Mm-wave near-field focused antenna array for chipless RFID detection

This work reports a focused antenna array that could allow for an accurate interrogation of passive sensors. In recent years, some passive sensors have been proposed [1, 2], however there are often problems reading these sensors due to interference with the surrounding environment. The proposed idea is therefore to focus the beam exclusively on the sensor. The reading system is formed by two cross-polarized near-field arrays which are able to concentrate the radiated fields in the area occupied by the sensor under test thus avoiding scattering from nearby objects with a consequent reduction of clutter. The proposed NF focused array is composed of 16x16 elements and it works around 20 GHz (λ equal to 15 mm). The array has a layered structure. There are two dielectric substrates (Itera MT40 material), the lower substrate has a thickness of 0.254 mm and the upper one 0.762 mm. The feeding network, which represents the bottom of the structure, is created on the first substrate. On the top of this substrate there is a perforated metal surface. Metallic rectangular patches are made on the top of the second substrate. Vias cross the entire structure to connect the feeding network with the patches.