An Ultrawideband Linear-to-Circular Polarization Converter With Good Angular Stability Performance for Satellite Communications

In this communication, an ultrawideband and compact linear-to-circular polarization converter (LTCPC) with good angular stability is presented and analyzed. It is structured as an array by periodic cells, and each cell has the same structure and contains two asymmetrical metallic patterns divided by a thin substrate. Specifically, the metallic patterns consist of a Jerusalem-cross-like structure (JCLS) on the top layer and a metal strip on the bottom. The design is optimized by 3-D electromagnetic (EM) simulation, while the equivalent circuit (EC) model analyzes its structure quantitatively. A long crossed branch in JCLS can be equated as a high-pass filter with a low cutoff frequency. In addition, this structure can independently change the horizontal and vertical phases to improve the passband. The bottom long strip resonates at a high out-of-band frequency, which can further increase the frequency band of interest. To check its performance, we fabricated and measured a sample with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$78\,\times \,78$ </tex-math></inline-formula> cells, with each cell’s size being just <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.006\lambda _{0}^{3}$ </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">$\lambda _{0}$ </tex-math></inline-formula> is the wavelength corresponding to the center frequency). The results reveal that the simulated/measured axial ratios (ARs) are below 3 dB from 13.7 to 30 GHz (75%)/14 to 29.7 GHz (72%) for a normal linear polarized (LP) incident wave. Moreover, the scanning angular stability is up to 55°, which is useful for wide-angle scanning phased array. Due to the ultrawide AR bandwidth and high angular stability of the proposed LTCPC, it can simultaneously meet the current application requirements of low Earth orbit (LEO) satellite communications (SATCOMs).