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Suppressing narrow-band interferences in direct sequence spread spectrum (DSSS) based communication systems is of great importance in both theoretical and practical aspects. Among the reported suppressing techniques, the adaptive frequency exciser based on subband transform is of particular interest because of its excellent interference-suppression performance. In this paper, we propose a novel method for designing perfect-reconstruction (PR) tree-structured filter banks acting as adaptive frequency excisers in DSSS systems. Particular attention in our design is paid to a low system delay requirement which is critical in delay-sensitive applications. This is achieved by decreasing the filter length with the depth increase of the tree and by using the filter banks with low-delay property. The numerical analysis and simulation results have shown that the system delay resulting from the proposed method is significantly lower than that of the original design while resulting in a small performance degradation due to the increased overlapping between the adjacent filters caused by reducing taps of filters in the tree structure.