We present a simple method for widening the Intermediate frequency (IF) bandwidth of high frequency superconductor-insulator-superconductor (SIS) mixers. The method only requires a mixer with a single ~1 μ m2tunnel junction and an IF transformer fabricated with standard printed circuit board technology, avoiding the complexity of requiring several very small tunnel junctions in series or the use of on-chip IF tuning circuits. The method is based on employing a multi-stage microstrip IF transformer to transform the dynamic impedance of the SIS mixer chip to 50 Ω output over a wide IF bandwidth. This method assumes moderately high capacitance junction (75 fF/μm2), and is particularly useful for high frequency SIS mixers. In this paper, we shall first describe the design methodology of the IF transformer using an existing 650 GHz SIS mixer chip design as an illustration and then present the measured IF performance of the mixer.
We present a simple method for widening the Intermediate frequency (IF) bandwidth of high frequency superconductor-insulator-superconductor (SIS) mixers. The method only requires a mixer with a single ~1 μ m2tunnel junction and an IF transformer fabricated with standard printed circuit board technology, avoiding the complexity of requiring several very small tunnel junctions in series or the use of on-chip IF tuning circuits. The method is based on employing a multi-stage microstrip IF transformer to transform the dynamic impedance of the SIS mixer chip to 50 Ω output over a wide IF bandwidth. This method assumes moderately high capacitance junction (75 fF/μm2), and is particularly useful for high frequency SIS mixers. In this paper, we shall first describe the design methodology of the IF transformer using an existing 650 GHz SIS mixer chip design as an illustration and then present the measured IF performance of the mixer.
In this paper, we describe a simple method for widening the instantaneous frequency (IF) bandwidth of a high frequency superconductor-insulator-superconductor (SIS) mixer. This method requires only a standard PCB technology, without incurring any difficulties or complication in altering the tunnel junction fabrication. It involves the use of a simple multi-stage IF transformer to match the dynamic output impedance of the SIS mixer to a 50 Ω load over a wide IF bandwidth. We use an existing 650 GHz SIS mixer chip as an example to illustrate the methodology of the IF transformer design. In this example, we show how we widen the IF bandwidth of the mixer to operate over 4–12 GHz bandwidth using this simple impedance matching method.
We describe the design and fabrication of a 220 GHz
superconductor-insulator-superconductor (SIS) mixer with ultrawide
IF bandwidth. The mixer is fabricated on a 100 µm thick
quartz substrate, with planar circuit on-chip integration. The
RF power is coupled to the tunnel junction via a unilateral
finline taper and a slotline-to-microstrip transition. We used a
double-stub tuning network to tune out the junction’s parasitic
capacitance at a broad RF bandwidth, and matched the output
impedance of the mixer to the input impedance of the IF amplifier
(50 Ω) from 4–18 GHz using a 6-stage IF impedance-transformer.
We have fabricated these devices and have measured good DC
current-voltage (IV) characteristic curves. The heterodyne mixing
performance of these devices is currently being measured, and we
expect to present the results in the forthcoming ISSTT conference
in March.
Abstract The wide intermediate frequency (IF) bandwidth is a core performance metric for terahertz heterodyne receivers, and a wide-IF superconductor–insulator–superconductor (SIS) mixer is key to achieving this. This paper presents the simulation-based design, optimization, and performance analysis of a 345 GHz superconducting SIS mixer developed for wide-IF applications. The mixer employs a parallel-connected twin-junction tuning structure and integrates a dedicated IF impedance matching circuit, achieving wideband impedance matching between the mixer output port and low-noise amplifier. The design is based on two tunnel junction technologies, AlO x and AlN, with critical current densities of 1 kA·cm −2 and 25 kA·cm −2 , respectively. We systematically studied the effects of different junction materials and junction areas on the RF and IF bandwidth performance of the SIS mixer. It is found that for AlN-barrier junctions with diameters of 0.6 μ m and 0.8 μ m, the receiver’s IF noise temperature slowly decreased as the IF frequency increased at a high local oscillator frequency. Furthermore, we incorporated the calculated IF output port impedance into the mixer model for correction and introduced an integrated IF circuit approach, overcoming the original IF bandwidth limitation. Simulations show that the newly designed mixer achieves the stringent sensitivity and bandwidth requirements across the 320–370 GHz range, delivering an IF bandwidth of 4–22 GHz and a receiver noise temperature of 39–73 K. Notably, the −3 dB IF bandwidth is improved by more than 1.5 times compared to conventional AlO x -based designs. These findings provide new design guidelines and quantitative criteria for next-generation wide-IF receivers and other high-frequency applications requiring a wide IF bandwidth.
Superconductor-Insulator-Superconductor (SIS) tunnel junction mixers are now commonly used in as- tronomical receivers at (sub)millimeter wavelengths because of their superb sensitivity, high dynamic range and stability of operation. Niobium SIS mixers operating at frequencies well below the super- conducting gap (∼680 GHz) have already achieved quantum limited sensitivity. Therefore to further enhance the receiver sensitivity, increasing the Intermediate Frequency (IF) bandwidth of SIS mixers has became crucial. This thesis focuses on the theoretical modeling, design and experimental verifi- cation of Nb SIS mixers operating around 230 GHz with a wide IF bandwidth of 1–15 GHz. These mixers were designed for a single baseline heterodyne interferometer (GUBBINS), which is being built to observe the Sunyaev-Zel’dovich effect in the Cosmic Microwave Background. The combination of wide IF bandwidth SIS mixers and complex analogue correlators will allow GUBBINS to feature high surface brightness sensitivity, that helps to distinguish the weak SZ effect from the background noise. The SIS mixer detector system was assembled inside the GUBBINS cryostat together with the IF electronics and RF/LO optical systems. Low noise temperatures of around 71 K were then measured in the GUBBINS system. The Nb SIS mixer we have developed uses a unilateral finline and fully integrated planar circuits deposited on a silicon substrate, to couple the electromagnetic radiation from the waveguide into the SIS junction. The finline mixer allows a broad-band RF coupling, an easy integration of the on-chip planar circuits and an easy-to-fabricate mixer block. To achieve a wide IF bandwidth, the output impedance of the SIS mixer was well matched to the input impedance of the amplifier by a multi-stage microstrip circuit. Additionally, the planar circuit of the SIS mixer was also designed to have a small lumped inductance and capacitance. The SIS mixer chip was extensively simulated by rigorous electromagnetic software (HFSS) and the S-parameter was exported to a quantum mixing package SuperMix to produce a full-wave model of the mixer. Experimental testing yielded a best noise temperature of 50 K with an average noise temperature of 75 K over an RF bandwidth of 160 GHz– 260 GHz. We have performed thorough experimental and computational investigation of the IF system in particular the constraints on the bandwidth caused by the lumped element capacitance of the mixer chip and the matching of the output impedance of the mixer to the IF amplifier. Our conclusion is that a bandwidth of 1–15 GHz could be achieved using our mixer design, subject to the performance of the amplifier. Finally, a variable temperature load system was successfully developed and tested inside the cryostat, to avoid the losses from the room-temperature optics. We have showed that the noise temperature of the SIS detector could be reduced by as much as 15 K by testing the mixer using a variable temperature load inside the cryostat.
Besides the sensitivity nearly approaching the quantum limit, the intermediate-frequency (IF) bandwidth is of particular interesting for Superconductor-insulator-superconductor (SIS) mixers for radio astronomy research. In this paper, we are going to present the characteristic of IF bandwidth of two type of NbN SIS mixers, Long distributed junctions and Parallel-connected twin junctions. Firstly, the relative mixer gain are measured with different IF load impedance (25Ω, 50Ω, 75Ω) for both two SIS mixers. And also the mixers gain with different IF load impedance is simulated to get the optimum IF load impedance over a relative large IF bandwidth (2-15GHz). Finally, an IF matching circuit is designed and measured associating with SIS mixers, the measurement results show that the mixers gain are flatter over a large IF bandwidth than with 50Ω IF load impedance.
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.