mirror of
https://github.com/NawfalMotii79/PLFM_RADAR.git
synced 2026-06-08 14:44:56 +00:00
sim(antenna): add probe-fed 2-layer patch model — 180 MHz BW vs aperture-coupled 60 MHz
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.
This commit is contained in:
Jason
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#!/usr/bin/env python3
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# probe_fed_aeris10_v3.py
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#
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# Single-element probe-fed patch antenna sim for AERIS-10 — true 2-layer
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# stackup (L1 patch / 0.508 mm RO4350B / L2 ground plane). Probe via through
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# ground plane feeds the patch; LumpedPort with R=50 Ω across the substrate
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# at the probe location models the coax launch.
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#
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# Why this topology: aperture-coupled v2 (4-layer Stack_Hybrid) capped at
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# ~60 MHz BW because the 0.11 mm L4 backshort acted as a near-short reflector
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# — wider BW is fundamentally coupling-limited there. Probe-fed patch on the
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# same 0.508 mm patch substrate has no slot bottleneck; physics BW from
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# 3.77·(εr-1)/εr²·(W/L)·(h/λ₀) is ~1.6% ≈ 170 MHz at 10.5 GHz.
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#
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# Patch geometry preserved from the existing 8x16 Gerber (Antenna_16_8.top):
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# W = 7.854 mm (D10 first dimension; sets X-pitch 14.27 mm in the array)
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# L = 6.56 mm (tuned at balanced profile to land f_res = 10.51 GHz; old
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# Gerber's 7.356 mm at 0.102 mm sub gave f_res ~10.6 GHz, the
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# thicker substrate adds ~1 mm of fringing-edge ΔL each side)
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#
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# Probe location:
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# y_off = 2.14 mm from -y radiating edge → R_in = 41 Ω, VSWR = 1.18 at 10.5
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# GHz. R_edge fitted from sim ≈ 152 Ω; cos²(π·y_off/L) gives R_in.
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#
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# Verified design point (PROFILE=balanced, λ/25 mesh, 13 s/run):
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# f_res = 10.510 GHz, S11 = -21.79 dB at 10.5 GHz, Zin = 42.7 + j2.0 Ω
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# -10 dB BW = 180 MHz (10.40 – 10.58 GHz, 1.71%)
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# Compare 4-layer Stack_Hybrid + cap: 60 MHz BW, -19 dB. 3× wider, no cap.
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#
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# Stackup:
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# L1 Cu 0.035 mm ← patch
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# -- RO4350B 0.508 mm εr=3.48 (patch substrate)
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# L2 Cu 0.035 mm ← ground plane (with antipad clearance)
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# air below; coax launches up through
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# to the probe via from L2 ground.
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#
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# Run:
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# cd /tmp && DYLD_LIBRARY_PATH=/Users/ganeshpanth/opt/openEMS/lib \
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# PROFILE=balanced PATCH_L_MM=7.54 FEED_OFFSET_MM=2.5 \
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# /Users/ganeshpanth/radar_venv/bin/python \
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# /Users/ganeshpanth/PLFM_RADAR/5_Simulations/Antenna/probe_fed_aeris10_v3.py
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#
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# Profiles:
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# sanity — λ/18 mesh, fast, borderline convergence
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# balanced — λ/25 mesh, slower, recommended for design verification
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#
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# Env overrides (all optional):
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# PATCH_W_MM PATCH_L_MM FEED_OFFSET_MM (mm from -y radiating edge)
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# FEED_X_MM (default 0; offset along W-axis, normally 0 for centred feed)
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import os
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import sys
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import time
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import csv
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import numpy as np
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import matplotlib
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matplotlib.use("Agg")
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import matplotlib.pyplot as plt
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from openEMS import openEMS
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from openEMS.physical_constants import C0
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from CSXCAD import ContinuousStructure
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from CSXCAD.SmoothMeshLines import SmoothMeshLines
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# ============================================================================
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# PROFILES
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# ============================================================================
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PROFILE = os.environ.get("PROFILE", "sanity")
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profiles = {
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"sanity": {"mesh_lambda_div": 18, "n_timesteps": 50000, "end_dB": -30},
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"balanced": {"mesh_lambda_div": 25, "n_timesteps": 80000, "end_dB": -40},
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}
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cfg = profiles[PROFILE]
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# ============================================================================
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# BAND
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# ============================================================================
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F0 = 10.5e9
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F_SPAN = 4.0e9
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F_START = F0 - F_SPAN/2
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F_STOP = F0 + F_SPAN/2
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# ============================================================================
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# STACKUP (mm) — true 2-layer probe-fed
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# ============================================================================
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T_CU = 0.035
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H_PATCH_SUB = 0.508 # RO4350B between L1 patch and L2 ground
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EPS_RO4350B = 3.48
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TAN_RO4350B = 0.0037
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# Z layers (L2 ground at z=0, patch on top)
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Z_GND = 0.0
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Z_PATCH = Z_GND + T_CU + H_PATCH_SUB
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Z_TOP = Z_PATCH + T_CU
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# ============================================================================
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# GEOMETRY (mm) — defaults preserve old Gerber's W; L recomputed for 0.508 mm
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# ============================================================================
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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", "6.56"))
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# Probe: feed offset along the L-axis (y), measured from -y radiating edge
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# inward. R_in(y_off) = R_edge·cos²(π·y_off/L). y_off=2.14 mm with iter#3 L
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# (R_edge≈152 Ω fitted) lands R_in=41 Ω, VSWR=1.18 at 10.5 GHz.
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FEED_OFFSET_MM = float(os.environ.get("FEED_OFFSET_MM", "2.14"))
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FEED_X_MM = float(os.environ.get("FEED_X_MM", "0.0"))
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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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GND_Y_MARGIN = 14.3
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GND_X_HALF = PATCH_W/2 + GND_X_MARGIN
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GND_Y_HALF = PATCH_L/2 + GND_Y_MARGIN
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# Air box (λ/2 above patch, λ/2 below ground)
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AIR_ABOVE = 14.3
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AIR_BELOW = 14.3
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AIR_X_HALF = GND_X_HALF + 8.0
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AIR_Y_HALF = GND_Y_HALF + 8.0
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OUT_DIR = "/tmp/aeris10_probefed_v3"
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os.makedirs(OUT_DIR, exist_ok=True)
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# ============================================================================
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# Build + run a single FDTD case
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# ============================================================================
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def run_case(patch_w, patch_l, feed_offset, feed_x, sim_path, profile_cfg, label=""):
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fdtd = openEMS(NrTS=profile_cfg["n_timesteps"],
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EndCriteria=10**(profile_cfg["end_dB"]/20.0))
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fdtd.SetGaussExcite(F0, F_SPAN/2.0)
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fdtd.SetBoundaryCond(["MUR"]*6)
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CSX = ContinuousStructure()
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fdtd.SetCSX(CSX)
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mesh = CSX.GetGrid()
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mesh.SetDeltaUnit(1e-3)
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# ---- materials ----
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eps0 = 8.854e-12
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patch_sub = CSX.AddMaterial("RO4350B",
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epsilon=EPS_RO4350B,
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kappa=2*np.pi*F0*EPS_RO4350B*eps0*TAN_RO4350B)
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copper = CSX.AddMetal("Copper")
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# ---- substrate ----
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patch_sub.AddBox([-GND_X_HALF, -GND_Y_HALF, Z_GND + T_CU],
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[+GND_X_HALF, +GND_Y_HALF, Z_PATCH], priority=1)
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# ---- L1: patch (centred on origin, L along y, W along x) ----
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copper.AddBox([-patch_w/2, -patch_l/2, Z_PATCH],
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[+patch_w/2, +patch_l/2, Z_PATCH + T_CU], priority=10)
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# ---- L2: full ground plane ----
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# Single-element sim — antipad clearance around the probe is implicit
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# in the LumpedPort box (FDTD treats the port column as the metal probe
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# and the surrounding cells as substrate). For a multi-element array
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# with real coax launches a physical clearance hole would be added.
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copper.AddBox([-GND_X_HALF, -GND_Y_HALF, Z_GND],
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[+GND_X_HALF, +GND_Y_HALF, Z_GND + T_CU], priority=10)
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# ---- mesh ----
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lambda_min_mm = (C0 / F_STOP) * 1000.0
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res = lambda_min_mm / profile_cfg["mesh_lambda_div"]
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# Probe location in patch frame
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feed_y = -patch_l/2 + feed_offset # offset from -y radiating edge
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feed_x_pos = feed_x
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xlines = [-AIR_X_HALF, -GND_X_HALF, -patch_w/2, feed_x_pos, +patch_w/2,
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+GND_X_HALF, +AIR_X_HALF]
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ylines = [-AIR_Y_HALF, -GND_Y_HALF, -patch_l/2, feed_y, +patch_l/2,
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+GND_Y_HALF, +AIR_Y_HALF]
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# Z mesh: substrate gets ≥6 interior cells for accurate field capture
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air_below = list(np.arange(Z_GND - T_CU - AIR_BELOW, Z_GND - T_CU, res))
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air_above = list(np.arange(Z_TOP + res, Z_TOP + AIR_ABOVE + res, res))
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sub_interior = list(np.linspace(Z_GND + T_CU, Z_PATCH, 7)[1:-1])
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zlines = sorted(set(air_below + [
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Z_GND - T_CU, Z_GND, Z_GND + T_CU,
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Z_PATCH, Z_PATCH + T_CU,
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] + sub_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 = 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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z_diff = np.diff(zlines)
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print(f"[mesh] x={len(xlines)} y={len(ylines)} z={len(zlines)} cells={n_cells:,}")
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print(f"[mesh] z min/max/avg cell: {z_diff.min()*1e3:.1f}/{z_diff.max()*1e3:.1f}/{z_diff.mean()*1e3:.1f} um")
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# ---- LumpedPort: vertical 50 Ω port across substrate at (feed_x, feed_y) ----
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# The lumped port replaces the coax+source: the 50 Ω resistor sits in the
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# box, the metal column from L2 to L1 is implicit. Excitation is z-direction
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# E-field across the substrate.
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port_start = [feed_x_pos, feed_y, Z_GND + T_CU]
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port_stop = [feed_x_pos, feed_y, Z_PATCH]
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port = fdtd.AddLumpedPort(1, 50, port_start, port_stop, 'z',
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excite=1.0, priority=5)
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# ---- run ----
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print(f"[case {label}] patch={patch_w:.2f}x{patch_l:.2f}mm "
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f"feed=({feed_x_pos:.2f},{feed_y:.2f})mm cells={n_cells:,}")
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t0 = time.time()
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fdtd.Run(sim_path, verbose=0, cleanup=True)
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dt = time.time() - t0
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# ---- post-process ----
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freq = np.linspace(F_START, F_STOP, 401)
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port.CalcPort(sim_path, freq)
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s11 = port.uf_ref / port.uf_inc
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s11_dB = 20.0 * np.log10(np.abs(s11) + 1e-30)
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zin = port.uf_tot / port.if_tot
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vswr = (1 + np.abs(s11)) / (1 - np.abs(s11) + 1e-30)
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return freq, s11_dB, zin, vswr, dt
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def find_resonance(freq, s11_dB, zin=None):
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"""Resonance: where R peaks AND Im(Z)=0 nearby. Falls back to min(S11)."""
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f_res, s11_min = None, None
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if zin is not None:
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# Find peak R in the band
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mask = (freq >= 9.0e9) & (freq <= 11.5e9)
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idx_band = np.where(mask)[0]
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if len(idx_band) > 1:
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r_band = np.real(zin[idx_band])
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i_pk = idx_band[int(np.argmax(r_band))]
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# Use the X=0 crossing closest to the R peak
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x = np.imag(zin)
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sign = np.sign(x)
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crossings = np.where(np.diff(sign) != 0)[0]
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crossings_in_band = [c for c in crossings if mask[c]]
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if crossings_in_band:
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k = min(crossings_in_band, key=lambda c: abs(c - i_pk))
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t = -x[k] / (x[k+1] - x[k]) if x[k+1] != x[k] else 0
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f_res = freq[k] + t * (freq[k+1] - freq[k])
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s11_min = s11_dB[k] + t * (s11_dB[k+1] - s11_dB[k])
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if f_res is None:
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imin = int(np.argmin(s11_dB))
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f_res = freq[imin]
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s11_min = float(s11_dB[imin])
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# walk outward to find -10 dB crossings around f_res
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below = s11_dB <= -10.0
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if not below.any():
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return f_res, s11_min, 0.0, 0.0, 0.0
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i_f = int(np.argmin(np.abs(freq - f_res)))
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if not below[i_f]:
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return f_res, s11_min, 0.0, 0.0, 0.0
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lo = i_f
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while lo > 0 and below[lo-1]:
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lo -= 1
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hi = i_f
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while hi < len(below)-1 and below[hi+1]:
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hi += 1
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f_lo, f_hi = freq[lo], freq[hi]
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bw = f_hi - f_lo
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bw_pct = bw / f_res * 100.0
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return f_res, s11_min, f_lo, f_hi, bw_pct
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# ============================================================================
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# MAIN
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# ============================================================================
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sim_path = os.path.join(OUT_DIR, "single")
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freq, s11_dB, zin, vswr, dt = run_case(
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PATCH_W, PATCH_L, FEED_OFFSET_MM, FEED_X_MM, sim_path, cfg)
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f_res, s11_min, f_lo, f_hi, bw_pct = find_resonance(freq, s11_dB, zin)
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i_res = int(np.argmin(np.abs(freq - f_res)))
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i_op = int(np.argmin(np.abs(freq - 10.5e9)))
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print()
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print("=" * 70)
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print(f" Resonance (R peak + Im=0): {f_res/1e9:.3f} GHz (target 10.5 GHz)")
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print(f" S11 at resonance : {s11_min:.2f} dB")
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print(f" Zin at resonance : {zin[i_res].real:.1f} + j{zin[i_res].imag:.1f} Ω")
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print(f" ── at 10.500 GHz exactly:")
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print(f" S11 @ 10.5GHz : {s11_dB[i_op]:.2f} dB")
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print(f" Zin @ 10.5GHz : {zin[i_op].real:.1f} + j{zin[i_op].imag:.1f} Ω")
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print(f" VSWR @ 10.5GHz : {vswr[i_op]:.2f}")
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print(f" -10 dB bandwidth : {(f_hi-f_lo)/1e6:.0f} MHz "
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f"({f_lo/1e9:.3f} – {f_hi/1e9:.3f} GHz, {bw_pct:.2f}%)")
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print(f" Sim time : {dt:.1f} s")
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print("=" * 70)
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fig, ax = plt.subplots(figsize=(8.5, 4.5))
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ax.plot(freq/1e9, s11_dB, "b-", lw=1.6, label="S11")
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ax.axhline(-10, color="r", ls="--", lw=0.8, label="-10 dB")
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ax.axvline(f_res/1e9, color="g", ls=":", lw=0.8,
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label=f"resonance {f_res/1e9:.3f} GHz")
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if (f_hi-f_lo) > 0:
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ax.axvspan(f_lo/1e9, f_hi/1e9, color="g", alpha=0.10,
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label=f"BW {(f_hi-f_lo)/1e6:.0f} MHz ({bw_pct:.2f}%)")
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ax.set_xlabel("Frequency (GHz)")
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ax.set_ylabel("S11 (dB)")
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ax.set_title(f"AERIS-10 Probe-Fed Patch v3 — 2-layer 0.508 mm RO4350B "
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f"(W={PATCH_W} L={PATCH_L} y_off={FEED_OFFSET_MM}mm)")
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ax.set_xlim(F_START/1e9, F_STOP/1e9)
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ax.set_ylim(-40, 0)
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ax.grid(True, alpha=0.3)
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ax.legend(loc="lower right")
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fig.tight_layout()
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fig.savefig(os.path.join(OUT_DIR, "S11.png"), dpi=140)
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plt.close(fig)
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with open(os.path.join(OUT_DIR, "S11_data.csv"), "w", newline="") as f:
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w = csv.writer(f)
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w.writerow(["freq_Hz", "S11_dB", "Zin_real", "Zin_imag", "VSWR"])
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for k in range(len(freq)):
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w.writerow([freq[k], s11_dB[k], zin[k].real, zin[k].imag, vswr[k]])
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print(f"[out] {OUT_DIR}/S11.png")
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print(f"[out] {OUT_DIR}/S11_data.csv")
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