[Lonesome in Massachussets]

Your understanding of LFM is spot on. Originally LFM used a dispersive delay line, with delay proportional to frequency to modulate the signal. Virtually all modern radar systems use digital waveform generators, and multiplier chains.

https://en.wikipedia.org/wiki/Chirp

[TXnMA]

Now that you mention the time-domain delay line aspect, I do seem to recall also reading something about "TWTs" (Traveling Wave Tubes) being used in Radar applications, as well...

Wow! that almost goes back so far as to touch on my present avocation -- archaeology! '-)

[TXnMA]

FReepMail for you...