High-Frequency Asymptotic Description of Resonant Antenna Formed by Two Metallic Parallel Disks

High-frequency asymptotic electromagnetic field solution is described for a resonant antenna formed by two perfectly conducting circular disks. The double-disk resonator is excited by a vertical electric dipole located at the center of the cylindrical space between the two horizontal disks. The solution is valid for comparatively large disks (at least few wavelengths in diameter). At the same time, the separation of the disks can be arbitrary. The proposed analysis is similar to the uniform geometrical theory of diffraction and provides asymptotic formulas describing the radiated field in both the far- and near-field zones. However, the method is novel since it is based on the canonical problem of diffraction on an open end of a parallel-plate waveguide and therefore takes into account the presence of higher order guided modes travelling between the disks. The method allows calculation of the total radiated power, which has maxima at frequencies equal to real parts of resonator's complex eigenfrequencies. Obtained theoretical directivity patterns in a broad frequency range show good agreement with full-wave numerical simulation.