20 . The trapezoid flat metal plate  22  has an open circuit end  28  and a short circuit end  29  that connects the metal ground plane  20  through the short circuit leg  24 . The feeding leg  26  is soldered to the trapezoid flat metal plate  22 . The feeding leg  26  passes through the metal bore  25  of the metal ground plane  20  for connecting with a matching circuit under the metal ground plane  20  (not shown in the drawing) for generating matching impedance, but does not contact with the metal ground plane  20 . 
     The flat metal plate  22  has a length about a quarter of wavelengths to form an open-circuit and short-circuit structure. The trapezoid-shaped structure can change the feeding current route to allow the antenna to receive signals of different frequencies thereby to increase the operative bandwidth of the antenna. 
     In the embodiment, the feeding leg  26  is located under the center of the trapezoid flat metal plate  22  and is symmetrical to both sides of the trapezoid flat metal plate  22  so that, a left and right symmetrical radiation field will be generated. As a result, signal quality for data transmitting or receiving will be improved over those that adopt conventional techniques. 
     In the first embodiment set forth above, the side width of the trapezoid flat metal plate  22  is gradually tapered off from the open circuit end  28  to the short circuit end  29 . 
     FIG. 2B shows a second embodiment of the invention that is substantially similar to the first embodiment previously discussed except that the side width of the trapezoid flat metal plate  22  is gradually tapered off from the short circuit end  29  to the open circuit end  28 . 
     FIG. 3 shows a third embodiment of the invention which consists of a metal ground plane  30 , a flat metal plate  32  in parallel with the metal ground plane  30 , a grounded short circuit leg  34 , a feeding leg  36 , and a metal bore  35  formed on the ground metal plane  30 . The flat metal plate  32  has an open circuit end  38  and a short circuit end  39  that connects the metal ground plane  30  through the short circuit leg  34 . The open circuit end  38  has at least one chamfered corner (preferably two chamfered corners). The feeding leg  36  is soldered to the flat metal plate  32 . The feeding leg  36  passes through the feeding metal bore  35  of the metal ground plane  30  to connect a matching circuit under the metal ground plane  30  (not shown in the drawing) for generating matching impedance, but does not contact with the metal ground plane  30 . 
     The flat metal plate  32  has a length about a quarter of wavelengths from the open circuit end  38  to the short circuit end  39 , in which the open circuit end  38  includes two chamfered corners for increasing the operative bandwidth of the antenna. Because of the chamfer corners formed at the open circuit end  38 , the lengths of the current route will be different, thus the antenna can receive signals of different frequencies so as to increase the operative bandwidth of the antenna. 
     In the embodiment, the feeding leg  36  is located under the center of the flat metal plate  32  and is symmetrical to two sides of the flat metal plate  32 , so that, a left and right symmetrical radiation field will be generated. As a result, signal quality for data transmitting or receiving will be improved over those that adopt conventional techniques. 
     FIG. 4 shows a fourth embodiment of the invention that is largely similar to the first embodiment of FIG. 2A previously discussed. In both embodiments, similar elements are marked by the same numerals. Different features and function will be discussed below while similar structure and function will be omitted. The trapezoid flat metal plate  22  corresponding to the feeding metal bore  25  is attached to an inverted U-shaped slit structure  47  which has a middle metal section bent downwards ninety degrees to form a feeding leg  46  passing through the feeding metal bore  25  and forming on the flat metal plate  22  a slit  47  with an area matching the feeding leg  46 . 
     The feeding leg  46  can be integrally formed. Hence, it can save both soldering time and costs, and is adaptable for mass production. 
     FIG. 5 shows a fifth embodiment of the invention that is substantially an alternation of the third embodiment of FIG. 3 previously discussed. In both embodiments, similar elements are marked by the same numerals. Except for inverted U-shaped slit structure  47 , detailed structure and function of this embodiment are the same as those of the third embodiment and thus will be omitted herein. Apparently from FIG. 4, the feeding current leg  46  and the slit structure  47  used in the fourth embodiment are applied to this embodiment for saving soldering time and costs. 
     In summary, the invention provides the following advantages over the conventional techniques: 
     a. The feeding leg of the invention is located in the center below the flat metal plate and is symmetrical to two sides on the surface distance. When signals are fed, a left and right symmetrical radiation field will be generated. Thus this invention can achieve better signal quality for data transmitting or receiving than those that adopt the conventional techniques. 
     b. The trapezoid flat metal plate structure can generate different lengths of electric current routes for the current and allows the antenna to receive changed signal frequencies and thus to increase the antenna operative bandwidth. 
     c. The inverted U-shaped slit structure under the flat metal plate is bent ninety degrees to form the feeding leg. It can be integrally formed to save production time and costs and is adaptable for mass production. 
     While the preferred embodiment of the inventions have been set forth for purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.