Switchable Electromagnetic Absorber/Reflectors Using Back-Loaded Active Radio Frequency Circuits

In this paper, three switchable electromagnetic absorbers/reflectors using back-loaded active radio frequency circuits are presented. In the first design, the incident waves are received by an antenna array, transmitted to the back-loaded active circuits and then reflected into the free space when the PIN diode in series in the circuit is off. When the diode is on, the incident waves can be absorbed by a matching load. In the second design, the phase of the reflected waves in the unit cell can be manipulated by adjusting the length of the microstrip lines, allowing the reflection polarization to be tuned. In the third design, by integrating RF switching chips into the back-loaded circuits, a switchable absorber/reflector with a switching polarization state is presented. The first design is fabricated and measured. The profile of the switchable absorber/reflector is approximately $0.14\lambda_{l}$. A total of 2 PIN diodes are used per unit cell for both TE and TM polarizations. By using active circuits, flat in-band reflection performance and stable absorption performance can be achieved in the frequency band of 7 to 18.5 GHz (FBW of 90%) for normal incidence, and an angular stability of 45° for TE and TM polarizations is realized.