Three-Tone Intermodulation Distortion Generated by Superconducting Bandpass Filters

TL;DR

This paper investigates the generation of three-tone intermodulation distortion in superconducting microwave bandpass filters, highlighting its impact on receiver performance and proposing simple design solutions to mitigate interference.

Contribution

It introduces a measurement procedure for IMD in superconducting filters and identifies design strategies to prevent problematic intermodulation spurs.

Findings

3-tone IMD can produce noticeable spurs in receivers

Certain interference scenarios cause significant IMD effects

Simple design modifications can prevent IMD issues

Abstract

Microwave bandpass filters constructed from materials exhibiting some nonlinearity, such as superconductors, will generate intermodulation distortion (IMD) when subjected to signals at more than one frequency. In commercial applications of superconductive receive filters, it is possible for IMD to be generated when a weak receive signal mixes with very strong out-of-band signals, such as those coming from the transmitter. A measurement procedure was developed and data were taken on several different types of superconducting bandpass filters, all developed for commercial application. It was found that in certain interference situations, the 3-tone mixing can produce a spur that is noticeable by the receiver, but that there are simple preventative design solutions.