Electromagnetic effects associated with a cavity-backed aperture loaded with nonlinear elements

The electromagnetic properties of cavity-backed apertures loaded with nonlinearly-loaded, electrically small dipole antennas are studied with an extended FDTD simulator. A nonlinearity in the antenna load is introduced by connecting a nonlinear circuit to the dipole antenna. The simplest nonlinear circuit, a nonlinear diode in series with a resistor, is treated in detail to illustrate the effects of a device that will generate well-defined harmonics to any driving frequency. Computational results are generated for both TM and TE cases and for broadband and narrowband excitations. The extended FDTD simulations show that various EMC and RCS effects associated with the presence of a nonlinearly-loaded electrically small dipole antenna are closely connected to the resonant features associated with the cavity-backed aperture. It is illustrated that if the antenna position is properly correlated to peaks of the modal distribution supported by the open cavity, then the fields associated with frequencies generated by the nonlinear load can be coupled significantly to other elements or structures within its interior. It is further demonstrated that the fields generated within the interior of the cavity can be resonantly coupled to its exterior at those frequencies; hence, the scattered fields in the far field will contain information about the characteristics of the interior of the cavity and its nonlinear loading.