An electromagnetic device includes: a first medium having a first material having a first dielectric constant, the first medium having a plurality of spaces filled with a second material having a second dielectric constant that is different from the first dielectric constant; and a plurality of antennas disposed proximate the first medium; wherein adjacent ones of the plurality of spaces of the first medium have an average spacing therebetween of less than one quarter of an operating wavelength of at least one of the plurality of antennas.