Abstract:
A body wearable antenna adapted to be worn against the body, comprising: a first antenna part ( 4 ); and a second antenna part ( 6 ) insulated from the first part ( 4 ); wherein the first antenna part ( 4 ) is adapted to be worn circumferentially around a body part ( 100 ); and the second antenna part ( 6 ) is adapted to be worn longitudinally against a body part ( 100 ). The body parts that the first antenna part ( 4 ) is adapted to be worn around and that the second antenna part ( 6 ) is adapted to be worn against maybe the same. The second antenna part ( 6 ) may extend circumferentially around the body part ( 100 ) to some extent and may extend along substantially the whole length of the body part ( 100 ). The second antenna part ( 6 ) may comprise a plurality of radial elements ( 61, 62, 63 ) that extend away from the first antenna part ( 4 ).

Description:
FIELD OF THE INVENTION 
     The present invention relates to body wearable antennas. In particular, the present invention relates to wideband body wearable antennas. 
     BACKGROUND 
     Body wearable antennas, and antennas that are portable by a person, are known. 
     Conventional body wearable antennas only operate well in a narrow frequency band. Conventional body wearable antennas operate at frequencies from 500 MHz to 5 GHz which allows them to be physically small in construction and relatively simple to wear unobtrusively on the body. However, such high frequency bands tend to have a very limited range. Also, use of such high frequency bands tend to suffer low propagation in many situations in which body wearable antennas are used, for example operations in urban environments. Antennas designed to operate using such narrow frequency bands also tend to suffer from detuning effects, such as those caused by body movements. 
     Thus, there is a requirement for wideband, low frequency (i.e. below 500 MHz) body wearable antennas that alleviate the problems suffered by narrowband antennas whilst maintaining advantages of being lightweight, being able to be worn unobtrusively and comfortably on the body, and being structurally strong. 
     There is also a requirement, particularly in military applications, for a body wearable antenna that is relatively discrete, i.e. does not advertise the position of a user, and that does not hinder the wearer&#39;s ability to carry other equipment, for example body armour and ammunition. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the present invention provides a body wearable antenna adapted to be worn against the body comprising: a first antenna part; and a second antenna part insulated from the first antenna part; wherein the first antenna part is adapted to be worn circumferentially around a body part; and the second antenna part is adapted to be worn longitudinally against a body part. 
     The body part that the first antenna part is adapted to be worn circumferentially around and the body part that the second antenna part is adapted to be worn longitudinally against may be different body parts 
     The body part that the first antenna part is adapted to be worn circumferentially around and the body part that the second antenna part is adapted to be worn longitudinally against may be the same body part. 
     The second antenna part may extend circumferentially around the body part to some extent. 
     At least a part of the second antenna part may extend along substantially the whole length of the body part. 
     The second antenna part may comprise a plurality of radial elements, arranged such that each radial element extends away from the first antenna part. 
     Each of the plurality of radial elements may be oblique with respect to another of the plurality of radial elements. 
     The second antenna part may comprise three radial elements. 
     A first of the three radial elements may extend around a first side of the body part; a second of the three radial elements may extend around a second side of the body part; and the first side may be opposite the second side. 
     One or more radial elements may each comprise one or more hinges. 
     The first antenna part may be a band of material. 
     One or both of the body parts may be a leg of a user. 
     The body wearable antenna may be adapted to be worn on top of a user&#39;s clothes. 
     In a further aspect, the present invention provides a communications system comprising: a body wearable antenna according to any of the above aspects; a radio transceiver adapted to send and receive signals via the body wearable antenna; and a connector arranged to connect the body wearable antenna to the radio transceiver. 
     The radio transceiver may be portable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a body wearable communication system in which a first embodiment of a body wearable antenna is implemented; 
         FIG. 2  is a perspective view of the body wearable antenna; 
         FIG. 3A  is a schematic illustration of a side view of the body wearable antenna strapped to a leg; 
         FIG. 3B  is a schematic illustration of a front view of the body wearable antenna strapped a the leg; 
         FIG. 4  is a schematic illustration of a side view of the body wearable antenna strapped to a leg which is in a bent position; 
         FIG. 5  is a process flow chart of an example operation of the body wearable communication system in which the body wearable antenna receives radio frequency signals; and 
         FIG. 6  is a process flow chart of a further example operation of the body wearable communication system in which the body wearable antenna transmits radio frequency signals. 
     
    
    
     DETAILED DESCRIPTION 
     The terminology “body wearable antenna” is used herein to refer to antennas that are adapted to be worn on or against a part of the human body by conforming to the contours of a human body part, for example a leg. Here the term “body wearable” refers only to the antenna. In other words, it is not necessary that a transceiver that is used in conjunction with the body wearable antenna is also body wearable. For example, a body wearable antenna may be operated with a portable, but non-body wearable, transceiver and signal processing means. 
     The terminology “portable antenna” is used herein to refer to antennas that may be easily or conveniently transported by a person. Thus, a body wearable antenna is more than merely a portable antenna. For example, a conventional ‘whip-style’ antenna, which may be carried by a person in a back-pack, is a portable antenna. However, since the conventional whip-antenna is not adapted to conform to the contours of the user&#39;s back, this type of antenna is not a body wearable antenna under the above definitions. 
       FIG. 1  is a schematic illustration of a communication system  1  in which a first embodiment of a body wearable antenna  2  is implemented. 
     The communication system  1  comprises a body wearable antenna  2 , and a radio transceiver  18 . The body wearable antenna  2  is connected to the radio transceiver  18  using a twin conductor feedline, hereinafter referred to as the “feedline  16 ”. The feedline  16  comprises two conductors, which are insulated from each other. 
     The body wearable antenna  2  comprises a leg band  4 , and a radial portion  6 . The leg band  4  is connected to the radial portion  6  via a connector  8 . The leg band  4 , the radial portion  6 , and the connector  8  will be described in more detail later below with reference to  FIG. 2 . 
     The radio transceiver  18  is portable. The radio transceiver  18  is connected to the body wearable antenna  2  via the feedline  16 . In this embodiment, the radio transceiver  18  is connected to the leg band  4  of the body wearable antenna  2  via a first conductor  10  of the feedline  16 , and the radio transceiver  18  is connected to the radial portion  6  of the body wearable antenna  2  via a second conductor  12  of the coaxial cable. In this embodiment, the feedline  16  is coaxial cable. The first conductor  10  is the outer conductor of the coaxial cable. The second conductor  12  is the inner conductor of the coaxial cable. 
     In this embodiment, the connector  8  allows the first conductor  10  to connect to the leg band  4  of the body wearable antenna  2 , and connects the second conductor  12  to the radial portion  6 , whilst insulating the two conductors  10 ,  12  from each other. 
       FIG. 2  is a perspective view of the body wearable antenna  2  shown in  FIG. 1 . 
     In this embodiment, the leg band  4  comprises a conductive element  40 , and an adjustable strap  42 . The conductive element is a U-shaped band made of metal. In this embodiment, the conductive element is made of insulated copper stranded wire. The conductive element  40  is U-shaped to fit around the thigh of a user. The first conductor  10  is connected to the conductive element  40 . During use, the conductive element  40  of the leg band  4  acts as an antenna for received and/or transmitted radio frequency signals, as described in more detail later blow with reference to  FIGS. 5 and 6 . 
     In this embodiment, the adjustable strap  42  is used to strap the leg band  4  to the thigh of a user, as described in more detail later below with reference to  FIGS. 3A and 3B . 
     In this embodiment, the connector  8  connects the feedline  16  to the leg band  4  and the radial portion  6 . The connector  8  contains and insulator which ensures there is no direct conductive path between the two feedline conductors  10 ,  12  and also ensures there is no direct conductive path between the radial and leg band portions of the body wearable antenna  2 . In this embodiment, the connector is made of copper with a PTFE insulator. 
     In this embodiment, the radial portion  6  comprises three conductive radial elements, or spokes. The three radial elements are hereinafter referred to as the first radial  61 , the second radial  62 , and the third radial  63 . In this embodiment, the first, second, and third radials  61 ,  62 ,  63  are each made of a stiff metal wire. Each of the first, second, and third radials  61 ,  62 ,  63  has a first and second end. 
     In this embodiment, the first, second, and third radials  61 ,  62 ,  63  are joined to together at the first ends of the radials. The joined together first ends of the first, second and third radials  61 ,  62 ,  63  are joined to the connector  8 . The connector joins the second conductor  12  to the joined together first ends of the first, second and third radials  61 ,  62 ,  63 . 
     In this embodiment, the second ends of each of the first, second, and third radials  61 ,  62 ,  63  are “free ends”. The radials  61 ,  62 ,  63  extend away from the connector  8  such that the second ends of each of the radials  61 ,  62 ,  63  are distal from the connector  8  and such that the second ends are not connected to any further element of the communication system  1 . 
     In this embodiment, the first radial  61  and the third radial  63  are of substantially equal length. The second radial  62  is longer than the first and third radials  61 ,  63  and is positioned between the first and third radials  61 ,  63 . The radials  61 ,  62 ,  63  are of a length such that when the body wearable antenna  2  is worn by a user, as described in more detail below with reference to  FIGS. 3A and 3B , the radials  61 ,  62 ,  63  extend from the wearer&#39;s thigh (onto which the leg band  4  is strapped), down the length of the wearer&#39;s leg. 
     In this embodiment, the radials  61 ,  62 ,  63  extend away from the connector  8  obliquely to each other, i.e. at angles with respect to each other. Advantageously, the angles between the radial may be varied depending on the radio signal transmission/reception properties that are required of the body wearable antenna  2  by a user. By changing the angle between the radials  61 ,  62 ,  63 , the range of frequencies which can be effectively received by the body wearable antenna  2  can be varied. In this embodiment, the angles between the radials  61 ,  62 ,  63  tend to be maintained by virtues of the rigidity of the radials  61 ,  62 ,  63  themselves, and the rigidity of the joint at the first ends of the radials  61 ,  62 ,  63 . However, in other embodiments the angles between the radials  61 ,  62 ,  63  are maintained by different appropriate means. For example, in other embodiments rigid spacers made of insulating material may be implemented between the radials  61 ,  62 ,  63 . In other embodiments the radials  61 ,  62 ,  63  may be directly attached to the clothing of a wearer by, for example, straps or Velcro™ on the clothing that keep the radials  61 ,  62 ,  63  in place. In other embodiments, the radials  61 ,  62 ,  63  may be integrated directly into the clothing of a user by, for example, by weaving a conductive material into clothing e.g. using silver loaded rip-stop nylon as clothing material. 
     In this embodiment, the first radial  61 , the second radial  62 , and the third radial  63  each comprises a hinge, hereinafter referred to as the “first hinge  65 ”, the “second hinge  66 ”, and the “third hinge  67 ” respectively. The first, second and third hinges  65 ,  66 ,  67  are positioned between the first and second ends of the first, second, and third radials  61 ,  62 ,  63  respectively, i.e. between the joined and free ends of the respective radials. The hinges  65 ,  66 ,  67  are positioned such that they allows a wearer of the body wearable antenna  2  to bend at the knee, as described in more detail later below with reference to  FIG. 4 . 
     In this embodiment, the conductive element  40  of the leg band  4 , i.e. the U-shaped band made of metal, is substantially wider than the thickness of the radials  61 ,  62 ,  63 . This advantageously provides a large grounded area to counterpoise the feed signal against the radial portion  6  of the antenna  2 . This forms a non-symmetric antenna which does not require a balun (which is required by many conventional body wearable antennas). Thus, as a balun component is not required, the overall size and cost of the antenna tends to be lower than that of a conventional body-wearable antenna. Moreover, the maximum power output of a body wearable antenna tends to be reduced. 
       FIGS. 3A and 3B  are schematic illustrations of the body wearable communications system  1  being worn by a user. 
     In this embodiment, the body wearable antenna  2  is strapped to a leg  100  of the user. In this embodiment, the body wearable antenna  2  is worn on top of any clothing the user is wearing. This advantageously provides that the body wearable communications system  1  tends to be able to be easily removed from a user, e.g. for use by another user, quickly and/or without the need of removing clothing. 
       FIG. 3A  is a schematic illustration of a side view of the body wearable antenna  2  strapped to the leg  100 .  FIG. 3B  is a schematic illustration of a front view of the body wearable antenna  2  strapped to the leg  100 . 
     The radio transceiver  18  (not shown in  FIGS. 3A and 3B ) is portable. For example, the radio transceiver  18  may be worn by the user at a location on the body, e.g. in a back-pack. 
     In this embodiment the body wearable antenna  2  is worn against the leg  100 , and is attached to the thigh portion of the leg  100 . The leg band  4  fits around the thigh of the leg  100  and is held in place using the adjustable strap  42 . 
     The radial portion  6  is positioned such that the first, second, and third radials extend down the length of the leg  100 . The radials  61 ,  62 ,  63  extend down the outer leg. Moreover, the second radial  62  extends down the outside of the leg  100 , the first radial  61  extends down the outside of the leg  100  and extends away from the second radial  62  around the back of the leg  100 , and the third radial  63  extends down the outside of the leg  100  and extends away from the second radial  62  around the front of the leg  100 . Thus, the radials  61 ,  62 ,  63  extend down the outside of the leg  100  obliquely to one another. 
     Moreover, the radials  61 ,  62 ,  63  are positioned such that the hinges  65 ,  66 ,  67  are appropriately positioned to advantageously allow bending of the leg  100  at the knee, as described in more detail later below with reference to  FIG. 4 . 
     In this embodiment the radials are held against the body by a further adjustable strap  44 . The further adjustable strap  44  ensures that the radials  61 ,  62 ,  63  are held against the leg, i.e. that they do not extend substantially away from the body. 
       FIG. 4  is a schematic illustration of a side view of the body wearable antenna  2  strapped to the leg  100 . The leg  100  shown in  FIG. 4  is in a bent position, i.e. the leg  100  is bent at the knee. The first hinge  65  advantageously provides for rotation between the portions of the first radial  61  on either side of the first hinge  65 . Similarly, the second hinge  66  advantageously provides for rotation between the portions of the second radial  62  on either side of the second hinge  62 . Similarly, the third hinge  67  advantageously provides for rotation between the portions of the third radial  63  on either side of the third hinge  63 . The hinges  65 ,  66 ,  67  are positioned on their respective radials proximate to the knee joint of the leg  100 . Thus, the hinges  65 ,  66 ,  67  advantageously allow a user to move freely when wearing the body wearable antenna  2 . 
     Moreover, the hinges  65 ,  66 ,  67  advantageously allow a user to move freely without detrimentally affecting the performance of the antenna. Movement of the body may cause slight detuning effects, but, due to the body wearable antenna  2  being wideband, this tends not to be detrimental to the performance of the antenna. 
     The advantage of allowing a user to move freely may also be provided by other embodiments. For example, forming the radials  61 ,  62 ,  63  by weaving a conductive material into clothing allows a user to move freely. 
     Thus, a body wearable communication system  1  comprising a body wearable antenna  2  is provided. Example operations of the body wearable communications system  1  will be described later below with reference to  FIGS. 5 and 6 . 
       FIG. 5  is a process flow chart of an example operation of the body wearable communication system  1 . In this example operation, the body wearable antenna  2  receives radio frequency signals. 
     At step s 2 , the leg band  4  and the radial portion  6  of the body wearable antenna  2  receive electromagnetic waves. 
     A step s 4 , the electromagnetic waves are converted into electrical signals in a conventional manner. 
     At step s 6 , the leg band  4  and the radial portion  6  send the electrical signals to the radio transceiver  18  via the coaxial cable  16 . 
     In this embodiment, the feedline  16  is a conventional coaxial cable, i.e. an electrical cable comprising two conductors: an inner conductor and a surrounding conductive layer (i.e. an outer conductor) which is separated from the inner conductor by an insulating layer. In this example operation, the signal corresponding to the leg band  4  is sent from the leg band  4  to the radio transceiver  18  via the outer conductor, i.e. the first conductor  10  of the feedline  16 . Also, the signal corresponding to the radial portion  6  is sent from the radial portion  6  to the radio transceiver  18  via the surrounding outer conductive layer (i.e. the second conductor  12 ) of the feedline  16 . 
     At step s 8 , the radio transceiver  18  converts the received signals into a form that is useable by a user of the body wearable communication system  1 . For example, the radio transceiver converts the received electrical signals into an audio signal that a wearer of the body wearable communication system  1  can hear. 
       FIG. 6  is a process flow chart of a further example operation of the body wearable communication system  1 . In this example operation, the body wearable antenna  2  transmits radio frequency signals. 
     At step s 10 , the radio transceiver  18  converts a user signal that is to be transmitted by the body wearable communication system  1  into electrical signals. For example, the radio transceiver converts spoken information that is spoken by a wearer of the body wearable communication system  1  in to electrical signals. 
     At step s 12 , the radio transceiver  18  sends the electrical signals to the leg band  4  and the radial portion  6  of the body wearable antenna  2  via the coaxial cable  16  in a manner corresponding to that described above at step s 6 , with reference to  FIG. 5 . In other words, the radio transceiver  18  sends an electrical signal via the first conductor  10  of the feedline  16  to the leg band  4 , and an electrical signal via the surrounding conductive layer (i.e. the second conductor  12 ) of the feedline  16  to the radial portion  6 . 
     At step s 14 , the electrical signals received by the leg band  4  and radial portion  6  of the body wearable antenna  2  are converted to radio frequency signals and transmitted by the leg band  4  and the radial portion respectively. 
     An advantage provided by the above described body wearable antenna  2  is that is the antenna tends to be wideband, i.e. the antenna has substantially similar operating characteristics over a very wide passband. 
     This wideband feature advantageously tends to allow for less detuning due to body movement or proximity of the body wearable antenna to other objects. 
     The wideband feature further advantageously allows for the body wearable antenna  2  to be suitable for use in a cognitive radio system, i.e. systems in which a wavelength of radio signals used for communication is chosen to avoid interference with other users. 
     The above described body wearable antenna  2  advantageously tends to alleviate or avoid problems caused by detuning effects which may arise, for example, as a result of body movement. 
     A further advantage provided by the above described body wearable antenna  2  is that the antenna tends to be wearable without extending beyond the body of a wearer to any significant degree. This tends to be in contrast to conventional portable antennas, e.g. back-pack whip antennas. This feature advantageously tends to provided increased maneuverability for a user. Also, the body wearable antenna tends to be more discrete and is less likely to be damaged during use. 
     A further advantage of the above described body wearable antenna  2  is that it is portable. 
     The feature that the above described body wearable antenna  2  is adapted to fit against a leg  100  of a wearer advantageously exploits the size and shape of the wearer&#39;s leg  100 . Wearing the body wearable antenna  2  on the leg  100  tends to provide that that the radial portion  6  of the body wearable antenna  2  is able to extend substantially down the complete length of the leg  100 . This length of the radial portion tends to provide that the body wearable antenna  2  operates at a low frequency. 
     The wearer&#39;s leg  100  is typically roughly cylindrical in shape. When the radial portion  6  of the body wearable antenna  2  is worn against the leg the second radial  62  extends down the outside of the leg  100 . Also, the first radial  61  extends down the outside of the leg  100  and extends away from the second radial  62  around the back of the leg  100 . Also, the third radial  63  extends down the outside of the leg  100  and extends away from the second radial  62  around the front of the leg  100 . Thus, the configuration of the radials  61 ,  62 ,  63  is such that each radial can be considered to lie on a cone. The circumference of the base of the cone encircles the leg  100 , and the vertex of the cone lies at a point of the surface of the leg  100 , i.e. where the three radials  61 ,  62 ,  63  are joined together. Thus, the body wearable antenna  2  benefits from the advantages of a conventional discone antenna, for example the body wearable antenna  2  is a wide-band antenna. 
     A further advantage of the body wearable antenna  2  being capable of being worn on the leg, as opposed to other areas of a user, is that the antenna  2  does not impinge on the wearing of other apparatus in these other areas. For example, a soldier is able to wear the body wearable antenna  2  on his/her leg without impacting on the soldier&#39;s ability to wear armour or carry ammunition on the soldier&#39;s torso. 
     In the above embodiments, the body wearable antenna is worn on the leg of a user, with the leg band  4  worn in effect substantially round the leg and the radial portion  6  worn in effect substantially along the leg. However, in other embodiments the leg band may be replaced by a corresponding part shaped to fit around a user&#39;s waist, such that the band part is worn around the waist and the radial portion is worn such as to extend down the leg from the waist. In other embodiments the body wearable antenna is worn on any other appropriate body part. For example, in another embodiment the body wearable antenna may be worn against an arm by adapting the leg band  4  to attach to a user&#39;s upper arm, and by adapting the radials to extend down the length of the user&#39;s arm towards to wrist. The radials may be hinged at or near the user&#39;s elbow to allow free movement of the user. 
     In the above embodiments, a single body wearable antenna is worn by a user. However, in other embodiments more than one body wearable antenna is worn. For example, in other embodiments a user may wear a body wearable antenna on each leg. This advantageously tends to provide better coverage in different directions by the communication system  1 . 
     In the above embodiments, the leg band comprises a conductive element which is a band adapted to fit around the thigh area of a leg. However, in other embodiments the conductive element may be any appropriate shape. 
     In the above embodiments, each radial comprises a single hinge. However, in other embodiments any number of radials may comprises any number of hinges or other means of allowing for the free movement of a user. 
     In the above embodiments, the body wearable antenna is strapped on to the body (using the adjustable strap and further adjustable strap as described above with reference to  FIGS. 3A and 3B ). However, in other embodiments the body wearable antenna is attached to the body using any appropriate means. For example, the antenna may be integrated into the clothing of a user. 
     In the above embodiments, the radial portion comprises three radial elements. However, in other embodiments the radial portion comprises any number of radial elements. 
     In the above embodiments, the first and third radials are substantially equal in length and the second radial is substantially longer than the other two. However, in other embodiments the relative sizes of the radials is different to those in the above embodiments. For example, in other embodiments the radials are all of substantially equal size. 
     In the above embodiments, a radial element, i.e. the second radial element, extends down substantially the whole length of the outside of the leg of a user. However, in other embodiments any number of radials extends down substantially the length of the whole leg of the user. Also, in other embodiments any number of radials extends only partially down the length of the leg of a user. 
     In the above embodiments, it is not necessary to balance the feeds of the leg band and the radial portion. Hence, in the above embodiments a balun is not used. However, in other embodiments the feeds to the body wearable antenna are balanced. For example, in other embodiments a balun is implemented. 
     In the above embodiments, the body wearable antenna is worn externally of the user&#39;s clothing. However, in other embodiments the body wearable antenna is worn underneath clothing, or the body wearable antenna is integrated in to the clothing of a user. Such implementation advantageously tends to provide that the body wearable antenna is more discrete than in embodiments in which the antenna is worn externally of clothing.