A low‐profile wideband spiral antenna with multiple stopbands

Abstract

AbstractA low‐profile spiral antenna with three stopbands (2.55 GHz band, 3.85 GHz band, and 5.45 GHz band) is developed. The stopbands are generated using three pairs of slots cut into the spiral arms. The antenna height is 0.077 wavelength at a low band edge frequency of 2 GHz. Firstly, the effects of the slot dimensions (length, width, ending angle, and position) on the stopbands are analysed, where the spiral antenna floating in free space radiates a bi‐directional beam. It is found that the stopband centre frequency is determined by the slot length, and the stopband bandwidth is determined by the slot width, ending angle, and position. Secondly, the fabrication tolerances are investigated. Thirdly, the bi‐directional beam from the floating spiral antenna is transformed into a unidirectional beam by using a low‐profile cavity. It is revealed that three stopbands are maintained. Finally, a prototype of the antenna is fabricated and measured to verify the analysed results.