The IF Output Impedance of SIS Mixers

Abstract

In this paper, we describe a measurement setup to characterize the intermediate frequency (IF) impedance of cryogenically cooled superconductor-insulator-superconductor (SIS) mixers. A setup based on a commercial vector network analyzer (VNA), a circulator and a low noise amplifier (LNA) has allowed to increase the dynamic of the VNA and to perform accurate one-port measurements across a high dynamic range of the SIS mixers IF band. The mixers were biased in three different regions of their unpumped IV curve to obtain three known impedances which are close to the classical calibration SOLT standards (Short, Open, Load, Thru): the reference plane was located at the SIS junction itself and the calibration procedure allowed to calibrate out all IF circuitry of the measurement setup, including the on-chip SIS mixer intrinsic capacitance and inductance without requiring to thermally cycle and open the cryostat to locate and measure the different calibration standards. Thus, the devised method provides a simple and direct measurement of the SIS mixers IF impedance which can be used for quick, accurate and highly repeatable IF characterization of any type of millimeter and sub-millimeter wave SIS mixers. The measurement method is described and the experimental results of the IF output impedances of 3 mm band DSB and SSB mixers with 4 GHz wide IFs (across 4-8 GHz) are presented and compared with simulated predictions obtained from combining Tucker's SIS mixer theory and accurate electromagnetic modeling of the mixer structure. Index Terms-Double side band (DSB) and single side band (SSB) tuning, intermediate frequency (IF) impedance, superconductor-insulator-superconductor (SIS) mixer, vector network analyzer (VNA) measurements.

Determining the Parameters of the SIS-Mixer at an Intermediate Frequency

“…In calibration measurements at 4 K the SIS junction itself is used as a calibrator [7]. This avoids errors that occur during calibration at room temperature and are associated with changes in the electrical length and impedance of circuit elements during cooling.…”

Low input reflection cryogenic low noise amplifier for Radio Astronomy multipixel receivers

“…An additional incentive for the elimination of the isolators from the receiver chain is their non-negligible noise contribution, which in some cases could be up to 80% [2,3]. From the standpoint of the mixer, another aspect that needs to be taken into account is that normally its design relies on a 50 Ω load presented at its IF output in order to guarantee stable operation [4]. This condition is obviously met when an isolator is used but for a standalone amplifier this is only achieved with a low input reflection amplifier.…”

Direct Measurement of Superconducting Tunnel Junction Capacitance

“…However, since the differential resistance at the subgap (area A) is high, the effect of capacitance would not be masked. Such distinctive characteristics of the junction at different bias points can be used as calibration standards [13], where the points in areas, A, B, and C on the IVC (cf. Fig.…”