Near-field measurements of submillimeter-wave reflectarrays

We present results of experimental characterization of static 650-GHz reflectarrays. The reflectarrays are based on 123-μm circular microstrip patch antennas with tuning stubs as phase shifters. The static reflectarrays are considered as predecessors for active reflectarrays, and therefore the reflectarray elements have two discrete phase-shift values: 0° and -180°. The reflectarrays have 95000 elements, and they have separation of 400 μm. The reflectarrays are fabricated on 150-mm silicon wafers with a ground plane and a 20-μm polyimide substrate atop. The fabricated static reflectarrays are characterized in a near-field measurement range and their beam patterns at the focusing distance of 20 m are calculated with plane-to-plane transform. At this high frequency, fabrication tolerances are difficult to meet and, e.g., over-etching of the antenna and phase-shifting structure may offset the resonance frequency of the reflectarray element by more than its bandwidth.