Two-dimensional planar passive retrodirective array

A simple passive microstrip array design is introduced comprising four square microstrip patches interconnected with transmission lines to form a Van-Atta retrodirective array suitable as a building block in a larger two-dimensional self-tracking array. The resulting circuit measures 48×48×0.254 mm, operates at 10.24 GHz and yields 5 dB increase in return signal at bore-sight relative to a flat metal sheet having the same dimensions for incident linear polarisation. The -5 dB monostatic radar cross-section response is ±25° compared to ±12° measured for a flat metal sheet of equivalent dimensions. The reradiation characteristics of circularly polarised signals from the retrodirective structure are briefly discussed.