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In the present paper we discuss the effect of artificial magneto-dielectric substrates on the impedance bandwidth properties of microstrip antennas. The results found in the literature for antenna miniaturization using magnetic or magneto-dielectric substrates are revised, and discussion is addressed to the practically realizable artificial magnetic media operating in the microwave regime. Using a transmission-line model we, first, reproduce the known results for antenna miniaturization with non-dispersive material fillings. Next, a realistic dispersive behavior of a practically realizable artificial substrate is embedded into the model, and we show that frequency dispersion of the substrate plays a very important role in the impedance bandwidth characteristics of the loaded antenna. The impedance bandwidths of reduced size patch antennas loaded with dispersive magneto-dielectric substrates and high-permittivity substrates are compared. It is shown that unlike substrates with dispersion-free permeability, practically realizable artificial substrates with dispersive magnetic permeability are not advantageous in antenna miniaturization. This conclusion is experimentally validated.

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Abstract-New possibilities to design artificial magnetic materials for microwave frequencies are considered. Such composites can be used in microwave engineering at frequencies where no natural lowloss magnetic materials are available. A new magnetic particle (metasolenoid) formed by a stack of many parallel and very closely spaced single broken loops is proposed and analyzed analytically, numerically, and experimentally. It is shown that the effective permeability can reach reasonably high values over a wide frequency range when using such inclusions.