DC and RF Measurements of Serial Bi-SQUID Arrays

SQUID arrays are promising candidates for low-profile antennas and low-noise amplifier applications. We present the integrated circuit designs and results of dc and radio frequency measurements of wideband serial arrays based on the integration of linear bi-SQUID cells forming a superconducting quantum interference filter (bi-SQUID SQIF). Various configurations of serial array designs are described. The measured linearity, power gain, and noise temperature are analyzed and compared. The experimental results are matched to results of mathematical modeling. A serial bi-SQUID SQIF arrays are integrated into a coplanar waveguide, and symmetrically grounded to corresponding sides of the coplanar waveguide. The radio frequency output comes out from the central common line, which is also used for dc biasing, and forms a symmetrical balanced output. The signal and dc flux biasing line is designed as coplanar lines passed in parallel over each bi-SQUID cell in a bidirectional fashion concentrating magnetic flux inside of each cell. Serial bi-SQUID SQIF arrays are fabricated on 5 mm $\times$ 5 mm chips using a standard HYPRES niobium 4.5 $ \hbox{kA/cm}^{2}$ fabrication process.