A Millimeter-Wave Multibeam Transparent Transmitarray Antenna at Ka-Band

This letter presents a transmitarray antenna (TA) in the 27.5–29.5 GHz frequency band. The proposed TA is optically transparent and offers the possibility of steering the beam in the H -plane from –30° to 30°. One can achieve these properties using a novel unit cell, composed of meshed double-circle rings printed on polymethylmethacrylate substrates, a plastic material transparent to visible light. This unit cell provides a phase shift of 300° for an insertion loss lower than 1 dB at 28.5 GHz. In turn, the TA sources consist of 2 × 2-element arrays of aperture-coupled stacked patch antennas. The choice of a patch array over a horn array allows one to reduce the total profile and weight of the TA. We have fabricated and tested a transparent TA with a diameter of 9.9 wavelengths at 28.5 GHz, yielding a broadside gain of 25 dBi and –1 dB gain bandwidth of 1.8 GHz; the off -axis 30° beam presents a peak gain of 21.5 dBi and –1 dB gain bandwidth of 1.4 GHz. The measured results are in good agreement with the simulated ones all over the frequency band of interest.