A distributed, active patch antenna model of a Josephson oscillator

TL;DR

This paper introduces a distributed, active patch antenna model for Josephson oscillators that accounts for internal electrodynamics, enabling better understanding and optimization of their microwave radiation efficiency.

Contribution

It presents a novel model that incorporates Josephson electrodynamics to analyze and optimize the microwave properties and radiation efficiency of Josephson oscillators.

Findings

Model explains low radiative power efficiency in Josephson oscillators.

Determines effective input resistance coupling Josephson current to cavity modes.

Guides design of high-efficiency, high-power Josephson patch oscillators.

Abstract

Optimization of Josephson oscillators requires a quantitative understanding of their microwave properties. A Josephson junction has a geometry similar to a microstrip patch antenna. However, it is biased by a dc-current, distributed over the whole area of the junction. The oscillating electric field is generated internally via the ac-Josephson effect. In this work I present a distributed, active patch antenna model of a Josephson oscillator. It takes into account the internal Josephson electrodynamics and allows determination of the effective input resistance, which couples Josephson current to cavity modes in the transmission line formed by the junction. The model provides full characterization of Josephson oscillators and explains the origin of low radiative power efficiency. Finally, I discuss the design of an optimized Josephson patch oscillator, capable of reaching high efficiency and radiation power for emission into free space.