fix(rf): SCRF-714 enforce far_field_approx=True for DirectivityMonitor

[dmarek-flex]

Greptile Overview

Updated On: 2025-10-15 18:28:06 UTC

Greptile Summary

This PR fixes the DirectivityMonitor class to enforce that the far_field_approx parameter must always be True. The change modifies the monitor class to use Literal[True] type constraint, preventing users from setting far_field_approx=False which would be physically incorrect for directivity calculations. Directivity measurements inherently require far-field approximations since they measure radiation patterns at distances much larger than the antenna/device size.

The implementation adds a field override in DirectivityMonitor that constrains far_field_approx to only accept True values, includes proper documentation noting this is for internal use, and maintains backward compatibility since the default was already True. The change integrates well with the existing monitor inheritance hierarchy and follows Tidy3D's pattern of using Pydantic field validation for enforcing physical constraints.

Important Files Changed

Changed Files

Filename	Score	Overview
tidy3d/components/monitor.py	5/5	Adds field enforcement to make far_field_approx always True in DirectivityMonitor using Literal[True] constraint
tests/test_components/test_monitor.py	5/5	Adds validation test ensuring DirectivityMonitor raises error when far_field_approx=False is attempted
CHANGELOG.md	5/5	Documents the breaking change that DirectivityMonitor now forces far_field_approx to True

Confidence score: 5/5

• This PR is safe to merge with minimal risk as it enforces a physically correct constraint and includes proper testing
• Score reflects simple, well-tested changes that prevent incorrect usage while maintaining backward compatibility
• No files require special attention as all changes are straightforward and properly validated

Sequence Diagram

sequenceDiagram
    participant User
    participant DirectivityMonitor
    participant PydanticValidator
    participant ValidationError

    User->>DirectivityMonitor: "Create DirectivityMonitor(far_field_approx=False)"
    DirectivityMonitor->>PydanticValidator: "Validate far_field_approx field"
    PydanticValidator->>PydanticValidator: "Check Literal[True] constraint"
    PydanticValidator->>ValidationError: "far_field_approx must be True"
    ValidationError->>User: "Raise ValidationError"
    
    Note over User,ValidationError: Invalid case: far_field_approx=False
    
    User->>DirectivityMonitor: "Create DirectivityMonitor() or DirectivityMonitor(far_field_approx=True)"
    DirectivityMonitor->>PydanticValidator: "Validate far_field_approx field"
    PydanticValidator->>PydanticValidator: "Check Literal[True] constraint - PASS"
    PydanticValidator->>DirectivityMonitor: "Validation successful"
    DirectivityMonitor->>User: "Return DirectivityMonitor instance"
    
    Note over User,DirectivityMonitor: Valid case: far_field_approx=True (default or explicit)

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Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/components/monitor.py (100%)

Summary

• Total: 1 line
• Missing: 0 lines
• Coverage: 100%