Scattering by a small cavity-backed hole

For plane-wave incidence, an integral equation is obtained for the magnetic current induced on a circular impedance insert in a perfectly conducting plane under the assumption that the radius is electrically small. This integral equation is solved numerically, and an analytical expression for the scattered field is determined. The complementary expression for a small disk is compared with a standard numerical code and conditions for the use of this expression are established. For a cavity-backed hole, the impedance of the insert is identified with the impedance looking into the hole as determined by a simple transmission line model, and results are presented for a few cavity geometries