In this paper, a low-profile equiangular spiral antenna is designed. The bi-directional beam from an equiangular spiral antenna (EAS) is changed to a unidirectional beam using an artificial magnetic conductor (AMC) reflector. The antenna height, measured from the upper surface of the AMC reflector to the spiral arms, is chosen to be extremely small to realize a low-profile antenna: 0.07 wavelength at the lowest analysis frequency of 3 GHz. The analysis shows that the EAS backed by the AMC reflector does not reproduce the inherent wideband axial ratio characteristic observed when the EAS is isolated in free space. To solve this problem the AMC reflector is modified by gradually removing the patch elements from the center region of the reflector. The results show that the spiral antenna with a modified artificial magnetic conductor reflector reduces the axial ratio in the working frequency band from 3 to 10 GHz, and greatly broadens the working bandwidth of the spiral antenna. A viable way is proposed to optimize the performance of the low-profile equiangular spiral antenna without change the dimensions.
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