Resonant enhancement of the field within a single ground-plane cavity: Comparison of different rectangular shapes

The resonant properties of a single cavity in a plane surface are investigated, when it is illuminated by an sor p-polarized Gaussian beam. We focus our attention on the rectangular geometry, and consider three different shapes of the grooves: (i) rectangular, (ii) bottle shaped, and (iii) bivalued. A modal approach in its simplest formulation is used to solve the problem for cases (i) and (ii), whereas the multilayer approximation is applied to model the third case. The numerical results exhibit a resonant behavior of the structures at certain wavelengths which can be associated with the resonant wavelengths of a cylindrical waveguide. In particular, a strong enhancement of the field within the: cavity is observed for the open rectangular groove when it is illuminated by a p-polarized beam. However, we show that s resonances are also very important when a bottle-shaped groove is considered. s resonances have also been found in a groove with square cross section, showing that in the case of a single ruling there is no need to have a narrow cavity to evidence a resonant behavior. [S1063-651X(99)06903-2].