Low-cost metal-only transmit array antennas at Ka band

We present here a design of metal-only unit-cell for transmitarray antenna (TA) applications at Ka-band, and we introduce a solution to reduce the total number of layers by polarization manipulation. The corresponding unit-cell is based on a C-shaped slot radiating element, fabricated by laser ablation on a thin metal sheet and operating in linear polarization. Thanks to the rotation of the slot, polarization of radiated wave can be manipulated to any arbitrary direction, particularly in the orthogonal direction of the incident wave. By combining two unit-cells with opposite rotation directions, we show that metal-only unit-cells made of three layers can be obtained, with a 360° phase shift, insertion loss lower than 1 dB and low cross-polarization level. This unit-cell with reduced profile is used to design several TA prototypes with a main beam direction pointing up to 50°. The experimental results demonstrate an 11% 3-dB fractional gain bandwidth with an aperture efficiency around 50% for a beam at boresight.