Patent Publication Number: US-11050148-B2

Title: Antenna structure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Taiwan Patent Application No. 108122731 filed on Jun. 28, 2019, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The disclosure generally relates to an antenna structure, and more particularly, it relates to a multiband antenna structure. 
     Description of the Related Art 
     With the advancements being made in mobile communication technology, mobile devices such as portable computers, mobile phones, multimedia players, and other hybrid functional portable electronic devices have become more common. To satisfy user demand, mobile devices can usually perform wireless communication functions. Some devices cover a large wireless communication area; these include mobile phones using 2G, 3G, and LTE (Long Term Evolution) systems and using frequency bands of 700 MHz, 850 MHz, 900 MHz, 1800 MHz, 1900 MHz, 2100 MHz, 2300 MHz, 2500 MHz, and 2700 MHz. Some devices cover a small wireless communication area; these include mobile phones using Wi-Fi and Bluetooth systems and using frequency bands of 2.4 GHz, 5.2 GHz, and 5.8 GHz. 
     Antennas are indispensable elements for wireless communication. If an antenna used for signal reception and transmission has insufficient bandwidth, it will affect the communication quality of the mobile device. Accordingly, it has become a critical challenge for antenna designers to design a wideband antenna element that is small in size. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment, the disclosure is directed to an antenna structure which includes a ground element, a feeding radiation element, a first radiation element, a second radiation element, a third radiation element, a first capacitor, and a second capacitor. The ground element has a notch region. The feeding radiation element has a feeding point. The first radiation element is coupled to the ground element. The first capacitor is coupled between the feeding radiation element and the first radiation element. The second radiation element is coupled to the ground element. The second capacitor is coupled between the first radiation element and the second radiation element. The third radiation element is coupled to the feeding radiation element. The feeding radiation element, the first radiation element, the second radiation element, the third radiation element, the first capacitor, and the second capacitor are all disposed inside the notch region of the ground element. 
     In some embodiments, the antenna structure covers a first frequency band at 1575 MHz, a second frequency band from 2400 MHz to 2500 MHz, and a third frequency band from 5150 MHz to 5850 MHz. 
     In some embodiments, each of the first radiation element and the second radiation element substantially has a straight-line shape. The first radiation element and the second radiation element are substantially parallel to each other. 
     In some embodiments, the third radiation element substantially has an L-shape. 
     In some embodiments, the feeding radiation element has a first end and a second end. The feeding point is positioned at the first end of the feeding radiation element. 
     In some embodiments, the first radiation element has a first end and a second end. The first end of the first radiation element is coupled to a first connection point on the ground element. The second end of the first radiation element is coupled through the first capacitor to the second end of the feeding radiation element. 
     In some embodiments, the second radiation element has a first end and a second end. The first end of the second radiation element is coupled to a second connection point on the ground element. The second end of the second radiation element is coupled through the second capacitor to the second end of the first radiation element. 
     In some embodiments, the third radiation element has a first end and a second end. The first end of the third radiation element is coupled to the second end of the feeding radiation element. 
     In some embodiments, the antenna structure further includes a matching radiation element having a first end and a second end. The first end of the matching radiation element is coupled to a third connection point on the feeding radiation element. 
     In some embodiments, the antenna structure further includes a first circuit element, a second circuit element, a third circuit element, a fourth circuit element, and a fifth circuit element. The first circuit element is coupled between the first end of the first radiation element and the first connection point on the ground element. The second circuit element is coupled between the first end of the second radiation element and the second connection point on the ground element. The third circuit element is coupled between the second end of the feeding radiation element and the first end of the third radiation element. The fourth circuit element is coupled between the second end of the third radiation element and a fourth connection point on the ground element. The fifth circuit element is coupled between the second end of the matching radiation element and a fifth connection point on the ground element. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a top view of an antenna structure according to an embodiment of the invention; 
         FIG. 2  is a diagram of VSWR (Voltage Standing Wave Ratio) of an antenna according to an embodiment of the invention; 
         FIG. 3  is a top view of an antenna structure according to another embodiment of the invention; and 
         FIG. 4  is a top view of an antenna structure according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to illustrate the purposes, features and advantages of the invention, the embodiments and figures of the invention are shown in detail as follows. 
     Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. The term “substantially” means the value is within an acceptable error range. One skilled in the art can solve the technical problem within a predetermined error range and achieve the proposed technical performance. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
       FIG. 1  is a top view of an antenna structure  100  according to an embodiment of the invention. The antenna structure  100  may be applied in a mobile device, such as a smartphone, a tablet computer, or a notebook computer. As shown in  FIG. 1 , the antenna structure  100  includes a ground element  110 , a feeding radiation element  120 , a first radiation element  130 , a second radiation element  140 , a third radiation element  150 , a first capacitor C 1 , and a second capacitor C 2 . The ground element  110 , the feeding radiation element  120 , the first radiation element  130 , the second radiation element  140 , and the third radiation element  150  may all be made of metal materials, such as copper, silver, aluminum, iron, or their alloys. Each of the first capacitor C 1  and the second capacitor C 2  may be a fixed capacitor or a variable capacitor. 
     The ground element  110  may be a metal plane for providing a ground voltage of the antenna structure  100 . The ground element  110  has a notch region  115 . The notch region  115  may substantially have a rectangular shape or a square shape. In some embodiments, the notch region  115  is substantially positioned at the central point of any edge of the ground element  110 , and it is relatively far away from the corners of the ground element  110 . It should be noted that the feeding radiation element  120 , the first radiation element  130 , the second radiation element  140 , the third radiation element  150 , the first capacitor C 1 , and the second capacitor C 2  are all disposed inside the notch region  115  of the ground element  110 . 
     The feeding radiation element  120  may substantially have a straight-line shape. Specifically, the feeding radiation element  120  has a first end  121  and a second end  122 . A feeding point FP is positioned at the first end  121  of the feeding radiation element  120 . The feeding point FP may be coupled to a signal source (not shown). For example, the aforementioned signal source may be an RF (Radio Frequency) module for exciting the antenna structure  100 . 
     The first radiation element  130  may substantially have a straight-line shape. The first capacitor C 1  is coupled between the feeding radiation element  120  and the first radiation element  130 . Specifically, the first radiation element  130  has a first end  131  and a second end  132 . The first end  131  of the first radiation element  130  is coupled to a first connection point CP 1  on the ground element  110 . The second end  132  of the first radiation element  130  is coupled through the first capacitor C 1  to the second end  122  of the feeding radiation element  120 . 
     The second radiation element  140  may substantially have a straight-line shape. In some embodiments, the first radiation element  130  and the second radiation element  140  are substantially parallel to each other. The length of the first radiation element  130  may be the same as the length of the second radiation element  140 . The second capacitor C 2  is coupled between the first radiation element  130  and the second radiation element  140 . Specifically, the second radiation element  140  has a first end  141  and a second end  142 . The first end  141  of the second radiation element  140  is coupled to a second connection point CP 2  on the ground element  110 . The second end  142  of the second radiation element  140  is coupled through the second capacitor C 2  to the second end  132  of the first radiation element  130 . The second connection point CP 2  may be different from the aforementioned first connection point CP 1 . 
     The third radiation element  150  may substantially have an L-shape, which may be partially perpendicular to and partially parallel to the feeding radiation element  120 . Specifically, the third radiation element  150  has a first end  151  and a second end  152 . The first end  151  of the third radiation element  150  is coupled to the second end  122  of the feeding radiation element  120 . The second end  152  of the third radiation element  150  is an open end. In some embodiments, the feeding radiation element  120  has a first side and a second side which are opposite to each other. The first radiation element  130  and the second radiation element  140  are both positioned at the first side (e.g., the right side) of the feeding radiation element  120 . The third radiation element  150  is positioned at the second side (e.g., the left side) of the feeding radiation element  120 . In other words, the feeding radiation element  120  may separate the third radiation element  150  from the first radiation element  130  and the third radiation element  150 . 
       FIG. 2  is a diagram of VSWR (Voltage Standing Wave Ratio) of the antenna structure  100  according to an embodiment of the invention. The horizontal axis represents the operation frequency (MHz), and the vertical axis represents the VSWR. According to the measurement of  FIG. 2 , the antenna structure  100  can cover a first frequency band FB 1 , a second frequency band FB 2 , and a third frequency band FB 3 . The first frequency band FB 1  may be substantially at 1575 MHz. The second frequency band FB 2  may be substantially from 2400 MHz to 2500 MHz. The third frequency band FB 3  may be substantially from 5150 MHz to 5850 MHz. Therefore, the antenna structure  100  can support at least the multiband operations of GPS (Global Positioning System) and WLAN (Wireless Local Area Networks) 2.4 GHz/5 GHz. 
     In some embodiments, the operation principles of the antenna structure  100  are described as follows. The feeding radiation element  120 , the first capacitor C 1 , and the first radiation element  130  may be excited to generate the first frequency band FB 1 . The feeding radiation element  120 , the first capacitor C 1 , the second capacitor C 2 , and the second radiation element  140  may be excited to generate the second frequency band FB 2 . In addition, the feeding radiation element  120  and the third radiation element  150  may be excited to generate the third frequency band FB 3 . According to practical measurements, the incorporation of the first capacitor C 1  and the second capacitor can control the effective resonant length of each radiation element. Since all of the radiation elements and capacitors are positioned inside the notch region  115  of the ground element  110 , they do not occupy additional design area, so as to minimize the total size of the antenna structure  100 . 
     In some embodiments, the element sizes and element parameters of the antenna structure  100  are described as follows. The notch region  115  has a length L and a width W. The length L may be at least twice the width W. The product of the length L and the width W may be from 1/16 to ⅛ times the square of wavelength of the antenna structure  100   
                 (     ⁢     i   .   e   .       ,         λ   2     16     ≤     L   ·   W     ≤       λ   2     8       ,         
where “λ” represents the wavelength of the lowest frequency of the first frequency band FB 1  of the antenna structure  100 ). The capacitance of the second capacitor C 2  may be greater than the capacitance of the first capacitor C 1 . The capacitance of the first capacitor C 1  may be smaller than 1 pF, such as 0.6 pF. The capacitance of the second capacitor C 2  may be smaller than 1 pF, such as 0.8 pF. The above ranges of element sizes and element parameters are calculated and obtained according to many experiment results, and they help to optimize the operation bandwidth and impedance matching of the antenna structure  100 .
 
       FIG. 3  is a top view of an antenna structure  300  according to another embodiment of the invention.  FIG. 3  is similar to  FIG. 1 . In the embodiment of  FIG. 3 , the antenna structure  300  further includes a matching radiation element  360 , which may be made of a metal material. The matching radiation element  360  may substantially have a straight-line shape, which may be substantially perpendicular to the feeding radiation element  120 . Specifically, the matching radiation element  360  has a first end  361  and a second end  362 . The first end  361  of the matching radiation element  360  is coupled to a third connection point CP 3  on the feeding radiation element  120 . The second end  362  of the matching radiation element  360  is an open end, which is adjacent to the second end  152  of the third radiation element  150 . It should be noted that the term “adjacent” or “close” over the disclosure means that the distance (spacing) between two corresponding elements is smaller than a predetermined distance (e.g., 10 mm or shorter), or it means that the two corresponding elements are touching each other directly (i.e., the aforementioned distance/spacing therebetween is reduced to 0). The third connection point CP 3  is positioned between the first end  121  and the second end  122  of the feeding radiation element  120 , and the third connection point CP 3  is relatively close to the first end  121  of the feeding radiation element  120 . According to practical measurements, the incorporation of the matching radiation element  360  can improve the impedance matching of any frequency band of the antenna structure  300 . Other features of the antenna structure  300  of  FIG. 3  are similar to those of the antenna structure  100  of  FIG. 1 . Accordingly, the two embodiments can achieve similar levels of performance. 
       FIG. 4  is a top view of an antenna structure  400  according to another embodiment of the invention.  FIG. 4  is similar to  FIG. 3 . In the embodiment of  FIG. 4 , the antenna structure  400  further includes a first circuit element  471 , a second circuit element  472 , a third circuit element  473 , a fourth circuit element  474 , and a fifth circuit element  475 . For example, any of the first circuit element  471 , the second circuit element  472 , the third circuit element  473 , the fourth circuit element  474 , and the fifth circuit element  475  may be a resistor, a capacitor, an inductor, a short-circuited element, or an open-circuited element. The first circuit element  471  is coupled between the first end  131  of the first radiation element  130  and the first connection point CP 1  on the ground element  110 . The second circuit element  472  is coupled between the first end  141  of the second radiation element  140  and the second connection point CP 2  on the ground element  110 . The third circuit element  473  is coupled between the second end  122  of the feeding radiation element  120  and the first end  151  of the third radiation element  150 . The fourth circuit element  474  is coupled between the second end  152  of the third radiation element  150  and a fourth connection point CP 4  on the ground element  110 . The fifth circuit element  475  is coupled between the second end  362  of the matching radiation element  360  and a fifth connection point CP 5  on the ground element  110 . The fifth connection point CP 5  may be different from the aforementioned fourth connection point CP 4 . In some embodiments, each of the first circuit element  471 , the second circuit element  472 , the third circuit element  473 , and the fifth circuit element  475  is a short-circuited element or an inductor, and the fourth circuit element  474  is an open-circuited element or a capacitor. According to practical measurements, the incorporation of the first circuit element  471 , the second circuit element  472 , the third circuit element  473 , the fourth circuit element  474 , and the fifth circuit element  475  can fine-tune the impedance matching of the first frequency band FB 1 , the second frequency band FB 2 , and the third frequency band FB 3  of the antenna structure  400 , thereby optimizing the radiation performance of the antenna structure  400 . Other features of the antenna structure  400  of  FIG. 4  are similar to those of the antenna structure  300  of  FIG. 3 . Accordingly, the two embodiments can achieve similar levels of performance. 
     The invention proposes a novel wideband antenna structure, which at least includes a plurality of radiation elements and capacitors disposed inside a notch region of a ground element. In conclusion, the invention has at least the advantages of small size, wide bandwidth, high radiation efficiency, and low manufacturing cost, and therefore it is suitable for application in a variety of mobile communication devices. 
     Note that the above element sizes, element shapes, element parameters, and frequency ranges are not limitations of the invention. An antenna designer can fine-tune these settings or values according to different requirements. It should be understood that the antenna structure of the invention is not limited to the configurations of  FIGS. 1-4 . The invention may merely include any one or more features of any one or more embodiments of  FIGS. 1-4 . In other words, not all of the features displayed in the figures should be implemented in the antenna structure of the invention. 
     Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having the same name (but for use of the ordinal term) to distinguish the claim elements. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.