# Lumped Port

A Lumped Port represents a rectangular port used to excite and measure a terminal between 2 metallic structures.

This object corresponds to tidy3d.rf.LumpedPort (opens new window).

# Name

name: Unique name for the port.

  • Required field

# Geometry

Specification of the lumped port region. The port can be planar, with one dimension set to 0, or one-dimensional, with two dimensions set to 0. Position the port between a signal and a reference or ground.

NOTE

One-dimensional line ports with two zero-size dimensions are supported. During meshing, a line port is represented by a single-grid-cell-wide Medium2D sheet whose normal axis is selected to straddle an adjacent material interface.

Planar lumped port geometry

# Center + Size

Object definition through a center position and size.

center: Center of the port in x, y, and z-directions.

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

size: Size of the port in x, y, and z-directions.

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

# Bounds

Object definition through minimum and maximum coordinate bounds.

min: Values of the x, y, and z coordinates defining the lower corner of the port.

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

max: Values of the x, y, and z coordinates defining the upper corner of the port.

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

# Settings

# Voltage Axis

voltage_axis: Axis along which the electric field line integral is performed when computing the port voltage. The voltage axis must lie in the plane of the lumped port.

  • Options: X/Y/Z
  • Required field

NOTE

Set the voltage axis direction based on the direction of the physical voltage drop between terminals.

# Impedance Specification

impedance: Reference port impedance used for scattering parameter computation. The GUI displays the real and imaginary parts separately.

real: Real part of the reference impedance.

  • Type: floating-point number
  • Unit: Ω (default unit), kΩ, MΩ, GΩ
  • Constraint: greater than 0
  • Default: 50

imag: Imaginary part of the reference impedance.

  • Type: floating-point number
  • Unit: Ω (default unit), kΩ, MΩ, GΩ
  • Default: 0

frequency (Measurement frequency): Frequency at which the complex reference impedance is defined.

  • Type: floating-point number
  • Unit: Hz, kHz, MHz, GHz (default unit), THz
  • Constraint: greater than 0
  • Default: None
  • Required when imag is nonzero

NOTE

A Lumped Port can use a complex impedance through ImpedanceSpec. A positive imaginary part is represented by an equivalent series RL load, while a negative imaginary part is represented by an equivalent series RC load at the measurement frequency. Purely reactive loads are not supported, so the real part must remain positive.

When imag is 0, Measurement frequency is optional. If no frequency is entered, the port uses the real impedance value directly.

# Advanced

# Distribution Type

dist_type: Distribution type used by the lumped element that models the port load.

  • Options:
    • On: Distribute the network portion of the lumped port, including the source, across the full lumped element bounding box.
    • Off: Restrict the network portion to one grid cell and use PEC connections to connect that cell to the edges of the lumped element.
    • Laterally only: Distribute the network portion only along the lateral axis of the lumped port.
  • Default: On

NOTE

Use On for most RF layouts. Use Off or Laterally only only when the network should not be distributed over the full bounding box, since the PEC connections can introduce additional parasitic series inductance and shunt capacitance.

Lumped port distribution type options

# Mesh

num_grid_cells: Number of mesh grid cells associated with the port along each direction. These cells are added through automatic mesh refinement. Increasing this value refines the mesh around the port and can improve port voltage/current accuracy at the cost of a larger simulation.

  • Type: integer
  • Constraint: greater than 0
  • Default: 3

snap_perimeter_to_grid: Toggle whether the perimeter of the port is snapped to the simulation grid. The lumped port is always snapped along its injection axis. This option controls snapping of the in-plane port perimeter.

  • Options:
    • True: Snap the port perimeter to the grid to improve accuracy when the element contains a small number of grid cells.
    • False: Do not snap the port perimeter to the grid.
  • Default: True

enable_snapping_points: Toggle whether snapping points are automatically generated at key geometric features of the lumped port.

  • Options:
    • True: Generate snapping points for more accurate modeling.
    • False: Do not generate snapping points.
  • Default: True

NOTE

Keep snap_perimeter_to_grid and enable_snapping_points enabled for most RF layouts, especially when the port spans only a few grid cells.

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