Abstract:
A surface wave launcher for launching electromagnetic surface waves, the launcher comprising: a waveguide having a feed end and a launch end; a feed structure coupled to the feed end of the waveguide; wherein the feed structure includes a first conductor; the waveguide comprises a first planar conductive layer having a feed end and a launch end, the feed end being coupled to the first conductor; and the waveguide is arranged to be positioned adjacent a surface suitable for guiding electromagnetic surface waves, wherein the width of the first planar conductive layer tapers from the launch end towards the feed end.

Description:
[0001]    The present invention relates to a surface wave launcher. 
       BACKGROUND 
       [0002]    The applicant&#39;s prior published patent application GB2,494,435A discloses a communication system which utilises a guiding medium which is suitable for sustaining electromagnetic surface waves. The contents of GB2,494,435A are hereby incorporated by reference. The present application presents various applications and improvements to the system disclosed in GB2,494,435A. 
       BRIEF SUMMARY 
       [0003]    In a first aspect, the present invention provides a surface wave launcher for launching electromagnetic surface waves, the launcher comprising: a waveguide having a feed end and a launch end; a feed structure coupled to the feed end of the waveguide; wherein the feed structure includes a first conductor; the waveguide comprises a first planar conductive layer having a feed end and a launch end, the feed end being coupled to the first conductor; and the waveguide is arranged to be positioned adjacent a surface suitable for guiding electromagnetic surface waves, wherein the width of the first planar conductive layer tapers from the launch end towards the feed end. 
         [0004]    In a second aspect, the present invention provides a surface wave launcher for launching electromagnetic surface waves, the launcher comprising: a waveguide having a feed end and a launch end; a feed structure coupled to the feed end of the waveguide; wherein the feed structure has a primary axis and includes a first conductor; the waveguide comprises a first planar conductive layer coupled to the first conductor and extending radially outward relative to the primary axis; the waveguide is arranged to be positioned adjacent a surface suitable for guiding electromagnetic surface waves; and the waveguide comprises one or more elements arranged to cause a signal generated by the waveguide to be emitted in a predetermined direction. 
         [0005]    Further examples of features of the present invention are recited in the claims. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]    Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: 
           [0007]      FIG. 1  shows a surface wave launcher in accordance with a first embodiment of the present invention; 
           [0008]      FIG. 2  shows cut-away view of the surface wave launcher shown in  FIG. 1 ; 
           [0009]      FIG. 3  shows a surface wave launcher in accordance with a second embodiment of the present invention; 
           [0010]      FIG. 4  shows cut-away view of the surface wave launcher shown in  FIG. 3 ; 
           [0011]      FIG. 5  shows a surface wave launcher in accordance with a third embodiment of the present invention; 
           [0012]      FIG. 6  shows cut-away view of the surface wave launcher shown in  FIG. 5 ; 
           [0013]      FIG. 7  shows cut-away view of a surface wave launcher in accordance with a fourth embodiment of the present invention; and 
           [0014]      FIG. 8  shows cut-away view of a surface wave launcher in accordance with a fifth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows a surface wave launcher  100  in accordance with a first embodiment of the present invention. The surface wave launcher includes a parallel-plate waveguide  101  and a feed section  102 . The waveguide  101  includes a feed end  103  and a launch end  104 . The feed section  102  is coupled to the waveguide  101  as the feed end  103 . The feed section includes a coaxial cable  105 . The coaxial cable includes an inner conductor  106 , an insulating layer  107  and an outer conductor  108 . The feed section  102  also includes a coupling pin  109  which is connected to the inner conductor  106  at an end of the coaxial cable. 
         [0016]    The waveguide  101  is a rectangular cuboid. The waveguide  101  includes a first planar conductor  110 , which is forms an upper surface of the waveguide. The first planar conductor  110  forms an isosceles triangle, the top vertex of which is connected to the coupling pin  109 . In this sense, the width of the first planar conductor  110  tapers from the launch end of the waveguide  101  to the feed end. The waveguide  101  also includes a dielectric layer  111 , positioned below the first planar conductor  110 , and which is also a rectangular cuboid. The dielectric  111  is preferably low loss for the frequency of operation. The waveguide  101  also includes a second planar conductor (not shown in  FIG. 1 ), which is positioned behind the dielectric layer  111 . The second planar conductor is rectangular in shape, and completely covers the underside of the dielectric  111 . 
         [0017]      FIG. 2  shows a cross-section through launcher  100 . The features of the launcher  100  are labelled in the same manner as in  FIG. 1 . In  FIG. 2 , the second planar conductor  112  is shown. The outer conductor  108  of the coaxial cable  105  is coupled to the second planar conductor  112 . 
         [0018]      FIG. 2  also shows a guiding medium  113  with which the surface wave launcher  100  is arranged to operate. The guiding medium may be similar to that described in the applicant&#39;s previously published UK patent application GB2,494,435. The guiding medium  113  includes a dielectric layer  114  and a conductive layer  115 . Together they form a dielectric coated conductor with a reactive impedance which is higher than the resistive impedance. Such a surface is suitable for the propagation of electromagnetic surface waves. In use, the launcher  100  can be placed at a shallow angle to the surface of a guiding medium  113  to launch waves in a particular direction. The performance of the launcher  100  at a particular frequency can be optimised by changing the length of the triangle. 
         [0019]      FIG. 3  shows a surface wave launcher  200  in accordance with a second embodiment of the present invention. The surface wave launcher includes a waveguide  201  and a feed section  202 . The launcher  200  is identical to launcher  100 , except that the waveguide  201  does not include a dielectric layer or a second planar conductor. The waveguide  201  includes a feed end  203  and a launch end  204 . The feed section  202  is coupled to the waveguide  201  as the feed end  203 . The feed section includes a coaxial cable  205 . The coaxial cable includes an inner conductor  206 , an insulating layer  207  and an outer conductor  208 . The feed section  202  also includes a coupling pin  209  which is connected to the inner conductor  206  at an end of the coaxial cable. 
         [0020]    The waveguide  201  includes a first planar conductor  210 . The first planar conductor  210  forms an isosceles triangle, the top vertex of which is connected to the coupling pin  209 . As in  FIG. 1 , the width of the first planar conductor  210  tapers from the launch end of the waveguide  201  to the feed end. 
         [0021]      FIG. 4  shows a cut-away through launcher  200 .  FIG. 4  also shows a guiding medium  213  with which the surface wave launcher  200  is arranged operate. The guiding medium may be similar to that described in connection with  FIG. 2 . In particular, it includes a dielectric layer  214  and a conductive layer  215 . 
         [0022]    In use, the triangular conductor  210  is positioned on top of the dielectric  214  of the guiding medium  213 . The first planar conductor  210  arranged in parallel and in contact with the top surface of the guiding medium  213 . The outer conductor  208  of the coaxial cable  205  contacts the conductive layer  215  at the bottom of the guiding medium  213 . In this manner, the launcher  200  acts as a parallel-plate waveguide by using the conductive layer  215  of the guiding medium  213  as a second plate. 
         [0023]      FIG. 5  shows a cross-section through a launcher  300  in accordance with a third embodiment of the present invention. The launcher  300  includes a radial waveguide  301  and a feed section  302 . The feed section  302  includes a coaxial cable  303 . The coaxial cable  303  includes an inner conductor  304 , an insulating layer  305  and an outer conductor  306 . The feed section  302  also includes a coupling pin  307 , for coupling the inner conductor  304  to the waveguide  301 . The waveguide  301  extends radially outward from the feed section. The waveguide  301  may comprise a disc of conductor  308  positioned on top of a disc of dielectric  309 . The coupling pin  307  of the coaxial cable  303  passes through the centre of the dielectric disc  309 . The launcher  300  can be used to launch surface waves along a guiding medium. The performance of the launcher at a particular frequency can be optimised by changing the radius of the conducting and dielectric discs, length of the pin and by adding a further disc of conductor to the bottom of the dielectric contacting the end of the pin. 
         [0024]      FIG. 6  shows a cut-away through launcher  300 . The features of the launcher are identified with the same reference numerals.  FIG. 6  also shows a guiding medium  310  which includes a dielectric layer  311  and a conductive layer  312 . The launcher  300  acts as an omnidirectional surface wave launcher. By placing the waveguide  301  in parallel to and adjacent to the dielectric layer  311  of the guiding medium  310 , surface waves may be made to propagate in all directions. 
         [0025]    The launcher design shown in  FIG. 7  is identical to that shown in  FIGS. 5 and 6  with the exception of two axially orientated conducting pins  313 , added approximately a half wavelength either side of the centre pin. These added pins act as reflectors making the launcher bi-directional. 
         [0026]    The launcher design shown in  FIG. 8  is identical to that shown in  FIG. 7  with the exception of one pin  314  added approximately a quarter wavelength behind the centre pin. This added pin act as reflectors making the launcher directional. 
         [0027]    In the above-described embodiments, surface wave launchers have been described. It will be appreciate that the aforementioned surface wave launchers may operate in reverse and act as surface wave collectors. In other words, a launcher of the present invention may either act to “launch” surface waves over a suitable surface, or to “collect” surface waves from a suitable surface. 
         [0028]    In the above described embodiments, the first planar conductor is triangular. The width of the first planar conductor tapers from the launch end to the feed end. It will be appreciated that the first planar conductor may be take other triangular shapes, or shapes that are not triangular, while tapering from the launch end to the feed end. 
         [0029]    In the above described embodiments, the axially orientated pins may be referred to as elements. These elements may be formed by other means, as will be appreciated by the person skilled in the art. For example, instead of conductive pins, air gaps could be formed in the waveguide. 
         [0030]    Features of the present invention are defined in the appended claims. While particular combinations of features have been presented in the claims, it will be appreciated that other combinations, such as those provided above, may be used. 
         [0031]    Further modifications and variations of the aforementioned systems and methods may be implemented within the scope of the appended claims.