## 1 Introduction
A spoofing detection method using the intersection angle between two directions of arrival (IA-DOA) is proposed. The IA-DOA method is proved to be insensitive to the platform attitude, which reduces the cost and complexity of the experiment, but this method cannot obtain the direction information about the spoofer in the airspace [21]. The multi-antenna DOA spoofing detection method is mainly based on the difference between the real signal and the spoofing signal and performs spoofing detection according to the different information of DOAs. In the case of spoofing, the direction-finding of the spoofer can be realized, and the method can eliminate the threat of spoofing from the source. Reference [22] pointed out that for the double-antenna DOA spoofing detection method, the DOAs corresponding to the same carrier phase difference are ambiguous and cannot be eliminated. Additionally, it proved that the triple-antenna in a non-linear arrangement is the minimum requirement to solve DOAs ambiguity. Most of the multi-antenna spoofing detection methods developed later follow this principle in terms of antenna configuration. There have been some studies on solving the DOA of traditional antenna array [23; 24]. [PERSON] used a rectangular antenna array to estimate DOA using the ESPRIT algorithm, and realized the joint estimation of DOAs and the attitude of the antenna array. However, it requires a professional antenna array and calculates at the signal level [25]. Professional antenna array equipment and processing algorithms have a high threshold for ordinary users. At this stage, with the continuous improvement of electronic equipment manufacturing technology, GNSS equipment is developing towards miniaturization and low cost. Many low-cost commercial boards and antennas have appeared. Low-cost commercial board components, including receiver boards and antennas, have been tested in various scenarios [26; 27]. However, due to the price and manufacturing process limitations of low-cost commercial board components, there are the following three main error sources that will affect the solution of spoofing detection and direction-finding. First, low-cost commercial boards have clock bias in the sampling of signals, and time synchronization cannot be achieved when multiple receivers work at the same time. There is a power-on clock error; that is, multiple receivers cannot sample observation data at the same time. Moreover, this error is related to the starting up of the receivers. The power-on clock error will be absorbed by the receiver clock offset and cannot be eliminated in the different processes, which will introduce an error to the carrier phase observation value. Second, the antenna phase center is the benchmark of the observation data of the high-precision GNSS receiver, and the stability of the antenna phase center is an important index to measure the performance of the antenna. However, the stability of the phase center of the low-cost antenna is poor, and the antenna phase center fluctuates greatly with factors such as pitch angle and azimuth angle. At this time, when the low-cost antenna receives satellite signals in different directions, it will introduce additional phase differences and increase the measurement error [28]. Third, low-cost antennas are more sensitive to multipath effects. The multipath effect is closely related to the user's environment, and traditional differential technology is difficult to eliminate its influence. The superimposition of multipath signals and normal signals will not only affect positioning [29] but also lead to deviations in the DOAs of signals. Multipath effects may cause spoofing signals and multipath signals to be indistinguishable [30]. Aiming at the high hardware requirements of traditional array antennas, this paper uses low-cost commercial boards and antennas to build an anti-spoofing platform. In this paper, the effects of various errors of low-cost commercial board components on the carrier phase observations are deduced and considered in detail.