A quadrifilar helical antenna printed on a dielectric prism

A quadrifilar helical antenna (QHA) is analyzed using the FDTD method. The four arms of the QHA are printed on a dielectric prism backed by a ground plane. The thickness of the prism is given as B=(1-r/sub AFRR/) c/2 with r/sub AFRR/ being the air-filled region ratio. It is found that the radiation pattern and gain obtained by a QHA whose arms are wound in free space (r/sub AFRR/=1) are reproduced by a QHA whose arms are wound on a reduced-size prism of r/sub AFRR/=0. The input impedance and gain as a function of r/sub AFRR/ are evaluated. In addition, the beam direction as a function of the ground plane size is revealed.