Abstract:
An antenna system includes a main antenna ( 16 ) and a parasitic element ( 18 ). The parasitic element ( 18 ) is rotatably coupled ( 24 ) to the main antenna ( 16 ), the antenna system being movable from a closed position to an open position, in which the main antenna ( 16 ) is coupled to the parasitic element ( 18 ) to cause the parasitic element ( 18 ) to operate as a passive radiator element and to radiate ( 32 ) along with the main antenna ( 34 ) to enhance the gain of the antenna system.

Description:
TECHNICAL FIELD 
     This invention relates generally to antennas and more specifically, to antennas for use in portable communication devices. 
     BACKGROUND 
     Antennas used in portable communication applications typically have problems with sensitivity when worn on, or used near, the human body because of the loading effects associated therewith. Additional problems associated with antennas used in portable communication applications are the limitation on the size of the antenna and the undesirability of antennas protruding from the communication device. As the size of the antenna becomes smaller to accommodate a shrinking communication device, the efficiency of the antenna decreases. 
     Communication devices, such as a phone and/or radio combination and other handsets are often designed as small as possible in order to make the device more portable. In order to keep the handset small, features such as retractable antennas are incorporated into the handset so that the handset will not occupy as much space when inserted into a pocket. The challenge is then to optimize antenna performance while providing an ergonomically suitable solution for the user. 
     Accordingly, it is desired to provide an antenna that may be used in a communication device that avoids the detriments of prior antennas used for the same or similar applications. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional side view of a portable communication device with an antenna array in the open position, in accordance with the present invention. 
     FIG. 2 is a back view of the communication device shown in FIG. 1, in accordance with the present invention. 
     FIG. 3 is a representation of the flip  14  of FIG. 2 showing a second embodiment of the parasitic radiator  18 . 
     FIG. 4 is a representation of the flip  14  of FIG. 2 showing a third embodiment of the parasitic radiator  18 . 
     FIG. 5 is a representation of the flip  14  of FIG. 2 showing a fourth embodiment of the parasitic radiator  18 . 
     FIG. 6 is a representation of the flip  14  of FIG. 2 showing a fifth embodiment of the parasitic radiator  18 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown a simplified cross-sectional view of the communication device  10 , in the open position. The communication device  10  is a portable handset or wireless phone for the present application but can be any other type of electronic devices. The communication device  10  includes a first member or a main housing  12  and a second member or a flip or a flap  14  for the main housing, not necessarily shown in the actual proportionate relationship with each other. For example, the flip  14  is often much thinner and smaller than the main housing  12 . In some applications, the second member may be a sliding or a planar rotating piece sliding or rotating away form the first member, respectively. 
     The second member  14  is rotatably attached to the first member by means of a hinge  24  (or any other hinge or rotational mounting means) in a clam-style arrangement. The communication device  10  is shown in an open position where the flip or second member  14  is positioned away from the housing or first member  12  at an obtuse angle  26  preferably within a range of 145 to 155 degrees for ergonomics or greater than 145 degrees for greater capacitive coupling of the antenna array consisting of a main antenna  16  and a parasitic element or radiator  18 . 
     The main antenna  16  is attached to the first member  12  for vertical or angled extension at an acute angle, preferably between 15 and 35 degrees with the flip  14 . The parasitic element or radiator  18  is attached to or disposed on the second member  14 . In this embodiment, the two components of the antenna array, the main antenna  16  and the radiator  18 , are not physically connected. They are, however, electromagnetically coupled to each other due to their substantially parallel arrangement. In the preferred embodiment, the two antenna components  16  and  18  radiate and receive simultaneously in the electric-field mode (i.e., they transmit and receive E field waves) and at the same resonating frequency. Alternatively, the main antenna  16  and the parasitic element  18  can resonate at two different frequencies, not too far apart, in case more of an impedance bandwidth is desired. The latter is necessary when an antenna for multimode products is desired. For instance, products operating at both the 800 MHz and 900 MHz range. Such products require that the antenna cover close to 200 MHz in bandwidth. This is very difficult to accomplish at such low frequencies due to the inherent bandwidth of the antenna topology and the size of the product. One approach to accommodate the increase in the bandwidth is to use a matching circuit, but these circuits do add losses to the signal path. A workable alternative is presented in the instant application. The ability to increase the bandwidth is becoming more and more common as portable communication devices tend to become more “world”-roaming capable. 
     Electrically, the incident electric field induces a current J to flow on the parasitic element  18  causing it to become excited and radiate to form an array system with the antenna  16 . The flow of this current on the element  18  radiates back in the direction or beam  32  towards the antenna  16  in such a way that the two elements of the array  16  and  18  constructively interfere with one another. The parasitic element  18 , when thus coupled with the main antenna  16 , forms a new radiation pattern which represents the combination of the main antenna  16  and the parasitic element  18 . This constructive combination is such that the radiated energy undergoes a change which allows an increase in the overall electric field magnitude in a direction opposite to the user. This very phenomenon improves the antenna overall efficiency. In addition, this constructive interference allows an improvement at the points in the radiation pattern where nulls are present in the case of a single element. 
     A display  20  and a keypad  36  are also located on the first member or housing  12 . A speaker  22  and a transparent display screen  28  for allowing the display  20  to show through underneath, when the flip is collapsed or otherwise closed on top of the housing  12  (as in a closed clam-shell configuration), is contained in the second member  14 . The speaker  22  is mounted within the second member  14  and a microphone  30  is mounted within the first member  12  so that persons using the communication device  10  may hold to their faces the side containing the exterior portions of the speaker  22  and of the microphone  30 . A keypad  36  may be located on this same side of the communication device  10 . 
     Signals  32  and  34  are radiated mostly in the direction shown by the arrow (i.e., they are unidirectional in a directed beam of an antenna array). This direction is intentionally away from the user in order to avoid the adverse loading effects the user presents to the signal. Analyzed from a different perspective, the parasitic radiator  18  also operates as an escape route for the highly excited currents from the speaker&#39;s wires or other audio lines connecting the speaker  22  on the flip  14  via the hinge  24  to the rest of the audio circuit in the main housing  12  PCB to flow into. This parasitic radiator  18  has also shown to reduce hand proximity effects when a users hand is holding the flip  14  and the housing  12 . Therefore, the communication device  10  has the advantage over other communication devices in that it includes an antenna array which helps to improve the overall radiation and reduce the unwanted hand proximity effects. 
     Referring to FIG. 2, a simplified back-view of the communication device  10  is represented to show the different variations contemplated by the teachings of the present invention for the parasitic element  18  of FIGS. 3-6. The parasitic radiator or element  18  or  183 - 186  (FIGS. 3-6) is a quarterwave or a half-wavelength element, at the operating frequency of the antenna  16 . Electrically, the parasitic radiator  18  is preferably a self-resonating metallic strip line which is plate or patch shaped in physical dimensions sufficient to result in an appropriate surface impedance which is directly proportional to the incident tangential field and inversely proportional to the amplitude of the surface current density of the surface of the plate. Because of the self resonance of the antenna array and proper coupling of elements  16  and  18 , there is no need for a direct connection for the element  18 . In addition to the aforementioned benefits, the strip line  18  will still contribute to the overall radiation of the antenna  16  to increase the overall antenna system gain. 
     The parasitic radiator  18  could be implemented as a metallized layer of paint, a metal plate or patch, on the inside or outside surfaces or within the flip  14  to form the self-resonating metallic strip line. Alternatively, the radiator  18  may be implemented as a metallized layer of paint in the form of a self resonance element. Due to the presence of the electric field, this element does not need a direct feed point. In this case, even though the parasitic radiator  18  does not need to be grounded, it could be optionally grounded at one end, or anywhere along the path of the element  18 , to a printed circuit board main ground point  48  in the housing  12 . 
     The ground selection and shape variation of the parasitic element  18  are optimized during testing, depending on the actual type of phone used and the frequency of operation. To correspond with the outer contour or otherwise follow the periphery or other portions of the phone to result in a sufficient surface impedance, the parasitic radiator  18 ,  183  or  185  can be implemented as a U-shaped metallic patch. Alternatively, a substantially D-shaped metallic patch  184  or  186  corresponding to the outer contour of the flip  14  or corresponding to the outer contour of the display screen  28  may be used. Optional cuts or openings  52  may be used in the path to add capacitance. An optional center stub or other tabs  54  may be employed to allow for inductance tuning. 
     In summary, an antenna system takes benefit from the form factor of a communication device to accomplish improved performance. This improvement is realized by having multiple elements which combine to produce better radiation and gain performance. 
     While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.