A Wideband Flat Gain Circularly Polarized Transmitarray Utilizing LP-to-CP Converter for Ka-Band CubeSat Applications

This article presents a wideband millimeter-wave circularly polarized (CP) transmitarray utilizing the linear-to-circular polarization (LP-to-CP) converter for Ka-band CubeSat applications. The present design aims at combining the multiple band antennas into a single wideband design. The LP-to-CP converter employs a single-layer substrate, providing angular stability up to 50° and achieving a 3-dB axial ratio bandwidth of 29% over the frequency range of 29.5–39.5 GHz. The dimensions of the unit cell are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.38\lambda \times 0.38\lambda \times 0.15\lambda $ </tex-math></inline-formula>, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> corresponds to a frequency of 30 GHz. A wideband 2-bit phase-quantized transmitarray is integrated with the proposed polarization converter, achieving the configuration of CP wideband transmitarray. The CP transmitarray is illuminated by a wideband linearly polarized (LP) Vivaldi antenna. The transmitarray surface consists of polarization rotating elements sized at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.3\lambda \times 0.3\lambda \times 0.15\lambda $ </tex-math></inline-formula> (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> corresponding to a frequency of 30 GHz). This CP transmitarray antenna demonstrates an axial ratio and 1-dB gain bandwidth of 27.3% (29.5–39.5 GHz) and 24.5%(30–38.5 GHz), respectively, with a maximum gain of 21.4 dBic. Fabrication and measurements of both the LP-to-CP converter and the integrated CP transmitarray have been done. The simulated outcomes align well with the measured results.