Passive Nonreciprocal Signal Switching: A Compact Backward Coupler Using a Nonlinear Metamaterial Structure

This study presents a compact passive backward coupler (CPBC) designed for efficient nonreciprocal switching, leveraging nonlinear Schottky diodes, microstrip transmission lines (MTLs), and metamaterial-based interdigital capacitors (MICs). Operating passively at 2.43 GHz, the CPBC achieves high isolation between transmitter and receiver ports without requiring external biasing voltage. The switch comprises four ports: Input (Port-1), Output (Port-2), Backward coupling (Port-3), and Forward coupling (Port-4). At low power, the input signal is directed solely to the output port, ensuring no signal coupling, while at high power, the signal is rerouted to Port-3 for backward coupling. The switch incorporates 32 anti-parallel Schottky diodes to facilitate bidirectional signal flow. The proposed structure is simulated and fabricated to validate its performance, and the measurement results show strong agreement with the simulations. This design effectively enhances signal routing and isolation performance for passive switching applications and enables efficient communication and power management by allowing seamless switching between data transmission and reception using a single antenna.