Ferrod radiator systems

A description is given of the use of ferrimagnetic dielectric rods, to be referred to as ferrods, as end-fire elements of broadside X-band antenna array systems. The high dielectric constant of 13.6 has made possible a single ferrod radiator 0.24 inch in diameter and 4.5 inches long having a pencil beam 25 degrees wide and a gain of 40. The back lobes are negligible and the side lobes are at least 20 db down. Either linear or circular polarization is used. Practical broad-band array design data and radiation patterns are given for ferrod spacings of1.5 \lambda_{o}in air and\lambda_{g}in the waveguide. This dimension is approximately 1.8 inches. A cavity-feed arrangement is also described for high gain ferrod arrays, which allows adjustment of impedance match and amplitude of one ferrod without disturbing the others. In addition to the dielectric properties, the ferrimagnetic properties are used by applications of small longitudinal magnetic fields to the ferrite-filled cylindrical feed section. This field is used to switch the radiation on and off, rotate the plane of polarization, change the radiation modes, and vary the phase of the propagating wave. Simple high speed magnetic lobing and scanning arrays are described. Scanning speeds at megacycle rates are indicated. Circular and spiral scans are also obtained. In order to utilize the small size of the ferrod antenna system, microwave switches, circulators and phase shifters were designed employing ferrite-filled cylindrical waveguide. The longitudinal magnetic field required, for actuating the devices, is of the order of a few oersteds. This is the optimum configuration for applying the magnetic field, as the ferrite demagnetizing factor is low and the filling factor of the solenoid is almost unity. The antenna systems described constitute a first step in the development of an improved concept in reducing the size of microwave radar antennas. These first efforts were directed toward the problem of relatively low power, highly portable radars and radar beacons. It is conceivable that for wide angle scan applications a combination of ferrod lobing or scanning systems with additional mechanical motion would prove to be of optimum design. Long ferrod arrays to produce beam widths much smaller than one degree offer possible advantages over other systems of similar characteristics. Some of the advantages would be cost of construction, simplicity of design and ability to adjust each radiating element in the array independently. Arrays of this type should be of particular interest for work in radio astronomy.