Patent Publication Number: US-6703983-B2

Title: Slot antenna having irregular geometric shape

Description:
FIELD OF THE INVENTION 
     The present invention relates to a slot antenna, and in particular to a slot antenna having an irregular geometric shape. 
     BACKGROUND OF THE INVENTION 
     There is a growing need for slot antennas for use in wireless communication devices. Referring to FIG. 1, a conventional slot antenna comprises a rectangular antenna body made from a metal foil, an elongated, narrow slot defined in the antenna body and a coaxial cable electrically connecting with the antenna body, wherein the cable has an inner core wire soldered to one side of the slot and an outer shield soldered to another side of the slot. The antenna body generally has a regular geometric shape. 
     However, when such a conventional slot antenna is mounted in an electronic device, the directionality of the slot antenna, and specifically the receiving angle and the gain value of the slot antenna, are affected by the geometric shape of the antenna itself and the structure of elements around the antenna in the device. Referring to FIG. 3, which shows measured radiation patterns in the X-Y plane of such a conventional slot antenna operating at three frequencies, the center line of the radiation pattern rotates around the origin an angle θ from the Y-axis. Because of the altered radiation pattern, such a conventional slot antenna often cannot operate in its best mode. 
     Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of existing antennas. 
     BRIEF SUMMARY OF THE INVENTION 
     A primary object, therefore, of the present invention is to provide an improved slot antenna having an irregular geometric shape for improving the operating characteristics of the slot antenna. 
     A slot antenna in accordance with the present invention comprises an antenna body and a coaxial feeder cable, wherein an elongated, narrow slot is defined in the antenna body and the cable has an inner core wire soldered to one side of the slot and an outer shield soldered to another side of the slot. The antenna body is made from a metal foil, and a plurality of notches is defined in the antenna body near the slot for changing the receiving angle and improving the gain value of the slot antenna. 
     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 top view of a conventional slot antenna; 
     FIG. 2 is a top view of a slot antenna in accordance with the present invention; 
     FIG. 3 shows measured radiation patterns in the X-Y plane of the conventional slot antenna of FIG. 1 operating at three frequencies, wherein a dash-dotted line shows the center line of the radiation patterns; and 
     FIG. 4 shows measured radiation patterns in the X-Y plane of the slot antenna of FIG. 2 operating at three frequencies. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to a preferred embodiment of the present invention. 
     Referring to FIG. 2, a slot antenna  1  in accordance with the present invention comprises an antenna body  10  and a coaxial feeder cable  2  electrically connected to the antenna body  10 . 
     The antenna body  10  is made from a metal foil. An elongated, narrow slot  11  is defined in the antenna body  10 . A first and second notches  12 ,  13  of predetermined geometric sizes and shapes are further defined in the antenna body  10  near the slot  11 . 
     The coaxial feeder cable  2  comprises a conductive inner core  21 , a conductive braiding layer  23 , an inner dielectric layer  22  insulating the inner core  21  from the braiding layer  23 , and an insulative outer jacket  24  surrounding the braiding layer  23 . The inner core  21  and the braiding layer  23  are respectively soldered to the corresponding circuits on the antenna body  10  at two opposite sides of the slot  11 . 
     FIG. 4 shows measured radiation patterns in the X-Y plane of the slot antenna  1  in accordance with the present invention, operating at frequencies of 2.40 GHz, 2.45 GHz and 2.50 GHz. Note that the center line of the radiation patterns align with the Y-axis. Compared with the patterns shown in FIG. 3 for the conventional antenna, the patterns for the slot antenna  1  of the present invention demonstrate higher maximum and average gain values, and directionality is improved. 
     It is noted that the presence of the first and second notches  12 ,  13  changes the electric current density near the slot  11  and thus changes the magnetic intensity produced by the electric current, so the directionality of the electromagnetic field is changed. Using the principle disclosed above, other notches, slots or holes of predetermined sizes can be cut in the antenna body  10 , affecting the directionality of the slot antenna  1 . Obvious variations of the slot antenna  1 , including different notch or hole patterns, are thus intended to be covered by the present disclosure. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms which the appended claims are expressed.