Distributed interferometric antenna arrays leverage simultaneous multi-antenna receptions to enhance detection sensitivity. Before phase-coherent signal combination for Signal-to-Noise Ratio (SNR) improvement, it is essential to accurately detect and compensate for time and frequency differences among the signals. The accuracy of frequency difference estimation at the receivers is inherently limited by the spectral leakage and grating lobe artifacts of the Fourier transform. This work proposes a method for optimizing the window function length in frequency difference estimation, reducing the Root Mean Square Error (RMSE) from 1kHz to under 30Hz in low SNR conditions. The algorithm's validity and superiority are demonstrated through the coherent combination of four signals, achieving an SNR improvement of 5.79dB (close to the theoretical gain of 6dB).