Patent Publication Number: US-8982005-B2

Title: Monopole slot antenna structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 201110166829.5, filed on Jun. 21, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a monopole slot antenna structure, and particularly relates to a monopole slot antenna structure having a tuning slot section for conveniently adjusting suitable frequencies, and the monopole slot antenna structure being capable of operating in dual-frequency environment. 
     2. Description of Related Art 
     As Internet develops vigorously, various kinds of network platform services, such as networked communication platforms (for example, message boards, forums, community websites and so forth) or data exchange platforms (for example, web albums, official download spaces, networked space and so forth) or personal service platforms (for example, electronic mailboxes, blogs, web games and so forth), all have been involved with everyone&#39;s lives. As such, these network platform services make it convenient for people to obtain necessary data when they are at home or in working environments. In particular, prevalence of wireless communications revolves the problem in which people can only use Internet in a particular area due to length limitations of physical connections. Therefore, communication devices with wireless communication functionality such as mobile phones, personal digital assistants (PDA) or tablet computers have gradually become necessity in people&#39;s lives. 
     Accordingly, in current communication devices, Wi-Fi™, one of most commonly used wireless communication protocol standards, is based on IEEE 802.11 standards. Wi-Fi™ operates in 2.4 GHz frequency band (802.11 b/g/n) and 5 GHz frequency band (802.11 a/n). Since people mainly require exterior designs of communication devices to be light, slim, short and small, vendors mainly concern simplification of electronic components or shortening of built-in antenna length in design of communication devices supporting Wi-Fi™, in order to meet the aforementioned design requirements. In general, most of the vendors currently apply a monopole antenna as the built-in antenna of the communication devices since the monopole antenna has simple structure and its resonance frequency is a quarter of wavelength of the operating frequency. As such, the length of the monopole antenna is shorter. An electric current generated in a closed loop due to potential difference on the antenna makes the antenna function normally. Thus, the ground point of the electric circuit board or the body of the electronic device are usually taken as a reference ground plane of the monopole antenna. Nonetheless, any electronic components or conductors closer to the monopole antenna may influence the monopole antenna, such as forming a closed electric circuit accidentally. As such, signal quality of the electromagnetic signals received by the monopole antenna may be poor. Thus, in order to maintain good antenna functionality, the vendors seem to allocate a larger clearance area around the monopole antenna, but such allocation design will greatly increase an overall volume of the communication device. 
     In order to resolve the monopole antenna being too sensitive or easily influenced by surrounding objects, some vendors attempt to use a slot antenna to be the antenna of the communication device operating in dual-frequencies, since the slot antenna is not easily influenced by neighbouring electronic components or conductors. As such, it is not necessary for the vendors to allocate an additionally larger clearance area around the slot antenna. However, the resonance frequency of the slot antenna is a half of the wavelength of the operating frequency. Thus, the required antenna length is far greater than that of the monopole antenna, for example, under the same operating frequency, the length of the slot antenna is twice of that of the monopole antenna, so the overall volume of the communication device cannot be greatly reduced. Further, the slot antenna is usually a long rectangular metal frame, where there will be a long rectangular slot allocated being extended in the same direction as the long rectangular metal frame in the middle of the long rectangular metal frame. The vendors may tune a plate width between the long rectangular metal frame and the long rectangular slot, in order to adjust effects of high operating frequencies and low operating frequencies. However, in the aforementioned tuning, the location where the long rectangular metal frame corresponding to a short edge of the long rectangular slot has two tuning widths, while the location where the long rectangular metal frame corresponding to the a long edge of the long rectangular slot has fourth tuning widths. All these tuning widths will interactively influence characteristics of high operating frequencies and low operating frequencies. Therefore, the vendors require spending longer operation time for tuning the slot antenna to an expected operating frequency, which greatly lowers operation efficiency of the vendors. 
     Based upon the aforementioned, no matter a monopole antenna or a slot antenna, which are all limited by antenna characteristics thereof, cannot be properly designed for allocation communication devices of small volumes. Therefore, in order to revolve the aforementioned drawbacks of the conventional art, it is a major issue for related antenna design vendors to design an antenna with a shorter length and with operating frequency which can be easily tuned. 
     SUMMARY 
     The invention is directed to a monopole slot antenna structure. 
     Due to the fact that antenna structures of the existing communication devices are not perfect, which may damage marketing interests of the vendors, a monopole slot antenna structure is developed by the Applicant, which is disclosed in the invention, and the monopole slot antenna structure has a tuning slot section, so as to provide the vendor with an antenna having easily-tuned operating frequency and smaller volume. 
     According to an embodiment of the invention, a monopole slot antenna structure is provided. Mainly, the resonance frequency of the monopole slot antenna is a quarter of a wavelength of an operating frequency of the monopole slot antenna. Further, it can easily tune suitable operating frequency of the monopole slot antenna by changing a width of the slot section thereof, in order to achieve a simple tuning operation procedure. The monopole slot antenna structure includes a dielectric substrate, the monopole slot antenna and a feed element. The monopole slot antenna is disposed on one side of the dielectric substrate and has a slot. Also, the slot includes a first slot section, a tuning slot section and a second slot section. One end of the first slot section is located at one edge of the monopole slot antenna with the other end of the first slot section being extended towards internal portions of the monopole slot antenna and being connected to the tuning slot section. One end of the second slot section is connected to the tuning slot section with the other end of the second slot section being extended away from the first slot section. A length of the first slot section is less than or equal to a length of the second slot section. Moreover, the feed element is disposed correspondingly to the second slot section, and is configured for exciting the monopole slot antenna to generate a first operating frequency band and a second operating frequency band. Under the circumstance of increasing the width of the slot section, i.e. in a direction corresponding to an extending direction of the first slot section or the second slot section, the frequency corresponding to the second operating frequency is accordingly lowered. As such, the vendors can adjust the frequency of the second operating frequency band by changing the width of the slot, thereby enabling a communication device in which the monopole slot antenna structure of the invention is disposed therein to operate in an expected dual-frequency environment. 
     In order to make the aforementioned and other features and advantages of the invention comprehensible, several exemplary embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic three-dimensional diagram of a monopole slot antenna structure according to an embodiment of the invention. 
         FIG. 2  is a schematic two-dimensional diagram of a monopole slot antenna structure according to an embodiment of the invention. 
         FIG. 3  illustrates measurement results of a reflection coefficient S 11  of an embodiment of the invention. 
         FIG. 4  is a schematic diagram comparing reflective coefficient S 11  of embodiments with a varied width W 1  in the invention. 
         FIG. 5  is a schematic two-dimensional diagram of a monopole slot antenna structure according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
     Since a monopole slot antenna has a resonance frequency of a quarter of a wavelength of its operating frequency, antenna length of the monopole slot antenna can be greatly reduced in comparison with a slot antenna. However, sensitivity of the monopole slot antenna is lower than that of the monopole antenna. It is disclosed that Applicant of the invention therefore designs a novel antenna structure whose operating frequency can be easily tuned by using the aforementioned characteristics of the monopole slot antenna. 
     The invention provides a monopole slot antenna structure, which is applicable to a wireless communication device with dual-frequency operating functionality. Referring to  FIG. 1 , in a preferred embodiment of the invention, a monopole slot antenna structure  1  includes a dielectric substrate  11 , a monopole slot antenna  13  and a feed element  15 . The dielectric substrate  11  is a system electric circuit board of the wireless communication device, and the monopole slot antenna  13  is disposed on one side of the dielectric substrate  11  and has a slot  130 . Also, the slot  130  includes a first slot section  132 , a tuning slot section  134  and a second slot section  136 . One end of the first slot section  132  is located at one edge of the monopole slot antenna  13  with the other end of the first slot section  132  being extended towards internal portions of the monopole slot antenna  13  and being connected to the tuning slot section  134 . One end of the second slot section  136  is connected to the tuning slot section  134  with the other end of the second slot section  136  being extended away from the first slot section  132 . There is an included angle θ between an extending direction of the second slot section  136  and an extending direction of the first slot section  132  so as to form a monopole slot antenna, as shown in  FIG. 2 . Meanwhile, a length L 1  of the first slot section  132  is less than or equal to a length L 2  of the second slot section  136  so that the monopole slot antenna  13  can operate in a dual-frequency environment. In the present embodiment, the included angle θ is 90 degrees such that the slot  130  has an L shape. However, it is noted that, in other embodiments of the invention, the included angle θ can be any degree to comply with design requirements of different products. 
     Following the aforementioned descriptions, referring back to  FIG. 1 , the feed element  15 , for example, a micro-strip line, is disposed on the other side of the dielectric substrate  11  and located between the tuning slot section  134  and the other end of the second slot section  136 . Moreover, the feed element  15  is disposed correspondingly to the second slot section  136 , and is configured for exciting the monopole slot antenna  13  to generate a first operating frequency band (e.g., a lower frequency) and a second operating frequency band (e.g., a higher frequency) as a result of a design of the first slot section  132  and the slot section  136 . However, in other embodiments of the invention, if the feed element  15  is a copper axial cable, the feed element  15  can be directly disposed on the monopole slot antenna  13 , and located correspondingly to the second slot section  136 . Thus, as long as the feed element  15  can excite the monopole slot antenna to generate two operating frequency bands, the feed element  15  is the feed element disclosed in the invention. Further, referring back to  FIG. 2 , a width W 1  refers to a distance of the tuning slot section  134  in an extending direction corresponding to the second slot section  136 . A width W 2  refers to a distance of the tuning slot section  134  in an extending direction corresponding to the first slot section  132 . Under the circumstance where the widths W 1 , W 2  are both increased, the frequency of the second operating frequency band is accordingly increased. As such, the vendors can only tune one of the widths W 1  and W 2  of the tuning slot section  134  according to a space requirement of the electric circuit design and convenience. Alternatively, the vendors can also increase both widths W 1  and W 2  of the tuning slot section  134  at the same time, in order to easily control space planning of the electric circuit design. 
     In order to clearly illustrate characteristics of the monopole slot antenna  1  of the invention, and describe how the variations of the widths W 1  and W 2  of the tuning slot section  134  can actually influence corresponding operating frequency bands, the following embodiments are described with adjustments of the width W 1  of the tuning slot section  134 . Referring back to both  FIG. 1  and  FIG. 2 , in the present embodiment, the length L 1  of the first slot section  132  is 4.5 mm, and the length L 2  of the second slot section  136  is 12.5 mm, such that the total length L of the slot  130  is 17 mm. Referring to measurement results of reflective coefficient S 11  shown in  FIG. 3 , the monopole slot antenna in fact has two operating frequency bands. The first operating frequency band of the monopole slot antenna is approximately 2.4 GHz, and the second operating frequency band is approximately 5.6 GHz. Thus, the vendors can increase a distance (i.e., the width W 1 ) of the tuning slot section  134  in an extending direction corresponding to the second slot section  136  according to design requirements. For example, the width W 1  can be adjusted to be 1 mm, 2 mm or 3 mm. Referring back to  FIG. 4 , it can be understood by the measurement results of the reflective coefficient S 11 , when the width W 1  of the tuning slot section  134  is increased, frequency of the second operating frequency band is accordingly lowered, which means that the frequency of the second operating frequency band is changed towards 5 GHz. As such, the vendors can adequately change the width W 1  of the tuning slot section  134 , so that the second operating frequency band of the monopole slot antenna structure  1  can operate in an operating frequency expected by the vendors. 
     Referring back to  FIG. 1  and  FIG. 2 , when the width W 2  of the tuning slot section  134  in an extending direction corresponding to the first slot section  132  is similarly increased, the frequency of the second operating frequency band is accordingly lowered. Accordingly, the vendors can only change the widths W 1  or W 2  of the tuning slot section  134 , in order to tune the frequency of the second operating frequency band, thereby enabling the monopole slot antenna structure  1  to operate in dual-frequency environment as expected by the vendors. Further, in comparison of the conventional slot antenna structure having six tuning sections required to be tuned, only two widths W 1  or W 2  of the tuning slot section  134  are required to be tuned in the monopole slot antenna structure  1  of the invention. Therefore, the monopole slot antenna structure  1  of the invention is not only more convenient than the conventional slot antenna, but also is far smaller than the conventional slot antenna in terms of overall length. Thus, the monopole slot antenna structure  1  of the invention can enhance marketing competitiveness of the vendors. 
     It is herein noted that, though the aforementioned embodiments are described with an example of the slot being in the L shape, in other embodiments of the invention, the vendors can make variations of the slot shape according to actual electric circuit requirements or frequency requirements. For example, referring to  FIG. 5 , the other end of the second slot section  136 A can be bended to form an arc section A (for example, as shown in an enclosed dashed line of  FIG. 5 ), so as to change the second operating frequency corresponding to the second slot section  136 A, thereby enabling the monopole slot antenna structure of the invention to adapt to dual-frequency operating environments of different requirements. Thus, the monopole slot antenna structure of the invention can have higher industrial utility. In addition, the shape of the turning slot section disclosed in the invention is not limited to the rectangular shape in the aforementioned figures. In other embodiments of the invention, the vendors can change the turning slot section to be arc-shaped (for example, like the tuning slot section as shown in  FIG. 6 ) or other shapes. Therefore, the vendors can have greater convenience in designing electric circuits. 
     It is noted that though the embodiments shown in  FIG. 1  illustrating the feed element  15  being disposed correspondingly to the second slot section  136 , and the dielectric substrate  11  being disposed between the monopole slot antenna  13  and the feed element  15 , in other embodiments, the feed element  15  can be disposed correspondingly to the second slot section  136 , and the monopole slot antenna  13  can be disposed between the dielectric substrate  11  and the feed element  15 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.