A Pattern Reconfigurable Circularly Polarized Quadrifilar Helix Antenna Through Phase Control

We have proved in theory and simulation that the circularly polarized (CP) radiation from a resonant quadrifilar helix antenna (QHA) is independent of the phase between two composed bifilar helices, while the CP radiation pattern can be reconfigured by controlling this phase. It is demonstrated that the QHA is capable of generating a wide range of CP radiation patterns, including two cardioid patterns toward both ends, two vertical toroid patterns in two different orientations, and the mixed patterns of cardioid and toroid. A wideband and multilayer feeding network was developed to excite the four basic modes of the proposed QHA through phase control in the experiment. The simulated and measured right-handed circular polarization (RHCP) radiation patterns agree quite well. The proposed QHA was also designed to cover several global navigation satellite system (GNSS) bands. The measured impedance bandwidth is 1.26–1.65 GHz (26.8%) and the 3 dB axial ratio bandwidth is 1.1–1.8 GHz (41.4%) in the endfire mode. It is shown that the proposed QHA can be easily operated in two endfire modes to have an equivalent isotropic pattern for flying objects. When the antenna is operating in the endfire mode, the gain is in the range of 2.1–3.5 dBi, and the radiation efficiency is 70%–85% in the operating band.