Low-Profile High-Gain Circularly Polarized Endfire Leaky Wave Antenna

We present a circularly polarized (CP) endfire leaky wave antenna with a high gain, low profile, wide axial ratio bandwidth, and high gain-to-length ratio in this communication. The proposed CP endfire leaky wave antenna comprises CP nonresonant radiation elements and double-sided parallel strip lines (DSPSLs). The DSPSLs feed CP radiation elements through spatial coupling, leveraging the identical E-field modes of DSPSLs and elements. The antenna achieves a low profile due to the same height of DSPSLs and elements. The enhanced CP nonresonant radiation elements are adopted to extend the aperture, achieving a high gain. Moreover, the amplitudes and phases of the orthogonal E-fields generated by the CP nonresonant radiation elements vary linearly with frequency, ensuring a wide axial ratio bandwidth. Energy propagation through two paths, including DSPSLs and spatial coupling of elements, results in a uniform aperture and a high gain-to-length ratio. The fabricated antenna demonstrated a maximum gain of 13.9 dBic, a gain-to-length ratio of 8.13, and an axial ratio bandwidth of 18.57%, with a low profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.04~\lambda _{0}$ </tex-math></inline-formula>.