220/293 GHz Dual-Band Anomalous Reflectors Using Higher-Order Diffraction Modes and Their Precise Characterization Using a Compact Antenna Test Range System

We propose dual-band anomalous reflectors operating at 220 GHz and 293.3 GHz for 6G applications. The anomalous reflectors consist of paired patch elements on single-layer and via-free substrates. Based on a local reflection phase design and optimization of paired patch elements, higher-order diffraction modes can be controlled simultaneously at the two harmonic frequencies to achieve highly efficient dual-band anomalous reflections in identical directions with wide reflection angles. Two reflectors are designed and fabricated on cyclo-olefin polymer (COP) substrates for the reflection angles of 45° and 50° and the incident angles of 0° and −10°, respectively. To evaluate their anomalous reflection performances under plane wave illumination in the J-band, we develop a compact reflector characterization system in the J-band exploiting a compact antenna test range (CATR) technique consisting of an offset Gregorian antenna. The developed CATR-based system generates a quasi-plane wave with a beam diameter of approximately 250 mm at 300 GHz at a position 900 mm from the antenna, enabling precise far-field bistatic radar cross section (BRCS) measurements with a compact system size. The measured BRCSs of the prototypes are in good agreement with the simulated results and highly efficient dual-band anomalous reflection operations are experimentally demonstrated with the efficiencies of over 80 % excluding the material losses in both the designed bands.