Equivalent External Noise Temperature of Time-Varying Receivers

TL;DR

This paper develops a theoretical framework to analyze the external noise temperature of time-varying antennas, highlighting how their noise characteristics depend on cross-frequency effects and broadband noise environments.

Contribution

It extends classical noise temperature theory to time-varying systems using the concept of cross-frequency effective aperture, providing new insights into their noise behavior.

Findings

Noise characteristics depend on cross-frequency effective aperture.

Time-varying systems exhibit unique intermodulation effects.

Applications include parametric amplifiers and time-modulated arrays.

Abstract

The equivalent external noise temperature of time-varying antennas is studied using the concept of cross-frequency effective aperture, which quantifies the intermodulation conversion of external noise across the frequency spectrum into a receiver's operational bandwidth. The theoretical tools for this approach are laid out following the classical method for describing external noise temperature of linear time-invariant antennas, with generalizations made along the way to capture the effects of time-varying components or materials. The results demonstrate the specific ways that a time-varying system's noise characteristics are dependent on its cross-frequency effective aperture and the broadband noise environment. The general theory is applied to several examples, including abstract models of hypothetical systems, antennas integrated with parametric amplification, and time-modulated arrays.