Unmanned aerial vehicle (UAV) data links operating in battlefield environments are highly susceptible to electromagnetic interference (EMI), frequently causing frame synchronization failures. direct sequence spread spectrum (DSSS) systems, while offering inherent interference resistance, remain vulnerable to intentional EMI attacks through front-door coupling pathways.

This study aims to establish loss-of-lock threshold models for DSSS-based UAV data links under two critical interference scenarios: in-band single-source single-tone and dual-source dual-tone EMI. The research further seeks to experimentally validate these models.

Through rigorous EMI mechanism analysis with emphasis on front-door coupling effects, the theoretical threshold models were developed for both interference scenarios. Test validation employed EMI injection testing on an operational UAV data link platform. Controlled variables included working signal power, interference frequencies, and interference power. The interference thresholds were obtained from the tests.

The test loss-of-lock thresholds demonstrated strong alignment with theoretical predictions across both interference scenarios. For single-source interference, the thresholds exhibited positive correlation with working signal power, and the absolute value of the frequency offset. Under dual-source interference, the thresholds of interference 1 showed inverse correlation with the power of interference 2.

The validated threshold models provide a theoretical foundation for EMI sensitivity assessment and test design in UAV data link systems. Key findings indicate: (1) The closer the interference frequency is to the carrier frequency of the working signal, the worse the anti-interference ability of the data link is. (2) Increasing the power of the working signal can improve the anti-interference ability of the data link. (3) Front-door coupling is an important way for EMI to enter the receiver in tactical scenarios. These findings could provide optimized EMI protection for the next generation of UAV data links.