Patent Publication Number: US-2011063185-A1

Title: Dielectric loaded sleeve dipole antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and hereby incorporates by reference U.S. Provisional Patent Application No. 61/243,360 filed Sep. 17, 2009 and titled “Dielectric Loaded Sleeve Dipole Antenna.” 
    
    
     FIELD OF INVENTION 
     The present invention relates generally to dipole antennas. More particularly, the present invention relates to dielectric loaded sleeve dipole antennas. 
     BACKGROUND 
     Dipole antennas are known in the art. Dipole antennas can include an inner conductor surrounded by a coaxial cable braid and, in many applications, can be housed in a radome. Thus, the mechanical characteristics of the antenna are limited by the mechanical characteristics of the radome in which the antenna is housed. 
       FIGS. 1A and 1B  are side views of a radome  100  and antenna  200 , respectively, known in the art. As seen in  FIG. 1A , the radome  100  can include a hollow elongated shaft  110  having a first end  112  and a second end  114 . The shaft  110  can include contiguous first, second, and third members  120 ,  130 , and  140 , respectively, which include length, width, circumference, and diameter measurements suitable for the environment in which the radome is employed. For example, the radome  100  can include mechanical characteristics to be compatible with an antenna operating at a frequency of 800 MHz. 
     The radome seen in  FIG. 1A  can have a total length of RL. For example, RL can be between approximately 10.0″ and 11.0″ and in some embodiments can be approximately 10.5″. The first member  120  can have a length of RL 1  and can include vertical ribbing  122  at a bottom end thereof to reinforce the first member  120 . For example, RL 1  can be between approximately 4.0″ and 5.0″ and in some embodiments can be approximately 4.7″. The second and third members  130  and  140 , respectively, can have a total length of RL 2 . For example, RL 2  can be between approximately 5.0″ and 6.0″ and in some embodiments can be approximately 5.8″. The third member  140  can have a diameter that tapers from the larger diameter of the second member  130  to the smaller diameter of the second end  114  of the shaft  110 . 
     To enhance flexibility of the radome  100 , a bottom end of the second member  130  can include an accordion-like ribbing  132  extending around an outer circumference of the shaft  100 . The accordion-like ribbing  132  can be useful when the radome  100  and antenna  200  are employed in an environment with a lot of vibration, for example, on a tractor. The radome  100  can be made of any polymer as would be known by those of skill in the art. Preferably, the radome  100  can be made of a flexible material to further enhance the flexibility of the radome  100 . 
     As seen in  FIG. 1B , the antenna  200  can include an elongated shaft  210  with an inner cable conductor surrounded by a coaxial cable braid and first and second ends  212  and  214 , respectively, at distal ends of the shaft  210 . The shaft  210  can include contiguous first, second, and third members  220 ,  230 , and  240 , respectively, which include length, width, circumference, and diameter measurements that are compatible with the radome  100  shown in  FIG. 1A . For example, the diameter of the antenna  200  at the second end  212  thereof can be AD, which can be between approximately 0.3″ and 0.4″ and in some embodiments can be approximately 0.32″. 
     The first member  220  of the antenna  100  can have a length of AL 1  and can include mechanical and electrical features for connecting to an antenna base or mount as would be known by those of skill in the art. For example, AL 1  can be between 0.5″ and 1.5″ and in some embodiments can be approximately 1.0″. 
     The second member  230  can have a length of AL 2  and can include a sleeve  232  encasing at least a portion of the second member  230 . For example, AL 2  can be between 3.0″ and 4.0″ and in some embodiments can be approximately 3.7″. The antenna sleeve  232  can facilitate the removal of feeder radiation from the antenna  200 . 
     The third member  240  can have a length of AL 3  and can have a diameter that is smaller than the diameter of the second member  230 . For example, AL 3  can be between approximately 3.0″ and 4.0″ and in some embodiments can be approximately 3.7″. The smaller diameter of the third member  240  can enable the antenna  200  to fit within the dimensions of the radome  100  and to be flexible relative to the accordion-like ribbing  132  of the second member  130  of the radome  100 . 
     The length of the antenna can be a function of the frequency of the antenna. That is, the length of the antenna  200  as a whole can be the sum of AL 1 +AL 2 +AL 2  or λ o /2 where λ o  is the wavelength of the antenna  200  in free space. λ o  can be defined as: 
       λ o   =c   o /( f√∈   r )
 
     where c o  is the speed of light, f is the antenna frequency, and ∈ r  is the relative dielectric constant. 
     The antenna  200  is in free space. Therefore, the relative dielectric constant ∈ r  is 1, and λ o  can be defined as: 
       λ o   =c   o /( f√ 1)= c   o   /f  
 
     The total length of the first and second members  220  and  230 , respectively, (including the antenna sleeve  232 ) can be the sum of AL 1 +AL 2  or λ o /4. The length of the third member  240  of the antenna  200  can be AL 3  or λ o /4. 
     The sum of AL 1 +AL 2  or λ o /4 can be approximately equal to RL 1 . Thus, the first and second members  220  and  230 , respectively, of the antenna  200  can fit within the radome  100  substantially below the accordion-like ribbing  132  of the second member  130  of the radome. 
     In some applications or environments, it may be desirable to employ a dipole antenna operating at a frequency lower than 800 MHz. However, as explained above, the length of the antenna is a function of the frequency of the antenna. Thus, changing the frequency of the antenna also changes the length and mechanical characteristics of the antenna. As also explained above, the mechanical characteristics and dimensions of the antenna are limited by the mechanical characteristics of the radome. 
     There is thus a continuing, ongoing need for a dipole antenna in which desired electrical characteristics are achieved within given mechanical parameters. Preferably, such a dipole antenna operates at a frequency lower than 800 MHz and fits suitably within a radome having fixed mechanical characteristics. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, an antenna operating at a frequency f is provided. The antenna can include an elongated shaft having a first end, a second end, a first member, a second member, and a third member, and an antenna sleeve surrounding at least a portion of the second member of the elongated shaft. The first, second, and third members can be contiguous with each other, and the antenna sleeve can be loaded with a dielectric material to shorten a length of the second member of the elongated shaft. 
     The antenna shaft can be compatible with a radome housing, and the frequency f of the antenna can be 400 MHz. 
     The elongated shaft can include an inner cable conductor surrounded by a coaxial cable braid. The first member of the elongated shaft can include at least one mechanical or electrical feature for connecting to at least one of an antenna base and an antenna mount. The antenna sleeve can remove feeder radiation emitted from the antenna. A diameter of the third member of the elongated shaft can be smaller than a diameter of the second member of the elongated shaft. 
     The antenna sleeve can surround substantially all of the second member of the elongated shaft. The antenna sleeve can include the dielectric material surrounded by an antenna choke. A relative dielectric constant of the dielectric material can be between 8 and 12, and the relative dielectric constant can be 10. 
     The sum of a length of the first member and a length of the second member of the elongated shaft can be λ g /4, wherein λ g /4=c o /(f√∈ r ), where c o  is the speed of light, f is the frequency of the antenna, and ∈ r  is a relative dielectric constant of the dielectric material. The length of the second member of the elongated shaft can be between approximately 2.0 inches and approximately 3.0 inches, and the length of the second member of the elongated shaft can be approximately 2.2 inches. 
     According to another embodiment of the present invention, an apparatus is provided including a radome and an antenna. The radome can include a hollow elongated shaft having a first end, a second end, a first member, a second member, and a third member. A bottom end of the second member of the radome can include accordion-like ribbing disposed on an outer circumference thereof, and a diameter of the third member of the radome can be smaller than a diameter of the second member of the radome. 
     The antenna can operate at a frequency f and can be housed within the radome. The antenna can include an elongated shaft having a first end, a second end, a first member, a second member, and a third member, and an antenna sleeve surrounding at least a portion of the second member of the antenna. The first, second, and third members of the antenna can be contiguous with each other, and the antenna sleeve can be loaded with a dielectric material to shorten a length of the second member of the antenna. The sum of a length of the first member and a length of the second member of the antenna can be less than or equal to a length of the first member of the radome. 
     The first member and the second member of the antenna can be housed within the radome substantially below the accordion-like ribbing of the radome. The sum of the length of the first member and the length of the second member of the antenna can be λ g /4, wherein λ g /4=c o /(f√∈ r ), where c o  is the speed of light, f is the frequency of the antenna, and ∈ r  is a relative dielectric constant of the dielectric material. The length of the second member of the elongated shaft can be between approximately 2.0 inches and approximately 3.0 inches, and the length of the second member of the elongated shaft can be approximately 2.2 inches. 
     In accordance with another embodiment of the present invention, a method of shortening the length of an antenna operating at a frequency f is provided. The method includes providing an antenna with an elongated shaft having a first end, a second end, a first member, a second member, and a third member, surrounding at least a portion of the second member of the elongated shaft with an antenna sleeve, and loading a dielectric material into the antenna sleeve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side view of a radome having fixed mechanical characteristics known in the art; 
         FIG. 1B  is a side view of a dipole antenna operating at 800 MHz known in the art; 
         FIG. 2  is a side view of a dipole antenna operating at 400 MHz; 
         FIG. 3A  is a side view of a dipole antenna operating at 400 MHz in accordance with the present invention; and 
         FIG. 3B  is a cross-sectional view of the antenna of  FIG. 3A  in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While this invention is susceptible of an embodiment in many different forms, there are shown in the drawings and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention. It is not intended to limit the invention to the specific illustrated embodiments. 
     Embodiments of the present invention include a dipole antenna in which desired electrical characteristics are achieved within given mechanical parameters. Preferably, such a dipole antenna operates at a frequency lower than 800 MHz and fits suitably within a radome having fixed mechanical characteristics. 
     In accordance with the present invention, electrical parameters of a dipole antenna can be altered to fit the antenna within given mechanical properties, i.e. the dimensions of a radome. In embodiments of the present invention, the antenna can operate at 400 MHz. 
     It is to be understood that an antenna in accordance with the present invention can operate at a frequency as would be desired that is less than 800 MHz but not lower than 400 MHz. An antenna in accordance with the present invention is shown and described herein operating at a frequency of 400 MHz. However, it is to be understood that an antenna in accordance with the present invention is not limited to operating at 400 MHz. 
       FIG. 2  is a side view of a dipole antenna  300  operating at 400 MHz. The antenna  300  can include an elongated shaft  310  with an inner cable conductor surrounded by a coaxial cable braid and first and second ends  312  and  314 , respectively, at distal ends of the shaft  310 . The shaft  310  can include contiguous first, second, and third members  320 ,  330 , and  340 , respectively. 
     The first member  320  of the antenna  300  can have a length of BL 1  and can include mechanical and electrical features for connecting to an antenna base or mount as would be known by those of skill in the art. The second member  330  of the antenna  300  can have a length BL 2  and can include a sleeve  332  encasing at least a portion of the second member  330 . The sleeve  332  can facilitate the removal of feeder radiation from the antenna  300 . The third member  340  of the antenna  300  can have a length BL 3  and can have a diameter that is smaller than the diameter of the second member  330 . 
     As explained above, the length of the antenna can be a function of the frequency of the antenna. That is, the length of the antenna  300  as a whole can be the sum of BL 1 +BL 2 +BL 3  or λ o /2 where λ o  is the wavelength of the antenna  100  in free space. λ o  can be defined as: 
       λ o   =c   o /( f√∈   r )
 
     where c o  is the speed of light, f is the antenna frequency, and ∈ r  is the relative dielectric constant. 
     The antenna  300  is in free space. Therefore, the relative dielectric constant ∈ r  is 1, and λ o  can be defined as: 
       λ o   =c   o /( f√∈ 1)= c   o   /f  
 
     The total length of the first and second members  320  and  330 , respectively, can be the sum of BL 1 +BL 2  or λ o /4, and the length of the third member  340  of the antenna  200  can be BL 3  or λ o /4. 
     Because the length of the antenna  300  is a function of the frequency of the antenna, BL 1  can be between approximately 0.5″ and 1.5″ and in some embodiments can be approximately 1.0″. BL 2  can be between approximately 6.5″ and 7.5″ and in some embodiments can be approximately 7.0″. BL 3  can be between approximately 6.5″ and 7.5″ and in some embodiments can be approximately 7.0″. In accordance with these lengths, the diameter of the antenna  300  at the second end  312  thereof can be BD, which can be between 0.8″ and 0.9″ and in some embodiments can be approximately 0.84″. 
     When the frequency of the antenna  300  is lowered to 400 MHz, the length of the antenna  300  is increased as a function of the frequency. Thus, the length of the antenna  300  as a whole (the sum of BL 1 +BL 2 +BL 3  or λ o /2) is not compatible with the length RL of the radome  100 , and the diameter BD of the second end  312  of the antenna  300  is not compatible with the diameter of the second end  112  of the radome  100 . Further, the length of the first and second members  320  and  330 , respectively, (BL 1 +BL 2  or λ o /4) is not compatible with the length of the first member  120  of the radome  100 . Thus, the antenna sleeve  332  of the antenna  300  does not fit substantially below the accordion-like ribbing  132  of the radome  100 . 
     In accordance with the present invention, the electrical parameters of an antenna operating at 400 MHz can be altered to fit within the fixed mechanical characteristics of the radome  100 . For example, a sleeve of the antenna can be shortened to accommodate the accordion-like ribbing  132  of the radome  100 , and the sleeve can be loaded with a dielectric material. 
       FIG. 3A  is a side view of a dipole antenna operating at 400 MHz in accordance with the present invention, and  FIG. 3B  is a cross-sectional view of the antenna of  FIG. 3A . The antenna  400  in accordance with the present invention can include an elongated shaft  410  with an inner cable conductor surrounded by a coaxial cable braid and first and second ends  412  and  414 , respectively, at distal ends of the shaft  410 . The shaft  410  can include contiguous first, second, and third members  420 ,  430 , and  440 , respectively. 
     The first member  420  of the antenna  400  can have a length of CL 1  and can include mechanical and electrical features for connecting to an antenna base or mount as would be known by those of skill in the art. The second member  430  of the antenna  400  can have a length CL 2  and can include a sleeve  432  encasing at least a portion of the second member  430 . The sleeve  432 , which is described in more detail herein, can facilitate the removal of feeder radiation from the antenna  400 . The third member  440  of the antenna  400  can have a length CL 3  and can have a diameter that is smaller than the diameter of the second member  430 . 
     As explained above with reference to  FIG. 2 , a 400 MHz antenna  300  is too long and wide and thus is not compatible with the fixed mechanical characteristics of the radome  100 . To shorten the length of the antenna while still operating at a frequency of 400 MHz, the electrical parameters of the antenna can altered. For example, in accordance with the present invention, the sleeve  432  of the antenna  300  can be shortened and loaded with a dielectric. 
     As best seen in  FIG. 3B , the second member  430  of the shaft  410  of the antenna  400  can include an inner cable conductor  500  surrounded by a coaxial cable braid  510 . The coaxial cable braid  510  can be surrounded by the antenna sleeve  432 , which can include a dielectric material  520  surrounded by an antenna choke  530 . 
     In embodiments of the present invention, the relative dielectric constant ∈ r  of the dielectric material  520  can be between 8 and 12. In some embodiments, the relative dielectric constant ∈ r  of the dielectric material can be 10. 
     As explained above, the length of the antenna can be a function of the frequency of the antenna. That is, the length of the antenna  400  as a whole can be the sum of CL 1 +CL 2 +CL 3  or λ g /2 where λ g  is the wavelength of the antenna  400  when the antenna sleeve  432  is loaded with the dielectric material  520 . λ g  can be defined as: 
       λ g   =c   o /( f√∈   r )
 
     where c o  is the speed of light, f is the antenna frequency, and ∈ r  is the relative dielectric constant of the dielectric material  520  loaded in the antenna sleeve  332 . 
     In embodiments where the relative dielectric constant ∈ r  of the dielectric material  520  is 10, λ g  can be defined as: 
       λ g   =c   o /( f√ 10)
 
     The total length of the first and second members  420  and  430 , respectively, of the antenna  400  can be the sum of CL 1 +CL 2  or λ g /4, and the length of the third member  440  of the antenna  400  can be CL 3  or λ o /4 because the third member  440  is not loaded with a dielectric material. 
     Because the length of the antenna  400  is a function of the frequency of the antenna  400  and because the antenna sleeve  432  is loaded with the dielectric material  520 , CL 1  can be between approximately 0.5″ and 1.5″ and in some embodiments can be approximately 1.0″. CL 2  can be between approximately 2.0″ and 3.0″ and in some embodiments can be approximately 2.2″. CL 3  can be between approximately 6.5″ and 7.5″ and in some embodiments can be approximately 7.0″. In accordance with these lengths, the diameter of the antenna  400  at the second end  412  thereof can be CD, which can be between approximately 0.3″ and 0.4″ and in some embodiments can be approximately 0.32″. 
     In accordance with the above, the length of the antenna  400  as a whole (the sum of CL 1 +CL 2 +CL 3  or λ g /2) can be compatible with the length RL of the radome  100  and fit within the radome  100 . Further, the length of the first and second members  420  and  430 , respectively, (the sum of CL 1 +CL 2  or λ g /4) can be compatible with the length of the first member  120  of the radome. That is, the sum of CL 1 +CL 2  or λ g /4 can be less than or equal to RL 1 . Thus, the first and second members  420  and  430 , respectively, of the antenna  400  can fit within the radome  100  substantially below the accordion-like ribbing  132  of the second member  130  of the radome. 
     In accordance with the length of the antenna  400 , the diameter CD of the second end  412  of the antenna  412  can be less than the diameter of the second end  112  of the radome  112 . Accordingly, the diameter of the antenna  400  can also be compatible with the diameter of the radome  100 . 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific system or method illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the sprit and scope of the claims.