Eigenmodes excitation in reflectors for resonant and wideband antennas

Two dimensional reflectors formed by thin conducting screens have been considered. Corresponding eigenvalue problems have been solved and the results of complex eigenfrequency analysis have been used in the investigation of fields radiated by antennas formed by cylindrical reflectors. Fields scattered by screens with resonant cavities (cavity-backed apertures (CBAs)) or by flat/curved strips have been studied both in the vicinity of the structure and in the far zone. It has been shown that an excitation of eigenmodes determines the scattering characteristics of CBAs. A structure formed by two cylindrical strips excited by a line magnetic current source has been used as a simple model for simulation of a TEM horn antenna. Characteristics of pulse signals radiated by the TEM-horn antennas under investigation and by a reflector antenna with a main cylindrical reflector and the TEM-horn antenna as a feed have been studied in detail. It has been shown that the neglect of the high modes excitation in the TEM-horn (i.e. taking into consideration only the TEM mode) can lead to obtaining incorrect results especially in the resonant frequency band and in a pulse radiation analysis.