SCATTERING FROM A DOUBLE-STRIP GRATING - RIGOROUS EQUIVALENT NETWORK FORMULATION

An exact solution for the problem of transverse electric (TE) or transverse magnetic (TM) plane-wave scattering from a periodic, planar double-strip grating at a dielectric interface is described. The metal-strip grating is assumed to be perfectly conductive and infinite in length, with two different strips within a unit-cell. The formulation is based on a multimode equivalent network representation (ENR), and uses a rigorous solution for the relevant integral equation that extends the novel solution developed previously for the single-strip grating. Expressions for the elements of the multimode coupling matrices are given, together with a comparison of results for power transmitted through the grating, obtained by using the networks developed with the present method and a simple point-matching solution. Results are also presented to illustrate the differences between single and double-strip gratings. It is seen that the addition of the extra strip within the unit cell can have a significant effect on the scattering behavior. One interesting feature that follows from the formulation is that double-strip structures maintain the symmetry of the scattered power with respect to the angle of incidence of the excitation, even if they are asymmetric.