## 1 Introduction
Based on the predicted and estimated values of IA-DOA, generalized likelihood ratio testing (GLRT) was performed to achieve multi-direction spoofing detection. [PERSON] et al. [14] proposed a spoofing-detection method using the norm of the difference of baseline vectors (NDB) of multiple receivers. This method has a low probability of fault detection and fast response time and can achieve instant anti-spoofing. The above methods require array antennas or multiple receivers, which is costly. Therefore, scholars proposed using a moving single antenna for signal direction estimation. [PERSON] et al. [15] proposed a spoofing-detection method based on a reciprocating antenna, which determines the direction of the signal by determining the relationship between the amplitude change caused by the antenna's up and down motion and the signal incidence angle, achieving spoofing detection. In addition, based on the architecture of a single rotating antenna, similarity testing can be performed on the changing trends of carrier phases [16], CNR [17], and power [18] under the single rotating antenna to determine whether the navigation signal direction is consistent, thus achieving spoofing detection. However, the spoofing-detection method based on a moving single antenna cannot detect spoofing from multiple directions, and achieving spoofing detection from multiple directions still requires multiple antennas or receivers. The achievement of multi-agent spoofing detection based on a moving single antenna remains a challenge. Therefore, this article applies the IA-DOA of two signals to a single rotating antenna and proposes a detection method for multi-agent spoofing. It is difficult for multi-agent spoofers to accurately simulate the directionality of navigation signals, which means that there may be deviations between the incident direction of the spoofing and the real signal. Based on the CNR and carrier phase single difference (CPSD) of the signal obtained from a single rotating antenna, the maximum likelihood estimation (MLE) is used to obtain the estimated values of IA-DOA for any two signals. The predicted values of IA-DOA are calculated using ephemeris information, and detection variables are established based on the predicted and estimated values to determine whether there is spoofing in the two signals. Performing GLRT testing on each set of signals can achieve spoofing detection. We conduct a detailed analysis of the parameters that affect detection performance through simulation. In addition, the effectiveness of the proposed method was verified and evaluated through on-site experiments. The method proposed in this article simultaneously utilizes the CNR and CPSD of a single rotating antenna to estimate IA-DOA, achieving real-time detection of multi-agent spoofing while improving the detection performance. It should be noted that in this method, the antenna is in motion, but the center of the motion trajectory should remain unchanged. The method proposed is only applicable to spoofing detection at fixed sites. The detailed derivation of the principles and theories is conducted in Section 2. The spoofing-detection method based on the IA-DOA with a single rotating antenna is proposed and a detailed analysis of the feature parameters that affect detection performance through simulation is conducted in Section 3. Section 4 validates and evaluates the proposed method based on the on-site experiments. Section 5 concludes with discussions.