Patent Publication Number: US-2007120747-A1

Title: High performance retractable half-wave antenna

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention generally relates to antennas and, more particularly, to retractable antennas.  
      2. Background of the Invention  
      In response to consumer demand, new mobile communication devices continue to be developed which are dimensionally smaller than previous models. For example, some communication devices that are now being developed are significantly shorter and thinner than models that they will replace. Such devices can be easily carried in one&#39;s pocket, making their use convenient.  
      Unfortunately, making a mobile communication device dimensionally smaller creates challenges for the RF engineer. In particular, as antennas for the devices become smaller, engineers are forced to operate the antennas in quarter-wave mode. With all other parameters being equal, the specific absorption rate (SAR) of an antenna in quarter-wave mode is typically higher than the SAR of an antenna operating in half-wave mode.  
     SUMMARY OF THE INVENTION  
      The present invention relates to an antenna that includes a first helical radiator and a second helical radiator positioned substantially collinear with the first helical radiator. The second helical radiator can be moveable between a first position wherein the second helical radiator is substantially adjacent to the first helical radiator and a second position wherein the second helical radiator is distal from the first helical radiator. The first helical radiator and the second helical radiator can cooperate to transmit and/or receive electromagnetic signals using an electrical connection and/or electromagnetic coupling. The electromagnetic coupling can primarily include capacitive coupling. The antenna also can include an impedance tuning member which electromagnetically couples to the first helical radiator and/or the second helical radiator.  
      The first helical radiator can be communicatively linked to a signal source. In one arrangement, the first helical radiator can be communicatively linked to the signal source when the second helical radiator is in the first position and not communicatively lined to the signal source when the second helical radiator is in the second position.  
      The antenna can include a whip to which the second helical radiator is attached. The whip can, for example, electrically connect the second helical radiator to the first helical radiator. For instance, the second helical radiator can be electrically connected to the first helical radiator when the second helical radiator is in the first position and electrically connected to the first helical radiator when the second helical radiator is in the second position. In another arrangement, the second helical radiator can be electromagnetically coupled to the first helical radiator when the second helical radiator is in the first position, and electrically connected to the first helical radiator when the second helical radiator is in the second position.  
      The present invention also relates to a method for tuning performance characteristics of an antenna. The method can include positioning a second helical radiator substantially collinear with a first helical radiator such that the second helical radiator is moveable between a first position wherein the second helical radiator is substantially adjacent to the first helical radiator, and a second position wherein the second helical radiator is distal from the first helical radiator. The first helical radiator and the second helical radiator can cooperate to transmit and/or receive electromagnetic signals using an electrical connection and/or electromagnetic coupling. For example, the method can include capacitively coupling the second helical radiator to the first helical radiator when the second helical radiator is in a first position.  
      The method also can include communicatively linking the first helical radiator to a signal source. In one arrangement, the second helical radiator can be communicatively linked to the signal source when the second helical radiator is in the first position and communicatively linked to the signal source when the second helical radiator is in the second position. In another arrangement, the second helical radiator is not communicatively linked to the signal source when the second helical radiator is in a first position, but can be communicatively linked to the signal source when the second helical radiator is in a second position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Preferred embodiments of the present invention will be described below in more detail, with reference to the accompanying drawings, in which:  
       FIG. 1  depicts a retractable antenna that is useful for understanding the present invention.  
       FIG. 2  depicts the antenna of  FIG. 1  in an extended position.  
       FIG. 3  depicts another arrangement of the antenna that is useful for understanding the present invention.  
       FIG. 4  depicts the antenna of  FIG. 3  in an extended position.  
       FIG. 5  depicts another arrangement of the antenna that is useful for understanding the present invention.  
       FIG. 6  depicts the antenna of  FIG. 5  in an extended position.  
       FIG. 7  depicts yet another arrangement of the antenna that is useful for understanding the present invention.  
       FIG. 8  depicts the antenna of  FIG. 7  in an extended position.  
       FIG. 9  is a flowchart useful for understanding the present invention. 
    
    
     DETAILED DESCRIPTION  
      While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the description in conjunction with the drawings. As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.  
      The present invention relates to a high performance retractable half-wave antenna. More particularly, the antenna of the present invention achieves a low specific absorption ratio (SAR) and transmit/receive efficiencies that are higher than a quarter-wave retracted antenna of similar size. These performance specifications are achieved while the antenna is operated in both an extended position and, importantly, when operated in a retracted position. Accordingly, the antenna can efficiently transmit and receive RF signals even though the antenna is small enough to be compactly integrated into today&#39;s very small mobile communication devices. In addition, the antenna can operate on multiple frequency bands in both the retracted position and in the extended position, thereby providing a versatile single antenna solution for multiple band transceivers.  
       FIG. 1  depicts a side view a retractable antenna  100  in a retracted position.  FIG. 2  depicts the antenna  100  in an extended position. Making reference both to  FIG. 1  and to  FIG. 2 , the antenna can include a first helical radiator  102  that comprises a helically wound electrical conductor  104 . The first helical radiator  102  can be communicatively linked to a signal source and/or a signal receiver  106 . For instance, a contact  108  can be electrically connected to a first portion  110  of the first helical radiator  102  to provide electrical continuity with one or more circuit traces  112  on a printed circuit board  114  to which the source/receiver  106  is communicatively linked.  
      The antenna  100  also can include a second helical radiator  116  that comprises a helically wound electrical conductor  1   18 . The first helical radiator  102  and the second helical radiator  116  can be substantially helically shaped, as shown in  FIGS. 1 and 2 . However, the invention is not so limited. For example, the first helical radiator  102  can have a modified helical shape in which the diameter  120  progressively changes along a length  122  of the helical radiator  102 . Similarly, the second helical radiator  116  also can have a diameter  124  that progressively changes along its length  126 . Still, other modifications to the helix shape can be made in one or both the helical radiators  102 ,  116 , and such modifications are within the scope of the present invention.  
      The first helical radiator  102  can be electrically connected to a first coupling  128 . A cup shaped cavity  130  can be defined in the coupling  128 , extending inward from a first end  132  of the coupling  128 . A dielectric insulator  136  can line an inner wall  134  of the cavity  130  and the first end  132  of the coupling  128 . Optionally, the dielectric insulator  136  also can line a wall  138  of the cavity  130 .  
      The second helical radiator  116  can be electrically connected to a second coupling  140 . The second coupling  140  can engage the first coupling  128 , as shown in  FIG. 1 , to form a capacitive coupler  141 . For example, the second coupling  140  can have a lower portion  142  which may insert into the cavity  130 . The dielectric insulator  136  can prevent the first and second couplings  128 ,  140  from electrically shorting. The dielectric insulator  136  can be formed of a dielectric material selected to have a dielectric constant (∈ r ) that provides a desired value of capacitance between the first and second couplings  128 ,  140 . Such dielectric materials are known to the skilled artisan.  
      The capacitance between the first and second couplings  128 ,  140  can couple the first and second helical radiators  102 ,  116  for operation in half-wave mode. Additional electrical components (not shown) can be coupled along the electrical path between the signal source/receiver  106  and the antenna  100  to tune the antenna&#39;s resonant frequency and to tune the net impedance of the antenna  100 . For example, resistors, capacitors and/or inductors can be communicatively linked between the signal source/receiver  106  and the antenna  100  to tune the antenna to have a half-wave resonance at 1.8 GHz with an impedance at that frequency of 50 ohms. The electrical components also can be used to tune the antenna&#39;s quarter-wave resonance characteristics. In addition, transmission line matching techniques can be used to adjust the impedance and/or the resonant frequencies of the antenna  100 . The electrical components and/or impedance line matching techniques also can be implemented to achieve a low VSWR in the operating frequency bands. Notably, the combination of maintaining low VSWR while also operating the antenna  100  in half-wave mode can result in a low SAR which, advantageously, provides exceptional transmission/receive efficiency.  
      The lengths  122 ,  126  and diameters  120 ,  124  of the respective helical radiators  102 ,  116  can be selected to achieve a desired electrical length. For instance, the coupled first and second helical radiators  102 ,  116  can present an electrical length that is one-half the wavelength of a first operating frequency, thereby enhancing the transmission and receive performance of the antenna  100  even further. In comparison to quarter-wave antenna operation, operation as a half-wave antenna can have the desirable effect of maximizing transmission currents in the antenna, while minimizing transmission currents in the printed circuit board  114 .  
      Notwithstanding that antenna operation in half-wave mode is desirable, the electrical length of the antenna also can be one-quarter the wavelength of a second operating frequency. For example, if the first operating frequency at which the antenna is tuned to operate in half-wave mode is 1.8 GHz, the antenna can operate in quarter-wave mode at 900 MHz.  
      The antenna  100  also can include a whip  150 . The whip  150  can comprise an electrically conductive member (hereinafter “conductive member”)  152 , a dielectric member  154  and a stop member  156 . The stop member  156  can be electrically conducive and electrically contact the conductive member  152 . The dielectric member  154  can minimize the influence of the whip  150  on the performance of the antenna  100  when the antenna  100  is in the retracted position shown in  FIG. 1 .  
      When the antenna  100  is in the extended position, as shown in  FIG. 2 , the stop member  156  can electrically contact the first coupling  128  to form a continuous electrical path between the conductive member  152 , the stop member  156 , the first coupling  128  and the first helical radiator  102 . In the extended position, the primary transmission/receive components of the antenna can be the first helical radiator  102  and the conductive member  152 . The dielectric member  154  can minimize the influence of the second helical radiator  116  on the transmission/receive characteristics of the antenna  100  when the antenna  100  is in the extended position.  
      Use of the antenna  100  in the extended position can improve antenna efficiency even further. As with operation in the retracted position, the antenna  100  also can efficiently operate in the extended position at a first frequency in which the antenna  100  is tuned for operation half-wave mode and at a second frequency in which the antenna  100  is tuned for operation in quarter-wave mode. For example, a length  122  of the first helical radiator  102  can be selected achieve a quarter-wave resonance at the first frequency. A length  158  of the conductive member  152  then can be selected to cooperate with the helical radiator  102  to achieve a half-wave resonance at the second frequency. Again, electrical components coupled along the electrical path can be used to tune the antenna&#39;s resonant frequencies and to tune the net impedance of the antenna  100  in the respective frequency bands.  
      Another arrangement of the antenna  100  is depicted in  FIGS. 3 and 4 . In this arrangement a switch  302  can be provided to electrically connect and disconnect an electrically conductive whip  304  to the second helical radiator  116 . In particular, the switch  302  can dielectrically insulate the whip  304  from the second helical radiator  116  when the antenna  100  is in the retracted position shown in  FIG. 3 , and the switch  302  can electrically connect the whip  304  to the second helical radiator  116  when the antenna  100  is in the extended position shown in  FIG. 4 . Accordingly, the whip  304  can be removed from the electrical circuit of the antenna  100  when the antenna  100  is in the retracted position, and placed in the electrical circuit when the antenna is in the extended position.  
      The switch  302  can comprise a first conductive plate  306 , a second conductive plate  308 , a conductive spring  310 , stop member  312 , a dielectrically insulated shaft  314  and a conductive whip contact  316 . The whip contact  316  can electrically contact the whip  304  in a position that is fixed with respect to the whip  304 .  
      In the retracted position shown in  FIG. 3 , the switch  302  can be inserted into the cavity  130  of the first coupling  128 . The conductive spring  310  can compress, enabling the shaft  314  to extend the whip contact member  316  away from the second conductive plate  308  to break the electrical contact between the whip contact  316  and the second conductive plate  308 . One or more flanges  318  can be provided to secure the switch  302  within the cavity  130 .  
      In one arrangement the first conductive plate  306  and/or the second conductive plate  308  can electrically contact the first coupling  128  to form a continuous electrical path between the first helical radiator  102  and the second helical radiator  116 . In another arrangement, a dielectric insulator (not shown) can be provided to insulate the first conductive plate  306  and the second conductive plate  308  from the first coupling  128 . In this arrangement, the switch  302  can capacitively couple to the first coupling  128 .  
      In the extended position shown in  FIG. 4 , the spring member  310  can expand to cause the second conductive plate  308  to engage the whip contact  316 , thus creating an electrical connection between the conductive plate  308  and the whip contact  316 . Accordingly, the first helical radiator  102 , the whip  304 , the second conductive plate  308 , the spring member  310 , the first conductive plate  306  and the second helical radiator  116  can create a continuous electrical path and form the primary transmission/receive components of the antenna  100 .  
      Another arrangement of the antenna  100  is depicted in  FIGS. 5 and 6 . In the retracted position shown in  FIG. 5 , the first helical radiator  102  and the second helical radiator  116  can be capacitively coupled via a first coupling  502  and a second coupling  504  in a manner similar to that previously described. In this position, the first helical radiator  102  and the second helical radiator  116  can comprise the primary radiating members of the antenna  100 .  
      When the antenna  100  is in the extended mode shown in  FIG. 6 , the first helical radiator  102  can be electrically disconnected from the circuit  112 , while the whip  506  is electrically connected to the second helical radiator  116  and the contact  108 . Thus, in the extended position, the whip  506  and second helical radiator  116  can comprise the primary radiating members of the antenna  100 .  
      A first switch  508  can electrically connect the first radiating member  102  to a conductive member  510  that provides an electrical connection to the contact  108 . The first switch  508  can include, for example, a resiliently biased dielectric spring member  512  that is connected to the first helical radiator  102 , for instance via a bracket  514 . The spring member  512  can compress when the antenna  100  is retracted to enable a lower portion  516  of the first helical radiator  102  to contact the conductive member  510 . A latch  518  can be provided to maintain the antenna  100  in the retracted position. Such latches are known to the skilled artisan. When the antenna  100  is disposed in the extended position, the spring member  512  can expand to disconnect the lower portion  516  of the first helical radiator  102  from the conductive member  510 , which disconnects first helical radiator  102  from the signal source/receiver  106 .  
      The conductive member  510  can be T-shaped, as shown, although the invention is not limited in this regard. Indeed, the conductive member  510  can be any shape suitable for providing an electrical connection to the first helical radiator  102 . A dielectric member  513  that slideably engages the whip  506  can dielectrically insulate the whip  506  from the conductive member  506  when the antenna  100  is in the retracted position.  
      The whip  506  can comprise a first conductive stop member  520 . In the retracted position, the first stop member  520  can engage a stop bracket  522 , which can unidirectionally limit linear movement of the whip  506 . In the extended position, the stop member  520  can engage the conductive member  510  to form an electrical contact between the whip  506  and the conductive member  510 .  
      A second switch  524  can be provided within the second coupling  504  to electrically disconnect the whip  506  from the second coupling  504  when the antenna  100  is in the retracted position, and electrically connect the whip  506  to the second coupling  504  when the whip is in the extended position. For example, the switch can define a cavity  526  within which a second conductive stop member  528  electrically connected to the whip  506  is slideably disposed. A dielectric liner  530  lining a sidewall  532  and first end wall  534  of the cavity  526  can insulate the second stop member  528  from the second coupling  504  when the antenna  100  is retracted. However, when the antenna  100  is extended, the second stop member  528  can make electrical contact with a second end wall  536  of the cavity, thereby creating a continuous electrical connection between the second helical radiator  116 , the whip  506 , the conductive member  510  and the contact  108 .  
      In one arrangement, an impedance tuning member  538  can be electromagnetically coupled to the first helical radiator  102  and/or coupled to the second helical radiator  116 . The tuning member  538  can comprise a material selected to result in desired impedance characteristics for the first helical radiator  102  and/or the second helical radiator  116 . For example, the tuning member  538  can comprise a ferromagnetic or metallic material. In addition, dimensions of the tuning member  538  also can be selected to achieve desired impedance characteristics for the first helical radiator  102  and/or the second helical radiator  116 .  
       FIGS. 7 and 8  present yet another arrangement of the antenna  100 . In this arrangement the first helical radiator  102  and the second helical radiator  116  can be electrically connected to each other both in the retracted position shown in  FIG. 7  and in the extended position shown in  FIG. 8 . In addition, the distance of the electrical path between the first helical radiator  102  and the second helical radiator  116  can be approximately the same in both the retracted and extended positions.  
      The antenna  100  can include an electrically conductive slide bushing  702  connected to a second portion  704  of the first helical radiator  102 . The slide bushing  702  can define a cavity  706  through which a first whip  708  slidably engages the slide bushing  702 . The first whip  708  can comprise an electrically conductive external surface  710  such that the first whip  708  is in electrical contact with the slide bushing  702 . Flanges  712 ,  714  can be formed at respective opposing ends  716 ,  718  of the first whip  708 . The flanges  712 ,  714  can limit movement of the first whip  708  to a first position in which the flange  712  engages the slide bushing  702 , as shown in  FIG. 7 , and to a second position in which the flange  714  engages the slide bushing  702 , as shown in  FIG. 8 .  
      A second whip  720  can slidably engage an inner surface  722  of the first whip  708 . The second whip  720  can comprise a conductor  726  and a stop member  724 . The stop member  724  can limit movement of the second whip  720  to a first position in which the stop member  724  engages the flange  714  of the first whip  708  (see  FIG. 7 ) and to a second position in which the stop member  724  engages the flange  712  of the first whip  708  (see  FIG. 8 ).  
      The second whip  720  can comprise a dielectric sheath  728  that insulates the conductor  726  from the first whip  708 . The stop member  724  and the inner surface  722  of the first whip  708  both can be electrically conductive, however, thus forming an electrical contact between the first whip  708  and the second whip  720 . In this arrangement, the electrical contact between the first whip  708  and the second whip  720  can be limited to the area  730  where the stop member  724  engages the inner surface  722  of the first whip  708 . Thus, when the antenna is in the retracted position shown in  FIG. 7 , the stop member  724  can provide an electrical connection between the first whip  708  and the first end  714  of the second whip  720 . When the antenna is in the extended position shown in  FIG. 8 , the stop member  724  can provide an electrical connection between the first whip  708  and the second end  716  of the second whip  720 . Thus, whether the antenna  100  is retracted or extended, the length of the electrical path between the first radiating member  102  and the second radiating member  116  is approximately the same.  
       FIG. 9  is a flowchart that presents a method  900  useful for understanding the present invention. Beginning at step  910 , a second helical radiator can be positioned substantially co-linear with a first helical radiator such that the second helical radiator is moveable between a first position substantially adjacent to the first helical radiator and a second position distal from the first helical radiator. At step  920 , the second helical radiator can be electrically connected and/or capacitively coupled to the first helical radiator. At step  930 , the first helical radiator can be communicatively linked to a signal source/receiver  
      The terms “a” and “an,” as used herein, are defined as one or more than one. The term “plurality”, as used herein, is defined as two or more than two. The term “another”, as used herein, is defined as at least a second or more. The terms “including” and/or “having”, as used herein, are defined as comprising (i.e., open language). The term “coupled”, as used herein, is defined as connected, although not necessarily through a conductive path, and not necessarily mechanically, e.g. linked through an electromagnetic field. The term electrically connected, as used herein, is defined as being connected via a continuously electrically conductive path (i.e. a path that, relative to the devices being connected, has low DC resistance). The term communicatively linked, as used herein, is defined as being linked via a signal path. The signal path can be a direct electrical connection having low DC resistance, but is not limited in this regard. For instance, a signal path also can comprise series components, such as capacitors, that impede or block DC current while propagating RF signals.  
      This invention can be embodied in other forms without departing from the spirit or essential attributes thereof. Accordingly, reference should be made to the following claims, rather than to the foregoing specification, as indicating the scope of the invention.