Patent Publication Number: US-6211828-B1

Title: Retractable antenna unit for a mobile phone

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a compact mobile phone, and more particularly a retractable antenna unit provided in a mobile phone operating in a low frequency band. 
     2. Description of the related art 
     A mobile phone, such as a cellular phone, is typically provided with a whip or helical antenna, whose length is λ/4 or 3λ/4, where λ is the wavelength of the received signal in accordance with the operating frequency. If a whip antenna is used, it must be in a extended position to maximize efficiency during calls, making it less compact and therefore, inconvenient for the user to carry. On the other hand, a helical antenna has a short physical length, and hence does not bring about such inconvenience. However, the efficiency of a helical antenna is low when compared to that of a whip antenna, due to its short physical height. Therefore, due to the helical antenna&#39;s degraded performance when compared to the whip antenna, it is desirable to have an antenna with a relatively longer physical height, such as the whip antenna. 
     In this view, a retractable antenna has been developed which combines a whip and helical antenna to realize the advantages of both types of antenna. Such an antenna is well disclosed in U.S. Pat. No. 5,479,178. Referring to this patent, when a mobile phone stands by to receive a call, the whip antenna may be retracted into the casing of the mobile phone, utilizing only the helical antenna for receiving incoming calls. When communication is established, the whip antenna may be completely extended from the casing to improve communication quality for the duration of the call. 
     However, such a retractable antenna would only be sufficient for the end if the body of the mobile phone is long enough to fully receive the retracted length of the whip antenna. Moreover, there is a trend toward making mobile phones more compact, especially with the current state of development of VLSI (very large system integration) technology, making space in a mobile phone&#39;s casing a premium. Further, when retracting the whip antenna into the casing, it must be decoupled from the wave feeding point. However, if the space for retracting the whip antenna into the casing is lacking, it becomes impractical to achieve complete decoupling. 
     Consequently, space is one of the key factors limiting the design of an antenna. Therefore, a need exists for a retractable antenna unit combining a whip antenna with a helical antenna, wherein the whip antenna of length λ/3 or 3λ/4 can be completely 
     retracted into a compact mobile phone while the helical antenna remains projected outside of the casing. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a retractable antenna unit for a compact mobile phone, having a metal tube contacted with and supplementing the length of the helical antenna, the metal tube also supplementing the length of the whip antenna while extended. 
     It is another object of the present invention to provide a retractable antenna unit with a metal tube to increase space for housing the whip antenna in a retracted position and achieve complete decoupling of the whip antenna, for a mobile phone operated in a low frequency band. 
     According to an embodiment of the present invention, a retractable antenna unit for a mobile phone includes an antenna housing, a helical antenna installed in the antenna housing, a whip antenna having an upper end provided with a knob and a lower end provided with a stopper, the stopper being also provided with a feeder part, and a metal tube for supplementing the length of the helical antenna when the whip antenna is completely retracted into the antenna housing, or serving to extend the physically effective length of the whip antenna when the whip antenna is completely extended from the antenna housing, whereby the wave feed position of the whip antenna is raised when the whip antenna is completely pulled out from the antenna housing. 
    
    
     BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS 
     The above and other objects, features, and advantages of the present invention will become more apparent in light of the following detailed description of an exemplary embodiment thereof taken in conjunction with attached drawings in which: 
     FIG. 1 is a perspective view for illustrating a flip type mobile phone provided with the antenna unit of the present invention; 
     FIG. 2 is a partial cross sectional view of the antenna housing portion of a mobile phone illustrating the whip antenna of the present invention retracted into the casing of the mobile phone; 
     FIG. 3 is a partial cross sectional view illustrating the whip antenna of the present invention completely extended from the casing; and 
     FIG. 4 is a perspective view for illustrating the retractable antenna unit provided with a metal tube according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, in which like reference numerals identify similar or identified elements throughout the several views, and the detailed descriptions of elements not directly relating to the invention are omitted for clarity. 
     FIG. 1 shows a flip-type mobile phone, wherein the antenna unit of the invention is incorporated. Note however, the antenna of the present invention can be used with other types of mobile phones. The casing of the flip-type mobile phone comprises a body  300 , flip  350 , and hinge mechanism  2   a  for connecting the flip to the body. The flip  350  may be opened away or closed toward the body  300 , pivoting about the central axis A 1  of the hinge mechanism  2   a . Mounted on the top right side of the body  300  is an antenna unit  200 , beneath which the keypad (not shown) is located. The microphone  312  is mounted below the key pad and an car piece (not shown) is mounted on the upper part of the folder  350 , including a speaker. The LCD (not shown) is provided below the ear piece. The LCD displays the operational information including the data input through the key pad. 
     The antenna of the present invention will now be described with reference to FIGS. 2 and 3. A metal tube  30  is employed to supplement the overall physical length of the whip antenna, which is limited by the compact height of the mobile phone. The metal tube  30  serves to extend both the operational length of the helical part  101  of the helical antenna  10 , when the whip antenna  20  is retracted into the casing (body) of the mobile phone, and the operational length of the whip antenna  10 , when the whip antenna  20  is fully extended from the casing of the mobile phone. Namely, the helical antenna  10  comprises the helical part  101  and the metal tube  30 , and the metal tube  30  also serves to supplement the length of the whip antenna  20  when the whip antenna  20  is completely extended from the casing. Hence, by adjusting the lengths of the helical part  101  and metal tube  30 , the overall storage space in the mobile phone will increase to accommodate the desired length whip antenna  30 , making the addition of metal tube  30  advantageous for a compact size mobile phone operated in a low frequency band. 
     The added space provided by the metal tube  30  allows the whip antenna to completely retract into the casing of a compact mobile phone, making it possible to store an antenna of length 0.25 λ, for instance, even in a low frequency band CDMA (Code Division Multiple Access) and GSM (Global System for Mobile Communication) system. The problems of the prior art are overcome by substituting the metal tube  30  for a potion of the helical antenna, so that the helical antenna  10  and whip antenna  20  each have an overall length of 0.25 λ, for instance, while providing enough storage space for retracting a whip antenna of sufficient length to maximize efficiency. 
     Referring to FIG. 2, when the whip antenna  20  is completely retracted into the casing, the helical antenna  10 , comprising the helical part  101  and metal tube  30  serves as the effective antenna. The metal tube  30  is integrally formed with a threaded antenna fitting  40  and inserted into an antenna housing  400 , which is mounted on the body  300  of the mobile phone by means of the antenna fitting  40 . The knob rod  202  of the whip antenna must be insulated to a length sufficient to prevent coupling between the antenna fitting  40  and helical part  101 , since, when completely retracted, the knob rod  202  is positioned throughout the helical part  101 , metal tube  30  and antenna fitting  40 . 
     Referring to FIG. 2, reference symbol L 1  represents the physical operational length of the helical part  101 , and L 2  the length of the metal tube  30  projected from the casing, so that the total operational length L 3  of the helical antenna  10  is L 1 +L 2 , while the whip antenna  20  is completely retracted into the casing. 
     Referring to FIG. 3, when fully extended from the casing, the whip antenna  20  has the stopper  205  contacting the upper end of the metal tube  30 , so that its operational length is supplemented by the length L 2  of the metal tube  30 . L 2  represents the length of the metal tube projected from the casing, and L 4  the length of the extended whip antenna  20 , so that the total operational length L 5  of the whip antenna  20  is L 2 +L 4 . Accordingly while, completely extended from the casing, the whip antenna  20  has an effective length of L 5 . Thus, the metal tube  30  is commonly used by both the helical antenna  10  and whip antenna  20 . 
     FIG. 4 illustrate s the structure of the antenna unit in more detail. The whip antenna  20  is designed to be retracted into or extended from the casing while the helical antenna  10  is fixedly installed in the antenna housing  400 . The whip antenna  20  has an antenna knob  201  at the upper end, and a stopper  205  at the lower end. The stopper  205  is provided with a first wave feeding a metal part  204 . The metal tube  30  and antenna fitting  40  serve as a second wave feeding metal part corresponding to the first wave feeding metal part  204 . The upper end  301  of the metal tube  30  is partially opened while the lower end fully opened (not shown). The whip antenna  20  may be retracted or extended through the cylindrical space of the second wave feeding metal. When the whip antenna is fully extended from the casing, the first wave feeding metal part  204  contacts the upper end  301  of the metal tube  30 . On the contrary, while the whip antenna is fully retracted into the casing, the knob rod  202  of the whip antenna  20  is positioned throughout the inside of the helical antenna  10  and the second wave feeding metal part, namely, the metal tube  30  and antenna fitting  40 . Additionally, the upper end  101   a  of the helical part  101  may be bent to reduce the space between the surface of the whip antenna  20  and the helical part  101 , and thereby improving the coupling action between the whip antenna  20  and the helical part  101 . Thus, the invention substitutes a metal tube for part of the helical antenna to supplement the physical length of the whip antenna for a compact mobile phone operated in a low frequency band. 
     While the present invention has been described in connection with specific embodiments accompanied by the attached drawings, it will be readily apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the scope and spirit of the present invention as defined by the appended claims.