Fig. 5: Experimental results on the capability of the time-mapped spectrogram analysis method to capture nanosecond-duration frequency transients along the incoming broadband microwave signal.
a The temporal trace of a microwave signal under test (SUT) consisting of a fast frequency hopping sequence, designed to test the time-mapped spectrogram (TM-SP) method performance. The sequence is composed by consecutive 5-ns-long tones with linearly increasing hopping frequencies, i.e., 0.4, 0.8, 1.2, 1.6, and 2 GHz. b The 2D spectrogram distribution that is directly recovered from the measured temporal trace at the output of the TM-SP setup, involving photonic sampling and dispersion with the parameters given in the text. The hopping frequency speed that can be captured with this setup is only limited by the time resolution of the calculated TM-SP, whose FWHM width is 5.9 ns in these experiments. c A zoom of the output temporal waveform over the 5-ns temporal window corresponding to the presence of the 0.4-GHz tone, confirming that the resultant time-mapped spectral shape is recovered repeatedly at every TR (=205.6 ps) along this analysis window. d The temporal trace of a microwave SUT composed by (i) a linearly increasing frequency chirp waveform, from 500 MHz to 2 GHz, and (ii) isolated interfering frequency transients with the same amplitude as that of the frequency chirp signal, each having a duration of 5 ns. The interfering frequency transients are centered at 1.6, 2, 0.8, and 1.2 GHz, occurring at the relative times of 25, 50, 150, and 180 ns, respectively. e The 2D spectrogram distribution that is directly recovered from the measured temporal trace at the output of the TM-SP setup. The TM-SP method is clearly able to capture and analyze the 5 ns duration isolated interfering frequency transients, consistently with the predicted temporal resolution of analysis in these experiments. f A zoom of the output temporal trace over the 5-ns temporal window corresponding to the 1.6-GHz interference event. To facilitate interpretation of the obtained results, in each 2D spectrogram representation, only the positive axis of frequencies is represented.
