Frequency measurement receiver with bandwidth improvement through phase shifted sampling of real signals using sampling rate selection

摘要

This is a technique for extending the frequency range which employs a power divider having two outputs, one output being supplied to a first A/D converter, and the other output being supplied via a delay device to a second A/D converter. A processor receives the outputs of the two A/D converters. In operation, the input signal is subjected to a known delay tau and both original and delayed signals are sampled simultaneously. Both sampled signals are Fourier transformed and the phase and amplitudes calculated, using the expressions: phi (f)=tan-1[I(f)/R(f)] A(f)=[R2(f)+I2(f)]1/2 where R(f) and I(f) are respectively the real and imaginary parts of the frequency transform. The phase difference between the original and delayed signals is calculated and an approximation to the true frequency for each peak observed in the amplitude spectrum is estimated using the expression phi =2 pi f tau where tau is the delay. In general, one would expect that when f tau <1, one can recover the input frequency. However, effects associated with the sampling limit the input bandwidth to f<1/ tau . A specific sampling rate is used which can restore the unambiguous bandwidth to f<1/ tau .