Three sources of beamforming deterioration are identified for an FMCW radar. These all relate to time-of-arrival and cable delays. There are small range-dependent phase errors at the receiver outputs. The delays cause frequency shifts, which produce phase errors at the discrete Fourier transform (DFT) outputs after ranging. These frequency shifts cause amplitude errors when the signals are resolved into the same range bin. Two methods of compensating for phase and amplitude errors are proposed. The first corrects for phase errors prior to beamforming. Amplitude errors are ignored but the residual error is usually small. The second method aligns the receiver frequencies digitally before ranging. This eliminates the phase errors and the amplitude errors at the DFT range estimates.
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