Electromagnetic Model

Description

The Electromagnetic Model provides electromagnetic (EM) signature characterization for physical objects in the simulation. This model enables angle-dependent gain or loss calculations for antennas, sensors, and other components that emit or receive electromagnetic radiation. The model supports both omnidirectional patterns with constant gain and directional patterns loaded from CSV lookup tables, making it suitable for link budget analysis, interference assessment, and RF system modeling.

Example Use Cases

Antenna Pattern Modeling: Define gain patterns for communication antennas to support link margin calculations.
Sensor Field of View: Characterize the angular sensitivity of RF sensors and receivers.
Interference Analysis: Model EM emissions from spacecraft components for electromagnetic compatibility studies.
Link Budget Computation: Provide transmitter and receiver gain values for communication link analysis.

Module Implementation

The Electromagnetic Model is a Universe Model that attaches to any Physical Object and provides electromagnetic signature information through an output message.

Gain Modes

The model supports two operational modes:

Mode	Description
Omnidirectional	Constant gain in all directions
Directional	Angle-dependent gain from lookup table

Omnidirectional Mode

When no lookup table is loaded, the model uses a constant omnidirectional gain:

G (θ) = G_{0}

where $G_{0}$ is the OmnidirectionalGain parameter in decibels.

Directional Mode

When initialized with a CSV file, the model provides angle-dependent gain through an interpolated lookup table. The gain is symmetric about the component’s up vector:

G (θ) = G_{0} - L (θ)

where $L (θ)$ is the loss value interpolated from the lookup table at angle $θ$ .

Lookup Table Format

The CSV file must contain two columns:

Column	Units	Description
Angle	deg	Off-boresight angle from the up vector
Loss	dB	Gain reduction at that angle

Interpolation Method

The model uses cubic spline interpolation to create a smooth gain pattern from discrete data points. The interpolation process:

Computes cumulative arc-length distances along the input data curve
Generates evenly spaced sample points (720 points for full hemisphere)
Applies cubic spline fitting to produce smooth transitions between data points

The spline interpolation ensures continuous first derivatives, avoiding discontinuities in the gain pattern that could cause numerical issues in link calculations.

Spline Formulation

For each segment between data points, the interpolated value is computed as:

y (t) = (1 - t) y_{i} + t y_{i + 1} + t (1 - t) [a_{i} (1 - t) + b_{i} t]

where:

$t$ is the normalized position within the segment $[0, 1]$
$y_{i}$ and $y_{i + 1}$ are the bounding data values
$a_{i}$ and $b_{i}$ are spline coefficients ensuring smoothness

Gain Lookup

The GetElectromagneticLoss method retrieves the loss value for a given off-boresight angle:

L = L (θ) where θ \in [0°, 360°]

The lookup performs linear search through the interpolated table to find the first entry with angle greater than or equal to the query angle.

Assumptions/Limitations

The gain pattern is assumed symmetric about the component’s up vector; asymmetric patterns are not supported.
The lookup table must be monotonically increasing in angle for correct interpolation.
The CSV file must have a header row that is skipped during parsing.
Angles outside the lookup table range return zero loss.
The model does not account for polarization effects or frequency-dependent gain variations.
A maximum of 720 interpolation points are generated regardless of input data density.
The omnidirectional gain is set to zero when a lookup table is loaded.

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