An X-/Ka- Band Shared-Aperture Linear-to-Circular Polarization Converter

This paper presents a novel design method for a dual-band shared-aperture linear-to-circular polarization (LP-to-CP) converter. High-impedance structures and a band-pass frequency selective surface (FSS) are employed to achieve low interferences between the X- and Ka-band elements. In this paper, a high-impedance structure is incorporated into the X-band element to eliminate high-order modes and prevent phase differences between TE and TM modes. Additionally, a band-pass FSS is employed to mitigate the influence of the high-frequency (HF) element on the low-frequency (LF) element. Based on this method, an X-/Ka-band converter with a two-layer structure is proposed. The X-band element consists of two groups of split rings and cross strips, which are printed on the topmost and bottom layers of the substrate. The Ka-band element comprises a Jerusalem cross printed in the middle layer and a metal strip printed on the same layer as the X-band element. Equivalent circuit model (ECM) is utilized to analyze the response of the converter. An X-/Ka-band LP-to-CP converter prototype is fabricated and integrated with array antennas to validate the design concept. The experimental results indicate that the array antennas integrated with the proposed converter can achieve an overlapped impedance and axial ratio (AR) bandwidths of 11.1% (8.18-9.14 GHz) and 13.6% (25.95 - 29.73 GHz), with maximum gains of 12.8 and 16.4 dBic in two frequency bands, respectively.