Implementation of SQUID array local oscillator into integrated circuit for 600 GHz superconducting receiver comprising log-periodic antenna and SIS mixer

Abstract

An integrated quasioptical receiver circuit comprising planar complementary log-periodic antenna, SIS mixer with microstrip matching transformers and parallel array of unshunted SIS junctions operating as a local oscillator has been designed, fabricated and dc tested. The array of parallel SIS junctions united in a microstrip transmission line can be described as a Josephson transmission line (JTL) with single flux quanta synchronously moving along the array of quantum interferometers. The JTL with 20 junctions 4 /spl mu/m in diameter has critical current 4.5 mA, normal resistance 0.3 /spl Omega/ and a self-detection step at about 1.1 mV. The step width is over 1.5 mA in current scale and 50 /spl mu/V in voltage scale that corresponds to 2.5 /spl mu/W oscillation power and 25 GHz tuning range with 550 GHz central frequency. A current applied along the top electrode of JTL allows to vary the output power of such oscillator. The advantages of such oscillator are higher impedance of microstrip line about 10 /spl Omega/ that makes easier matching to SIS mixer, lower losses at frequencies about the energy gap for Nb and the possibility to tune output power. The SIS junction IV curve shows self-resonant steps at about 1.2 mV that corresponds to the matching circuit central frequency about 600 GHz and is close to the JTL central frequency.