RF Analysis of 2D Unshunted Josephson Arrays: Frequency of Oscillation 
and Coupling to a Detector

S.V.Shitov
Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 
103907 Moscow, Russia

P. Barbara, C. Lobb and B.Vasilic
Center for Superconductivity Research, University of Maryland, College Park, MD, 
USA

ABSTRACT

Two-dimensional (2D) arrays of Josephson junctions over a ground plane are 
numerically analyzed within RF band of 1-700 GHz in order to obtain optimal 
coupling of emitted power into a SIS detector. A broadband coupling circuit was 
designed on the base of a microstrip capacitor and empirically synthesized impedance 
transformer avoiding loss to unwanted modes [1,2]. A DC to RF conversion 
efficiency greater than 30% has been reported recently for such a 2D array oscillator 
employing unshunted Nb tunnel junctions [3]. The numerical RF analysis supports 
the assumption that the array oscillating frequency is related to the resonant frequency 
of the discrete transmission line, given by (1/LCJ)^1/2, where L is the inductance of the 
microstrip line connecting two junctions and CJ is the junction capacitance. The 
specific RF mode that can be excited at the resonant frequency is discussed, along 
with the possible role of unbiased junctions in the array.

[1] P. Barbara, A. B. Cawthorne, S. V. Shitov, and C. J. Lobb, Stimulated Emission 
and Amplification in Josephson-Junction Arrays, Phys. Rev. Lett. 82, 1963 (1999).
[2] B. Cawthorne, P. Barbara, S. V. Shitov, C. J. Lobb, K. Wiesenfeld, and 
A. Zangwill, Synchronized Oscillations in Josephson-Junction Arrays: The Role of 
Distributed Coupling, Phys. Rev. B 60, 7575 (1999).
[3] B. Vasilic, P. Barbara, S. V. Shitov, and C. J. Lobb, Josephson-junction arrays as 
high-efficiency sources of coherent microwave radiation, to be submitted to Appl. 
Phys. Lett.