Abstract:
An antenna comprises an external high-band portion and an internal low-band portion. The external high-band portion reduces energy dissipation from nearby components, and the internal low-band portion reduces the phantom head effect. The antenna combines the external high-band portion and the internal low-band portion, utilizing the advantages of the two portions to benefit the receiving efficiency of the antenna.

Description:
RELATED APPLICATIONS 
   The present application is based on, and claims priority from, Taiwan Application Ser. No. 94132321, filed Sep. 19, 2005, the disclosure of which is hereby incorporated by reference herein in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The invention relates to an antenna and, in particular, to an antenna that can reduce energy dissipation from nearby components and phantom head effect. 
   2. Related Art 
   With technological advances, the primary hotbed of communication techniques has gradually shifted from wired communications to wireless communications, as can be seen from their popularity in wireless home electronics and mobile phones. The transmitting medium of choice has changed from conventional metal wires (such as coaxial cables) to air. Antennas are the key component of wireless communication devices for sending and receiving electromagnetic (EM) signals. That is, a wireless communication device needs to have an antenna in order to send or receive EM waves. Therefore, the antenna is an indispensable component in wireless communication devices. 
   In conventional wireless communication devices, most antennas are external. In recent years, with the rapid advances of mobile technology, more antennas have become internal. 
   Nevertheless, both external and internal antennas have their drawbacks in transmitting and receiving signals. For example, external antennas experience the phantom head effect at low frequencies and thus have large efficiency loss. Internal antennas have serious energy dissipation when in close proximity to components such as microphones or cameras. 
   It is therefore desirable to provide an antenna that can solve the aforementioned problems simultaneously. 
   SUMMARY OF THE INVENTION 
   An objective of the invention is to provide an antenna not only for reducing energy dissipation caused by internal components at high frequencies but also for reducing efficiency loss caused by the phantom head effect at low frequencies. 
   According to a preferred embodiment of the invention, a high-band portion and a low-band portion of an antenna are separately formed and disposed on an antenna case. The high-band portion is exposed outside the antenna case to avoid the energy dissipation at high frequencies due to nearby components. The low-band portion is hidden inside the antenna case to reduce the efficiency loss at low frequencies due to the phantom head effect. Therefore, the invention can solve the conventional problems described above. 
   According to another embodiment of the invention, a high-band portion and a low-band portion are separately formed and disposed on an antenna case. In addition, the high-band portion is bent so that it is completely hidden inside the antenna case, and a clearance area is formed in the antenna case to keep the high-band portion from the grounded surface of the substrate by an appropriate distance. Therefore, the antenna is prevented from being damaged as a result of being exposed to the environment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the invention will become apparent by reference to the following description and accompanying drawings which are given by way of illustration only, and thus are not limitative of the invention, and wherein: 
       FIG. 1A  shows an antenna according to a preferred embodiment of the invention; 
       FIG. 1B  shows a wireless communication device using the antenna of  FIG. 1A ; 
       FIG. 2A  shows an antenna according to another embodiment of the invention; and 
       FIG. 2B  shows a wireless communication device using the antenna of  FIG. 2A . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
     FIG. 1A  shows an antenna  100  according to a preferred embodiment of the invention. The antenna  100  includes a high-band portion  101 , a low-band portion  102 , and an antenna case  103 . 
   In this embodiment, the high-band portion  101  is a meander-line antenna exposed outside the antenna case  103 . The low-band portion  102  is a planar inverted-F antenna (PIFA) hidden inside the antenna case  103 . The high-band portion  101  is coupled to the low-band portion  102  and has a feeding point  104  and a ground point  105 . The feeding point  104  is coupled to a RF (radio frequency) module  140  disposed on a substrate  120  of the system, as shown in  FIG. 1B . 
     FIG. 1B  shows a wireless communication device  150  using the antenna  100  of  FIG. 1A . The wireless communication device  150  includes an antenna  100 , an antenna installation region  130 , a substrate  120 , and a housing  110 . When the antenna  100  is mounted to the housing  110 , the antenna  100  is disposed in the antenna installation region  130 , away from other components on the substrate  120 . The high-band portion  101  is exposed outside the substrate  120  of the wireless communication device  150 . 
   As shown in  FIG. 1B , the high-band portion  101  is used to transmit and receive high-frequency signals and can prevent energy dissipation caused by nearby components, such as microphones and cameras, at high frequencies. The low-band portion  102  is used to transmit and receive low-frequency signals and can prevent efficiency loss due to the phantom head effect. 
     FIG. 2A  shows the antenna  200  according to another embodiment of the invention. The antenna  200  includes a high-band portion  201 , a low-band portion  202 , and an antenna case  203 . 
   In this embodiment, the high-band portion  201  is an inverted-F antenna (IFA), and the low-band portion  202  is a PIFA. The high-band portion  201  and the low-band portion  202  are coupled to share the same feeding point  204  and ground point  205 . The feeding point  204  is coupled to a RF module  240  disposed on a substrate  220  of the system, as shown in  FIG. 2B . The low-band portion  202  is disposed on the antenna case  203 , and the high-band portion  201  has a turning portion. 
     FIG. 2B  shows a wireless communication device  250  containing the antenna  200  of  FIG. 2A . The wireless communication device  250  includes an antenna  200 , an antenna installation region  230 , a substrate  220 , and a housing  210 . When the antenna  200  is mounted to the housing  210 , the antenna  200  is disposed in the antenna installation region  230 , away from other components on the substrate  220 . 
   In comparison with  FIG. 1A , the high-band portion  201  in this embodiment is hidden inside the case  203  of the antenna  200 . However, a clearance area is required for the high-band portion  201  to keep an appropriate distance from the grounded surface of the substrate. This embodiment thereby achieves the same effects as in the first embodiment. Moreover, not only does this embodiment prevent the antenna from being damaged as a result of being exposed to the environment, but it also reduces additional complications in circuit design and inconvenience in carrying. In addition, the entire case of the wireless communication device can keep its integrity, and the antenna has a longer lifetime. 
   The disclosed antenna can simultaneously prevent efficiency loss caused by nearby components and the phantom head effect. Combining the aforementioned advantages, the disclosed antenna can be widely applied to future wireless communication devices. 
   It should be emphasized that the antennas in the above-mentioned embodiments are only examples of the invention and thus should not be used to restrict the types of antennas in the invention. For example, the high-band portion of the invention may be a spiral antenna, IFA, or meander-line antenna. 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 
   While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. To 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.