Millimeter-wave beam forming and dynamic steering using an optically controlled photo-injected Fresnel zone plate antenna at 94 GHz

We present results for a rapid, precise and wide field-of-view scanning antenna for use at millimeter and submillimeter wavelengths, based on the photo-injected Fresnel zone plate antenna (piFZPA) method. Our work demonstrates the potential of this technology as a viable solution to a range of applications demanding video rate imagery at these frequencies. This technique is based on optically exciting free carriers in a semiconductor substrate, to form a plasma-based Fresnel zone plate antenna, which focuses and steers incident millimeter-wave beams. By reconfiguring the optically projected pattern, it is possible to dynamically, and rapidly, manipulate (sub) millimeter-wave beams within a 3D volume. It is believed that the little attention devoted to this method since it was first demonstrated 20 years ago has been due to the high illumination densities required for sufficient plasma injection. Our work has made significant improvements in addressing this requirement and the technique is demonstrated using simple, commercially available hardware. We present proof-of-principle experiments at 94GHz incorporating a commercial data projector. The 100mm diameter piFZPA achieves 37dBi directivity, excellent beam symmetry, beam steering in two dimensions over a +/- 30 degrees field-of-view, and precise beam control and repeatability. Whilst current demonstrations are restricted to less than 20 beams per second with the current implementation, the technique is capable of achieving beam scanning rates of more than 10,000 beams per second, suitable for video-rate imagery. We also present, believed to be for the first time, results of a piFZPA integrated into a short range, 94GHz, 3D imaging radar.