Patent Publication Number: US-6707431-B2

Title: Dual antenna capable of controlling radiation characteristics in a mobile communication terminal

Description:
PRIORITY 
     This application claims priority to an application entitled “Dual Antenna Capable of Controlling Radiation Characteristics in a Mobile Communication Terminal” filed in the Korean Industrial Property Office on Jul. 20, 2001 and assigned Serial No. 2001-43729, and an application entitled “Dual Antenna Capable of Controlling Radiation Characteristics in a Mobile Communication Terminal” filed in the Korean Industrial Property Office on Sep. 21, 2001 and assigned Serial No. 2001-58697, the contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an antenna for a mobile communication terminal such as a mobile phone, and in particular, to a dual antenna capable of controlling radiation characteristics in a mobile communication terminal. The mobile communication terminal, preferably, a folder type (or dual-LCD (Liquid Crystal Display) folder type) mobile communication terminal, has two directional antennas—one is mounted on a folder and another on a body of the mobile communication terminal such that the radiation characteristics are separately controlled in a suspended state where the folder is folded toward the body and a call state where the folder is unfolded away from the body, contributing to an improvement in antenna performance and a reduction in electromagnetic waves that radiate toward a user&#39;s head. 
     2. Description of the Related Art 
     In general, a mobile communication terminal employs an omni-directional, retractable antenna to support duplex transmission and secure portability. A conventional mobile communication terminal has two separate antennas—one is used in a suspended state and another in a call state. The antennas are designed to easily receive and transmit linearly polarized signals. Typically, a spring-shaped helical antenna is mounted on an upper end of the mobile communication terminal. The helical antenna is advantageous in that it enables a call regardless of the direction in which the mobile communication terminal is placed. Further, a monopole-type retractable whip antenna shows better performance than the helical antenna in a state where the mobile communication terminal (or the whip antenna) stands at right angles to the ground. Ideally, however, it is known that when the whip antenna is kept horizontal to the ground, it cannot receive signals. The isotropic (or omni-directional) helix/whip combined antenna of FIGS. 1 and 2 is mounted on an upper end of the mobile communication terminal, as illustrated in FIG.  3 . 
     FIGS. 4A and 4B illustrate an equivalent circuit of the isotropic helix/whip combined antenna. Since the combined antenna is isotropic, it has the omni-directional radiation characteristics centering on a mobile communication terminal  412  as represented by a circle  411  of FIGS. 4A and 4B, causing radiation of electromagnetic waves toward a head of the user during a call. The isotropic combined antenna has a good radiation characteristic when it is spaced apart from the head of the user. However, when it comes close to the head of the user, an amount of the electromagnetic waves absorbed into the user&#39;s head is increased, resulting in a reduction in antenna performance and an increase in SAR (Specific Absorption Rate) representing a degree of the influence of electromagnetic waves on the human body. Accordingly, mobile phone makers and antenna makers are investing a lot of money and manpower in developing an improved antenna capable of preventing the electromagnetic waves from being radiated toward the head of the user. As an alternative, a scheme for radiating most of the electromagnetic waves at the rear of the mobile phone has been proposed. To accomplish this, a patch antenna or a PIFA (Planar Inverted-F Antenna) antenna is typically mounted on an upper end of the rear side of the mobile phone. The antenna prevents the electromagnetic waves from being radiated in the front of the mobile phone, i.e., toward the human body, resulting in an improvement in call quality and a reduction in SAR when it approach the user&#39;s head. However, when it is spaced apart from the user&#39;s head, the antenna may not properly receive waves from a specific direction, thus deteriorating performance of the mobile phone. In this case, the electromagnetic waves radiated in the front of the mobile phone are deceased, whereas the electromagnetic waves radiated in the rear of the mobile phone are increased. Accordingly, when the user talks over the mobile phone with the phone put in his or her pocket, damages caused by the electromagnetic waves may increase undesirably. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a dual antenna capable of minimizing the influence of electromagnetic waves on the human body without performance reduction, by separately controlling two antennas mounted on a mobile phone in a call state and a suspended state. 
     It is another object of the present invention to provide a dual antenna with improved performance in a folder type mobile communication terminal, wherein two antennas have directivities, i.e. radiate and receive signals, in the same direction to reduce electromagnetic waves radiated toward a user&#39;s head in a call state where a folder is unfolded while the two antennas have directivities in an opposite direction to make the overall directivity omni-directional thus to increasing performance in a suspended state where the folder is folded. 
     It is further another object of the present invention to provide a dual antenna capable of minimizing the influence of electromagnetic waves on the human body without performance reduction by mounting two patch antennas on the rear of a body of a dual-LCD folder type mobile communication terminal and an outer widow of the dual-LCD folder, respectively. 
     According to one aspect of the present invention, there is provided a dual antenna capable of controlling a radiation characteristic in a folder type mobile communication terminal. The dual antenna comprises a first directional antenna mounted on a folder of the mobile communication terminal, and a second directional antenna mounted on a body of the mobile communication terminal. In a suspended state where the folder is folded against the body, the first and second directional antennas have directivities in an opposite direction. However, in a call state where the folder is unfolded away from the body, the first and second directional antennas have directivities in the same direction. 
     Preferably, the second directional antenna is mounted on a rear side of the body of the mobile communication terminal, and the first directional antenna is mounted on an outer side of the folder of the mobile communication terminal. 
     Preferably, the first and second directional antennas are each comprised of a microstrip patch. 
     According to another aspect of the present invention, there is provided a dual antenna capable of controlling a radiation characteristic in a dual-LCD (Liquid Crystal Display) folder type mobile communication terminal with a dual-LCD folder and a body. The dual antenna comprises a first directional antenna mounted on the dual-LCD folder, and a second directional antenna mounted on the body. In a suspended state, the first and second directional antennas have directivities in an opposite direction. However, in a call state, the first and second directional antennas have directivities in the same direction. 
     Preferably, the first directional antenna is a POD (Printed-On-Display) antenna. Further, the POD antenna is mounted on an outer window of the dual-LCD folder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
     FIGS. 1 and 2 illustrate general helical and whip antennas, wherein the helical antenna is coupled to an end of the whip antenna; 
     FIG. 3 illustrates general helical and whip antennas, wherein the helical antenna is coupled to a body of a flip type mobile communication terminal; 
     FIGS. 4A and 4B illustrate an equivalent circuit of an antenna in a folder type mobile communication terminal with conventional helical and whip antennas, and also illustrate a radiation pattern in an azimuth pattern according to whether a folder is folded or unfolded; 
     FIGS. 5A and 5B illustrate directional antennas comprised of a microstrip patch according to an embodiment of the present invention; 
     FIGS. 6A and 6B illustrate a folder type mobile communication terminal with the direction antennas of FIGS. 5A and 5B mounted respectively on a folder and a body thereof; 
     FIGS. 7A and 7B illustrate an equivalent circuit of the directional antennas in a folder type mobile communication terminal according to an embodiment of the present invention; 
     FIG. 8 illustrates a radiation pattern in an azimuth pattern depending on whether a folder is folded or unfolded according to an embodiment of the present invention; and 
     FIGS. 9 and 10 illustrate a dual-LCD folder type mobile communication terminal with directional antennas according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
     FIGS. 5A and 5B illustrate first and second directional antennas each comprised of a microstrip patch according to an embodiment of the present invention. Specifically, FIG. 5A is a side view of a microstrip patch antenna mounted on the front side of a folder  400  or the rear side of a body  401  in FIGS. 4A and 4B. FIG. 5B is a plane view of the microstrip patch antenna mounted on the front side of the folder  400  or the rear side of the body  401 . 
     In FIGS. 5A and 5B, reference numeral  502  represents a substrate having a predetermined dielectric constant, and reference numeral  501  represents a microstrip line made of high-conductivity material. The microstrip patch antenna is advantageous in that it does not have space limitation. Ferrite and air or composite material thereof can be used as dielectrics for, the substrate  502 . In addition, a multi-layered substrate can also be used as the substrate  502 . 
     FIGS. 6A and 6B illustrate a folder type mobile communication terminal with the microstrip patch antennas of FIGS. 5A and 5B mounted respectively on a folder  400  and a body  401  thereof. Specifically, FIG. 6A illustrates a suspended state where the folder  400  is folded against the body  401 , and FIG. 6B illustrates a call state where the folder  400  is unfolded away from the body  401 . In FIGS. 6A and 6B, reference numerals  501   a  and  501   b  represent microstrip lines of the microstrip patch antennas, and reference numerals  502   a  and  502   b  represent dielectric substrates. Further, reference numeral  601  represents a PCB (printed circuit board) on which electronic circuits of the folder  400  and the body  401  are arranged. The microstrip patch antennas mounted on the folder  400  and the body  401  are connected to the electronic circuits on the PCB  601 . In addition, reference numeral  706  represents a feeding point. 
     FIGS. 7A and 7B illustrate a folder type mobile communication terminal with first and second directional antennas mounted respectively on a folder  400  and a body  401  according to an embodiment of the present invention, and its equivalent circuit. Specifically, FIG. 7A illustrates a suspended state where the folder  400  is folded against the body  401  of the mobile communication terminal, wherein the two directional antennas have directivities in the opposite direction, thus providing an omni-directional radiation characteristic  701 . FIG. 7B illustrates a call state where the folder  400  is unfolded away from the body  401  of the mobile communication terminal, wherein the first and second directional antennas have directivities in the same direction, providing a directional radiation characteristic  702 , so that the electromagnetic waves radiated toward the user&#39;s head are remarkably decreased. 
     In the suspended state of FIG. 7A, the mobile communication terminal maintains the omni-directional radiation characteristic  701  like the conventional mobile communication terminal of FIG.  4 A. However, in the call state of FIG. 7B where the user unfolds the folder  400  to make or answer a call, the mobile communication terminal has the directional radiation characteristic  702 , thus making it possible to reduce electromagnetic waves absorbed into the user&#39;s body during the call. 
     Therefore, unlike the conventional mobile communication terminal illustrated in FIGS. 4A and 4B, the mobile communication terminal according to the present invention has the first and second directional microstrip patch antennas mounted respectively on the folder  400  and the body  401 . The two antennas have directivities in the same direction or opposite direction according to whether the folder  400  is folded against or unfolded away from the body  401 . To be specific, the antennas have directivities in the opposite direction in the suspended state, thus securing the omni-directional radiation characteristic  701 , and have directivities in the same direction in the call state, thus providing the directional radiation characteristic  702 . 
     FIG. 8 illustrates a change in the radiation characteristics when the folder  400  is folded against and unfolded away from the body  401 . Reference numeral  801  represents a radiation pattern when the folder  400  is unfolded, and reference numeral  802  represents a radiation pattern when the folder is folded. When the folder  400  is folded, the radiation pattern becomes omni-directional, so the antennas have the same radiation characteristics as the conventional antennas. However, when the folder  401  is unfolded, the electromagnetic waves radiated toward the user&#39;s head are reduced, thus contributing to a decrease in SAR representing an amount of electromagnetic waves absorbed into the user&#39;s head. The first and second directional microstrip patch antennas  501   a  and  501   b  show a first directional antenna characteristic and a second directional antenna characteristic centering on the folder  400  and the body  401 , respectively. 
     In the suspended state illustrated in FIG. 7A where the folder  400  is folded, the antennas  700  and  707  comprised of the microstrip path antennas  501   a  and  501   b  have directivities in the opposite direction, thus providing omni-directional radiation characteristics like the conventional omni-directional antennas. 
     However, in the call state illustrated in FIG. 7B where the folder  400  is unfolded away from the body  401  at a specific angle, the antennas  700  and  707  comprised of microstrip patch antennas  501   a  and  501   b  have directivities in the same direction, thus providing directional radiation characteristics. Therefore, the electromagnetic waves radiated toward the user&#39;s head are reduced as represented by reference numeral  702  of FIG.  7 B. 
     Another embodiment of the present invention will be described with reference to FIGS. 9 and 10. 
     FIG. 9 illustrates a dual-LCD folder type mobile communication terminal with a separate window  611  formed on an outer side of a dual-LCD folder  402 . The body  401  has the microstrip patch antenna  501   b  of FIGS. 5A and 5B mounted on the rear side thereof, whereas the dual-LCD folder  402  has a POD (Printed-On-Display) antenna  612  mounted on the LCD window  611 . The POD antenna  612  is made of ITO (Indium oxide doped with Thin Oxide), which is electrically conductive and optically transparent. The POD antenna  612  is well disclosed in a pager “Realization of a Printed-On-Display Antenna for Mobile Terminals”, Antennas and Propagation Society International Symposium and UNSNC/URSI National Radio Science Meeting, 2001 IEEE. According to the pager, the POD antenna is designed to replace the conventional helical or monopole antenna, and to support both the display function and the antenna function. Further, the POD antenna is designed to make up for the mechanical drawback of the conventional antenna. Also in this embodiment, when the dual body  401  with the microstrip patch antenna  501   b,  the two antennas have directivities in the opposite direction, providing omni-directional radiation characteristics. However, when the dual-LCD folder  402  is unfolded away from the body  401 , the two antennas have directivities in the same direction, providing radiation characteristics such that the electromagnetic waves are radiated in an opposite direction of the user&#39;s head. 
     As described above, the antennas have different radiation patterns according to whether the folder (or dual-LCD folder) is folded or unfolded. Specifically, in the call state where the folder is unfolded, the two antennas have directional radiation characteristics so that the electromagnetic waves radiated toward the user&#39;s head are reduced. In the suspended state where the folder is folded, the two antennas have directivities in the opposite direction, thus providing omni-directional radiation characteristics so that the mobile communication terminal correctly receives signals. 
     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.