Secondary radars are important equipment in the aviation industry. The basis of this system is the use of the L-band Q&A system for aircraft identification. In this paper, the design of a secondary radar system based on a broad spectrum of direct sequence architecture is proposed. The main purpose of this project is to increase the resistance of the system to noise disturbances and to equip the secondary radar system with LPI signals. For this purpose, the proposed scheme offers two different working modes, namely Z1 and Z2 modes. The practical implementation of the scheme is based on the BPSK modulation of a broad spectrum direct sequence architecture, whose initial synchronization is based on the matching filter and final synchronization using the Split Bit method (such as link 16). In Z1 mode (as normal system mode), a 32-bit word is achieved by processing 14.9 dB. Also in the design of the Z2 mode (referred to as storage mode) by sending a 16-bit word, the processing gain is 21.03 dB. The Z2 is intended for use in a noisy environment. The results of the system analysis show that in Z2 mode the effect of disturbance is reduced by 9.39 times compared to similar systems. The innovation of the proposal is to convert the secondary radar to radar with low probability and resistant to noise disturbance.