Branch Line Coupler

Palace is an open-source 3D electromagnetic simulator supporting eigenmode, driven (S-parameter), and electrostatic simulations. This notebook demonstrates using the gsim.palace API to run a driven simulation on a branch line coupler.

Requirements:

IHP PDK: uv pip install ihp-gdsfactory
GDSFactory+ account for cloud simulation

Load a pcell from IHP PDK¶

import gdsfactory as gf
from ihp import LAYER, PDK, cells

PDK.activate()

c = gf.Component()
r1 = c << cells.branch_line_coupler(
    width=8.85, width_coupled=14.96, quarter_wave_length=769.235, connection_length=50
)
c.add_ports(r1.ports)

# Save port info before flatten
ports = [(p.name, p.center, p.width, p.orientation, p.layer) for p in c.ports]

c.flatten()

# Fill holes in Metal3 ground plane
r = c.get_region(layer=LAYER.Metal3drawing)
r_filled = gf.kdb.Region([gf.kdb.Polygon(list(p.each_point_hull())) for p in r.each()])
c.remove_layers(layers=[LAYER.Metal3drawing])
c.add_polygon(r_filled, layer=LAYER.Metal3drawing)

# Re-add ports
for name, center, width, orientation, layer in ports:
    c.add_port(
        name=name, center=center, width=width, orientation=orientation, layer=layer
    )

cc = c.copy()
cc.draw_ports()
cc

png

Configure and run simulation with DrivenSim¶

from gsim.palace import DrivenSim

# Create simulation object
sim = DrivenSim()

# Set output directory
sim.set_output_dir("./palace-sim-branch-coupler")

# Set the component geometry
sim.set_geometry(c)

# Configure layer stack from active PDK
sim.set_stack(substrate_thickness=2.0, air_above=300.0)

# Configure via ports (Metal3 ground plane to TopMetal2 signal)
for port in c.ports:
    sim.add_port(port.name, from_layer="metal3", to_layer="topmetal2", geometry="via")

# Configure driven simulation (frequency sweep for S-parameters)
sim.set_driven(fmin=1e9, fmax=100e9, num_points=80)

# Validate configuration
print(sim.validate_config())

Validation: PASSED

# Generate mesh (presets: "coarse", "default", "fine")
sim.mesh(preset="default")

Warning : 325 ill-shaped tets are still in the mesh


Warning : 173 ill-shaped tets are still in the mesh
Warning : ------------------------------
Warning : Mesh generation error summary
Warning :     2 warnings
Warning :     0 errors
Warning : Check the full log for details
Warning : ------------------------------





Mesh Summary
========================================
Dimensions: 1031.2 x 974.0 x 318.3 µm
Nodes:      18,517
Elements:   141,698
Tetrahedra: 102,236
Edge length: 0.40 - 351.31 µm
Quality:    0.414 (min: 0.000)
SICN:       0.456 (all valid)
----------------------------------------
Volumes (3):
  - SiO2 [1]
  - passive [2]
  - air [3]
Surfaces (13):
  - metal3_xy [4]
  - metal3_z [5]
  - topmetal2_xy [6]
  - topmetal2_z [7]
  - P1 [8]
  - P2 [9]
  - P3 [10]
  - P4 [11]
  - SiO2__None [12]
  - SiO2__passive [13]
  - passive__None [14]
  - air__passive [15]
  - air__None [16]
----------------------------------------
Mesh:   palace-sim-branch-coupler/palace.msh

# Static PNG
sim.plot_mesh(show_groups=["metal", "P"], interactive=False)

# Interactive
# sim.plot_mesh(show_groups=["metal", "P"], interactive=True)

png

Run simulation on GDSFactory+ Cloud¶

# Run simulation on GDSFactory+ cloud
results = sim.run()

  palace-5d784391  completed  37m 23s


Extracting results.tar.gz...
Downloaded 6 files to /home/runner/work/gsim/gsim/nbs/sim-data-palace-5d784391

import matplotlib.pyplot as plt
import pandas as pd

df = pd.read_csv(results["port-S.csv"])
df.columns = df.columns.str.strip()

freq = df["f (GHz)"]

# fig, axes = plt.subplots(1, 4, figsize=(10, 3))
plt.figure()

for j, label in enumerate(["S11", "S21", "S31", "S41"]):
    col_mag = f"|S[{j + 1}][1]| (dB)"
    if col_mag in df.columns:
        plt.plot(freq, df[col_mag], marker=".", markersize=3, label=label)
plt.xlabel("Frequency (GHz)")
plt.ylabel("Magnitude (dB)")
plt.title(label)
plt.grid(True)
plt.legend()

plt.tight_layout()

png