Excitation of surface waves on a unidirectionally conducting screen by a phased line source

The excitation of surface waves on a unidirectionally conducting screen produced by a phased line source located above the screen and perpendicular to the wire elements is considered. The screen consists of an infinite number of straight, perfectly conducting, parallel wires and conducts only in the direction of the wire elements. The phased line source consists of a periodic line current with an electric charge distributed along its length. The complete electromagnetic field is determined exactly and simple expressions are given for the scattered far field. It is shown that surface waves exist and simple expressions for the amplitudes are given. Another principal result is the determination of the magnitude of the complex Poynting vector for the radiated power. It is found that the pattern function lies on a cone independent of the presence of the screen and that the cone angle depends only on the phasing of the source. The pattern function at points below the screen is independent of the location of the source above the screen. Furthermore, the pattern function vanishes in the direction of the screen and this seems concomittant to the existence of surface waves. Two pattern functions are drawn for typical cases of interest. The power propagated by the surface waves is also determined. The method employed to solve the problem is based on the deduction that the scattered magnetic field component in the direction of the wire elements is zero. A consequence of this deduction is that the electromagnetic field can be derived from a single scalar wave function that satisfies a partial differential equation in the plane of the screen and a jump condition across the screen. This method is quite general and can be applied to a large class of interesting propagation problems arising from different types of excitation. The scattered far field is obtained using another method that is algebraic in character and does not require a complete solution of the problem.