Robust direction finding by time-modulated array with all phase FFT

The effectiveness and accuracy of time-modulated array (TMA) based direction finding with harmonic characteristic analysis depend on the accuracy of harmonic estimation. During estimating the harmonic amplitudes and phases with conventional discrete Fourier transform (DFT) or fast Fourier transform (FFT), the fence effect generates if the carrier frequency of the received signal deviates the integer multiple of the frequency resolution. Therefore, it will decrease the accuracy of direction finding, even cause failure. According to this problem, this manuscript introduces the all-phase FFT into the analysis to received harmonics by the two-element TMA, which improves the robustness of estimation to amplitudes and phases of harmonics and the robustness of direction finding by TMA. Numeric simulations show that the proposed all-phase FFT direction finding method with time modulated array can acquire correct results, when the carrier frequency of the signal is any fractional multiple of the spectral resolution. And the root mean square error (RMSE) converges to 0 with the increase of SNR. This work improves the stability of the single-channel direction finding method with time modulated array based on harmonic characteristic analysis.