Third-order intermodulation distortion in high-temperature superconductor Josephson junction downconverter at 12 GHz

Abstract

First we report on the microwave characteristics of the third order intermodulation distortion (IMD3) in a High-Tc Superconductor (HTS) Josephson Junction (JJ) Downconverter at 12 GHz. We have successfully developed high quality nonlinear YBCO microbridge Josephson junctions for such an active MMIC as a mixer with RF, LO, IF and bias filters, which have been fabricated on (100) MgO substrates with 20 mm X 20 mm X 0.5 mm dimensions. The minimum conversion loss of the JJ mixer is 11 dB at very small local microwave input power LO equals -20 dBm which is two order less than a Schottky diode mixer. Consequently, this small optimum LO power gives the small rf input power at which the output IF power of the YBCO mixer saturates. Two-tone third-order intercept point (IP3) performance is a significantly important figure of merit typically used to define linearity of devices and circuits. The rf input power equals -15 dBm at the IP3 point is obtained for the YBCO mixer at 15 K and LO equals 10.935 GHz with -22 dBm. We have successfully measured the dependence of IMD3 on temperature, bias current, and LO power.