Patent Publication Number: US-9425514-B2

Title: Wideband antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 103100056, filed on Jan. 2, 2014. 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 an antenna and more particularly to a wideband antenna. 
     2. Description of Related Art 
     With the development of mobile communication devices with multi-functions and characterized by miniaturization, a newly developed antenna (i.e., antenna under test, AUT) must pass verification tests and product certification tests in a short-range test environment, so as to ensure that the radiation pattern of the antenna meets the application requirements of the mobile communication devices. The AUT is placed in a small shield room in the short-range test environment, and a calibration antenna in the shield room is used in the verification test or product certification test for the AUT. 
     In general, because the horn antenna is characterized by its wide bandwidth, most of the existing shield rooms employ the horn antenna as the calibration antenna of the AUT in the verification test and the product certification test. However, the horn antenna is often so large and thus may not be applied in the small shield rooms. Therefore, how to design a wideband antenna within a limited space as a calibration antenna applied in the small shield rooms is one of the major issues occurring in the verification test and the product certification. 
     SUMMARY 
     One of exemplary embodiments provides a wideband antenna characterized by its wideband and its advantages of miniaturization. Therefore, the wideband antenna may be used as the calibration antenna in small shield rooms and applied to various kinds of mobile communication devices. 
     In an exemplary embodiment, a wideband antenna includes a radiation element, a first extension element and a second extension element, a first reflection element and a second reflection element, and a feeding element. The radiation element is symmetric to a reference direction and has a top edge, a bottom edge, a first side edge, and a second side edge. A width of the radiation element increases along the reference direction. The first extension element and the second extension element are extended toward the reference direction respectively from two ends of the top edge and are mirror-symmetric to each other with respect to the reference direction. Widths of the first and second extension elements decrease along the reference direction. The first and second reflection elements are respectively opposite to the first and second side edges and are mirror-symmetric to each other with respect to the reference direction. The feeding element connected to the bottom edge has a feeding point. 
     Based on the above, according to an exemplary embodiment, the width of the radiation element in the wideband antenna increases along the reference direction, and the widths of the two extension elements extending from the top edge of the radiation element decrease along the reference direction. Furthermore, the two reflection elements are respectively disposed on both sides of the radiation element. Thereby, the wideband antenna provided herein and characterized by its wideband and the advantages of miniaturization may serve as the calibration antenna in the small shield rooms and may be applied to various kinds of mobile communication devices. 
     Several exemplary embodiments accompanied with figures are described in detail below to further describe the invention in details. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram illustrating a structure of a wideband antenna according to an exemplary embodiment. 
         FIG. 2  illustrates a voltage standing wave ratio (VSWR) figure of a wideband antenna according to an exemplary embodiment. 
         FIG. 3  and  FIG. 4  are diagrams of gain and radiation efficiency of a wideband antenna according to an exemplary embodiment. 
         FIG. 5  is illustrates a radiation pattern of a wideband antenna according to an exemplary embodiment. 
         FIG. 6  is a schematic diagram illustrating a combination of components in a wideband antenna according to an exemplary embodiment. 
         FIG. 7  is a schematic diagram illustrating a structure of a wideband antenna according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
       FIG. 1  is a schematic diagram illustrating a structure of a wideband antenna according to an exemplary embodiment. As shown in  FIG. 1 , the wideband antenna  100  includes a radiation element  110 , a first extension element  120 , a second extension element  130 , a first reflection element  140 , a second reflection elements  150 , and a feeding element  160 , wherein the radiation element  110  is symmetric to a reference direction, for example, the z-axis direction. The radiation element  110  has a top edge  111 , a bottom edge  112 , a first side edge  113 , and a second side edge  114 . 
     The top edge  111  of the radiation element  110  is opposite to the bottom edge  112 , and the first side edge  113  of the radiation element  110  is opposite to the second side edge  114 . In addition, the first side edge  113  and the second side edge  114  define the width of the radiation element  110 . For example, plural distances between the first side edge  113  and the second side edge  114  in the z-axis direction define the width of the radiation element  110 . Furthermore, the width of the radiation element increases along the reference direction (i.e., the z-axis direction), and the first side edge  113  and the second side edge  114  are inwardly concave. Therefore, the first side edge  113  and the second side edge  114  have an arc shape, respectively, and the radiation element  110  has a fan-like shape. 
     The first extension element  120  and the second extension element  130  extend toward the reference direction (i.e., the z-axis direction) respectively from two ends of the top edge  111  of the radiation element  110 , and the first extension element  120  and the second extension element  130  are mirror-symmetric to each other with respect to the reference direction (i.e., the z-axis direction). In other words, the first extension element  120  and the second extension element  130  have substantially the same shape. 
     For example, the first extension element  120  has a first bevel edge  121  and a second bevel edge  122 , and the first bevel edge  121  and the second bevel edge  122  intersect with each other and define the width of the first extension element  120 . For instance, plural distances between the first bevel edge  121  and the second bevel edge  122  in the x-axis direction are the width of the first extension element  120 . Similarly, the second extension element  130  has a third bevel edge  131  and a fourth bevel edge  132 , and the third bevel edge  131  and the fourth bevel edge  132  intersect with each other and define the width of the second extension element  130 . For instance, plural distances between the third bevel edge  131  and the fourth bevel edge  132  in the x-axis direction are the width of the second extension element  130 . 
     Furthermore, the widths of the first extension element  120  and the second extension element  130  decrease along the reference direction (i.e., the z-axis direction). In addition, the first bevel edge  121  of the first extension element  120  and the third bevel edge  131  of the second extension element  130  have a linear shape, and the second bevel edge  122  of the first extension element  120  and the fourth bevel edge  132  of the second extension element  130  have an arc shape. Besides, an intersection of an extension direction of the second bevel edge  122  and an extension direction of the fourth bevel edge  132  forms an angle θ1, and said angle θ1 may be 17 degrees, for example. 
     The first reflection element  140  is opposite to the first edge  113  of the radiation element  110 . The second reflection element  150  is opposite to the second side edge  114  of the radiation element  110 . In addition, the first reflection element  140  and the second reflection element  150  are mirror-symmetric to each other with respect to the reference direction (i.e., the z-axis direction). In other words, the first reflection element  140  and the second reflection element  150  have substantially the same shape. For example, the first reflection element  140  has a notch  141 , and an opening of the notch  141  faces away from the first side edge  113  of the radiation element  110 . Similarly, the second reflection element  150  has a notch  151 , and an opening of the notch  151  faces away from the second side edge  114  of the radiation element  110 . 
     From another point of view, the first reflection element  140  and the second reflection element  150  in  FIG. 1  are roughly shaped as the letter C. Although the exemplary embodiment depicted in  FIG. 1  demonstrates several ways to implement the first reflection element  140  and the second reflection element  150 , the invention is not limited thereto, and those having ordinary skill in the art may make various modifications and variations to the shape of the first reflection element  140  and the second reflection element  150  based on actual design requirements, for instance, the first reflection element  140  and the second reflection element  150  may respectively have a rectangular shape, a square shape, an elliptical shape, or any geometric shape. 
     The feeding element  160  is electrically connected to the bottom edge  112  of the radiation element  110  and has a feeding point. In addition, the wideband antenna  100  is a monopole antenna substantially. In teems of operation, the wideband antenna  100  receives a feeding signal through the feeding element  160 . Through the excitation of the feeding signal, the wideband antenna  100  generates a resonant mode through a plurality of current paths formed by the radiation element  110  and then is operated in the first band (e.g., the middle frequency band). Additionally, the wideband antenna  100  extends a part of the current paths in the radiation element  110  through the first extension element  120  and the second extension element  130  so as to be operated in the second band (e.g., the low frequency band). Moreover, the wideband antenna  100  can be operated in the third band (i.e., the high frequency band) through a second harmonic in the resonant mode. 
     For example,  FIG. 2  illustrates a voltage standing wave ratio (VSWR) figure of a wideband antenna according to an exemplary embodiment. As shown in  FIG. 2 , the first band (e.g., the middle frequency band) of the wideband antenna  100  is, for instance, from 1.5 GHz to 3.6 GHz; thereby, the wideband antenna  100  may be operated in the GPS/GSM/LTE bands. Furthermore, the second band (i.e., the low frequency band) of the wideband antenna  100  is, for instance, from 500 MHz to 960 MHz, and the third frequency (i.e., the high frequency band) is, for instance, from 4.8 GHz to 5.8 GHz; thereby, the wideband antenna  100  may be operated in the 802.11a band. Furthermore,  FIG. 3  and  FIG. 4  are diagrams of gain and radiation efficiency of a wideband antenna according to an exemplary embodiment.  FIG. 3  and  FIG. 4  both show that the wideband antenna  100  has great performance on low, middle, and high frequency bands. 
     In other words, the operating band of the wideband antenna  100  may be widely applied to cover various application bands, and the wideband antenna  100  has good performance on each band. Furthermore, the wideband antenna  100  not only has the characteristics of wideband but also has the advantages of miniaturization in structure. Therefore, the wideband antenna  100  may be used as the calibration antenna in small shield rooms to test the radiation patterns of the AUT in various application bands. Specifically, the wideband antenna  100  may be placed on top or bottom of the AUT, thereby increasing the convenience of the verification test or the product certification test on AUT. Moreover, the wideband antenna  100  may be applied to various kinds of mobile communication devices. 
     In addition, as shown in  FIG. 1 , the wideband antenna  100  may reflect or guide the radiated electromagnetic energy through the first reflection element  140  and the second reflection element  150 . Thus, the radiated electromagnetic energy of the wideband antenna  100  on the first band (e.g., the middle frequency band) may leak out from the front side and back side of the wideband antenna  100 , and thereby the wideband antenna  100  is equivalent to a wideband directional antenna. For example,  FIG. 5  illustrates a radiation pattern of a wideband antenna according to an exemplary embodiment. According to the embodiment depicted in  FIG. 5 , the wideband antenna  100  is operated at 2.5 GHz, a curve  510  shows the radiation pattern of the wideband antenna  100  in the X-Z plane, and a curve  520  shows the radiation pattern of the wideband antenna  100  in the X-Y plane. As shown by the curve  510 , the electromagnetic energy of the wideband antenna  100  may be focused on the front side and back side of the wideband antenna  100 . 
     According to an exemplary embodiment, it is worth mentioning that a total width W1 of the wideband antenna  100  may be a quarter wavelength of the maximum frequency of the first band (e.g., 3.6 GHz), for example, and a total length L1 of the wideband antenna  100  may be a quarter wavelength of the minimum frequency of the first band (e.g., 1.5 GHz), for example. In addition, the wideband antenna  100  has a first length L11 and a second length L12 in the reference direction (e.g., the z-axis direction), if observed from one end of the top edge  111  of the radiation element  110  as a boundary, and the ratio of the first length L11 to the second length L12 is 2:1. 
     As shown in  FIG. 1 , the wideband antenna  100  further includes a first substrate  101  and a second substrate  102 , wherein the radiation element  110 , the first extension element  120 , the second extension member  130 , the first reflection element  140 , the second reflection element  150 , and the feeding element  160  are all located on one surface of the first substrate  101 . Furthermore, the second substrate  102  is mainly served as a holder of the wideband antenna  100 . Here, a signal line  170  and a ground plane  180  are located on one surface of the second substrate  102 , and an antenna connector  190  (e.g., an SMA connector) is located on the other surface of the second substrate  102 . In addition, a number of through-holes (e.g., through-holes  191  and  192 ) penetrate through the second substrate  102 . 
     Specifically,  FIG. 6  is a schematic diagram illustrating a combination of components in a wideband antenna according to an exemplary embodiment. As shown in  FIG. 6 , the second substrate  102  is perpendicular to the first substrate  101 . In addition, the signal pin of the antenna connector  190  is electrically connected to the signal line  170  through the through-hole  191 , and a plurality of positioning pins of the antenna connector  190  are electrically connected to the ground plane  180  through at least one through-hole (e.g., the through-hole  192 ). On the other hand, the feeding element  160  is electrically connected to the signal line  170  on the second substrate  102 . The first reflection element  140  and the second reflection element  150  are electrically connected to the ground plane  180  which is on the second substrate  102 . Thus, the wideband antenna  100  may receive the feeding signals through the antenna connector  190  on the second substrate  102 . 
     Although the embodiment shown in  FIG. 6  discloses a way to combine the first substrate  101  and the second substrate  102 , it should not be construed as a limitation to the invention. For example, in another embodiment, the second substrate  102  and the first substrate  101  are parallel to each other. In this case, the ground plane  180  on the second substrate  102  can improve the characteristics of the wideband antenna  100  operated in the second band (e.g., the low band). 
     Notably, in terms of operations, the first extension element  120  and the second element  130  of the wideband antenna  100  generate an inductance effect, respectively, and a capacitance effect is generated between the first extension element  120  and the second extension element  130 . Furthermore, the inductance effect and the capacitance effect are determined by the shapes of the radiation element  110 , the first extension element  120 , and the second extension element  130 . Therefore, the characteristic parameters of the wideband antenna  100 , such as the bandwidth, the gain, the radiation efficiency, or the directivity, may be adjusted by changing the shapes of the radiation element  110 , the first extension element  120 , and the second extension element  130 . 
     For example,  FIG. 7  is a schematic diagram illustrating a structure of a wideband antenna according to another exemplary embodiment, wherein a wideband antenna  700  shown in  FIG. 7  is substantially similar to the wideband antenna  100  shown in  FIG. 1 . The main difference between the two embodiments is that the top side  111  of the radiation element  110  in  FIG. 1  is shaped as a smooth arc, and a top side  711  of the radiation element  710  in  FIG. 7  includes a middle section  711   a . Specifically, the middle section  711   a  is located between the first extension element  120  and the second extension element  130 . Furthermore, the middle section  711   a  protrudes outwardly, and the middle section  711   a  has an arc shape. In another embodiment, the middle section  711   a  may have a triangular shape, a curved shape, or an arbitrary geometric shape, for example. Thus, the directivity of the wideband antenna  700  operated in the first band can be adjusted through the middle section. Since the detailed structure of the wideband antenna  700  has been described in the above embodiments, it is not further explained hereinafter. 
     In summary, according to an embodiment, the wideband antenna has a radiation element which the width increases along the reference direction, and two extension elements extend from two opposite ends of the top edge. The widths of the two extension elements decrease along the reference direction. Furthermore, the two reflection elements are respectively disposed on the two sides of the radiation element. Thereby, the wideband antenna may have the characteristics of wideband and the advantages of miniaturization. Particularly, the wideband antenna has the wide bandwidth and great directivity when the wideband antenna is operated in the first band. Accordingly, the wideband antenna may by used as the calibration antenna in the small shield room and may also be applied to various kind of mobile communication devices. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments 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.