Sweep CONN_LEN at PROFILE=balanced to land the operating-mode dip on the
chirp-band center instead of 60 MHz above it. Sensitivity is df/dCONN ≈
-0.20 GHz/mm (longer line → lower op freq).
CONN=8.00 → dip 10.560 GHz, S11@10.520 = -12.6 dB (above TX)
CONN=8.15 → dip 10.520 GHz, S11@10.520 = -18.8 dB (TX-centered)
CONN=8.20 → dip 10.510 GHz, S11@10.510 = -18.4 dB (TX low edge)
CONN=8.25 → dip 10.500 GHz, S11@10.500 = -18.4 dB (LO-centered)
CONN_LEN=8.15 wins because the radar TX 10.510-10.530 GHz sees -17 to -19 dB
symmetrically across the band, with -15 dB margin at the LO frequency. -10 dB
BW spans 10.470-10.580 GHz (110 MHz). Pitch 15.10 mm vs old Gerber 15.01 mm.
Daisy-chain validation for 2-layer 0.508 mm RO4350B stackup. Row of 8 patches
edge-connected via 8.0 mm microstrip segments (pitch 14.95 mm matches old
Gerber). With direct edge feed on patch 0 (no inset; inset would drop the row
input Z to ~6 Ω), the natural input impedance at the operating mode is ~80 Ω,
close enough to 50 Ω for direct match without a quarter-wave transformer.
Topology behaves as a finite periodic resonator with N=8 modes (~0.5 GHz
spacing) and a stopband centered on the patch self-resonance. Operating point
is the top-below-stopband mode at 10.56 GHz: S11 = -22.5 dB, Zin = 79.9 - j3 Ω.
-10 dB BW spans 10.51-10.61 GHz (100 MHz), covering the 10.510-10.530 GHz
chirp band with S11 = -10.4 to -14.6 dB across that interval.
Mesh sensitivity: sanity profile (lambda/18) gave a misleading deepest-dip at
11.4 GHz; balanced (lambda/25) is required to land the operating-mode
characterization correctly. PROFILE=balanced is now the documented run mode.
