Antenna Patterns in SpaceLink

Executive Summary

High-fidelity antenna pattern modeling is essential for credible link analysis during all phases of a space mission. Oversimplified assumptions, such as representing an antenna with a single gain value or using crude pointing-loss approximations, can lead to overdesign (excess mass, power, cost and complexity) or communication blackouts during critical operations. The antenna modeling capabilities developed by Cascade Space make it easy to replace fragile assumptions with the precise calculations needed for mission success.

This paper introduces SpaceLink's antenna modeling capabilities. SpaceLink is Cascade's open-source Python package for RF link analysis with an emphasis on space applications. To our knowledge, it is the only free, open-source option that supports interpolation of antenna patterns in three dimensions. In this paper we describe how SpaceLink represents antenna radiation patterns and how it derives key link design quantities such as directivity, gain, and axial ratio. We also give an overview of the API and a quickstart.

The Challenge: From Real Patterns to Trustworthy Analysis

Incorporating antenna gain into link analysis presents several challenges:

• Space vehicle attitude and position relative to ground stations is rarely constant. A single "antenna gain" value is inadequate for dynamic scenarios.
• Polarization matters. Cross-pol leakage and axial-ratio variation can materially change link margin, especially across off-boresight angles.
• Gain is frequency-dependent.
• Patterns come from diverse sources: EM solvers, vendor catalogs, and measurements.
• Sampled pattern data requires interpolation over a spherical coordinate system.
• Phase information must be preserved to accurately model passive combinations of multiple antennas.
• Software capable of leveraging antenna patterns is typically expensive, closed-source, and cumbersome to use.

SpaceLink addresses these needs by making it easy to calculate antenna pattern quantities in any direction for any frequency and polarization via accurate modeling and fully vectorized operations.

Math of Radiation Patterns in SpaceLink

In this section we present the math implemented in SpaceLink to represent radiation patterns.