Design of a Broadband Inverted Conical Quadrifilar Helix Antenna and a Small GPS Helix Antenna

This chapter introduces two type helix antennas. One is a broadband inverted conical circularly
polarized quadrifilar helix antenna (QHA). The antenna has many good characteristics, including wide
beam and broad bandwidth, which are achieved by utilizing inverted conical geometry and adjusting
the dimensions of the inverted conical support. The antenna is fed by a wideband network to provide
90° phase difference between the four arms with constant amplitude. The antenna impedance and
axial ratio bandwidth values are more than 39% and 31.5%, respectively. The measured results
coincide well with the simulated ones, which verified the effectiveness of the proposed design.
Another step type helix line technology is also proposed to reduce the size of helix antenna. A small
GPS helix antenna using the step helix line technology is designed, the antenna size is
0.032λ×0.032λ×0.063λ, the maximum gain is 5.3dBi, the peak to peak of circumference gain pattern
within 0.3dBi, and the bandwidth is larger than 100MHz.