Design Methodology for Single-Feed Circularly Polarized X-Band Antenna Arrays for CubeSats Using Multilevel Sequential Rotation

This article presents a streamlined design methodology for single-feed circularly polarized antenna arrays for CubeSats. The presented method was created with student-led teams in mind and employs a geometrically simple approach, opting for circular patches and ring-shaped feed networks instead of complex geometries. High- and low-impedance radiating elements are designed, and design restrictions are introduced such that all other geometries may be solved through a set of simple cascading equations. These deliberate choices minimize the number of design parameters and simplify the design process. Circular polarization is achieved through a multilevel implementation of sequentially arranged linearly polarized circular patches fed in a series-parallel fashion by ring-shaped feed lines of constant impedance. This article also demonstrates a 4x4 right-hand circularly polarized (RHCP) CubeSat downlink array antenna designed for operation in the 8025-8400-MHz Earth exploration satellite band which was developed using the proposed methodology. The antenna comprises four sequentially rotated RHCP subarrays, each consisting of four sequentially rotated linearly polarized circular patches. The antenna's boresight RHCP gain exceeds 16.19 dBic at 8.389 GHz with a simulated 27.9% 3-dB axial ratio bandwidth, a 20 degrees half-power beamwidth, and an aperture efficiency of 53%. The antenna has a sub-2 VSWR bandwidth of 26.6%, and its radiation efficiency ranges from 60% to 82% across the target band. Its compact size of 9 cm x 9 cm enables it to fit on one face of a 10 cm x 10 cm CubeSat unit.