Compact circularly polarized antenna with highly directional signal-interference-ratio pattern for secure P2P CubeSat communications

This letter presents a compact circularly polarized (CP) antenna with an equivalent highly directional signal-interference-ratio (SIR) pattern, designed for secure point-to-point (P2P) CubeSat communications. The proposed antenna integrates a 3D rotational symmetric CP jamming element and a unidirectional CP data element within a compact structure, achieving dynamic control over the secure communication region. By adjusting the excitation power ratio (EPR) between the elements, the antenna enables adjustable 2D secure coverage (±5∘ to ±15∘ with SIR>10 dB). The jamming element, composed of four rotationally symmetric dipoles fed in phase, generates a rotational symmetric CP differential pattern for omnidirectional interference, while the data element, centrally integrated within the jamming element, consists of cross-dipoles fed orthogonally to ensure reliable CP transmission. This integration eliminates the need for separate antenna arrays, optimizing space for CubeSat applications. The proposed C-band prototype achieves high radiation efficiency and isolation (>27 dB), confirming its effectiveness for secure satellite communications.