This paper presents a conformal retrodirective metagrating with multi-azimuthal-angle operating ability. First, a flat metagrating composed of a periodic array of single rectangular patch elements, two-layer stacked substrates, and a ground plane is implemented to achieve one-directional retroreflection at a specific angle. The elevation angle of the retroreflection is manipulated by precisely tuning the value of the period. To control the energy coupling to the retrodirective mode, the dimensions of the length and width of the rectangular patch are investigated under the effect of changing the substrate thickness. Three values of the length, width, and thickness are then chosen to obtain a high retroreflection power efficiency. Next, to create a conformal design operating simultaneously at multiple azimuthal angles, the rectangular patch array using a flexible ultra-thin guiding layer is conformed to a dielectric cylindrical substrate backed by a perfect electric conductor ground plane. Furthermore, to further optimize the retroreflection efficiency, two circular metallic plates are added at the two ends of the cylindrical substrate to eliminate the specular reflection inside the space of the cylinder. The measured radar cross-section shows a power efficiency of the retrodirective metagrating of approximately 91% and 93% for 30° retrodirected elevation angle at the azimuthal angles of 0° and 90°, respectively, at 5.8GHz.

The design, manufacture, and test results are presented for a 90polarization-rotating Van Atta array reflector with suppressed scattered field for the 1.27-GHz band. The reflector consists of 48 element antennas, half for horizontal polarization and half for vertical polarization. It receives a horizontally or vertically polarized wave and retransmits a vertically or horizontally polarized wave, respectively. The measured cross-polarized radar cross section of the reflector was 15.8 dBm2 on average, which agreed well with a theoretical prediction. Although the suppression of the scattered field was limited to about -20 dB relative to the retransmitted field, we could suppress more the scattered field by accurate positioning and careful characteristics adjustment of element antennas. Theoretical calculations showed that total phase errors of the element antennas including positioning errors and impedance characteristics errors have to be within 7.5to suppress the scattered field by less than -30 dB.