A High Gain Series-Fed Circularly Polarized Traveling-Wave Antenna at W-Band Using a New Butterfly Radiating Element

We propose a novel series-fed circularly polarized (CP) traveling-wave antenna known as the “Butterfly” antenna suitable for operation at the millimeter-wave frequencies. The Butterfly unit-cell consists of a sequentially rotated series-fed linear array of four microstrip patch antennas. The proposed CP Butterfly structure offers low cross-polarization radiation and wide axial ratio (AR) beamwidth. A periodic leaky-wave antenna (LWA) analysis provides insights into the radiation characteristics of the Butterfly series-fed linear array antenna, which is validated by the full-wave electromagnetic simulations. The open-stopband (OSB) is suppressed in the broadside direction due to the cancellation of the internal reflections within each cell of the sequential-phase fed linear array. The measured and the simulated AR, radiation patterns, and gain are presented for the broadside radiation of the parallel-series fed 8 χ 24 and 32 χ 24 planar array antenna at 86 GHz. The average measured 3 dB gain beamwidths are 9.5° and 2.9° along the φ = 0° plane of the 8 χ 24 and 32 χ 24 planar array antenna, respectively.