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https://github.com/NawfalMotii79/PLFM_RADAR.git
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sim(antenna): tune aperture-coupled v2 to design point — R matched, X residual documented
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.
This commit is contained in:
Jason
@@ -1,16 +1,31 @@
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#!/usr/bin/env python3
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# aperture_coupled_aeris10_v2.py
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#
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# Single-element aperture-coupled patch antenna characterization for the
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# UPDATED Stack_Hybrid stackup (committed 1de2296, 2026-04-29).
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# Single-element aperture-coupled patch antenna sim for the Stack_Hybrid
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# 4-layer stackup (committed 1de2296, 2026-04-29). Default parameters are the
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# best design point from a 10-iteration analytic-tune sweep run 2026-05-02.
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#
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# Patch geometry is INTERPOLATED from the as-built 2-layer Gerber
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# (Antenna_16_8.top, March 2025) and rescaled for the new 0.508 mm RO4350B
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# substrate via the εr_eff + ΔL closed-form shift:
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# L_new ≈ L_old × ((λ_eff_new/2 − 2·ΔL_new) / (λ_eff_old/2 − 2·ΔL_old))
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# L_old (Gerber) = 7.356 mm on 0.102 mm RO4350B → εr_eff ≈ 3.39
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# L_new (predict) = 7.250 mm on 0.508 mm RO4350B → εr_eff ≈ 3.17
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# W stays 7.854 mm (only depends on εr, not h)
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# DESIGN POINT @ 10.5 GHz (defaults below):
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# patch : W=9.55 mm L=7.77 mm
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# slot : L=3.00 mm W=0.50 mm (centered under patch)
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# stub : L=4.16 mm (= λ_g/4 in feed sub at f0 — short across slot at 10.5)
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# feed : lead=12.34 mm W=0.25 mm
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# total feed length = lead + stub = 16.50 mm = 1·λ_g at 10.5 GHz
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# ⇒ feed line is TRANSPARENT at f0 (port sees true antenna Z)
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#
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# Result @ 10.5 GHz: Z ≈ R + j350 Ω where R = 33–51 Ω across reruns
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# (R varies ~30% with sim convergence — sanity profile is borderline; the
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# physics-meaningful result is "R within matching ballpark, X stable at
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# +350"). The +j350 inductive residual cannot be canceled in this topology
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# by simple stub tuning — it stems from the L4 backshort continuous ground
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# under the antenna footprint. Two production-grade fixes:
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# (a) Series matching cap at the port: C ≈ 1/(2π·10.5GHz·350) ≈ 0.043 pF
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# standard 0402 ATC cap → drops |Γ| from 0.97 to ~0.01 (S11 ≈ -40 dB).
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# (b) Open the L4 backshort under the antenna footprint (stackup edit) →
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# restores standard open-back aperture-coupled, stub naturally tunes X.
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# Either is the antenna designer's call. This script's role is to provide
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# the verified starting point in (W,L,slot,stub,feed_lead) plus the X that
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# needs to be matched out.
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#
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# Stackup (Stack_Hybrid.png, ANTENNA column):
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# L1 Cu 0.035 mm ← patch
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@@ -19,17 +34,30 @@
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# -- RO4450F 1.2 mm εr=3.52 (bonding ply)
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# L3 Cu 0.035 mm ← microstrip feed line + λ_g/4 stub
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# -- RO4350B 0.11 mm εr=3.48 (feed substrate)
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# L4 Cu 0.035 mm ← bottom ground plane
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# L4 Cu 0.035 mm ← bottom ground plane (backshort)
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#
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# Notable bug-fixes baked into this version (vs commit 42056b8 baseline):
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# - Z mesh: explicit fine substrate-interior lines (≥5 cells per substrate)
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# bypassing SmoothMeshLines collapse — feed sub at 0.11 mm now has proper
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# microstrip Z0. Without this, the patch resonance is hidden by mesh-Z0
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# artifacts and the sim measures essentially line-only behavior.
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# - slot_y_off env var: was read but never applied to the L2 slot box. Now
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# the slot is correctly offset in y when SLOT_Y_OFF_MM != 0.
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# - FEED_LEAD_L: now env-tunable (was hardcoded 14.0 mm). The default 12.34
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# mm makes total feed = 1·λ_g at 10.5 GHz, killing the spurious feed-line
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# full-wave resonance that masked the true patch resonance in the
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# baseline script (showed up as a persistent 9.4-9.5 GHz "resonance").
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#
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# Run modes:
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# PROFILE=sanity : 1 run with current SLOT_L / STUB_L env vars
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# PROFILE=balanced : 1 run, finer mesh
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# PROFILE=sanity : 1 run, mesh λ_min/18, ~30s/run
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# PROFILE=balanced : 1 run, finer mesh λ_min/25, slower
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# PROFILE=sweep : 5×5 grid over slot_L × stub_L, picks best, reports
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#
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# Env overrides:
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# SLOT_L_MM (default 5.0) Slot length in y
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# STUB_L_MM (default 4.32) Stub past slot center
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# PATCH_L_MM (default 7.25) Patch length (re-tunable)
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# Env overrides (all optional, defaults at iter #6 design point):
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# PATCH_W_MM PATCH_L_MM
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# SLOT_L_MM SLOT_W_MM SLOT_Y_OFF_MM
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# STUB_L_MM FEED_LEAD_L_MM
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# MESH_DEBUG=1 prints mesh density before each run
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#
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# Outputs in /tmp/aeris10_aperture_v2/:
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# single run : S11.png, S11_data.csv
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@@ -88,24 +116,30 @@ Z_L1 = Z_L2 + T_CU + H_PATCH_SUB
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Z_TOP = Z_L1 + T_CU
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# ============================================================================
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# GEOMETRY (mm)
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# GEOMETRY (mm) — defaults are iter #6 best design point (see header)
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# ============================================================================
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# Patch: from Gerber.top D10 = 0.30921 × 0.28961 in = 7.854 × 7.356 mm,
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# L rescaled −1.4% for the substrate-thickness shift (0.102 → 0.508 mm RO4350B).
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PATCH_W = float(os.environ.get("PATCH_W_MM", "7.854"))
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PATCH_L = float(os.environ.get("PATCH_L_MM", "7.25"))
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# Patch: empirically tuned for the Stack_Hybrid 4-layer stack (with L4
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# backshort). Note that with L4 present, εr_eff at the patch is ~4.0 in sim
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# (not the 3.21 a single-substrate Balanis formula predicts), so L is larger
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# than open-back textbook value — the L4 dielectric loading lowers f_res.
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PATCH_W = float(os.environ.get("PATCH_W_MM", "9.55"))
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PATCH_L = float(os.environ.get("PATCH_L_MM", "7.77"))
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# Slot (under patch in L2). Length perpendicular to feed line direction.
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SLOT_L = float(os.environ.get("SLOT_L_MM", "5.0"))
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SLOT_W = float(os.environ.get("SLOT_W_MM", "0.4"))
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# Slot (under patch in L2), length perpendicular to feed direction.
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# Slot resonance λ_g_slot/2 ≈ 7.65 mm in the L2-L4 cavity; SLOT_L=3.0 keeps
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# the slot well sub-resonant (slot is a coupling aperture, not a radiator).
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SLOT_L = float(os.environ.get("SLOT_L_MM", "3.0"))
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SLOT_W = float(os.environ.get("SLOT_W_MM", "0.5"))
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# Microstrip feed on L3, dominant ground = L4 (0.11 mm RO4350B). 50 Ω target.
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# Hammerstad: W ≈ 0.25 mm for 50 Ω on 0.11 mm RO4350B.
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FEED_W = 0.25
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FEED_STUB_L = float(os.environ.get("STUB_L_MM", "4.32")) # λ_g/4 starting
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# Need 4+ mm of pure-microstrip lead before L2 ground catches the line, so
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# MSLPort feed/measurement planes both sit in microstrip-only region (Z0=50).
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FEED_LEAD_L = 14.0 # length from board edge (port) to slot center
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FEED_STUB_L = float(os.environ.get("STUB_L_MM", "4.16")) # λ_g/4 @ 10.5 GHz
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# Total feed length = FEED_LEAD_L + STUB_L should be n·λ_g at f0 for the line
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# to be transparent at the operating freq (sim sees the antenna's true impedance
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# at port without TL transformation). λ_g_feed @ 10.5 GHz on 0.11 mm RO4350B
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# microstrip ≈ 16.5 mm → FEED_LEAD_L = 16.5 - STUB_L for n=1.
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FEED_LEAD_L = float(os.environ.get("FEED_LEAD_L_MM", "12.34")) # n=1 λ_g default
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# Substrate / ground extents (~λ/2 margin around patch)
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GND_X_MARGIN = 14.3
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@@ -176,18 +210,20 @@ def run_case(slot_l, stub_l, patch_l, sim_path, profile_cfg, label="", slot_w=No
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# full-extent L2 plane would form between L2↔L4 around the lumped port.
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# L2 patch covers ~2·PATCH_L in y, full board width in x.
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L2_HALF_Y = PATCH_L # ground extends ±PATCH_L in y around slot at y=0
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# Above slot (y > +slot_w/2)
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copper.AddBox([-GND_X_HALF, +slot_w/2, Z_L2],
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sy0 = slot_y_off - slot_w/2
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sy1 = slot_y_off + slot_w/2
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# Above slot (y > sy1)
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copper.AddBox([-GND_X_HALF, sy1, Z_L2],
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[+GND_X_HALF, +L2_HALF_Y, Z_L2 + T_CU], priority=10)
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# Below slot (y < -slot_w/2)
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# Below slot (y < sy0)
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copper.AddBox([-GND_X_HALF, -L2_HALF_Y, Z_L2],
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[+GND_X_HALF, -slot_w/2, Z_L2 + T_CU], priority=10)
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# Left of slot (x < -slot_l/2, |y| <= slot_w/2)
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copper.AddBox([-GND_X_HALF, -slot_w/2, Z_L2],
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[-slot_l/2, +slot_w/2, Z_L2 + T_CU], priority=10)
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# Right of slot (x > +slot_l/2, |y| <= slot_w/2)
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copper.AddBox([+slot_l/2, -slot_w/2, Z_L2],
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[+GND_X_HALF, +slot_w/2, Z_L2 + T_CU], priority=10)
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[+GND_X_HALF, sy0, Z_L2 + T_CU], priority=10)
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# Left of slot (x < -slot_l/2, sy0 <= y <= sy1)
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copper.AddBox([-GND_X_HALF, sy0, Z_L2],
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[-slot_l/2, sy1, Z_L2 + T_CU], priority=10)
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# Right of slot (x > +slot_l/2, sy0 <= y <= sy1)
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copper.AddBox([+slot_l/2, sy0, Z_L2],
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[+GND_X_HALF, sy1, Z_L2 + T_CU], priority=10)
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# ---- L3: microstrip feed line — runs in y direction, ⟂ to slot ----
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feed_y_start = -FEED_LEAD_L # board edge (port location)
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@@ -214,19 +250,36 @@ def run_case(slot_l, stub_l, patch_l, sim_path, profile_cfg, label="", slot_w=No
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ylines = [-AIR_Y_HALF, -GND_Y_HALF, -PATCH_L/2, -slot_w/2,
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0, +slot_w/2, +PATCH_L/2, feed_y_end, +GND_Y_HALF, +AIR_Y_HALF,
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-PATCH_L] + port_y_lines
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zlines = [Z_L4 - AIR_BELOW,
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Z_L4, Z_L4 + T_CU,
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Z_L3, Z_L3 + T_CU,
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Z_L2, Z_L2 + T_CU,
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Z_L1, Z_L1 + T_CU,
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Z_TOP + AIR_ABOVE]
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# Z mesh: built MANUALLY (not via SmoothMeshLines) because the substrates
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# need ≥5 cells for accurate microstrip Z0 (esp. feed sub at 0.11 mm).
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# SmoothMeshLines collapses lines closer than ~res/3, which kills the fine
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# substrate refinement we need. Build it explicitly:
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# - Air below/above: res-spaced
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# - Each metal layer: one line at top + one at bottom of copper
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# - Each dielectric: 6 interior cells (7-pt linspace, drop endpoints)
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air_below = list(np.arange(Z_L4 - AIR_BELOW, Z_L4, res))
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air_above = list(np.arange(Z_TOP + res, Z_TOP + AIR_ABOVE + res, res))
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feed_interior = list(np.linspace(Z_L4 + T_CU, Z_L3, 7)[1:-1]) # 0.018 mm pitch
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bond_interior = list(np.linspace(Z_L3 + T_CU, Z_L2, 7)[1:-1]) # 0.20 mm pitch
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patch_interior = list(np.linspace(Z_L2 + T_CU, Z_L1, 7)[1:-1]) # 0.085 mm pitch
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zlines = sorted(set(air_below + [
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Z_L4, Z_L4 + T_CU,
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Z_L3, Z_L3 + T_CU,
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Z_L2, Z_L2 + T_CU,
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Z_L1, Z_L1 + T_CU,
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] + feed_interior + bond_interior + patch_interior + air_above))
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xlines = SmoothMeshLines(np.array(xlines), res)
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ylines = SmoothMeshLines(np.array(ylines), res)
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zlines = SmoothMeshLines(np.array(zlines), res)
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zlines = np.array(zlines)
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mesh.AddLine("x", xlines)
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mesh.AddLine("y", ylines)
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mesh.AddLine("z", zlines)
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n_cells = len(xlines) * len(ylines) * len(zlines)
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if os.environ.get("MESH_DEBUG"):
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print(f"[mesh] xlines={len(xlines)} ylines={len(ylines)} zlines={len(zlines)}")
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z_diff = np.diff(zlines)
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print(f"[mesh] z min/max/avg cell: {z_diff.min()*1e3:.3f}/{z_diff.max()*1e3:.3f}/{z_diff.mean()*1e3:.3f} um")
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print(f"[mesh] zlines (mm): {[f'{z:.3f}' for z in zlines]}")
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# ---- Microstrip-line port (after mesh is in place; checks line count) ----
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# The L2 inner ground was pulled back to y = -PATCH_L (= -7.25 mm), so
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@@ -314,10 +367,10 @@ def find_resonance(freq, s11_dB, zin=None):
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# MAIN
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# ============================================================================
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if PROFILE == "sweep":
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# 5x5 grid
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slot_grid = [4.0, 5.0, 6.0, 7.0, 8.0]
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stub_grid = [3.0, 3.5, 4.0, 4.5, 5.0]
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patch_l = float(os.environ.get("PATCH_L_MM", "7.25"))
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# 5x5 grid centered on the iter #6 design point (slot=3.0, stub=4.16)
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slot_grid = [2.0, 2.5, 3.0, 3.5, 4.0]
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stub_grid = [3.5, 3.85, 4.16, 4.5, 4.85]
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patch_l = float(os.environ.get("PATCH_L_MM", "7.77"))
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rows = []
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print(f"[sweep] {len(slot_grid)}×{len(stub_grid)} = {len(slot_grid)*len(stub_grid)} cases")
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for i, sl in enumerate(slot_grid):
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