Design of a Microstrip Highly Directional Weak Coupler

The coupler is capable of real-time acquisition of RF signals within the circuit, primarily for testing the transmission power of the transmitting system and monitoring the normal operation of the transmission system. In case of abnormalities, timely feedback to the protection circuit helps prevent damage to critical components. Key indicators for couplers include in-band coupling coefficients, coupling flatness, and directionality. Microstrip line couplers are characterized by easy integration, making them widely applicable in systems that demand high integration. For weak couplers, improving directionality is the primary challenge. Enhancing coupler directionality can be achieved by adding branch-line resonator units in the coupling circuit. Experimental results indicate: within the 3400MHz~3600MHz range, a coupling coefficient of 27 dB, coupling flatness <0.7dB, and directionality across the band >20dB.