Patent Publication Number: US-6903696-B1

Title: Planar E-inverted antenna

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a planar antenna structure, and more particularly to a planar E-inverted antenna structure. 
   2. Related Art 
   An antenna structure is usually used to transmit and receive electromagnetic waves. To this purpose, specific designs are usually required to be able to irradiate signals in electromagnetic waveforms of radio frequency from the transmitter through the air medium, and/or to intercept electromagnetic waves carried by air media and convert it to meaningful radio-frequency signals. Antenna design is therefore an important in the actual performance of wireless equipment. 
   Presently, planar F-inverted antennae are known in the art, called like this because of its F-inverted shape. The operating length of the planar F-inverted antenna is only about λ/4, while that of the grounding area is λ/2. On the other hand, because the planar F-inverted antenna only uses a metallic conductor in association with adequate feeding and antenna short-circuits to the grounding area, its manufacturing cost is relatively low, and it can be soldered to the printed circuit board. 
     FIG. 1  illustrates a planar F-inverted antenna known in the art. The known antenna includes an open-circuit area  11 , a short-circuit end  12 , and a grounding area  13 . A signal line  14  connects the open-circuit area  11  to the grounding area  13 . A radio-frequency signal travels via the signal line  14  to the open-circuit area  11 , or from the open-circuit area  11  to the signal line  14 . With the short-circuit end  12  connected to the grounding area  13 , signals therefore travel from the open-circuit area  11  via the short-circuit end  12  to the grounding area  13 . 
   The metallic conductor of the planar F-inverted antenna of the prior art can be either in a linear shape or flat shape. In  FIG. 1 , the metallic conductor is in a flat plate shape, and thereby can be soldered on the printed circuit board as a surface-mount device, being thereby used as a concealed type antenna. 
   To support the metallic conductor, e.g. the open-circuit area  11  in a manner not to short-circuit the grounding area  13 , an insulating material  15  such as sponge material is usually inserted between the open-circuit area  11  and the grounding area  13  to support the open-circuit area. 
   Some problems may occur when a sponge material is used to support the open-circuit area  11  in the planar F-inverted antenna. The sponge or insulating material can absorb electromagnetic waves so that signal loss occurs at the transmission and reception. The antenna gain therefore is decreased. If sponge materials are used as support, additional and specific processing steps are needed, which increases manufacturing costs. As shown in  FIG. 4 , when the antenna is placed in a horizontal position, the radiation pattern further exhibits a central recessed area, and the radiation pattern therefore is not satisfactory. In addition, if the antenna has a baseband frequency f, its next harmonic is 3f, which is not suitable for double-baseband use, such as 900 MHz and 1800 MHz. 
   SUMMARY OF THE INVENTION 
   It is therefore an objective of the invention to provide a planar E-inverted antenna structure that can overcome the above problems of the prior art. 
   To achieve the above and other objectives, a planar E-inverted antenna structure of the invention comprises a radio-frequency area, first and second short-circuits ends, and a grounding area. A signal line connects the radio-frequency area to the grounding area, the signal line being connected to a signal source. The radio-frequency signal, e.g. a voltage, travels from the signal line to the radio-frequency area, or from the radio-frequency area to the signal line. 
   The connection of the first and second shot-circuit ends to the grounding area enables to support the radio-frequency area over the grounding area to change the antenna characteristics. The radio-frequency area and the grounding area have approximately the same length so that the operating length of the antenna is about λ/2. 
   T he planar E-inverted antenna according to the invention does not occupy a larger area than the planar F-inverted antenna, and further has a next resonance frequency which is doubled, which makes the antenna of the invention particularly suitable for use in double-baseband configuration. Due to different directions of polarization, more flexibility in utilization is offered. 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1  is a schematic view of a conventional planar F-inverted antenna; 
       FIG. 2  is a schematic view of a planar E-inverted antenna according to an embodiment of the invention; 
       FIG. 3  is a schematic view of a planar E-inverted antenna according to a second embodiment of the invention; 
       FIG. 4  is a schematic diagram illustrating the radiation pattern in the E-plane of a conventional planar F-inverted antenna being placed in horizontal position; 
       FIG. 5  is a schematic diagram illustrating the radiation pattern in the H-plane of a conventional planar F-inverted antenna being placed in a vertical position; 
       FIG. 6  is a schematic diagram illustrating the radiation pattern in the H-plane of a planar E-inverted antenna according to the invention being placed in horizontal position; and 
       FIG. 7  is a schematic diagram illustrating the radiation pattern in the E-plane of a planar E-inverted antenna according to the invention being placed in vertical position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention describes a planar E-inverted antenna structure, which has a side in an “E” inverted shape. 
   Referring to  FIG. 2 , the planar E-inverted antenna of the invention includes a radio-frequency area  11 A, first and second short-circuit ends  12 A,  12 B, and a grounding area  13 . A signal line  14  coupled with a signal source connects the radio-frequency area  11 A to the grounding area  13 . A radio-frequency signal (i.e. voltage) travels either from the signal line  14  to the radio-frequency area  22 A, or from the radio-frequency area  11 A to the signal line  14 . 
   The connection of the first and second short-circuit ends  12 A,  12 B to the grounding area  13  enables to support open-circuit area  11  over the grounding area  13 , and further changes the antenna characteristics. The antenna structure therefore does not need a sponge material to achieve support function, the support member formed along with the formation of the short-circuit ends. As a result, the manufacturing process is simplified, and production costs are reduced. 
   As shown, the open-circuit area  11  and the grounding area  13  have approximately the same length, and the operating length of the antennae is about λ/2. 
   In comparison with the conventional structure as shown in  FIG. 1 , the embodiment of the invention does not have one short-circuit part directly connecting to the grounding area at the right side of the radio-frequency area  11 A (in the direction of the figure). Such a design will negatively double the baseband of the radio-frequency area, which renders the antenna use incompatible with the associated product. 
   Therefore, a design in which first and second short-circuit ends  12 A,  12 B are connected to the grounding area  13  enables to obtain a baseband similar to that of the original PIFA antenna. Other parts described in the drawings are used to illustrate various uses of the antenna structure of the invention, and therefore should not be construed in a manner to limit the scope of the invention. 
   Besides improving the manufacturing process, the planar E-inverted antenna of the invention provides better performance, compared to the conventional planar F-inverted antenna.  FIG. 6  is a schematic diagram illustrating the radiation pattern in the H-plane of the planar E-inverted antenna of the invention, the antenna being placed in a horizontal position. The antenna then has a vertical direction of polarization. In contrast,  FIG. 4  is a schematic diagram of the radiation pattern in the E-plane of a conventional planar F-inverted antenna, being placed in a horizontal position. The conventional antenna is hence placed has a horizontal direction of polarization. A comparison between both radiation pattern diagrams shows that the recessed portion of the radiation pattern exhibited by the planar F-inverted antenna is substantially improved in the planar E-inverted antenna of the invention. Furthermore, a gain increase can be observed. These results show that the antenna structure of the invention has better performance. Furthermore, the direction of polarization of the antenna structure according to the invention is the inverse of that of the planar F-inverted antenna. 
     FIG. 7  is a schematic diagram illustrating the radiation pattern in the E-plane of the planar E-inverted antenna of the invention, the antenna being placed in a vertical position. The direction of polarization is horizontal. In contrast,  FIG. 5  is a schematic diagram illustrating the radiation pattern in the H-plane of the conventional planar F-inverted antenna, the antenna being placed in a vertical position. As shown, the direction of polarization for the conventional F-inverted planar antenna is vertical. The above observation shows that regardless of whether they are placed in a vertical or horizontal position, the planar E-inverted antenna and the planar F-inverted antenna have different polarization directions. This provides a flexible and advantageous use of the antenna in various situations. For example: when the antenna in use can be disposed in only one position (either horizontal or vertical), which is the case for a concealed type antenna, and the direction of polarization has to be in the direction different from that of the antenna placement to obtain optimal reception, the planar E-inverted antenna is more advantageous than the planar F-inverted antenna and provides an increased gain. 
     FIG. 3  illustrates a second embodiment of the invention. In this second embodiment, the planar F-inverted antenna is directly soldered on the printing circuit board, and includes the radio-frequency area  11 A, first and second short-circuits ends  12 A,  12 B, and the grounding area  13 . A feeding portion  16  connects to the radio-frequency area  11 A. A radio-frequency signal (voltage) is fed from a radio-frequency output of the printing circuit board and travels via the feeding portion  16  to the radio-frequency area  11 A or vice-versa from the radio-frequency area  11 A via the feeding portion  16  to the radio-frequency output of the printing circuit board. 
   The connection of the first and second short-circuit ends  12 A,  12 B to the grounding area  13  enables to support open-circuit area  11  over the grounding area  13 , and further changes the antenna characteristics. The antenna structure therefore does not need a sponge material to achieve support function, the support member being formed along with the formation of the short-circuit ends. As a result, the manufacturing process is simplified, and the production cost is reduced. 
   As shown, the open-circuit area  11  and the grounding area  13  have approximately the same length, and the operating length of the antenna is about λ/2. 
   The planar E-inverted antenna of the invention does not occupy a larger area than the planar F-inverted antenna of the prior art, and further has a next resonance frequency which is doubled, which makes the antenna of the invention particularly suitable for use in double-baseband configuration. Owing to different directions of polarization, more flexibility is therefore offered. 
   Via a structural modification, the planar E-inverted antenna of the invention is more convenient and economical to manufacture, and has a modified direction of polarization, as a result it has better transmission and reception performance. In addition to an advantageous reduction in size, no extra fixation elements are further needed, and the maximum surface area of the structure can be used, while the gain is increased. 
   It will be apparent to the person skilled in the art that the invention as described above may be varied in many ways, and notwithstanding remaining within the spirit and scope of the invention as defined in the following claims.