  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.
