Multiband switchable antenna structure

A multiband switchable antenna structure includes a feeding element, a first radiation element, a second radiation element, circuit branches, and a switch circuit. A first end of the feeding element is a feeding point. A first end of the first radiation element is coupled to a second end of the feeding element. A second end of the first radiation element is open. A first end of the second radiation element is coupled to the second end of the feeding element. The circuit branches have different impedance values. The switch circuit selects one of the circuit branches as a matching branch according to a control signal. A second end of the second radiation element is coupled through the matching branch to a ground voltage.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority of Taiwan Patent Application No. 103141339 filed on Nov. 28, 2014, 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 specifically, to a multiband switchable antenna structure for use in a mobile device.

Description of the Related Art

With the progress of mobile communication technology, mobile devices, for example, portable computers, mobile phones, tablet computers, multimedia players, and other hybrid functional portable electronic devices, have become more common. To satisfy the needs of users, mobile devices usually can perform wireless communication functions. Some functions cover a large wireless communication area; for example, 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, and 2500 MHz. Some functions cover a small wireless communication area; for example, mobile phones using Wi-Fi and Bluetooth systems and using frequency bands of 2.4 GHz, 5.2 GHz, and 5.8 GHz.

A conventional design often uses a metal element with a fixed size as an antenna body of a mobile device. The metal element has a length of 0.5 or 0.25 wavelength corresponding to the desired frequency band. As a result, a conventional antenna design merely covers a single frequency band or a narrow frequency band, and it cannot meet the requirements of a current mobile device operating in multiple or wide frequency bands.

BRIEF SUMMARY OF THE INVENTION

In a preferred embodiment, the disclosure is directed to a multiband switchable antenna structure including a feeding element, a first radiation element, a second radiation element, circuit branches, and a switch circuit. A first end of the feeding element is a feeding point. A first end of the first radiation element is coupled to a second end of the feeding element. A second end of the first radiation element is open. A first end of the second radiation element is coupled to the second end of the feeding element. The circuit branches have different impedance values. The switch circuit selects one of the circuit branches as a matching branch according to a control signal. A second end of the second radiation element is coupled through the matching branch to a ground voltage.

In some embodiments, the second end of the first radiation element extends away from the feeding point, and the second end of the second radiation element extends toward the feeding point.

In some embodiments, the feeding element substantially has an L-shape.

In some embodiments, the first radiation element substantially has an L-shape.

In some embodiments, the second radiation element substantially has an L-shape.

In some embodiments, the circuit branches include an open-circuited branch, an inductive branch, a capacitive branch, and a short-circuited branch.

In some embodiments, the feeding element, the first radiation element, the second radiation element, and the matching branch are excited to generate a low-frequency band, and the low-frequency band is substantially from 700 MHz to 960 MHz.

In some embodiments, the multiband switchable antenna structure further includes a third radiation element. A first end of the third radiation element is the feeding point, and a second end of the third radiation element is open and adjacent to the feeding point.

In some embodiments, the multiband switchable antenna structure further includes a fourth radiation element. A first end of the fourth radiation element is coupled to a central portion of the feeding element, and a second end of the fourth radiation element is open.

In some embodiments, the third radiation element is excited to generate a first high-frequency band, the fourth radiation element is excited to generate a second high-frequency band, the first high-frequency band is substantially from 2300 MHz to 2700 MHz, and the second high-frequency band is substantially from 1710 MHz to 2170 MHz.

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.

FIG. 1is a diagram of a multiband switchable antenna structure100according to an embodiment of the invention. The multiband switchable antenna structure100may be applied to a mobile device, such as a smartphone, a tablet computer, or a notebook computer. In some embodiments, the multiband switchable antenna structure100is disposed on a nonconductive carrier element (e.g., a dielectric substrate), and at an edge of the interior of the mobile device.

As shown inFIG. 1, the multiband switchable antenna structure100at least includes a feeding element110, a first radiation element120, a second radiation element130, a switch circuit140, and circuit branches150-1,150-2, . . . , and150-N (N may be a positive integer which is greater than or equal to 2). The feeding element110, the first radiation element120, and the second radiation element130may be all made of conductive materials, such as metal. The switch circuit140may be implemented with one or more transistors. The circuit branches150-1,150-2, . . . , and150-N may include a variety of circuit elements which have different impedance values.

The feeding element110may substantially have an L-shape. The feeding element110has a first end111and a second end112. The first end111of the feeding element110is a feeding point FP. The feeding point FP may be coupled to a signal source (not shown), such as an RF (Radio Frequency) module for exciting the multiband switchable antenna structure100. The first radiation element120may substantially have an L-shape. The first radiation element120has a first end121and a second end122. The first end121of the first radiation element120is coupled to a second end112of the feeding element110. The second end122of the first radiation element120is open. The second radiation element130has a first end131and a second end132. The first end131of the second radiation element130is coupled to the second end112of the feeding element110. The second end132of the second radiation element130is coupled to the switch circuit140. In particular, the second end122of the first radiation element120may extend away from the feeding point FP, and the second end132of the second radiation element130may extend toward the feeding point FP. The length of the first radiation element120may generally longer than that of the second radiation element130. A combination of the first radiation element120and the second radiation element130may substantially have an N-shape or a Z-shape.

The switch circuit140selects one of the circuit branches150-1,150-2, . . . , and150-N as a matching branch according to a control signal SC. The second end132of the second radiation element130is coupled through the selected matching branch to a ground voltage VSS. The feeding element110, the first radiation element120, the second radiation element130, and the selected matching branch are excited to generate a low-frequency band. The low-frequency band may be substantially from 700 MHz to 960 MHz. In some embodiments, the control signal SC is generated by a processor (not shown). In alternative embodiments, the control signal SC is generated according to a user input signal. In other embodiments, the control signal SC is generated according to a detection signal. The detection signal is a detection result of a sensor for detecting the frequency of nearby electromagnetic waves (not shown). By controlling the switch circuit140, the second radiation element130of the multiband switchable antenna structure100can be coupled through different impedance elements to the ground voltage VSS, so as to generate a variety of effective resonant lengths. As a result, the multiband switchable antenna structure100can achieve multiband and wideband operations without changing the total antenna size. The multiband switchable antenna structure100of the invention is suitable for application in a variety of current small mobile communication devices.

FIG. 2is a diagram of a switch circuit240and circuit branches251and252according to an embodiment of the invention. The switch circuit240and the circuit branches251and252ofFIG. 2may be applied to the multiband switchable antenna structure100ofFIG. 1. In the embodiment ofFIG. 2, the circuit branches251and252include a short-circuited branch and an inductive branch. When the switch circuit240switches to the inductive branch, the low operating frequency of the multiband switchable antenna structure100is relatively low. When the switch circuit240switches to the short-circuited branch, the low operating frequency of the multiband switchable antenna structure100is relatively medial.

FIG. 3is a diagram of a switch circuit340and circuit branches351,352,353, and354according to an embodiment of the invention. The switch circuit340and the circuit branches351,352,353, and354ofFIG. 3may be applied to the multiband switchable antenna structure100ofFIG. 1. In the embodiment ofFIG. 3, the circuit branches351,352,353, and354include an open-circuited branch, an inductive branch, a capacitive branch, and a short-circuited branch. When the switch circuit340switches to the inductive branch, the low operating frequency of the multiband switchable antenna structure100is relatively low. When the switch circuit340switches to the short-circuited branch, the low operating frequency of the multiband switchable antenna structure100is relatively medial. When the switch circuit340switches to the capacitive branch, the low operating frequency of the multiband switchable antenna structure100is relatively high. On the other hand, the open-circuited branch is configured to adjust the high operating frequency of the multiband switchable antenna structure100.

FIG. 4is a diagram of a switch circuit440and circuit branches451,452,453, and454according to an embodiment of the invention. The switch circuit440and the circuit branches451,452,453, and454ofFIG. 4may be applied to the multiband switchable antenna structure100ofFIG. 1. In the embodiment ofFIG. 4, the circuit branches451,452,453, and454include an inductive branch, a short-circuited branch, a first capacitive branch, and a second capacitive branch. The first capacitive branch and the second capacitive branch may have different capacitances. When the switch circuit440switches to the inductive branch, the low operating frequency of the multiband switchable antenna structure100is relatively low. When the switch circuit440switches to the short-circuited branch, the low operating frequency of the multiband switchable antenna structure100is relatively medial. When the switch circuit440switches to the first capacitive branch or the second capacitive branch, the low operating frequency of the multiband switchable antenna structure100is relatively high.

FIG. 5is a diagram of a multiband switchable antenna structure500according to an embodiment of the invention.FIG. 5is similar toFIG. 1. The difference between the two embodiments is that the multiband switchable antenna structure500further includes a third radiation element560. The third radiation element560may substantially have a C-shape. The third radiation element560has a first end561and a second end562. The first end561of the third radiation element560is a feeding point FP of the multiband switchable antenna structure500. The second end562of the third radiation element560is open and adjacent to the feeding point FP. The third radiation element560can be excited to generate a first high-frequency band. The first high-frequency band is substantially from 2300 MHz to 2700 MHz. Other features of the multiband switchable antenna structure500ofFIG. 5are similar to those of the multiband switchable antenna structure100ofFIG. 1. Therefore, the two embodiments can achieve similar levels of performance.

FIG. 6is a diagram of a multiband switchable antenna structure600according to an embodiment of the invention.FIG. 6is similar toFIG. 5. The difference between the two embodiments is that the multiband switchable antenna structure600further includes a fourth radiation element670. The fourth radiation element670may substantially have a T-shape or an L-shape (not shown). The fourth radiation element670has a first end671, a second end672, and a third end673. The first end671of the fourth radiation element670is coupled to a central portion of the feeding element110(e.g., the right-angle turning point of the L-shaped feeding element110). The second end672and the third end673of the fourth radiation element670are open, and extend away from each other. The fourth radiation element670can be excited to generate a second high-frequency band, and the second high-frequency band is substantially from 1710 MHz to 2170 MHz. The fourth radiation element670is configured to adjust the impedance matching of the multiband switchable antenna structure600. Other features of the multiband switchable antenna structure600ofFIG. 6are similar to those of the multiband switchable antenna structure500ofFIG. 5. Therefore, the two embodiments can achieve similar levels of performance.

FIG. 7is a diagram of a VSWR (Voltage Standing Wave Ratio) of the multiband switchable antenna structure600according to an embodiment of the invention. The horizontal axis represents operating frequency (MHz), and the vertical axis represents the VSWR.FIG. 7shows the measurement result of the multiband switchable antenna structure600ofFIG. 6. The multiband switchable antenna structure600may include the inductive branch, the short-circuited branch, the first capacitive branch, and the second capacitive branch ofFIG. 4. As shown inFIG. 7, a first curve CC1represents the selection of the inductive branch (e.g., the inductance is about 6.8 nH) as the matching branch, a second curve CC2represents the selection of the short-circuited branch as the matching branch, a third curve CC3represents the selection of the first capacitive branch (e.g., the capacitance is about 15 pF) as the matching branch, and a fourth curve CC4represents the selection of the second capacitive branch (e.g., the capacitance is about 4.7 pF) as the matching branch. According to the measurement result ofFIG. 7, when the inductive branch is selected, the low operating frequency of the multiband switchable antenna structure600is relatively low; when the short-circuited branch is selected, the low operating frequency of the multiband switchable antenna structure600is relatively medial; and when the first capacitive branch or the second capacitive branch is selected, the low operating frequency of the multiband switchable antenna structure600is relatively high. The high operating frequency of the multiband switchable antenna structure600also varies with the selection of different matching branches. Therefore, by switching between circuit branches with different impedance values, the multiband switchable antenna structure600can easily support multiband and wideband operations, and meet the requirements of functions of current mobile communication devices.

FIG. 8is a diagram of antenna gain of the multiband switchable antenna structure600according to an embodiment of the invention. The horizontal axis represents operating frequency (MHz), and the vertical axis represents the antenna gain (dBi). According to the measurement result ofFIG. 8, the multiband switchable antenna structure600of the invention has good antenna gain over the frequency bands of LTE B28/B17/B20/B5/B8/B4/B3/B2/B1/B40/B7, and it can meet the criterion of general mobile communication devices.

The invention proposes a novel multiband switchable antenna structure. The proposed multiband switchable antenna structure can be designed in limited space of a mobile device, and it has at least the advantages of simple structure, low cost, wide frequency band, and high efficiency. The invention can solve the problem in the prior art.

Note that the above element sizes, element shapes, and frequency ranges are not limitations of the invention. An antenna engineer can adjust these settings or values according to different requirements. It is understood that the multiband switchable antenna structure of the invention are not limited to the configurations ofFIGS. 1-8. The invention may merely include any one or more features of any one or more embodiments ofFIGS. 1-8. In other words, not all of the features shown in the figures should be implemented in the multiband switchable antenna structure of the invention.

It will be apparent to those skilled in the art that various modifications and variations can be made in the invention. It is intended that the standard and examples be considered as exemplary only, with a true scope of the disclosed embodiments being indicated by the following claims and their equivalents.