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I reference the below diagram, from Stimson's Airborne Radar, 2nd Ed. In the text he discusses how the frequency increases linearly throughout the duration of tau. The sketch of the frequency x time matches this description, but looking at the diagram of the transmitter sending out the pulse, it appears that the frequency is decreasing which would seem to contradict both the graph and the narrative. If you turn the transmitter picture upside down, that is the waveform I would expect to see given the graph and the text.

I'm obviously missing something elementary here but I don't know what it is.

He does also mention about widening pulses in the previous paragraph, but that's not the same as frequency.

Further in the text, he shows the same graph, flipped on its side, so it is time x frequency, which shows the line going down, i.e. frequency decreases as time goes up which does match the transmitter diagram below. Is this a case of looking at the same phenomena in two different ways, in which case only one of those ways makes sense to me.

I'm neither a radar engineer (obviously) nor studying to be one, but just an interested 3rd party, and this seems like something elementary I should be able to grasp.

Stimson Chirp

fpd011
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  • A simple error, easily corrected; if you're an interested enough 3rd party, you might contact the author with the correction. – Tim Williams Jun 23 '23 at 15:11
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    It may be a conceptual error on the viewer's part. The axis you're interpreting as "time" as an oscilloscope displays time - should be interpreted as wavelength in space...the rightmost point represents the wave *first transmitted*. In that case, the first wave is the right-most (and has the longest wavelength) – glen_geek Jun 23 '23 at 15:22
  • glen_geek, thank you that was the perspective I wasn't getting. Now it is crystal clear, – fpd011 Jun 24 '23 at 17:16
  • @glen_geek This is correct, it's on reflection that you get a properly "flipped" and time delayed version of the pulse that you can then match filter. – Envidia Aug 20 '23 at 00:00

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