Validates the "Option C" hardware path: keep the old 8x16 Gerber's series-fed
edge-fed topology, just thicken the patch substrate from 0.102 mm to 0.508 mm
RO4350B. Single-element edge-fed with inset notch matched to 50 Ω microstrip.
Verified at PROFILE=balanced (λ/25 mesh):
W = 7.854 mm (preserved from old Gerber → array compatible)
L = 6.95 mm (tuned for f_res = 10.5 GHz on 0.508 mm sub)
inset_depth = 3.40 mm (~49 % of L)
inset_gap = 0.30 mm (each side of feed line, in the inset notch)
feed_W = 1.16 mm (50 Ω microstrip on 0.508 mm RO4350B)
feed_lead = 15.5 mm (= 1·λ_g at 10.5 GHz → port sees true antenna Z)
Result:
f_res = 10.509 GHz, S11 @ 10.5 = -18.5 dB, VSWR = 1.27
Z @ 10.5 = 61.8 + j3.2 Ω
-10 dB BW = 180 MHz (10.41-10.59 GHz, 1.71 %)
This is identical BW to probe_fed_v3 — confirming BW is set by substrate
thickness alone, not feed method. Edge-fed Option C is therefore the simpler
2-layer hardware path: same series-fed-row architecture as the old Gerber,
single PCB stackup, no probe vias / antipads / back-board splitter complexity.
Next step: extend to a 1x8 series-fed row to verify the daisy-chain topology
still gives in-phase feeding at the new substrate's λ_g.
Single-port-driven, 15-port-terminated FDTD sim built on the same v3 patch
design point (W=7.854, L=6.56, FEED_OFFSET=2.14) at the Gerber pitch
(14.27 mm X / 15.01 mm Y). Reads out S_jd for all elements when port
(DRIVEN_X, DRIVEN_Y) is excited. Configurable array size + driven port via
env vars; default = 4x4, drive inner element (1,1).
Result at PROFILE=balanced, drive (1,1):
Active S11 @ 10.5 GHz : -16.7 dB, Z = 45.7 + j13.5 Ω
Active -10 dB BW : 190 MHz (10.44-10.63 GHz; ≈ single-element 180)
Nearest-neighbour coupling:
-x edge neighbour (0,1): -18.3 dB (strongest — edge element loads less)
-y/+y in-array : -22 dB
+x interior neighbour : -24.7 dB
Diagonal : -32 dB
Far corners : -45 to -53 dB
Outputs: coupling_grid.png heatmap + S_matrix.csv (all S_jd full sweep) +
S11_data.csv (driven-port only).
Known limitation: port box must align with mesh lines; SmoothMeshLines may
sub-cell-shift seed lines, causing some DRIVEN_X/DRIVEN_Y choices to give
"Unused primitive" warning + zero excitation. Default (1,1) is verified;
other choices are best-effort. Documented inline.
Single-element OpenEMS sim for a 2-layer probe-fed patch on 0.508 mm RO4350B.
Verified at PROFILE=balanced (λ/25 mesh): f_res = 10.51 GHz, S11 = -21.8 dB,
VSWR 1.18, -10 dB BW = 180 MHz (10.40-10.58 GHz). Direct 50 Ω match — no port
matching cap needed.
Design point baked into defaults:
PATCH_W = 7.854 mm (preserved from old 8x16 Gerber → array compatible)
PATCH_L = 6.56 mm (tuned for f_res = 10.5 GHz at 0.508 mm sub)
FEED_OFFSET = 2.14 mm (probe via, from -y radiating edge)
Why probe-fed: aperture-coupled v2 (4-layer Stack_Hybrid) capped at ~60 MHz BW
because the 0.11 mm L4 acts as a near-short reflector — beneficial for slot
coupling but creates an L2-L4 cavity that's the BW ceiling. Tested removing L4
(open-back aperture-coupled): coupling collapsed, R stayed >1000 Ω regardless
of patch tuning. Probe-fed has no slot bottleneck; physics BW = 1.7% on h=0.508
matches sim 180 MHz directly.
Hardware change required to deploy: 2-layer stackup (patch on top, ground on
bottom, probe vias with antipads). Old 8x16 Gerber was edge-fed; v3 is probe-
fed → top-layer feed network goes away, ADAR1000 carrier on a separate board
with SMP RF launches. Stackup signoff with antenna designer needed before PCB.
aperture_coupled_v2 retained as the 4-layer fallback (with the 0.043 pF cap)
if 2-layer redesign isn't approved.
10-iteration analytic-tune sweep (no DE optimizer — that was a wrong
direction for this topology) on the Stack_Hybrid 4-layer stackup. Key
findings from the sweep are baked into the script defaults and header.
Best design point @ 10.5 GHz (now the env-var defaults):
patch W=9.55 mm L=7.77 mm
slot L=3.00 mm W=0.50 mm (centered under patch)
stub L=4.16 mm (= λ_g/4 in feed sub at f0)
feed lead=12.34 mm W=0.25 mm
total feed length = 1·λ_g at 10.5 GHz, line transparent at f0
Result: Z ≈ R + j350 Ω at 10.5 GHz, R = 33–51 across reruns (sanity-profile
convergence drift; X is stable). R is within matching range; the +j350
inductive residual is fundamental to the topology (L4 backshort under the
antenna footprint), not a tuning artifact. Two production-grade fixes:
(a) Series cap at port C ≈ 0.043 pF — drops S11 to ≈ -40 dB
(b) Open L4 backshort under antenna — restores standard open-back
aperture-coupled, stub naturally tunes X
Three real bugs fixed in the underlying sim (without these, the baseline
script was measuring artifacts, not the antenna):
1. Z mesh under-density. Default SmoothMeshLines at λ/18 gave the 0.11 mm
feed substrate ~0.1 cells vertically — microstrip Z0 was a pure mesh
artifact. Now built explicitly with ≥5 substrate-interior lines per
dielectric (bypassing SmoothMeshLines collapse for z-axis only). Fine
substrate cells visible via MESH_DEBUG=1.
2. SLOT_Y_OFF_MM env var was read but never applied to the L2 slot box,
silently making the parameter inert. Slot is now correctly offset in y.
3. FEED_LEAD_L was hardcoded at 14.0 mm, making total feed length 18.16 mm
= exactly 1·λ_g at 9.5 GHz (in feed substrate). This created a parasitic
feed-line full-wave standing wave in-band that masked the patch as a
persistent "9.4 GHz resonance" regardless of patch dimensions. Now
parameterized via FEED_LEAD_L_MM with default 12.34 mm so total feed =
1·λ_g at 10.5 GHz instead — line is transparent at the operating freq
and sim measures the actual antenna impedance at the port.
Sweep grids updated to span ±1 step around the iter #6 design point.
Re-simulation infrastructure for the new 4-layer aperture-coupled antenna
stackup (Stack_Hybrid.png, committed 1de2296). Renders the full multilayer
geometry (L1 patch / L2 slot ground / L3 microstrip feed / L4 backplane)
on the actual substrate stack (RO4350B 0.508 mm + RO4450F 1.2 mm + RO4350B
0.11 mm) and runs FDTD via openEMS to characterize S11 vs frequency.
Geometry interpolated from existing 2-layer Gerber:
patch W from Gerber (7.854 mm, set by εr only)
patch L re-tunable for new substrate (env var PATCH_L_MM, default 7.25 mm)
slot/feed/stub fully parameterized via env vars
Run modes:
PROFILE=sanity : single run, λ/18 mesh, ~30 s
PROFILE=balanced : single run, λ/25 mesh, ~60 s
PROFILE=sweep : 5×5 grid over slot_L × stub_L, ~25 min
Env overrides for parametric exploration:
PATCH_W_MM, PATCH_L_MM, SLOT_L_MM, SLOT_W_MM, STUB_L_MM, SLOT_Y_OFF_MM
Setup: openEMS Python bindings built from source against /opt/openEMS for
Python 3.12 in radar_venv; run with
DYLD_LIBRARY_PATH=~/opt/openEMS/lib ~/radar_venv/bin/python
under cwd != openEMS-Project/openEMS/python (avoids CSXCAD shadow import).
Status: simulation infrastructure verified end-to-end; patch resonates at
10.4 GHz with W=9.0 / L=5.5–6.0 mm. Full 50 Ω impedance match not yet
converged — the L4 backplane (non-standard for aperture-coupled) reduces
slot coupling vs textbook formulas; needs proper EM optimizer (scipy
wrapping or CST/HFSS handoff) to fully tune. ~150 MHz baseline BW
predicted from substrate physics; 30/40 MHz chirp target comfortably
under any plausible match outcome.
Resolve all 374 ruff errors across 36 Python files (E501, E702, E722,
E741, F821, F841, invalid-syntax) bringing `ruff check .` to zero
errors repo-wide with line-length=100.
Rewrite CI workflow to use uv for dependency management, whole-repo
`ruff check .`, py_compile syntax gate, and merged python-tests job.
Add pyproject.toml with ruff config and uv dependency groups.
CI structure proposed by hcm444.
Jason