Ferrod Radiator System

Commercially available ferrites with low dielectric and magnetic losses at microwave frequencies have brought about the development of ferrod radiator systems for 3-cm wavelength. These ferrites are, in general, characterized by high dielectric constants (approximately 13) and initial permeabilities slightly less than unity. The use of these ferrimagnetic materials as ferrite rod (ferrod) radiators considerably reduces the physical size of microwave antenna systems. The high dielectric constant of the ferrite allows the diameter of the radiating elements of circular cross section to be approximately ¼ inch for 3-cm wavelength use. This makes possible magnetic coupling of the ferrod radiator from resonant cavities or from the narrow side of standard rectangular waveguides to obtain various types of linear arrays. A short feeding section (5/16 inch long) is used to support and lock the position of the ferrod. This device simplifies adjustments and reduces the mechanical tolerances necessary for the ferrod radiators. Microwave ferrites are also characterized by a tensor permeability which changes with applied magnetic field. This phenomenon is used to change the magnetic properties of the ferrod radiator to obtain electrical switching, scanning, lobing, changes in polarization, and amplitude or phase modulation of the radiated energy. Phase shifters, switches, and circulators, which consist of short sections of ferrite-filled cylindrical waveguide, have also been developed for use with the ferrod radiator system.