Abstract: In order to obtain the characteristics of 48 narrowband array signals,the method of orthogonal demodulation is presented,and two methods to realize it are compared.A quadratic orthogonal demodulation algorithm is put forward to decrease the demand of operation and memory resource so as to meet real-time processing,and the algorithm is realized by FPGA.A built-in self test(BIST) technology is used to test the quadratic orthogonal demodulation module and data transfer channels,which implements a sine wave adding pseudorandom sequence as test pattern generators.DSP works as a testing response analyzer to analyze signal characteristics.The result shows the effectiveness of the algorithm and BIST.