## 4 Experiment and Results
### Sensitivity Law of Navigation Receiver  
The above definition of the sensitivity criterion and the effect experiment method are adopted. Based on the consideration of the stability of the experiment, the critical interference power of the navigation receiver at the working frequency point is measured firstly, then extend to the left and right sides, respectively, when the output power of navigation simulator is \(-90\) dBm and \(-110\) dBm. The position replacement method is used to convert the power to field intensity in the experiment. When the transmitting power \(P_{0}\) of the signal generator is 29 dBm, the field intensity at the receiving antenna position of the navigation receiver is 5 V/m, that is \(E_{0}=14\) dBV/m. Then the critical interference field intensity \(E\) at each frequency point can be obtained by \(E=E_{0}+P-P_{0}\) (dBV/m) defined in the linear interpolation/extrapolation method [28], where \(E_{0}\) and \(P_{0}\) are the reference field intensity and power separately, \(P\) is the measurement power for each frequency point. According to the experiment, \(E=P-15\) (dBV/m). The sensitivity curves are shown in Figure 4. To understand the feature of the navigation receiver, the sensitivity curves within the bandwidth of \(f_{0}\pm 2.5\) MHz in Figure 4 are enlarged. The partial enlarged drawing of it as shown in Figure 5.  
When the output signal power of navigation simulator is \(-90\) dBm and \(-110\) dBm, the bandwidths of sensitive interference frequency offset of the tested navigation receiver are \(-11.5\)-\(53.5\) MHz and \(-13.5\)-\(55.5\) MHz, respectively. Although the stronger the navigation working signal is, the narrower the sensitive interference frequency bandwidth is, the law of variation for the sensitivity of different working signals is always consistent.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Working Power** & **Interference Frequency** & **Measurement 1** & **Measurement 2** \\
**(dBm)** & **Offsets (MHz)** & **(dBm)** & **(dBm)** \\ \hline \multirow{6}{*}{\(-90\)} & \(-2.5\) & \(-37\) & \(-38\) \\  & \(-1.5\) & \(-38.5\) & \(-39\) \\  & \(-0.5\) & \(-39\) & \(-39.5\) \\  & \(0.5\) & \(-38.5\) & \(-40\) \\  & \(1.5\) & \(-37.5\) & \(-38\) \\ \hline \multirow{6}{*}{\(-110\)} & \(-2.5\) & \(-45.5\) & \(-46\) \\  & \(-1.5\) & \(-47.5\) & \(-47.5\) \\ \cline{1-1}  & \(-0.5\) & \(-52\) & \(-52.5\) \\ \cline{1-1}  & \(0.5\) & \(-49\) & \(-49\) \\ \cline{1-1}  & \(1.5\) & \(-46.5\) & \(-46\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Measurement values of critical interference power when the sensitivity criterion is used.  
The working frequency bandwidth of the tested navigation receiver is within the frequency offset of \(\pm 2\) MHz. In reality, the working frequency point measured in the experiment deviates from the nominal working frequency point, with a deviation value of about 0.4 MHz. Although it is related to the characteristics of the front-end filter of the tested navigation receiver, it is still within the nominal working frequency bandwidth.  
The anti-jamming performance of the tested navigation receiver is directly proportional to the working signal intensity of the system. The stronger the working power of the system is, the higher the critical interference field intensity of each frequency point is. It indicates that the anti-jamming ability will be stronger with the decrease in the sensitivity of the navigation receiver.