Design and performance of an ultrawide-band ceramic-loaded slot spiral

The miniaturization of a broadband square slot spiral antenna is proposed using high-contrast (ε_r>30) dielectric materials. A previously developed circular slot spiral antenna is the starting point of the design. This spiral is first modified in terms of its feed and termination to facilitate the dielectric loading of the antenna by means of a superstrate. The subsequently placed superstrate is also modified by tapering its thickness to improve impedance matching. Several measurements were carried out using square spiral apertures having diameters of 2´´ and 6´´, respectively. It is demonstrated that the ceramic loading of a 2´´ spiral with an ε_r=90 shifts the initial operating frequency by nearly 320 MHz down to 564 MHz representing a size reduction of 36%. Additionally, a 6´´ aperture loaded with a superstrate having ε_r=30 is shown to operate down to 270 MHz corresponding to a size reduction of 18%.