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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

A 700 GHz unilateral finline SIS mixer fed by a multi-flare angle smooth-walled horn

Boon-Kok Tan, G. Yassin, Paul Grimes, Jamie Leech, Karl Jacobs, S. Withington, Mike Tacon, Christopher Groppi

Published Jun 22, 2010• 5 citations
Publisher

Abstract

We present the design of a broadband superconductor-insulator-superconductor (SIS) mixer operating near 700 GHz. A key feature of our design is the utilisation of a new type of waveguide to planar circuit transition comprising a unilateral finline taper. This transition is markedly easier to design, simulate and fabricate than the antipodal finline we employed previously. The finline taper and the superconducting circuitry are deposited on a 15 μm thick silicon substrate. The employment of the very thin substrate, achieved using Silicon-On-Insulator (SOI) technology, makes it easy to match the incoming signal to the loaded waveguide. The lightweight mixer chip is held in the E-plane of the waveguide using gold beam leads, avoiding the need for deep grooves in the waveguide wall. This new design yields a significantly shorter chip, free of serrations and a wider RF bandwidth. Since tuning and all other circuits are integrated on the mixer chip, the mixer block is extremely simple, comprising a feed horn and a waveguide section without any complicated mechanical features. We employ a new type of smooth-walled horn which exhibits excellent beam circularity and low cross polarisation, comparable to the conventional corrugated horn, and yet is easier to fabricate. The horn is machined by standard milling with a drill tool shaped into the horn profile. In this paper, we describe the detailed design of the mixer chip including electromagnetic simulations, and the mixer performance obtained with SuperMix simulations. We also present the preliminary measurements of the smooth-walled horn radiation patterns near the mixer operating frequencies.

DOI
10.1117/12.856711

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We report the design and successful operation of an superconductor-insulator-superconductor (SIS) mixer operating near the superconducting gap of niobium. A key feature of this design is the employment of a unilateral finline taper to transform the waveguide modes to microstrip signals. This transition is easy to design since it can be rigorously modeled, and also easy to fabricate being a single-layer structure. We will show that unilateral finline mixers have important advantages at THz frequencies since they exhibit wideband operation at both radio frequency (RF) and intermediate frequency (IF), allow elegant on-chip integration of the mixer circuits and result in an extremely simple mixer block that does not require a backshort or any mechanical tuners. The mixer we describe below is fed by a multiple flare-angle smooth-walled horn which exhibits beam pattern characteristic comparable to the conventional corrugated horn and yet is much easier to fabricate. In this paper, we shall present a brief discussion of the testing of the multiple flare-angle horn and detailed description of the design and testing of the mixer, covering ~100 GHz bandwidth centered at 650 GHz. In particular, we will present full electromagnetic de sign description of the mixer chip including the superconducting effects, and the heterodyne properties of the mixer using quantum mixing theory. Mixer performance tests that we carried out from 595 to 702 GHz gave a best receiver noise temperature of 145 K at 600 GHz, corrected for a 75 μm beam splitter. Finally, we performed a thorough analysis of the mixer performance, comparing the experimental results with theoretical models. Our investigation demonstrated that unilateral finline mixers fed by a multiple flare-angle horn can yield performance comparable to conventional designs, hence are suitable for large format mixer array at THz frequencies.

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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.

ORA review team•Jan 1, 2015•7 citations
We present the design of a broadband superconductor-insulator-superconductor (SIS) mixer operating near 700 GHz. A key feature of our design is the utilisation of a new type of waveguide to planar circuit transition comprising a unilateral finline taper. This transition is markedly easier to design, simulate and fabricate than the antipodal finline we employed previously. The finline taper and the superconducting circuitry are deposited on a 15 μm thick silicon substrate. The employment of the very thin substrate, achieved using Silicon-On-Insulator (SOI) technology, makes it easy to match the incoming signal to the loaded waveguide. The lightweight mixer chip is held in the E-plane of the waveguide using gold beam leads, avoiding the need for deep grooves in the waveguide wall. This new design yields a significantly shorter chip, free of serrations and a wider RF bandwidth. Since tuning and all other circuits are integrated on the mixer chip, the mixer block is extremely simple, comprising a feed horn and a waveguide section without any complicated mechanical features. We employ a new type of smooth-walled horn which exhibits excellent beam circularity and low cross polarisation, comparable to the conventional corrugated horn, and yet is easier to fabricate. The horn is machined by standard milling with a drill tool shaped into the horn profile. In this paper, we describe the detailed design of the mixer chip including electromagnetic simulations, and the mixer performance obtained with SuperMix simulations. We also present the preliminary measurements of the smooth-walled horn radiation patterns near the mixer operating frequencies.
We report the design and successful operation of an superconductor-insulator-superconductor (SIS) mixer operating near the superconducting gap of niobium. A key feature of this design is the employment of a unilateral finline taper to transform the waveguide modes to microstrip signals. This transition is easy to design since it can be rigorously modeled, and also easy to fabricate being a single-layer structure. We will show that unilateral finline mixers have important advantages at THz frequencies since they exhibit wideband operation at both radio frequency (RF) and intermediate frequency (IF), allow elegant on-chip integration of the mixer circuits and result in an extremely simple mixer block that does not require a backshort or any mechanical tuners. The mixer we describe below is fed by a multiple flare-angle smooth-walled horn which exhibits beam pattern characteristic comparable to the conventional corrugated horn and yet is much easier to fabricate. In this paper, we shall present a brief discussion of the testing of the multiple flare-angle horn and detailed description of the design and testing of the mixer, covering ~100 GHz bandwidth centered at 650 GHz. In particular, we will present full electromagnetic de sign description of the mixer chip including the superconducting effects, and the heterodyne properties of the mixer using quantum mixing theory. Mixer performance tests that we carried out from 595 to 702 GHz gave a best receiver noise temperature of 145 K at 600 GHz, corrected for a 75 μm beam splitter. Finally, we performed a thorough analysis of the mixer performance, comparing the experimental results with theoretical models. Our investigation demonstrated that unilateral finline mixers fed by a multiple flare-angle horn can yield performance comparable to conventional designs, hence are suitable for large format mixer array at THz frequencies.
In this paper, we describe the design and operation of a 350-GHz finline superconductor-insulator-superconductor mixer. The mixer is fed by a horn-reflector antenna, and the superconducting circuit is fabricated using planar-circuit technology and fully integrated tuning. An important feature of the mixer is that it employs an antipodal finline section, deposited on one side of a quartz substrate, which transforms the high impedance of the waveguide (/spl ap/300 /spl Omega/) to the low impedance of the microstrip (/spl ap/20 /spl Omega/). The Nb/Al-oxide/Nb tunnel junction is fabricated at the same time as the finline circuit. In this paper, we describe the design procedure in some detail. We pay particular attention to the synthesis of the finline taper and the electromagnetic design of the horn-reflector antenna. We have tested a finline mixer over the frequency range of 330-370 GHz and measured a receiver noise temperature of 90 K, which remained unchanged over the whole frequency range. Our investigation has demonstrated that it is possible to make superconducting finline mixers for frequencies as high as 350 GHz.
Fig. 1. (Top) A 700 GHz finline mixer chip. The finline taper runs from the left to center of the chip, and the mixer tuning circuit, RF block and bond pads are on the right (Bottom) Cross-sections through the finline taper, showing the metallization and the E-field lines. The finline taper gradually transforms the waveguide mode at A through unilateral finline (B) to antipodal finline (C), before transitioning from antipodal finline to microstrip (D-F). Abstract—SIS mixers using finline waveguide to microstrip transitions show a number of advantageous features, particularly in providing a broadband, fixed impedance feed to the SIS mixer tuning circuit. The large chip area and insensitivity to mixer block machining tolerances simplifies the assembly of the mixer, as well as allowing more advanced mixer designs to be fabricated on a single chip. Finline SIS mixers have shown good performance in the 230 and 350 GHz bands[1][2], and we have also previously reported results from two finline SIS mixers in the 600-720 GHz band[3][4], obtaining best receiver noise temperatures of ~250 K. In this paper we present results from several finline mixers in the 600-720 GHz band, using both variants of our original 3-stage Chebyshev filter tuned single junction mixers and new Belitsky tuned mixers. These dual junction tuned mixers show significantly better performance than our previously reported results, with receiver noise temperatures below 200 K. We present detailed SuperMix simulations of the receiver performance and compare these with measured results. We find good agreement between simulations and measured performance can be achieved by introducing a small amount of attenuation in the RF circuit of the mixer. We also present simulations of the IF bandwidth of finline mixers, and suggest a method by which this can be greatly improved.
We report the successful operation of a superconductor-insulator-superconductor (SIS) finline mixer operating near the superconducting energy gap of Nb. The mixer employs a new type of Pickett-Potter horn-reflector (PPHR) antenna, which exhibits low sidelobes and low cross-polarization levels, and yet is easy to fabricate. The SIS tunnel junction and all of the integrated superconducting tuning circuits are fabricated from Nb using planar-circuit technology. The mixer employs an antipodal finline section, deposited on one side of a quartz substrate, which transforms the high impedance of the waveguide (/spl ap/300 /spl Omega/) to the low impedance of the microstrip line (/spl ap/20 /spl Omega/). The Nb/Al-oxide/Nb tunnel junction is fabricated at the same time as the finline circuit. In this paper, we describe the design and testing of the mixer, and pay particular attention to the electromagnetic design of the PPHR antenna. We investigate the noise temperature and gain of the mixer over 642-714 GHz, and analyze the experimental results using rigorous theories that were developed specifically for the purpose. Our investigation demonstrates that finline mixers have good performance both below and above the superconducting energy gap.
The successful operation of a 650 GHz unilateral finline superconductor–insulator–superconductor mixer with a wide IF bandwidth is reported. The mixer was fabricated using silicon‐on‐insulator (SOI) technology, with planar circuit on‐chip integration. The mixer was tested over the frequency range of 630–702 GHz, and the best recorded DSB noise temperature was 226 K. The measured RF and IF behaviour of the mixer agreed very well with the simulation predictions. This demonstrates that superconducting finline mixers fabricated on an SOI substrate can achieve state‐of‐the‐art performance, and yet are much more compact and highly reproducible, and hence suitable for large‐format arrays in astronomy instruments, at THz frequencies.
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.