2-bit Reflective Electromagnetic Surface for X-band Beam Control Function

This paper presents a 2-bit reflective electromagnetic surface (RES) design for X-band beam control function based on tunable resonator approach. The beam control function is usually involved in X-band radio systems that require deflection of reflected waves in a certain direction. The proposed RES is configured by three layers with the dimensions of $\mathrm{1 6 0 ~ m m} \times \mathrm{8 0 ~ m m}$. The top layer is structured by $16 \times 16$ unit cells, which are a combination of 2 -bit or four state configurations of unit cell structure, namely state 00, state 01, state 10, and state 11. Basically, the unit cell structure in each state consists of four tunable open-ended resonators with varied length which can be connected or disconnected to produce the state configurations. The four state configurations produce four phase variations with the phase difference between states of 90°. This structure configuration is deployed on an FR4 epoxy dielectric substrate with the groundplane on the opposite side. Theoretically, the maximum reflected wave for the normal incident wave can be deflected by the proposed RES in the direction of approximately 21° from the normal reflection angle. This prediction is then confirmed through simulation and measurement. The proposed RES can be developed later by integrating PIN diodes to control the state of configuration, thereby improving its reconfigurability.