## 6 Conclusions  
In order to obtain the accurate critical interference threshold value of a certain navigation receiver at a specific frequency point, we must understand its anti-jamming performance, and prepare for further electromagnetic environmental effect prediction research. The sensitivity criterion is defined based on the sensitivity phenomenon levels of the navigation receiver. The sensitivity measurement method is established according to the overall consideration of C/N0 recovery requirements and the working signal feature of the navigation receiver. The accuracy of the sensitivity threshold can be improved with the proposed sensitivity criterion and measurement method. The experimental results of the single-frequency continuous wave effect on the tested navigation receiver show that:The initial C/N0 of each satellite is identical under the same working signal intensity, while it is distinct when the navigation receiver works at a different signal intensity. The critical interference C/N0 is also different when the tested navigation receiver is in a different electromagnetic radiation intensity. Although a fixed C/N0 is taken as the sensitivity criterion which will lead to an increase of measurement error, the initial fixed C/N0 still can be used as the reference to evaluate whether the system gets back to the normal positioning state after the jamming is turned off.  
The sensitive phenomenon which is caused by electromagnetic radiation of the tested navigation receiver can be classified into four levels. The \"loss of the positioning within first 4 s and the duration lasts for 30 s\" is taken as the sensitivity criterion, the strategy of variable step size is employed to gradually increase the interference power at each frequency point, and the system recovery state is required to ensure the measurement accuracy and efficiency.  
The interference of the navigation receiver mainly comes from the blocking interference of the RF front-end, and its anti-jamming performance is proportional to the intensity of the useful signal. The stronger the useful signal is, the narrower the sensitive bandwidth is, while the higher the critical interference field intensity of each frequency point is, the stronger the anti-interference ability is. The curves of critical interference field intensity are almost the same pattern under different working signal intensities. The positive frequency offset sensitive bandwidth is about 5 times that of the negative frequency offset, which shows that the stronger anti-interference capability in the negative frequency offset.  
[PERSON] proposed the main concept of the experimental method and emphasized the importance of this work; in addition, he analyzed and discussed the recent developed research works related to the sensitivity criterion. Moreover, [PERSON] reviewed the writing. [PERSON] carried out the experiment and validated the performance of the proposed method. In addition, [PERSON] analyzed and discussed the obtained results with [PERSON]. [PERSON] also wrote this paper. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Defense Basic Research Key Project of China, grant number 41409030301.  
Not applicable.  
The authors would like to acknowledge the financial support for this work, received from the National Defense Basic Research Key Project of China, under grant number 41409030301.  
The authors declare no conflict of interest.