The preconditioned conjugate gradient method(PCG) for solving triple Toeplitz linear systems is put forward and is combined with the fast Fourier transform(FFT).The combining algorithm

called PCGFFT

is applied to RCS analysis of large dipole-array antennas.Because of the preconditioner

the condition number of the coefficient matrix is largely improved.The numerical results show that PCGFFT reduces the need for computer memory

speeds the iteration and enhances the convergence.