Patent Publication Number: US-8988306-B2

Title: Multi-feed antenna

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a multi-feed antenna, and more particularly, to a multi-feed antenna capable of switching between different feed terminals via a control circuit. 
     2. Description of the Prior Art 
     The antenna is utilized for transmitting or receiving radio waves, so as to transmit or to exchange radio signals. Generally speaking, electronic products with communication function of Wireless Local Area Network (WLAN), such as laptops, mobile phones, tablets, or other hand-held devices having communication function, utilize internal antennas for accessing a wireless network. With progress of communication technology, the operating frequencies of different wireless communication systems may be different, for example, a carrier central frequency of Wireless Local Area Network standard 802.11a set by Institute of Electrical and Electronics Engineers (IEEE) is about 5 GHz and a carrier central frequency of IEEE 802.11b is about 2.4 GHz. Therefore, in order to allow users to access different wireless communication network more conveniently, an ideal antenna should be capable of covering different desired frequency bands of different wireless communication network in single antenna. Besides, the size of the ideal antenna should be as small as possible, so as to match the trends of degrading size of the wireless communication device and to integrate the antenna in the wireless communication device. 
     With the continuously increasing of demand and quality of the wireless communication system, broadband antenna and the multi-band antenna are not only for fulfilling the requirement of bandwidth but for improving the quality of communication, especially for improving the quality of communicating on phones. As to insufficient bandwidth, there are practical difficulties of designing Planar Inverted F antenna (PIFA) with multi frequency bands if multiple desired frequency bands are close. In addition, a coupling on the resonant path of the Planar Inverted F antenna of multi frequency bands complicates the design of Planar Inverted F antenna of multi frequency bands. Generally speaking, a tradeoff between bandwidth and performance of the broadband Planar Inverted F antenna decreases the area of antenna. As to poor quality of communicating on the phones, the performance of the antenna of mobile phone could degrade because of effects of human body, such as the methods/position of hand holding or the antenna is too close to human body, and could degrade the quality of communication. 
     SUMMARY OF THE INVENTION 
     Therefore, the present disclosure mainly provides a multi-feed antenna for changing a field pattern of the multi-feed antenna through changing a feeding point. 
     The present disclosure discloses a multi-feed antenna. The multi-feed antenna comprises a first feed terminal; a second feed terminal; a first ground terminal; a second ground terminal; a radiator and a control circuit. The radiator is coupled to the first feed terminal, the first ground terminal, the second feed terminal and the second ground terminal. The control circuit is coupled to the first feed terminal and the second feed terminal and used for switching a radio frequency (RF) between the first feed terminal to the first feed ground terminal and the second feed terminal to the second ground terminal. 
     The present disclosure further discloses a multi-feed antenna. The multi-feed antenna comprises a first feed terminal; a second feed terminal; a first ground terminal; a second ground terminal; a first radiator; a second radiator; and a control circuit. The first radiator is couple to the first feed terminal and the first ground terminal. The second radiator is coupled to the second feed terminal and the second ground terminal. The control circuit is coupled to the first feed terminal and the second feed terminal and used for switching a radio frequency (RF) signal between the first feed terminal to the first ground terminal and the second feed terminal to the second ground terminal. 
     These and other objectives of the present disclosure will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred example that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a multi-feed antenna according to an example of the present disclosure. 
         FIG. 2  is a schematic diagram of the multi-feed antenna shown in  FIG. 1  when a control voltage is a positive voltage. 
         FIG. 3  is a schematic diagram of the multi-feed antenna shown in  FIG. 1  when a control voltage is a negative voltage. 
         FIG. 4  is a schematic diagram of an asymmetric multi-feed antenna according to an example of the present disclosure. 
         FIG. 5  is a schematic diagram of another asymmetric multi-feed antenna according to an example of the present disclosure. 
         FIG. 6  is a field pattern diagram of a multi-feed antenna according to an example of the present disclosure. 
         FIG. 7  is another field pattern diagram of a multi-feed antenna according to an example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , which is a schematic diagram of a multi-feed antenna  10  according to an example of the present disclosure. The multi-feed antenna  10  includes a feed terminal F 1 , a feed terminal F 2 , a ground terminal G 1 , a ground terminal G 2 , a radiator  100  and a control circuit  120 . The radiator  100  comprises at least a metal strip L 1 , a metal strip L 2 , and a metal strip L 3 . Preferably, the metal strip L 1  and the metal strip L 2  are L-shaped. The metal strip L 1  has a first terminal open and a second terminal coupled to the feed terminal F 1 . The metal strip L 2  has a first terminal open and a second terminal coupled to the feed terminal F 2 . The metal strip L 3  has a first terminal coupled to second terminal of the metal strip L 1  (i.e. the feed terminal F 1 ) and the second terminal coupled to the second terminal of the metal strip L 2  (i.e. the feed terminal F 2 ). In the present example, preferably, the shape and the size of the metal strip L 1  and the metal strip L 2  are the same and symmetric. Therefore, the metal strip L 1 , the metal strip L 2  and the metal strip L 3  form two opposite notches. The control circuit  120  is capable of switching the feed terminal of radio frequency (RF) signal. The control circuit  120  includes a transceiver R for transmitting/receiving wireless signals (such as RF signal); a diode D 1  having a positive terminal coupled to the transceiver R and a negative terminal coupled to the feed terminal F 1 ; a diode D 2  having a positive terminal coupled to the feed terminal F 2  and a negative terminal coupled to the transceiver R and the positive terminal of the diode D 1 ; and a control voltage Vctr 1  coupled to the transceiver R, the positive terminal of the diode D 1  and the negative terminal of diode D 2  and used for controlling the conducting states of the diode D 1  and the diode D 2 . Besides, the multi-feed antenna further includes a diode D 3  having a positive terminal coupled to the metal strip L 3  and a negative terminal coupled to the ground terminal G 1 ; and a diode D 4  having a positive terminal coupled to the ground terminal G 2  and a negative terminal coupled to the metal strip L 3 . The method of configuration of the diode D 1 -D 4  is not limited to the connection method above mentioned, and those skilled in the art can alter the connection of each diode according to different applications. 
     Please refer to an example shown in  FIG. 2 , the multi-feed antenna  10  can be designed at any position of a hand-held device (not shown herein) when the multi-feed antenna  10  is configured into the hand held device. Preferably, the multi-feed antenna  10  is designed at the top or the bottom of the hand-held device. When the holding position of the user is too close to the metal strip L 2 , the user affects the radiation performance of the multi-feed antenna  10 . In order to improve the disadvantage in the prior art, the feed terminal of the RF signal can be adaptively switched according to different operating environments or different methods of hand-holding through the existed electronic components (such as CPU, RF circuit, detecting circuit, etc.) which cooperates with the control circuit  120  to switch a transmission path of the RF signal from a resonant path to another resonant path and maintain the communication quality of the multi-feed antenna  10 . For example, please refer to  FIG. 2 , which is a schematic diagram of the multi-feed antenna  10  when the control voltage Vctr 1  is a positive voltage. As shown in  FIG. 2 , the diode D 1  and the diode D 3  are conducted, and the diode D 2  and the diode D 4  are cut-off when the control voltage Vctr 1  provides a positive voltage. Therefore, the RF signal is fed from the feed terminal F 1 , such that the metal strip L 1  can transmit and receive a high frequency band signal, and the metal strip L 2  and the metal strip L 3  can transmit and receive a low frequency band signal. Please refer to  FIG. 3 , which is a schematic diagram of the multi-feed antenna  10  when the holding position of the user is too close to the metal strip L 1  and the control voltage Vctr 1  is a negative voltage. As shown in  FIG. 3 , the diode D 2  and the diode D 4  are conducted, and the diode D 1  and the diode D 3  are cut-off when the control voltage Vctr 1  provides a negative voltage. Therefore, the RF signal is fed from the feed terminal F 2 , such that the metal strip L 2  can transmit and receive a high frequency band signal, and the metal strip L 1  and the metal strip L 3  can transmit and receive a low frequency band signal. 
     Therefore, the control circuit  120  is coupled to the feed terminal F 1  and the feed terminal F 2 , and controls the conducting states of the diode D 1  and the diode D 2  through outputting the positive voltage or the negative voltage. In other words, the control circuit  120  changes the feeding terminal of the multi-feed antenna  10  and accordingly lowers the effect of human body to the multi-feed antenna  10 . Besides, the ground terminal of the multi-feed terminal is also changed according to the control voltage Vctr 1  is a positive voltage or a negative voltage. Understandably, different feed terminals corresponds to different field patterns of antenna and the different field patterns also corresponds to different radiation abilities, thus, the overall performance of the multi-feed antenna  10  can be improved. 
     Noticeably, the metal strip L 1  and the metal strip L 2  could be different or asymmetric. In other words, the multi-feed antenna  10  can be an asymmetric type. Please refer to  FIG. 4 , which is a schematic diagram of an asymmetric multi-feed antenna  40  according to an example of the present disclosure. The multi-feed antenna  40  is similar to the multi-feed antenna  10 . Therefore, identical components use identical symbols and names. The difference between the multi-feed antenna  40  and the multi-feed antenna  10  is that a length of the metal strip L 1  is different from a length of the metal strip L 2 , wherein the length of the metal strip L 1  could be larger than the length of the metal strip L 2  or the length of the metal strip L 1  also could be smaller than the length of the metal strip L 2 . In other words, when the control voltage Vctr 1  provides a positive voltage, the RF signal is fed from the feed terminal F 1 , such that the metal strip L 1  can transmit and receive a high frequency band signal B 1 , and the metal strip L 2  and the metal strip L 3  can transmit and receive a low frequency band signal B 2 . When the control voltage Vctr 1  provides a negative voltage, the RF signal is fed from the feed terminal F 2 , such that the metal strip L 2  can transmit and receive a high frequency band signal B 3 , and the metal strip L 1  and the metal strip L 3  can transmit and receive a low frequency band signal B 4 . When the feed terminal of the multi-feed antenna  40  is adaptively switched, a central frequency of the high frequency band signal B 1  is higher than a central frequency of the high frequency band signal B 3 , i.e. a bandwidth of the high frequency band signal is between the high frequency band signal B 1  and the high frequency band signal B 3 , and a central frequency of the low frequency band signal B 4  is higher than a central frequency of the low frequency band signal B 2 , i.e. a bandwidth of the low frequency band signal is between the low frequency band signal B 4  and the low frequency band signal B 2 . In comparison with the multi-feed antenna  10 , the multi-feed antenna  40  not only can degrade the effect of human body to the multi-feed antenna  40  but can cover broader bandwidth through switching different feed terminals of the RF signal. In addition, those skilled in the art also can change the corresponding bandwidth through changing the distance between the feed terminal F 1  and the feed terminal F 2 , and is not limited thereto. 
     Please refer to  FIG. 5 , which is a schematic diagram of a multi-feed antenna  50  according to an example of the present disclosure. A structure of the multi-feed antenna  50  is similar to the structure of multi-feed antenna  10 , thus identical components use identical symbols and the same name. A difference between the multi-feed antenna  50  and the multi-feed antenna  10  is that an arrangement of the radiators is slightly different when the multi-feed antenna  50  is configured on a hand-held device. As shown in  FIG. 5 , the multi-feed antenna  50  includes a radiator  500  and a radiator  520 . The radiator  500  includes a metal strip L 1  and a metal strip L 2  and is configured at the upper portion of the hand-held device. The metal strip L 1  is L-shaped and the metal strip L 2  is notch-shaped. The metal strip L 1  has a first terminal open and a second terminal coupled to a feed terminal F 1 . The metal strip L 2  has a first terminal open and a second terminal coupled to the feed terminal F 1 . The radiator  520  includes a metal strip L 3  and a metal strip L 4  and is configured at lower portion of the hand-held device. Similarly, the metal strip L 3  is L-shaped and the metal strip L 4  is notch-shaped. The metal strip L 3  has a first terminal open and a second terminal coupled to a feed terminal F 2 . The metal strip L 4  has a first terminal open and a second terminal coupled to the feed terminal F 2 . Preferably, shapes of the metal strip L 1  and the metal strip L 3  are symmetric to the shapes of the metal strip L 2  and the metal strip L 4 . A control circuit  540  is used for switching a feed terminal of the RF signal, wherein the control circuit  540  includes a transceiver R for transmitting and receiving the RF signal; a diode D 1  having a positive terminal coupled to the transceiver R and a negative terminal coupled to the feed terminal F 1 ; a diode D 2  having a positive terminal coupled to the feed terminal F 2  and a negative terminal coupled to the transceiver R; and a control voltage Vctr 1  coupled to the transceiver R, the positive terminal of the feed terminal F 1  and the negative terminal of the feed terminal F 2  for controlling the conducting states of the diode D 1  and the diode D 2 . Similarly, the multi-feed antenna  50  further comprises a diode D 3  having a positive terminal coupled to the metal strip L 2  and a negative terminal coupled to the ground terminal G 1 ; and a diode D 4  having a positive terminal coupled to the ground terminal G 2  and a negative terminal coupled to the metal strip L 4 . 
     Similarly, the radiation performance is affected when the holding position of the user is too close to the radiator of the multi-feed antenna  50 . Therefore, when the control voltage Vctr 1  provides a positive voltage, the diode D 1  and the diode D 3  are conducted and the diode D 2  and the diode D 4  are cut-off. In other words, the upper portion of the multi-feed antenna  50  is conducted and the lower portion of the multi-feed antenna is cut-off when the control voltage Vctr 1  provides a positive voltage. The RF signal is fed from the feed terminal F 1 , such that the metal strip L 1  can transmit and receive a high frequency band signal and the metal strip L 2  can transmit and receive a low frequency band signal. When the control voltage Vctr 1  provides a negative voltage, the diode D 2  and the diode D 4  are conducted and the diode D 1  and the diode D 3  are cut-off. In other words, the lower portion of the multi-feed antenna  50  is conducted and the upper portion of the multi-feed antenna  50  is cut-off. Therefore, the RF signal is fed from the feed terminal F 2 , such that the metal strip L 3  can transmit and receive a high frequency band signal and the metal strip L 4  can transmit and receive a low frequency band signal. Though switching the feed terminal of the RF signal, the effect of the human body to the multi-feed antenna can be lowed. Noticeably, those skilled in the art can adjust the lengths of the metal strip L 1 -L 4  according to different applications, such that the multi-feed antenna  50  can transmit and receive broader range of the frequency band signal, and is not limited thereto. 
     Please refer to  FIG. 6 , which is a field pattern of a multi-feed antenna according to the example shown in  FIG. 1  and  FIG. 2  of the present disclosure. In  FIG. 6 , a position of a feed point is close to the bottom and left half of the antenna when the control voltage Vctr 1  is a positive voltage, so there are two null points at bottom and left separately in the field pattern diagram. Please refer to  FIG. 7 , which is a field pattern of the multi-feed antenna according to the example shown in  FIG. 1  and  FIG. 3  of the present disclosure. In the  FIG. 7 , a position of a feed point is close to bottom and right half of the multi-feed antenna, so there are two null points separately at bottom and at right of the field pattern diagram. Therefore, when the metal strip L 1  and the metal strip L 2  are symmetric, the present disclosure can change the radiation pattern of the antenna according to the operation methods (i.e. the holding methods of the user) through switching the feed terminal and the ground terminal simultaneously. As a result, the present disclosure can prevent effects of radio waves to human and can acquire better antenna performance through changing the field pattern of the antenna. On the other hand, when the metal strip L 1  and the metal strip L 2  are asymmetry, the present disclosure further broadens the bandwidth of the frequency band signal. 
     To sum up, the multi-feed antenna of the present disclosure includes a control circuit for changing the feed terminals of the multi-feed antenna. Through changing the feed terminals of the multi-feed antenna, the different radiation pattern can be obtained, so as to improve overall performance of the multi-feed antenna. On the other hand, through changing the feed terminals of the multi-feed antenna and changing lengths of the metal strips, the multi-feed antenna of the present disclosure can transmit and receive wireless signals in a broader bandwidth. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.