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Electronics Letters

Broadband 230 GHz finline mixer for astronomicalimaging arrays

G. Yassin, Rachael Padman, S. Withington, Karl Jacobs, S. Wulff

Published Mar 13, 1997• 13 citations
Publisher

Abstract

The authors report the successful operation of an antipodal finline quasi-particle SIS mixer at 230 GHz. The mixer is fed by a waveguide diagonal horn and uses planar circuit technology and integrated tuning. The mixer is tested over the frequency range 213–265 GHz and a receiver noise temperature of ~60 K DSB over the whole of this range is obtained. This work has shown that superconducting finline mixers have low noise and are easy to manufacture, and are therefore suitable for large-format imaging arrays.

DOI
10.1049/el:19970314

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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.

•Jan 1, 2007•0 citations
The authors report the successful operation of an antipodal finline quasi-particle SIS mixer at 230 GHz. The mixer is fed by a waveguide diagonal horn and uses planar circuit technology and integrated tuning. The mixer is tested over the frequency range 213–265 GHz and a receiver noise temperature of ~60 K DSB over the whole of this range is obtained. This work has shown that superconducting finline mixers have low noise and are easy to manufacture, and are therefore suitable for large-format imaging arrays.
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.
In pursuit of advancing large array receiver capabilities and enhancing the 16-element Heterodyne Array Receiver Program (HARP) instrument on the James Clerk Maxwell Telescope (JCMT), we have successfully fabricated 230 GHz finline superconductor-insulator-superconductor (SIS) mixers. These mixers are critical for assessing the potential and prospective for the HARP instrument’s upgrade. Unlike the existing HARP’s mixer, we replace the probe antenna with an end-fire unilateral finline as the waveguide to planar circuit transition. This mixer design is expected to operate from about 160–260 GHz (approximately 47% bandwidth), and the mixer chips’ current-voltage (I-V) curves have been characterized, showing promising results with a quality factor (Rsg/Rn) exceeding 9.3. Evaluation of the double-sideband (DSB) receiver noise temperature (Trx) is currently underway. Once successfully characterised, our immediate aim is to scale the mixer to operate at HARP’s frequency range near 345 GHz to achieve similar broad RF bandwidth performance. Ongoing simulations are currently being conducted for the design of the 345 GHz finline mixer. This work marks a crucial step toward enhancing HARP receiver performance with better sensitivity and wider Intermediate Frequency (IF) bandwidth, enabling higher-frequency observations, and expanding the scientific potential of the JCMT and its collaborative partners.
In this letter, we report the near quantum-limited performance of a 230 GHz endfire superconductor-insulator-superconductor (SIS) mixer utilizing a Nb/Al-AlOx/Nb trilayer. An important feature of this mixer is its use of a unilateral finline for the waveguide-to-planar circuit transition, which allows for a wide radiofrequency (RF) bandwidth, a simple waveguide structure with easy alignment, and for the mixer chip to be aligned along the optical axis. Each of these factors is beneficial in the construction of large-format focal plane arrays. We tested the new finline mixer from 210 to 260 GHz in a liquid helium cryostat at ~4 K. The best recorded noise temperature was approximately twice the quantum limit, which is comparable to conventional radial probe mixers. This suggests that endfire SIS mixers can be used in large format arrays, comprising 100s or even 1000s of SIS mixing elements, while retaining state-of-the-art quantum mixing performance.
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.
The authors have tested the performance of planar SIS (superconductor-insulator-superconductor) mixers with log-periodic antennas at near millimeter and submillimeter wave frequencies from 90 to 360 GHz. The large omega R/sub N/C product ( approximately 10 at 90 GHz) of the Nb/NbO/sub x//Pb-In-Au junctions requires an integrated inductive tuning element to resonate the junction capacitance at the operating frequencies. Two types of integrated tuning element were used which were designed with the aid of measurements using a Fourier transform spectrometer. Preliminary results indicate that the tuning elements can give very good mixer performance up to at least 200 GHz. An inductive wire in parallel with a 5-junction array gives a minimum mixer noise temperature of 115 K (DSB) at 90 GHz with a FWHM (full width at half maximum) bandwidth of 8 GHz. An open-ended microstrip stub in parallel with a single junction gives minimum mixer noise temperatures at 150 and 200 K (DSB) near 90 and 180 GHz with FWHM bandwidths of 4 and 3 GHz, respectively. The relatively high mixer noise temperatures compared to those of waveguide SIS mixers in a similar frequency range are attributed mainly to the losses in the optical system.>
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.