Dual-loop slot array antenna radiating circularly polarised wave

An array antenna consisting of dual-loop slot elements with a simple feeding system is realised. Each dual-loop element has two loop slots that are simultaneously fed by a single triplate transmission line. A narrowed beam, of circular polarisation, with an axial ratio of less than 3 dB, is obtained over a 3% bandwidth. The measured radiation pattern agrees well with a pattern calculated using array theory.