CPW

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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 CPW (coplanar waveguide) structure.

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

PDK.activate()


@gf.cell
def gsg_electrode(
    length: float = 800,
    s_width: float = 20,
    g_width: float = 40,
    gap_width: float = 15,
    layer=LAYER.TopMetal2drawing,
) -> gf.Component:
    """
    Create a GSG (Ground-Signal-Ground) electrode.

    Args:
        length: horizontal length of the electrodes
        s_width: width of the signal (center) electrode
        g_width: width of the ground electrodes
        gap_width: gap between signal and ground electrodes
        layer: layer for the metal
    """
    c = gf.Component()

    # Top ground electrode
    r1 = c << gf.c.rectangle((length, g_width), centered=True, layer=layer)
    r1.move((0, (g_width + s_width) / 2 + gap_width))

    # Center signal electrode
    _r2 = c << gf.c.rectangle((length, s_width), centered=True, layer=layer)

    # Bottom ground electrode
    r3 = c << gf.c.rectangle((length, g_width), centered=True, layer=layer)
    r3.move((0, -(g_width + s_width) / 2 - gap_width))

    # Add ports at the signal center (one per side)
    # The CPW port API computes the gap element surfaces from s_width and gap_width
    c.add_port(
        name="o1",
        center=(-length / 2, 0),
        width=s_width,
        orientation=0,
        port_type="electrical",
        layer=layer,
    )

    c.add_port(
        name="o2",
        center=(length / 2, 0),
        width=s_width,
        orientation=180,
        port_type="electrical",
        layer=layer,
    )

    return c


c = gsg_electrode()
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-cpw")

# 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 left CPW port (single port at signal center)
sim.add_cpw_port("o1", layer="topmetal2", s_width=20, gap_width=15, length=5.0)

# Configure right CPW port (single port at signal center)
sim.add_cpw_port("o2", layer="topmetal2", s_width=20, gap_width=15, length=5.0)

# Configure driven simulation (frequency sweep for S-parameters)
sim.set_driven(fmin=1e9, fmax=100e9, num_points=40)

# Validate configuration
print(sim.validate_config())

Validation: PASSED

# Generate mesh with planar conductors (presets: "coarse", "default", "fine")
sim.mesh(preset="default", planar_conductors=False)

Warning : 3 ill-shaped tets are still in the mesh


Warning : ------------------------------
Warning : Mesh generation error summary
Warning :     1 warning
Warning :     0 errors
Warning : Check the full log for details
Warning : ------------------------------





Mesh Summary
========================================
Dimensions: 900.0 x 230.0 x 318.3 µm
Nodes:      9,184
Elements:   70,549
Tetrahedra: 51,455
Edge length: 0.40 - 300.00 µm
Quality:    0.468 (min: 0.001)
SICN:       0.517 (all valid)
----------------------------------------
Volumes (3):
  - SiO2 [1]
  - passive [2]
  - air [3]
Surfaces (11):
  - topmetal2_xy [4]
  - topmetal2_z [5]
  - P1_E0 [6]
  - P1_E1 [7]
  - P2_E0 [8]
  - P2_E1 [9]
  - SiO2__None [10]
  - SiO2__passive [11]
  - passive__None [12]
  - air__passive [13]
  - air__None [14]
----------------------------------------
Mesh:   palace-sim-cpw/palace.msh

# Static PNG (wireframe, filtered to metal + port groups)
sim.plot_mesh(show_groups=["metal", "P"], interactive=False)

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

# Solid view — coloured surfaces per physical group, boundary transparent
# sim.plot_mesh(
#     style="solid",
#     transparent_groups=["Absorbing_boundary", "air__airbox", "air__passive"],
#     interactive=False,
# )

png

Run simulation on cloud

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

  palace-b69e592f  completed  5m 21s


Extracting results.tar.gz...
Downloaded 6 files to /home/runner/work/gsim/gsim/nbs/sim-data-palace-b69e592f

import matplotlib.pyplot as plt
import pandas as pd

df = pd.read_csv(results["port-S.csv"])
df.columns = df.columns.str.strip()  # Remove whitespace from column names

freq = df["f (GHz)"]

fig, (ax1, ax2) = plt.subplots(2, 1, figsize=(6, 6))

# Magnitude plot
ax1.plot(freq, df["|S[1][1]| (dB)"], marker=".", label="S11")
ax1.plot(freq, df["|S[2][1]| (dB)"], marker=".", label="S21")
ax1.set_xlabel("Frequency (GHz)")
ax1.set_ylabel("Magnitude (dB)")
ax1.set_title("S-Parameters")
ax1.legend()
ax1.grid(True)

# Phase plot
ax2.plot(freq, df["arg(S[1][1]) (deg.)"], marker=".", label="S11")
ax2.plot(freq, df["arg(S[2][1]) (deg.)"], marker=".", label="S21")
ax2.set_xlabel("Frequency (GHz)")
ax2.set_ylabel("Phase (deg)")
ax2.legend()
ax2.grid(True)

plt.tight_layout()

png

Crossing Microstrip