RF Mode Analysis

MicrowaveModeSpec extends the standard mode specification with characteristic impedance calculation. It is useful for RF and microwave transmission lines where Z0 is a key result.

Unlike a standard mode spec, MicrowaveModeSpec includes impedance_specs, which defines how voltage and current path integrals are computed for each mode.

from flex_rf.tidy3d import AutoImpedanceSpec, MicrowaveModeMonitor, MicrowaveModeSpec

mode_spec = MicrowaveModeSpec(
    num_modes=2,
    target_neff=1.5,
    impedance_specs=AutoImpedanceSpec(),
)

monitor = MicrowaveModeMonitor(
    center=(0, 0, 0),
    size=(2, 2, 0),
    freqs=[1e9, 2e9, 3e9],
    mode_spec=mode_spec,
    name="mode_monitor",
)

Automatic Impedance

AutoImpedanceSpec automatically determines voltage and current integration paths from the mode field distribution. This is the recommended starting point.

from flex_rf.tidy3d import AutoImpedanceSpec, MicrowaveModeSpec

mode_spec_auto = MicrowaveModeSpec(
    num_modes=1,
    impedance_specs=AutoImpedanceSpec(),
)

Custom Impedance

Use CustomImpedanceSpec when you need precise control over voltage and current path placement.

from flex_rf.tidy3d import (
    AxisAlignedCurrentIntegralSpec,
    AxisAlignedVoltageIntegralSpec,
    CustomImpedanceSpec,
    MicrowaveModeSpec,
)

voltage_spec = AxisAlignedVoltageIntegralSpec(
    center=(0, 0, 0),
    size=(0, 0, 1),
    sign="+",
)

current_spec = AxisAlignedCurrentIntegralSpec(
    center=(0, 0, 0),
    size=(2, 1, 0),
    sign="+",
)

custom_impedance = CustomImpedanceSpec(
    voltage_spec=voltage_spec,
    current_spec=current_spec,
)

mode_spec_custom = MicrowaveModeSpec(
    num_modes=1,
    impedance_specs=custom_impedance,
)

Multiple Modes

Provide one impedance specification per mode, or provide a single specification that is applied to all modes.

mode_spec_multi = MicrowaveModeSpec(
    num_modes=2,
    impedance_specs=(
        AutoImpedanceSpec(),
        custom_impedance,
    ),
)

mode_spec_shared = MicrowaveModeSpec(
    num_modes=2,
    impedance_specs=AutoImpedanceSpec(),
)

Mode Solver Monitors

Monitor	Use
`MicrowaveModeMonitor`	Records mode amplitudes and transmission-line parameters during a full 3D simulation.
`MicrowaveModeSolverMonitor`	Stores complete 2D mode field profiles from a standalone mode solver calculation.

from flex_rf.tidy3d import MicrowaveModeMonitor, MicrowaveModeSolverMonitor

mode_monitor = MicrowaveModeMonitor(
    center=(0, 0, 0),
    size=(2, 2, 0),
    freqs=[1e9, 2e9],
    mode_spec=mode_spec,
    name="mode_monitor",
)

mode_solver_monitor = MicrowaveModeSolverMonitor(
    center=(0, 0, 0),
    size=(2, 2, 0),
    freqs=[1e9, 2e9],
    mode_spec=mode_spec,
    name="mode_solver_monitor",
)

Standalone Mode Simulation

Use ModeSimulation to solve modes without a full 3D FDTD run.

from flex_rf import web
from flex_rf.tidy3d import GridSpec, ModeSimulation

mode_sim = ModeSimulation(
    size=(10, 10, 0),
    grid_spec=GridSpec.auto(wavelength=0.3),
    structures=[...],
    mode_spec=mode_spec,
    freqs=[1e9, 2e9, 3e9],
)

mode_sim_data = web.run(mode_sim, task_name="mode_analysis")
z0 = mode_sim_data.modes.transmission_line_data.Z0

Page	Why open it
Path Integrals	Define voltage and current paths used by impedance specs.
Impedance Calculator	Calculate impedance from mode or field data after a run.
Wave Ports	Use microwave mode specs in modal RF ports.