Abstract:
A variable extended cable antenna designed for cellular telephone use and which has two electrical functions; first, as a fully extended directly coupled helical top loaded 3/4 wave antenna and second, as a 1/4 wave helical antenna when it is recessed down into the cellular telephone.

Description:
This is a continuation-in-part application of application Ser. No. 08/595,360 filed Feb. 1, 1996, entitled &#34;A Variable Extended Cable Antenna for a Cellular Telephone&#34; now abandoned, which is a continuation application of application Ser. No. 08/094,783 filed Jul. 20, 1993, entitled &#34;A Variable Extended Cable Antenna for a Cellular Telephone&#34; now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an antenna for a cellular telephone and more particularly to a variable extended cable antenna which has two electrical functions; namely, first as a fully extended directly coupled helical top loaded 3/4 wave antenna and second as a 1/4 wave helical antenna when the antenna is retracted into the telephone. 
     2. Description of the Prior Art 
     Cellular telephones have become extremely popular in recent years. It has been found that the cellular telephones are more compact and portable when they are provided with retractable antennas. However, the retractable characteristics of the antenna interferes with the performance thereto especially when the antenna is retracted. 
     One type of retractable antenna is that manufactured by Galtronics which has been marketed as a &#34;Retractable&#34; two-in-one antenna. The Galtronics antenna consists of a full 1/4 wave element plus a 1/4 wave helical element in one antenna. There is no electrical connection between the two elements which therefore limits the antenna to a 1/4 wave antenna. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating the intent of this invention and its relationship to a cellular telephone; 
     FIG. 2 is an exploded perspective view of the antenna of this invention; 
     FIG. 3 is a partial sectional view of the telephone; 
     FIG. 4 is a vertical sectional view illustrating this antenna and its relationship to a cellular telephone; 
     FIG. 5 is a view similar to FIG. 4 except that the antenna is shown in its retracted position; and 
     FIG. 6 is a schematic of the circuitry of the antenna. 
    
    
     SUMMARY OF THE INVENTION 
     A retractable antenna is disclosed for use with a cellular telephone which has a housing including an antenna receptacle at the upper end thereof which is RF coupled to the telephone circuitry within the telephone housing. The antenna of this invention comprises an elongated pin having an elongated cable antenna element connected to the upper end thereof. A 1/4 wave helical antenna element is connected to the upper end of the metal shaft and is enclosed by an adapter and a cap. A connector is removably secured to the antenna receptacle in the housing and has the antenna selectively slidably mounted therein. The antenna may be moved from a fully retracted position within the housing to a fully extended position. 
     The helical antenna element is RF coupled to the antenna receptacle and the telephone circuitry, when the retractable antenna is in its fully retracted position, whereby the antenna functions as a 1/4 wave antenna. When the antenna is in its fully extended position, the cable antenna element and the helical antenna element are RF coupled to the antenna receptacle and the telephone circuitry, through the pin, whereby the antenna functions as a 3/4 wave antenna when the antenna is in its fully extended position. 
     A principal object of the invention is to provide a retractable antenna for a cellular telephone. 
     A further object of the invention is to provide a retractable antenna which functions as a 1/4 wave antenna when the antenna is in its retracted position and which functions as a 3/4 wave antenna when it is in a fully extended position. 
     A further object of the invention is to provide a variable extended cable antenna designed for cellular telephone use wherein the antenna has two electrical functions, first as a fully extended directly coupled helical top loaded 3/4 wave antenna and second as a 1/4 wave helical antenna when it is recessed down into the cellular telephone. 
     Yet another object of the invention is to provide a retractable antenna of the type described above wherein the recessed cable portion of the antenna acts as a matching stub to provide a constant impedance match at both feed points. 
     These and other objects of the present invention will be apparent to those skilled in the art. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The numeral 10 refers to a conventional cellular telephone having a housing 12 which has an electrical connector receptacle 14 (FIG. 3) positioned in the upper end thereof. Receptacle 14 is electrically connected to the internal circuitry of the telephone 10 in conventional fashion and has a threaded opening 16 formed therein which threadably receives the connector of the antenna, as will be described in more detail hereinafter. 
     The numeral 18 refers to the antenna of this invention which includes a metal pin 20 having a base end 22 and a hollow upper end 24. Annular shoulder 26 protrudes from the exterior of pin 20, as seen in FIGS. 2 and 4. 
     Antenna 18 also includes an elongated metal cable 28 having an end 30 received in end 24 of pin 20 and held therein by crimping or the like. End 32 of cable 28 is received in the hollow end 34 of metal shaft 36 and is held therein by crimping or the like. 
     As seen in the drawings, shaft 36 is provided with an externally threaded portion 38 which receives a hollow adapter 39 thereon. A 1/4 wave, metal helical spring element 40 is positioned in adapter 39 and has one end 42 received in base 44 of shaft 36. Cap 46 embraces adapter 39, as seen in FIG. 5. Cable 28, except for its ends, is enclosed by a sheath 48. As seen in FIGS. 4 and 6, a capacitor 43 is provided which is formed by the close (air gap) proximity of end 42 of helical spring element 40 and end 32 of cable 28. 
     Metal connector 50 is threadably received by receptacle 14 and includes a split end 52 which is positioned within receptacle 14. Connector 50 has a bore 54 extending therethrough which is adapted to slidably receive the upper end of pin 20, cable 28 and the lower end of shaft 36. 
     When the antenna 18 is fully extended from housing 12, the upper end of pin 20 is positioned within connector 50 so that the antenna 18 is RF coupled to the connector 50 to provide a fully extended, directly coupled helical top loaded 3/4 wave antenna RF coupled at its base. 
     When the antenna 18 is fully recessed down into the telephone housing 12, shaft 36 is positioned within connector 50 and is RF coupled thereto to provide a 1/4 wave helical antenna which is RF coupled at the bottom end of the top loaded coil 40. The recessed cable 28 acts as a matching stub. Thus, a constant impedance match is maintained at either the retracted feed point (shaft 36) or the extended feed point (pin 20). 
     It should be noted that the antenna 18 may be modified so that when the antenna 18 is fully extended from the housing 12, the antenna could provide a fully extended, directly coupled helical top loaded 1/2 wave antenna RF coupled at its base. 
     Thus it can be seen that a 3/4 wave antenna consisting of a 1/4 wave helical with a 1/2 wave rod is provided which is electrically coupled together (capacitively). In the retracted position, the 1/4 wave helical feed point is at the base of the helical looking decoupled at the feed point from the 1/2 wave portion that represents a high impedance therefore, not seen electrically by the 1/4 wave helical radiation from the 1/2 wave rod. In the extended position, since the 1/4 wave helical is electrically coupled to the 1/2 wave by capacitance, the 1/4 wave helical and 1/2 wave rod look like a 3/4 wave antenna. Both feed points then look like a low impedance to the duplexor. The primary difference in the device of this invention and the prior art is that the antenna of this invention utilizes a common low impedance feed point without any matching being required. The antenna of this invention has a larger capture area, thus more gain in the extended and retracted positions. Additionally, at a low impedance, feed input an electrically coupled high impedance element is not seen. At a high impedance feed input, 1/4 wave top loading is a result of a low impedance capacitive coupled helical, thus resulting in an electrical 3/4 wave antenna. 
     Thus it can be seen that the invention accomplishes at least all of its stated objectives.