PATENT ABSTRACT
A communications system, comprising: a surface wave channel for guiding electromagnetic surface waves; a transmitter, coupled to said surface wave channel for transmitting signals along said surface wave channel; one or more disrupters, arranged to be positioned at arbitrary locations on or adjacent said surface wave channel, and arranged to convert said surface wave signals to space wave signals; and one or more receiver terminals, arranged to be positioned at locations corresponding to said disrupters, each terminal comprising an antenna for receiving said space wave signals.

PATENT DESCRIPTION
BACKGROUND 
       [0001]    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 
       [0002]    In a first aspect, the present invention provides a communications system, comprising: a surface wave channel for guiding electromagnetic surface waves; a transmitter, coupled to said surface wave channel for transmitting signals along said surface wave channel; one or more disrupters, arranged to be positioned at arbitrary locations on or adjacent said surface wave channel, and arranged to convert said surface wave signals to space wave signals; and one or more receiver terminals, arranged to be positioned at locations corresponding to said disrupters, each terminal comprising an antenna for receiving said space wave signals. 
         [0003]    In a second aspect, the present invention provides a surface wave to space wave converter, comprising: a surface wave collector; and an antenna; wherein the surface wave collector is coupled to the antenna; the surface wave collector is arranged to collect surface wave signals from a surface wave channel; and the antenna is arranged to radiate said signal as a space wave. 
         [0004]    Further examples of features of the present invention are recited in the claims. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0005]    Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: 
           [0006]      FIG. 1  shows a communications system in accordance with an embodiment of the present invention; 
           [0007]      FIG. 2  shows a surface wave launcher for use with the system of  FIG. 1 ; 
           [0008]      FIG. 3  shows further details of the surface wave launcher of  FIG. 2 ; and 
           [0009]      FIG. 4  shows a surface wave to space wave converter in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  shows a communications system  100  in accordance with an embodiment of the present invention. The system  100  includes a surface wave channel  101 . The surface wave channel may take the form of the surface wave channels disclosed in the applicant&#39;s published UK patent application, GB2,494,435A. In particular, the surface wave channel has a high surface impedance, and is suitable for guiding electromagnetic surface waves. The channel  101  is elongate, and is generally arranged to guide surface waves in the direction of its length. The channel may be made of a dielectric coated conductor, corrugated surface, or any other material which has a high surface impedance suitable for the transmission of electromagnetic surface waves. 
         [0011]    The system  100  further comprises a surface wave launcher  102 . The surface wave launcher  102  is arranged to convert electrical signals to surface wave signals. Further details of a suitable launcher are provided in GB2,494,435A, and are also described below. The system  100  also includes a server  103 . The server  103  is coupled to the surface wave launcher  102  by connection  104 . The server  103  is includes a transmitter, and is arranged to transmit data along the surface wave channel  101 . The surface wave launcher  102  converts signals received from the server  103  to surface wave signals. 
         [0012]    The system  100  also includes a plurality of disrupters  105 A,  105 B,  105 C. The disrupters may be positioned at arbitrary positions along the surface wave channel. The disrupters are arranged to disrupt the surface wave signals, and to cause the surface wave signals to be scattered as space waves. In the present embodiment, the disrupters  105 A,  105 B,  105 C are metallic plates, which act as reflectors. The metallic plates are positioned on the surface wave channel so that they are perpendicular to the surface. They are orientated to cause specular scattering at an angle of ninety degrees to the direction of the channel. In order to achieve this, the plates are orientated at a forty five degree angle. In use, when a surface wave hits the plate, it is reflected as a space wave. The reflectors may be arranged to reflect the surface waves towards the edge of the channel  101 , where they reradiate as space waves. Alternatively, the reflectors may be arranged to reflect the surface waves upwards, away from the surface. 
         [0013]    The system  100  also includes a plurality of user terminals  106 A,  106 B,  106 C. Each user terminal is coupled to an antenna  107 A,  107 B,  107 C. The antennas are arranged to receive the space waves reflected from the disrupters  105 A,  105 B,  105 C. As such, in use, the antennas and their corresponding user terminals are positioned in close proximity to the positions of the corresponding disrupters. In particular, the antennas  107 A,  107 B,  107 C are positioned close enough to the disrupters so that they may adequately receive the space wave signals. 
         [0014]    The user terminals  106 A,  106 B,  106 C may include a user interface which may include a display. The terminals may therefore be arranged to display data sent by the server  103 . One application of this system may be in a television broadcast system. For example, the system may be used as an in-flight entertainment system on a passenger airplane. 
         [0015]    In use, the server  103  broadcasts a data signal which may include multimedia data to be viewed by the user terminals  106 A,  106 B,  106 C. The signal is converted to a surface wave by surface wave launcher  102 . The surface wave propagates along the surface wave channel  101 . The disrupters  105 A,  105 B,  105 C are positioned such that only some of the surface wave is reflected, the remainder propagating along the surface channel towards the other disrupters. The reflected surface wave propagates as a space wave towards a corresponding antenna  107 A,  107 B,  107 C. The space wave is then converted to an electrical signal by the corresponding antenna. The converted signal is then received by the corresponding user terminal  106 A,  106 B,  106 C. 
         [0016]      FIG. 2  shows an example of a surface wave launcher which may be used with the system  100  shown in  FIG. 1 .  FIG. 2  shows a surface wave launcher  200  in accordance with a first embodiment of the present invention. The surface wave launcher includes a parallel-plate waveguide  201  and a feed section  202 . 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. 
         [0017]    The waveguide  201  is a rectangular cuboid. The waveguide  201  includes a first planar conductor  210 , which is forms an upper surface of the waveguide. The first planar conductor  210  forms an isosceles triangle, the top vertex of which is connected to the coupling pin  209 . The waveguide  201  also includes a dielectric layer  211 , positioned below the first planar conductor  210 , and which is also a rectangular cuboid. The dielectric  211  is preferably low loss for the frequency of operation. The waveguide  201  also includes a second planar conductor (not shown in  FIG. 2 ), which is positioned behind the dielectric layer  211 . The second planar conductor is rectangular in shape, and completely covers the underside of the dielectric  211 . 
         [0018]      FIG. 3  shows a cross-section through launcher  200 . The features of the launcher  200  are labelled in the same manner as in  FIG. 2 . In  FIG. 3 , the second planar conductor  212  is shown. The outer conductor  208  of the coaxial cable  205  is coupled to the second planar conductor  212 . 
         [0019]      FIG. 3  also shows a guiding medium  213  with which the surface wave launcher  200  is arranged to operate. The guiding medium may be similar to that described in the applicant&#39;s previously published UK patent application GB2,494,435A. The guiding medium  213  includes a dielectric layer  214  and a conductive layer  215 . 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  200  can be placed at a shallow angle to the surface of a guiding medium  213  to launch waves in a particular direction. The performance of the launcher  200  at a particular frequency can be optimised by changing the length of the triangle. 
         [0020]    The surface wave launcher  200  may also operate in reverse, as a surface wave collector. Furthermore, the system  100  may operate in reverse, with user terminals transmitting signals which are reflected by the disrupters onto the surface wave channel, to generate surface waves. 
         [0021]    As noted, above the system  100  includes a number of disrupters.  FIG. 4  shows a surface wave to space wave converter  300  in accordance with an alternative embodiment of the present invention. The converter  300  includes a surface wave collector  301  and an antenna  302 . An output of the surface wave collector  301  is coupled to an input of the antenna  302 . The collector  301  may take the form of the surface wave launcher described above in connection with  FIGS. 2 and 3 . As noted there, the surface wave launcher may operate in reverse as a surface wave collector. In use, the waveguide of the surface wave collector is positioned against the surface wave channel  101 . The collector  301  collects surface waves and converts them to electrical signals which are sent to the antenna  302 . The antenna  302  then radiates a corresponding space wave which may be received by a user terminal. The antenna  302  may take many forms. For example, it can be directional or omni-directional depending on the requirements of the system. 
         [0022]    In an alternative embodiment of the present invention, the converter  300  may be used to transmit a space wave signal to another converter, which then launchers a surface wave onto a further surface wave channel. This embodiment could be used where it is not possible to lay a surface wave channel, for example where a gap needs bridging. 
         [0023]    In the above-described embodiments, surface wave launchers and surface wave collectors have been described. These devices may in fact identical in construction. However, in use, the device will either act to “collect” surface waves, or to “launch” surface waves. The terminology used above has been selected dependent on the context in which the device is being used. It will be appreciated that in some contexts, the devices may be used for both purposes, even though they are referred to as either collectors or launchers. 
         [0024]    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. 
         [0025]    Further modifications and variations of the aforementioned systems and methods may be implemented within the scope of the appended claims.