Frequency-Diverse Metacavity Cassegrain Antenna for Differential Coincidence Imaging

— In order to solve the low signal-to-noise ratio (SNR) problem of the differential coincidence imaging (DCI) system, a frequency-diverse metacavity Cassegrain antenna (FDMCA) that is able to generate low-correlated bunching radiation patterns is proposed in this communication. The FDMCA is designed according to the Cassegrain antenna form, which consists of a frequency-diverse half-spherical metacavity etched with backprojecting slot arrays and a parabolic reflector. In total, 81 useful measurement modes with a bunching angle of 40^◦ are obtained from 32 to 36 GHz. First, frequency-diverse field distributions in the metacavity are obtained utilizing a high-dispersion metasurface. Backprojecting slot arrays etched on the metacavity would couple the energy from the metacavity and backradiate to the reflector. When placing the phase center of the feed source at the reflector focal point, the reflected patterns would be focused. Then, the performance of the proposed FDMCA is evaluated. In total, 81 radiation patterns with correlation coefficients (CCs) under 0.3 are generated. Finally, imaging experiments using the proposed FDMCA are carried out and the target image is reconstructed successfully using the DCI method. Comparative experiments are also implemented under the same conditions using a nonbunching frequency-diverse metasurface antenna (FDMA) to verify the bunching advantage of the FDMCA. The design is validated by simulations and measurements.