Insertion loss is one of the most critical electrical performance indicators of RF duplexers, referring to the signal power attenuation generated when electromagnetic signals pass through the duplexer’s transmit (Tx) and receive (Rx) paths, usually measured in decibels (dB). Duplexer insertion loss directly determines the signal transmission efficiency and communication quality of the entire RF front-end system, and different loss standards are required for Tx and Rx paths due to their distinct working characteristics. In general communication systems, excessive insertion loss will lead to reduced transmit signal power, shortened communication distance, and weakened received signal strength, resulting in increased system bit error rate and degraded communication stability. Therefore, precise control and optimization of Tx and Rx path insertion loss are core links in duplexer design, production, and performance evaluation.

The transmit path insertion loss of a duplexer reflects the attenuation degree of high-power transmit signals output by the power amplifier when passing through the duplexer. The Tx path bears high-power RF signals, so its insertion loss optimization focuses on reducing power loss to ensure sufficient signal radiation power from the antenna. For cellular base station and satcom equipment, each 1dB increase in Tx insertion loss will cause about 20% reduction of effective transmit power, which not only reduces communication coverage but also increases the power consumption and heat generation of the front-end power amplifier. Duplexer designers adopt low-loss dielectric materials, optimized resonant circuit structures, and minimal impedance mutation design to control Tx path insertion loss within 1-3dB for most communication bands. Meanwhile, the Tx path needs to maintain stable low-loss characteristics under high-power working conditions to avoid performance degradation caused by device heating and dielectric saturation.

The receive path insertion loss is more sensitive to signal attenuation due to the ultra-weak characteristic of antenna-received signals. The Rx path transmits low-power ambient RF signals to the low-noise amplifier, and excessive insertion loss will directly reduce the signal-to-noise ratio of the received signal, reduce receiver sensitivity, and lead to failure to capture weak distant signals. Compared with the Tx path, the Rx path usually requires stricter insertion loss indicators, generally controlled below 2dB for high-precision communication systems. In addition, Rx path insertion loss must maintain flatness in the entire passband to avoid amplitude distortion of different frequency components of the received signal. The difference between Tx and Rx insertion loss is determined by the duplexer’s internal filtering structure: the Tx filter prioritizes power tolerance and interference suppression, while the Rx filter prioritizes low loss and high selectivity.