PLFM_RADAR/5_Simulations/Antenna/Quartz_Waveguide.py

# openems_quartz_slotted_wg_10p5GHz.py
# Full script: geometry, mesh (no GetLine calls), S-params/impedance sweep, 3D pattern & gain.
# Requires: openEMS (Python bindings), CSXCAD (Python), matplotlib, numpy.

import os
import tempfile
import numpy as np
import matplotlib.pyplot as plt

from CSXCAD  import ContinuousStructure, AppCSXCAD_BIN
from openEMS import openEMS
from openEMS.physical_constants import C0

# -------------------------
# User controls
# -------------------------
view_geom_in_AppCSXCAD = True   # True => launch AppCSXCAD to view 3D geometry
simulate = True                  # False => skip FDTD run
threads = 0                      # 0 => auto/max

# Far-field angular sampling
n_theta, n_phi = 91, 181        # theta 0..180, phi 0..360

# -------------------------
# Band & element sizing
# -------------------------
f0     = 10.5e9
f_span = 2.0e9
f_start, f_stop = f0 - f_span/2, f0 + f_span/2

# Quartz-filled rectangular waveguide (full dielectric block)
er_quartz = 3.8
# Array-driven constraints (λ0/2 column pitch, 1 mm septum) ⇒ a ~ 13.28 mm
a = 13.28     # mm (broad wall, internal)
b = 6.50      # mm (narrow wall, internal; comfortable to machine)
L = 281.0     # mm (≈32-slot column incl. λg/4 margins at 10.5 GHz)

# Slot starters (tune in EM for taper)
slot_w = 0.60    # mm (across x)
lambda0_mm = (C0/f0) * 1e3
fc10 = (C0/(2.0*np.sqrt(er_quartz))) * (1.0/(a*1e-3))  # Hz
lambda_d = (C0/f0) / np.sqrt(er_quartz)                # m
lambda_g = lambda_d / np.sqrt(1.0 - (fc10/f0)**2)      # m
lambda_g_mm = lambda_g * 1e3
slot_s  = 0.5*lambda_g_mm
slot_L  = 0.47*lambda_g_mm
margin  = 0.25*lambda_g_mm
Nslots  = 32
delta0  = 0.90   # mm offset from centerline (± alternated)

# Metal & air padding for the radiation domain
t_metal = 0.8       # mm wall thickness
air_x   = 10.0      # mm on each side
air_y   = 40.0      # mm above slots
air_z   = 15.0      # mm front/back

# Mesh resolution target (mm)
mesh_res = min(0.5, lambda0_mm/30.0)

# -------------------------
# Build FDTD & CSX
# -------------------------
unit = 1e-3                                    # mm
Sim_Path = os.path.join(tempfile.gettempdir(), 'openems_quartz_slotted_wg')

FDTD = openEMS(NrTS=int(6e5), EndCriteria=1e-5)
FDTD.SetGaussExcite(0.5*(f_start+f_stop), 0.5*(f_stop-f_start))
FDTD.SetBoundaryCond(['PML_8']*6)
FDTD.SetOverSampling(4)
FDTD.SetTimeStepFactor(0.95)

CSX = ContinuousStructure()
FDTD.SetCSX(CSX)

mesh = CSX.GetGrid()
mesh.SetDeltaUnit(unit)

# -------------------------
# Geometry extents (mm)
# -------------------------
x_min, x_max = -air_x, a + air_x
y_min, y_max = -5.0,   b + t_metal + air_y
z_min, z_max = -air_z, L + air_z

# Slot centers and edges (mm)
z_centers = margin + np.arange(Nslots)*slot_s
x_centers = (a/2.0) + np.array([+delta0 if i%2==0 else -delta0 for i in range(Nslots)])
x_edges = np.concatenate([x_centers - slot_w/2.0, x_centers + slot_w/2.0])
z_edges = np.concatenate([z_centers - slot_L/2.0, z_centers + slot_L/2.0])

# -------------------------
# Mesh lines — EXPLICIT (no GetLine calls)
# -------------------------
x_lines = sorted({x_min, -t_metal, 0.0, a, a + t_metal, x_max, *list(x_edges)})
y_lines = [y_min, 0.0, b, b+t_metal, y_max]
z_lines = sorted({z_min, 0.0, L, z_max, *list(z_edges)})

mesh.AddLine('x', x_lines)
mesh.AddLine('y', y_lines)
mesh.AddLine('z', z_lines)

# Optional smoothing to max cell size around ~mesh_res
mesh.SmoothMeshLines('all', mesh_res, ratio=1.4)

# -------------------------
# Materials
# -------------------------
pec    = CSX.AddMetal('PEC')
quartz = CSX.AddMaterial('QUARTZ')
quartz.SetMaterialProperty(epsilon=er_quartz)
air    = CSX.AddMaterial('AIR')     # explicit for slot holes

# -------------------------
# Solids: quartz block + metal walls + slots
# -------------------------
# Quartz full block (inside tube)
quartz.AddBox([0, 0, 0], [a, b, L])

# PEC tube: left/right/bottom/top (top will be perforated by slots)
pec.AddBox([-t_metal, 0, 0],     [0,        b,       L])          # left
pec.AddBox([a,        0, 0],     [a+t_metal,b,       L])          # right
pec.AddBox([-t_metal,-t_metal,0],[a+t_metal,0,       L])          # bottom
pec.AddBox([-t_metal, b, 0],     [a+t_metal,b+t_metal,L])         # top

# Slots = AIR boxes overriding the top metal
for zc, xc in zip(z_centers, x_centers, strict=False):
    x1, x2 = xc - slot_w/2.0, xc + slot_w/2.0
    z1, z2 = zc - slot_L/2.0, zc + slot_L/2.0
    prim = air.AddBox([x1, b, z1], [x2, b+t_metal, z2])
    prim.SetPriority(10)  # ensure it cuts the metal

# -------------------------
# Ports: Rectangular WG TE10, z-directed
# -------------------------
port_thick = max(4*mesh_res, 2.0)  # mm
p1_start = [0, 0, max(0.5, 10*mesh_res)]
p1_stop  = [a, b, p1_start[2] + port_thick]
FDTD.AddRectWaveGuidePort(port_nr=1, start=p1_start, stop=p1_stop,
                          p_dir='z', a=a*unit, b=b*unit, mode_name='TE10', excite=1)

p2_stop  = [a, b, L - max(0.5, 10*mesh_res)]
p2_start = [0, 0, p2_stop[2] - port_thick]
FDTD.AddRectWaveGuidePort(port_nr=2, start=p2_start, stop=p2_stop,
                          p_dir='z', a=a*unit, b=b*unit, mode_name='TE10', excite=0)

# -------------------------
# NF2FF setup (surround the radiator region)
# -------------------------
def create_nf2ff(FDTD_obj, name, start, stop, frequency):
    """Compat wrapper: older/newer openEMS builds may expose NF2FF creation differently."""
    try:
        return FDTD_obj.CreateNF2FFBox(name=name, start=start, stop=stop, frequency=frequency)
    except AttributeError:
        # Fallback: try AddNF2FFBox returning a handle-like object
        return FDTD_obj.AddNF2FFBox(name=name, start=start, stop=stop, frequency=frequency)

nf2ff = create_nf2ff(
    FDTD,
    name='nf2ff',
    start=[x_min+1.0,  y_min+1.0,  z_min+1.0],
    stop =[x_max-1.0,  y_max-1.0,  z_max-1.0],
    frequency=[f0]
)

# -------------------------
# (Optional) view geometry
# -------------------------
if view_geom_in_AppCSXCAD:
    os.makedirs(Sim_Path, exist_ok=True)
    csx_xml = os.path.join(Sim_Path, 'quartz_slotted_wg.xml')
    CSX.Write2XML(csx_xml)
    os.system(f'"{AppCSXCAD_BIN}" "{csx_xml}"')

# -------------------------
# Run FDTD
# -------------------------
if simulate:
    FDTD.Run(Sim_Path, cleanup=True, verbose=2, numThreads=threads)

# -------------------------
# Post-processing: S-params & impedance
# -------------------------
freq = np.linspace(f_start, f_stop, 401)
ports = list(FDTD.ports)   # Port 1 & Port 2 in creation order
for p in ports:
    p.CalcPort(Sim_Path, freq)

S11 = ports[0].uf_ref / ports[0].uf_inc
S21 = ports[1].uf_ref / ports[0].uf_inc
Zin = ports[0].uf_tot / ports[0].if_tot

plt.figure(figsize=(7.6,4.6))
plt.plot(freq*1e-9, 20*np.log10(np.abs(S11)), lw=2, label='|S11|')
plt.plot(freq*1e-9, 20*np.log10(np.abs(S21)), lw=2, ls='--', label='|S21|')
plt.grid(True)
plt.legend()
plt.xlabel('Frequency (GHz)')
plt.ylabel('Magnitude (dB)')
plt.title('S-Parameters: Slotted Quartz-Filled WG')

plt.figure(figsize=(7.6,4.6))
plt.plot(freq*1e-9, np.real(Zin), lw=2, label='Re{Zin}')
plt.plot(freq*1e-9, np.imag(Zin), lw=2, ls='--', label='Im{Zin}')
plt.grid(True)
plt.legend()
plt.xlabel('Frequency (GHz)')
plt.ylabel('Ohms')
plt.title('Input Impedance (Port 1)')

# -------------------------
# Far-field @ f0 and 3D pattern
# -------------------------
theta = np.linspace(0, np.pi, n_theta)
phi   = np.linspace(0, 2*np.pi, n_phi)

# Compatibility: some builds expect nf2ff.CalcNF2FF(...), others FDTD.CalcNF2FF(nf2ff,...)
try:
    res = nf2ff.CalcNF2FF(Sim_Path, [f0], theta, phi)
except AttributeError:
    res = FDTD.CalcNF2FF(nf2ff, Sim_Path, [f0], theta, phi)

# Max directivity (linear) & realized gain estimate
idx_f0   = np.argmin(np.abs(freq - f0))
Dmax_lin = float(res.Dmax[0])             # at f0
mismatch = 1.0 - np.abs(S11[idx_f0])**2   # (1 - |S11|^2)
Gmax_lin = Dmax_lin * float(mismatch)
Gmax_dBi = 10*np.log10(Gmax_lin)


# 3D normalized pattern
E = np.squeeze(res.E_norm)     # shape [f, th, ph] -> [th, ph]
E = E / np.max(E)
TH, PH = np.meshgrid(theta, phi, indexing='ij')
R = E
X = R * np.sin(TH) * np.cos(PH)
Y = R * np.sin(TH) * np.sin(PH)
Z = R * np.cos(TH)

fig = plt.figure(figsize=(7.2,6.2))
ax = fig.add_subplot(111, projection='3d')
ax.plot_surface(X, Y, Z, rstride=2, cstride=2, linewidth=0, antialiased=True, alpha=0.92)
ax.set_title(f'Normalized 3D Pattern @ {f0/1e9:.2f} GHz\n(peak ≈ {Gmax_dBi:.1f} dBi)')
ax.set_box_aspect((1,1,1))
ax.set_xlabel('x')
ax.set_ylabel('y')
ax.set_zlabel('z')
plt.tight_layout()

# Quick 2D geometry preview (top view at y=b)
plt.figure(figsize=(8.4,2.8))
plt.fill_between(
    [0, a], [0, 0], [L, L], color='#dddddd', alpha=0.5, step='pre', label='WG aperture (top)'
)
for zc, xc in zip(z_centers, x_centers, strict=False):
    plt.gca().add_patch(plt.Rectangle((xc - slot_w/2.0, zc - slot_L/2.0),
                                      slot_w, slot_L, fc='#3355ff', ec='k'))
plt.xlim(-2, a + 2)
plt.ylim(-5, L + 5)
plt.gca().invert_yaxis()
plt.xlabel('x (mm)')
plt.ylabel('z (mm)')
plt.title('Top-view slot layout (y=b plane)')
plt.grid(True)
plt.legend()

plt.show()