flex_rf.tidy3d.DirectivityMonitor

Type: class │ Base(s): MicrowaveBaseModel, FieldProjectionAngleMonitor, FluxMonitor

Description

Monitor that records the radiation characteristics of antennas in the frequency domain at specified observation angles.

Notes

For directivity, the computation is based on the ratio of the radiation intensity in a given direction to the average radiation intensity over all directions:

Balanis, Constantine A., “Antenna Theory: Analysis and Design,” John Wiley & Sons, Chapter 2.6 (2016).

For axial ratio, the computation is based on:

Balanis, Constantine A., “Antenna Theory: Analysis and Design,” John Wiley & Sons, Chapter 2.12 (2016).

Example(s)

import numpy as np
monitor = DirectivityMonitor(  # doctest: +SKIP
    center=(0, 0, 0),
    size=(2, 2, 2),
    freqs=[1e9, 2e9, 3e9],
    name='directivity_monitor',
    theta=np.linspace(0, np.pi, 10),
    phi=np.linspace(0, 2*np.pi, 20),
)

Parameters

size [TracedSize]

Size in x, y, and z directions.

name [str]

Unique name for monitor.

freqs [FreqArray]

Array or list of frequencies stored by the field monitor.

theta [ObsGridArray]

Polar angles with respect to the global z axis, relative to the location of local_origin, at which to project fields.

phi [ObsGridArray]

Azimuth angles with respect to the global z axis, relative to the location of local_origin, at which to project fields.

center [TracedCoordinate] = (0.0, 0.0, 0.0)

Center of object in x, y, and z.

interval_space [tuple[PositiveInt, PositiveInt, PositiveInt]] = (1, 1, 1)

Number of grid step intervals at which near fields are recorded for projection to the far field, along each direction. If equal to 1, there will be no downsampling. If greater than 1, the step will be applied, but the first and last point of the monitor grid are always included. Using values greater than 1 can help speed up server-side far field projections with minimal accuracy loss, especially in cases where it is necessary for the grid resolution to be high for the FDTD simulation, but such a high resolution is unnecessary for the purpose of projecting the recorded near fields to the far field.

colocate [Literal[True]] = True

Defines whether fields are colocated to grid cell boundaries (i.e. to the primal grid). Can be toggled for field recording monitors and is hard-coded for other monitors depending on their specific function.

use_colocated_integration [Literal[True]] = True

Whether to use colocated fields for flux, dot products, and overlap integrals. Hard-coded to True for most monitor types. Can be toggled on field and overlap monitors.

apodization [ApodizationSpec] = factory: ApodizationSpec

Sets parameters of (optional) apodization. Apodization applies a windowing function to the Fourier transform of the time-domain fields into frequency-domain ones, and can be used to truncate the beginning and/or end of the time signal, for example to eliminate the source pulse when studying the eigenmodes of a system. Note: apodization affects the normalization of the frequency-domain fields.

normal_dir [Direction | None] = None

Direction of the surface monitor’s normal vector w.r.t. the positive x, y or z unit vectors. Must be one of '+' or '-'. Applies to surface monitors only, and defaults to '+' if not provided.

exclude_surfaces [tuple[BoxSurface, ...] | None] = None

Surfaces to exclude in the integration, if a volume monitor.

custom_origin [Coordinate | None] = None

Local origin used for defining observation points. If None, uses the monitor’s center.

window_size [tuple[NonNegativeFloat, NonNegativeFloat]] = (0, 0)

Size of the transition region of the windowing function used to ensure that the recorded near fields decay to zero near the edges of the monitor. The two components refer to the two tangential directions associated with each surface. For surfaces with the normal along x, the two components are (y, z). For surfaces with the normal along y, the two components are (x, z). For surfaces with the normal along z, the two components are (x, y). Each value must be between 0 and 1, inclusive, and denotes the size of the transition region over which fields are scaled to less than a thousandth of the original amplitude, relative to half the size of the monitor in that direction. A value of 0 turns windowing off in that direction, while a value of 1 indicates that the window will be applied to the entire monitor in that direction. This field is applicable for surface monitors only, and otherwise must remain (0, 0).

medium [MediumType | None] = None

Medium through which to project fields. Generally, the fields should be projected through the same medium as the one in which this monitor is placed, and this is the default behavior when medium=None. A custom medium can be useful in some situations for advanced users, but we recommend trying to avoid using a non-default medium.

proj_distance [float] = 1000000.0

Radial distance of the projection points from local_origin.

far_field_approx [Literal[True]] = True

Directivity calculations require the far field approximation. This field is hard-coded to be True and cannot be changed.

Methods

storage_size(num_cells: int, tmesh: ArrayFloat1D)

Size of monitor storage given the number of points after discretization.