Antennas with artificial magneto-dielectric substrates: the dominant role of frequency dispersion

In this review paper we discuss the impact of frequency dispersion of artificial magneto-dielectric materials designed for antenna applications. The emphasis is on artificial substrates for microstrip antennas, used with the intention to reduce the antenna size or/and improve the impedance bandwidth characteristics. Here we compare the impedance bandwidths of miniaturized resonant antennas loaded with practically realizable, dispersive magneto-dielectric substrates and conventional high-permittivity substrates. Analytical expression is derived for the ratio between the radiation quality factors obtained using these substrates. It is shown that the ratio always exceeds unity, thus, artificial magneto-dielectric substrates offer no advantages in antenna miniaturization. This observation is experimentally validated