Regular paper Performance evaluation of the adaptive sidelobe canceller system with various auxiliary configurations Jafar Ramadhan Mohammed ⇑ , Khalil Hassan Sayidmarie College of Electronic Engineering, Ninevah University, Mosul 41001, Iraq article info Article history: Received 15 November 2016 Accepted 19 June 2017 Keywords: Adaptive arrays Adaptive sidelobe canceller Adaptive nulling Interference suppression abstract In practical radar systems, the conventional adaptive sidelobe canceller (SLC) works very well as long as the input signal-to-interference-plus-noise (SINR) ratio is low or when the desired signal is known to be absent during certain time intervals. However, under high SINR, attenuation in the direction of the desired signal is inevitable. In this paper, the conventional sidelobe canceller is improved by replacing the separate auxiliary antennas by a number of existing elements of the main antenna array. This mod- ification makes the proposed SLC different from the conventional one because the desired signal compo- nents of the main channel and auxiliary signals may be correlated. Such correlation may cause serious attenuation in the desired signal especially when the number of reused elements from both of the main array and auxiliary antenna is increased. The resulting malfunctioning of the desired signal cancellation is eliminated by adjusting the weights of the reused elements to produce a specific cancellation pattern. The required cancellation pattern should have two main features: first, it should have a level equal to that of the main array pattern at the interferer direction. Second, it should have a very low level or a null at the direction of the desired signal. The simulation results show that good performance for interference can- cellation, maintaining a distortionless response for the desired signal, and low sidelobe level can be obtained by using the proposed technique. Besides the simplicity and low cost, the other advantage of the proposed SLC is that it can work effectively regardless of the strengths of the desired signal. Ó 2017 Published by Elsevier GmbH. 1. Introduction A sidelobe canceller (SLC) is an adaptive antenna system that can suppress interfering signals incident on the sidelobes of the main antenna. Conventional SLC’s that are employed in practical radar systems are effective only when the desired signal is very weak (relative to the interference signal) or when the desired sig- nal is known to be absent during certain time intervals [1–3]. In applications where the desired signal may be of unknown strength and may always be present, then the problem of desired signal can- cellation is inevitable [1,4]. The weights of the auxiliary antenna elements are usually chosen by minimizing the total output power. Choosing the weights to minimize output power can cause cancel- lation of the desired signal, since the desired signal also contributes to total output power. In fact, as the desired signal gets stronger it contributes to a larger fraction of the total output power and thus the percentage cancellation increases. Clearly, this is an undesir- able effect. This limitation can be overcome through the applica- tion of linear constraints to the weight vector of the auxiliary antenna. This design criterion yields the well-known minimum variance distortionless response (MVDR) beamformer [5,6]. How- ever, with the standard MVDR beamformer, desired signal cancel- lation also occurs in the presence of steering vector errors or in the case of smart interference in which the interference is correlated with desired signal [7–11]. Also, the performance of the MVDR beamformer is known to degrade substantially when the number of snapshots used for covariance matrix estimation is insufficient [12]. This often occurs in practical radar systems due to the requirement for fast tracking of the moving target. Furthermore, in real-life applications of phased arrays, the accu- racy of pointing an adaptive null toward an interfering signal is known to degrade substantially when the effect of mutual coupling between array elements is not taken into account [13] and/or due to the effect of frequency fluctuation [14]. Thus, there has been considerable interest in synthesizing array patterns with broad nulls [15–17] or extremely low sidelobes [18–20] to cope with these problems. It is also desirable to make the practical imple- mentation of such phased arrays as simple as possible where the null steering in adaptive arrays is usually achieved by controlling http://dx.doi.org/10.1016/j.aeue.2017.06.039 1434-8411/Ó 2017 Published by Elsevier GmbH. ⇑ Corresponding author. E-mail addresses: jafarram@yahoo.com (J.R. Mohammed), kh.sayidmarie@gmail. com (K.H. Sayidmarie). Int. J. Electron. Commun. (AEÜ) 80 (2017) 179–185 Contents lists available at ScienceDirect International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue