Ultrawideband Spiral Antenna with Unidirectional Radiation and Band-Notch Characteristics

An ultrawideband spiral antenna with both unidirectional radiation and band-notch characteristics is proposed in this paper. The proposed antenna consists of a spiral element, a wideband balun and a metal cavity filled with stepped absorbing material, which is used to achieve unidirectional radiation and flat realized gain. In addition, an extra split-ring resonator is loaded above the spiral element to introduce a notched band for the realized gain to suppress the undesired interference. The simulation results demonstrate that the proposed antenna could achieve ultrawideband and unidirectional radiation performances from 2 to 18 GHz while a notched band with center frequency of 5.57 GHz is realized.