# Impedance and Calibration

Impedance and Calibration controls how voltage, current, and characteristic impedance are computed for microwave modes.

These settings configure the impedance_specs property in tidy3d.rf.MicrowaveModeSpec (opens new window).

# Reference Impedance

reference_impedance: Reference impedance used for S-parameter computation.

  • Options:
    • Z0: Use the characteristic impedance of each mode.
    • Complex value: Use a specified reference impedance.
    • Data array: Use mode-dependent or terminal-dependent reference impedance data.
  • Unit: Ω\Omega
  • Default: Z0

If a data array misses some modes, 50 Ohm is applied to the missing modes.

# Same Impedance Spec for All Modes

use_same_impedance_spec_for_all_modes: Toggle whether one impedance specification is applied to all modes.

  • Options:
    • True: Use one impedance specification for all modes.
    • False: Configure impedance specifications per mode.

# Type

impedance_specs: Impedance specification type used to compute voltage, current, and characteristic impedance for microwave modes.

When Custom is selected, enable at least one of Voltage integral or Current integral.

# Voltage Integral

voltage_spec: Optional voltage path specification for tidy3d.rf.CustomImpedanceSpec (opens new window).

When enabled, the GUI uses tidy3d.rf.AxisAlignedVoltageIntegralSpec (opens new window) to compute voltage between two points defined by an axis-aligned line.

# Center + Size

Object definition through a center position and size.

center: Center of the voltage integration path in x, y, and z-directions.

  • Type: floating-point number
  • Unit: m, mm (default unit), um

size: Size of the voltage integration path in x, y, and z-directions.

  • Type: floating-point number
  • Unit: m, mm (default unit), um
  • Constraint: greater than or equal to 0

# Bounds

Object definition through minimum and maximum coordinate bounds.

min: Values defining the lower endpoint or lower corner of the voltage integration path.

max: Values defining the upper endpoint or upper corner of the voltage integration path.

# Sign

sign: Orientation of the voltage integral.

  • Options: +/-
  • Required field

For an axis-aligned voltage integral, positive sign means the voltage is evaluated from the lower coordinate endpoint to the higher coordinate endpoint along the integration axis.

extrapolate_to_endpoints: Toggle whether to extrapolate fields to the endpoints of the voltage path.

  • Options:
    • True: Ignore fields outside and on the bounds of the integral when endpoints are near material interfaces.
    • False: Do not extrapolate to endpoints.
  • Default: False

snap_path_to_grid: Toggle whether the voltage integration path is snapped to the Yee grid.

  • Options:
    • True: Snap the path to the grid.
    • False: Do not snap the path to the grid.
  • Default: False

# Current Integral

current_spec: Optional current contour specification for tidy3d.rf.CustomImpedanceSpec (opens new window).

When enabled, the GUI uses tidy3d.rf.AxisAlignedCurrentIntegralSpec (opens new window) to compute current around an axis-aligned rectangular loop.

# Center + Size

Object definition through a center position and size.

center: Center of the current integration loop in x, y, and z-directions.

  • Type: floating-point number
  • Unit: m, mm (default unit), um

size: Size of the current integration loop in x, y, and z-directions.

  • Type: floating-point number
  • Unit: m, mm (default unit), um
  • Constraint: greater than or equal to 0

# Bounds

Object definition through minimum and maximum coordinate bounds.

min: Values defining the lower corner of the current integration loop.

max: Values defining the upper corner of the current integration loop.

# Sign

sign: Orientation of the current integral.

  • Options: +/-
  • Required field

Positive sign means current flowing in the positive normal-axis direction of the loop.

extrapolate_to_endpoints: Toggle whether endpoint extrapolation is used for the path integrals that form the current loop.

  • Options:
    • True: Use endpoint extrapolation.
    • False: Do not use endpoint extrapolation.
  • Default: False

snap_contour_to_grid: Toggle whether the current integration loop is snapped to the Yee grid.

  • Options:
    • True: Snap the loop to the grid.
    • False: Do not snap the loop to the grid.
  • Default: False

NOTE

For custom impedance calculation, at least one voltage or current integral must be enabled. Voltage paths should follow the electric field line between conductors, while current contours should enclose the current-carrying region.

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