Low-Cost Low-Power Reflection Amplifier for Active Reconfigurable Intelligent Surfaces

Active Reconfigurable Intelligent Surface (RIS) architectures require unit-cell-level gain while keeping the per-element power consumption and fabrication cost low. This work presents a compact low-power reflection amplifier operating in C-band for 5G and 6G applications, implemented with a single SiGe HBT on a standard FR4 substrate. The design was carried out using nonlinear circuit simulations and layout-level electromagnetic co-simulation. The fabricated prototype, biased at 1.8V, provides a measured reflection gain of approximately 13dB around the target frequency with a sub-mW DC power consumption. The measurement campaign aimed to verify the negative resistance condition, the gain value, and the absence of self-sustained oscillations. These results demonstrate the feasibility of a compact low-power C-band reflection amplifier on low-cost FR4 for scalable active RIS implementations.