A Bifilar Helices-Based Bidirectional Same-Sense Circularly Polarized Antenna With Wide Bandwidth and High Gain

This communication presents a novel bifilar helices-based bidirectional same-sense circularly polarized (CP) antenna. It consists of two conical bifilar helices with a back-to-back configuration and a wideband feeding network. Since the helices are identical and each of them radiates unidirectional CP waves, the proposed antenna is able to produce same-sense CP waves in opposite directions. For each helix, a pair of conformal fan-shaped structures are designed for impedance matching while they act as reflecting surfaces for generating endfire radiation. A parallel strip line is adopted to connect the two helices and provide differential feeds for them. Thanks to the wide band feature of both the bifilar helices and the feeding network, the proposed antenna exhibits superior bandwidth performance over the existing studies. In addition, due to the full metal structure, the dielectric loss can be avoided and thus the proposed antenna has the advantage of high gain. To validate the design idea, a prototype is fabricated by using metal 3-D printing technology. The experimental results show that the 3-dB axial ratio bandwidth (ARBW) is 40% from 1.9 to 2.86 GHz and the peak gain is 8 dBic.