Design and preliminary experimental results for a high-frequency crossed electrode phased array, based on a reconfigurable Fresnel lens

A reconfigurable Fresnel lens approach for 3D imaging on crossed electrode array is described. A Fresnel lens can provide a focus comparable to traditional beamforming if the Fresnel focus is used in one direction, combined with conventional beamforming in the other direction. For example, in azimuth the Fresnel pattern is applied on transmit and dynamic beamforming is completed on receive. A second feature to our crossed electrode design arises from the fact that although a Fresnel lens can create a tight lateral focus, inherently long axial pulses result in poor axial resolution. This is because the phase delays are quantized to 0 or 180 degrees, and at wide steering angles the element path distance spans multiple wavelengths. We have developed a split and delay subaperture technique that maintains axial resolution throughout the image. At 0, 15 and 25 degrees the axial resolution using a single aperture was 64, 180 and 321 um. After splitting the aperture into 8 sub-apertures the resolution is 53, 64 and 77 um. The beamwidths using this technique are comparable to a traditional array and agree well with simulation suggesting that this Fresnel approach shows promise for 3D imaging.