Antenna

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Description

The Antenna is the base class for all communication components in the telemetry system, providing the common interface and functionality for both transmitters and receivers. Antennas handle connections between spacecraft, ground stations, and other entities, enabling data transfer across the simulation. They define the electromagnetic characteristics required for link budget calculations, including frequency, bandwidth, gain, and pointing losses. The Telemetry System manages all antenna instances and creates the appropriate links between compatible transmitter-receiver pairs.

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Example Use Cases

• Spacecraft Communication: Define transmitter and receiver antennas for uplink and downlink operations.
• Ground Station Networks: Configure ground-based antennas for tracking and data reception.
• Inter-Satellite Links: Establish crosslinks between spacecraft in a constellation.
• RF Pattern Analysis: Load electromagnetic lookup tables for realistic antenna gain patterns.

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Module Implementation

The antenna class extends PhysicalObject and provides the foundation for all telemetry components. Upon creation, each antenna registers itself with the Telemetry System, which automatically creates links to compatible antennas on other root objects.

Antenna Configuration

Each antenna exposes key electromagnetic parameters used in link budget calculations:

Parameter	Description	Default
Frequency	Operating frequency [Hz]	6.0 GHz
Bandwidth	Channel bandwidth [Hz]	10 MHz
BitRate	Maximum data rate [bps]	8 Mbps
AntennaGain	Antenna gain [dB]	25 dB
DivergenceAngle	Beam divergence [deg]	0.0057°
OpticalLoss	Optical component losses [dB]	2.5 dB
PointingLoss	Misalignment losses [dB]	0.0 dB

These parameters are stored in an AntennaConfigMessage output message, making them available to other simulation components.

Transmission Types

Antennas are classified by their transmission type, which determines compatibility for link creation:

Type	Description
Radio	Traditional RF communication
Optical	Laser-based free-space optical communication

The Telemetry System only creates links between antennas of matching transmission types. A radio transmitter cannot communicate with an optical receiver, and vice versa.

Link Management

The Telemetry System automatically creates DataLinkMessage objects connecting each transmitter to compatible receivers. Links are only created between antennas on different root objects (e.g., a spacecraft and a ground station, or two different spacecraft).

Each antenna maintains a dictionary of its connected links, accessible via:

$$N_{\text{links}}=|\mathbf{L}|$$

where $\mathbf{L}$ is the set of all links. The number of active connections (those with line-of-sight and valid frequency overlap) is tracked separately:

$$N_{\text{connected}}=\sum _{i=1}^{N_{\text{links}}}1[{\text{IsConnected}}_i]$$ $$N_{\text{available}}=\sum _{i=1}^{N_{\text{links}}}1[{\text{IsConnected}}_i\wedge f_c>0]$$

where $f_c$ is the connection fraction indicating frequency overlap.

Electromagnetic Model

Antennas support two analysis modes for determining pointing losses:

Fixed Mode: A constant pointing loss value is used regardless of off-axis angle:

$$L_{\text{pointing}}=L_{\text{fixed}}$$

Lookup Mode: Pointing losses are interpolated from a loaded electromagnetic pattern table:

$$L_{\text{pointing}}=f(\theta )$$

where $\theta$ is the off-axis angle to the target and $f$ is the interpolated gain pattern.

The lookup table is loaded from a CSV file using ConfigureEMLookupTable(), which attaches an Electromagnetic Model to the antenna. The table contains angle-loss pairs that define the antenna’s radiation pattern.

Pointing Loss Calculation

For lookup-based antennas, the pointing loss at a given angle is calculated by interpolating between table entries. If the requested angle falls between two data points, linear interpolation is applied:

$$L(\theta )=L_1+\frac{L_2-L_1}{{\theta }_2-{\theta }_1}(\theta -{\theta }_1)$$

where $({\theta }_1,L_1)$ and $({\theta }_2,L_2)$ are adjacent entries in the lookup table.

Signature Pattern Extraction

For visualization and analysis, the antenna can export its loaded RF pattern as an array of loss values across a specified angular range:

$$\mathbf{L}=[L({\theta }_0),L({\theta }_0+\Delta \theta ),L({\theta }_0+2\Delta \theta ),\dots ,L({\theta }_{\text{max}})]$$

An optional floor correction can be applied to normalize the pattern by subtracting the minimum value:

$$L_i^{\prime }=L_i-\min (\mathbf{L})$$

Ground Station Integration

When an antenna is attached to a Ground Station, special link handling is enabled. Links to spacecraft are registered with the ground station’s access tracking system, enabling:

• Pass scheduling and prediction
• Contact time accumulation
• Link availability analysis

This integration is automatic when the antenna’s root object is a ground station.

Reproducibility

The antenna includes a random number generator that can be seeded for reproducible simulation results:

$$\text{SetRandomSeed}(s)\to \text{RNG}=\text{Random}(s)$$

This enables Monte Carlo analyses and regression testing with consistent stochastic behavior.

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Assumptions/Limitations

• Links are only created between antennas on different root objects; intra-spacecraft communication is not modelled.
• The transmission type must match exactly for link creation; no cross-mode communication is supported.
• Electromagnetic lookup tables assume azimuthal symmetry; 2D patterns are not supported.
• Linear interpolation is used for lookup tables; higher-order interpolation is not available.
• The pointing loss from lookup tables is additive with other link losses.
• Antenna gain is assumed constant across the bandwidth; frequency-dependent gain variations are not modelled.
• Polarization mismatch losses are not explicitly modelled.
• The antenna does not model near-field effects; far-field assumptions apply.
• Multiple antennas on the same root object do not interfere with each other.