Abstract
With their high relative permeability, magneto-dielectric (or magnetoelectric) materials show great potential in antenna miniaturization. In this chapter, the effects of ferrite substrate on antenna resonant frequency, radiation patterns, polarization, radiation efficiency, and tunable radiation beams are discussed with the finite element-boundary integral, method of moment, cavity model and experiments in the second section. Magnetic films have great potential in the device industry as they can be used for enhancing the performance of microwave devices such as antennas, filters, phase shifters, and inductors. Spin spray deposited spinel ferrites films have been fabricated using spin spray process, including, nickel zinc ferrite thin films, nickel zinc cobalt ferrite thin films, manganese zinc ferrite thin films, etc. One of the most promising bulk ferrites for offering low-loss operation in the microwave region is the hexagonal ferrites, including ‘Z-type’ hexaferrites and ‘M-type’ hexaferrites. Composites with mixed ferrites and bismuth strontium titanate are introduced as well. To get a thick magnetodielectric material substrate, the layered ferrite film composed of self-biased spinel NiCo-ferrite films and woodpile structure of layered bulk ferrite are presented in the fifth section. Magnetically tunable patch antennas designed with metal magnetic films (Fe60Co40)85B15 show the tunability of resonant frequencies, radiation patterns and gain enhancement as well. Patch antennas with self-biased single layer film Ni0.23Co0.13Fe2.64O4 and planar microstrip ring antenna with multilayer Ni0.23Co0.13Fe2.64O4 ferrite films are illustrated as ferrite thin films provide a unique opportunity for achieving self-biased magnetic antenna substrates with mr >1 at frequencies larger than 1 GHz. Miniaturized helical antenna with hexagonal Z-type an M-type bulk ferrite materials are realized in the sixth section. Antennas with substrate with large and equal relative permittivity and relative permeability is prepared for miniaturization and impedance match to free space, in which this substrate is made of nickel zinc ferrite and bismuth strontium titanate that prepared by conventional ceramic processing.
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