The DAC short/long chirp LUTs are 10..30 MHz upchirps (Hilbert-confirmed).
With TX_LO=10.500 GHz, RX_LO=10.380 GHz (adf4382a_manager.h) and the
120 MHz DDC NCO (ddc_400m.v), high-side mixing places the post-DDC echo
at 10..30 MHz baseband. The matched-filter reference (gen_chirp_mem.py)
was generating 0..20 MHz, implicitly assuming the chirp's low edge mixed
to DC. This caused a 10 MHz spectral offset and ~5 dB matched-filter loss.
Adds F_BASEBAND_LOW=10e6 in both gen_chirp_mem.py and radar_scene.py,
with phase formula 2*pi*F_BASEBAND_LOW*t + pi*rate*t^2 in all chirp
generators. Regenerates the 6 .mem files. Adds analyze_short_chirp_mismatch.py
for the Hilbert-based diagnosis. Fixes the misleading "30MHz to 10MHz"
comment in plfm_chirp_controller.v and adds an end-to-end frequency plan
in the LUT header.
Sideband orientation (high-side at both mixers) is the conventional choice
and consistent with antenna match (10.25..10.75 GHz, 8x16 patch designed
at 10.5 GHz). Loopback capture would settle definitively; if either mixer
is low-side the F_BASEBAND_LOW sign flips and/or chirp direction reverses.
Jason
5ff5671fe2