## 1 Introduction  
The Global Navigation Satellite System (GNSS) can provide high-precision positioning, navigation and timing services [1]. However, the satellite navigation signal is very weak and buried in noise, which is easily affected by intentional and unintentional interference [2; 3; 4]. The array anti-jamming method can improve the interference suppression capabilities by using an adaptive antenna array, and has become one of the most useful anti-jamming methods [5; 6]. The blind interference suppression algorithms, such as the power inversion (PI) algorithm [7; 8], can suppress the interference without using the prior knowledge of the direction of arrival (DOA) parameter of the satellite signal. However, these methods are unable to enhance the navigation signal energy, and may even reduce the signal-to-noise ratio [9]. The beamforming method [10] forms a null in the direction of the interference and points the beam in the direction of the navigation signal, thereby achieving interference suppression while increasing the energy of the useful signal, which can effectively improve the weak signal reception capability. The Minimum Variance Distortionless Response (MVDR) method [11] is the most commonly used beamforming method, which uses the prior DOA information of the incident signal to construct the beamformer. This method generally needs to obtain the real-time attitude information of the array antenna by means of inertial navigation; however, most array antennas cannot provide this. Blind beamforming algorithms can achieve similar effects to MVDR by using the DOA estimation method without prior information [12; 13]. The DOA parameters of the incident signal are estimated in real time by the array signal processing method. The attitude information of the array antenna is not required as a priori information. The commonly used DOA parameter estimation methods include subspace-based methods such as MUSIC [14] and ESPRIT [15], the maximum likelihood estimator (MLE) method [16], the parse recovery method [17], etc. However, the DOA estimation performance of these methods in dynamic scenes will decrease because the target motion will degrade the spectral resolution of the array [18]. At the same time, the computational complexity of these methods is high, which is not applicable for the actual navigation receiver. Direction lock loop (DiLL) [19; 20; 21] can achieve high-precision DOA parameter tracking, which is very suitable for a direct sequence code division multiple access (DS-CDMA) system. DiLL uses the left-shifted and right-shifted spatial array response vectors to construct a closed loop for direction tracking, which can reduce the computational complexity significantly [22]. In Ref. [23], DiLL is used for the DOA estimation of mobile target, which can achieve a high-resolution DOA estimate signal. In Ref. [24], a DOA tracking method based on DiLL with tracking bias compensation for GNSS receivers was proposed, in which the tracking bias was effectively eliminated by estimating and compensating the error in real time. In Ref. [22], the rotate-to-zero DiLL (RZ-DiLL) method was proposed, which could effectively improve the DOA parameter estimation accuracy of large-angle incident signals. In Ref. [25], a DiLL method for a three-element L-shaped array was proposed to achieve the fast acquisition and tracking of two-dimensional DOA parameters, which significantly simplified the antenna structure and eliminated the dead-zone effect. However, most of the above methods are only suitable for non-interference scenarios. The realization of DOA tracking in strong interference scenarios is in urgent need of research. In this paper, a blind beamforming method for a GNSS array receiver based on DiLL is proposed. Firstly, the subspace projection method is used to suppress the interference signal. Secondly, the DOA parameter of the navigation signal is tracked and estimated by using the DiLL method after interference suppression.