A low-profile spiral antenna array above an EBG reflector

A spiral antenna array with an EBG reflector is analyzed using the FDTD method and the radiation characteristics are discussed, where the number of array elements is chosen to be four. It is emphasized that the antenna height above the surface of the EBG reflector is smaller (0.06 wavelength) than the antenna height for conventional spiral arrays above a PEC reflector (0.25 wavelength). The spiral arms are optimized to obtain CP wave radiation, taking into account mutual coupling among the four spirals. It is found that the array shows a frequency bandwidth of approximately 17% for a 3-dB axial ratio criterion. Within this axial ratio bandwidth, the impedance shows a relatively constant value and the gain reaches a maximum value of 16.1 dBi.