This thesis presents the work done in the field of development of low noise instruments for radio astronomy applications, and addresses some of the key components in the receiver. Part of this thesis describes the design and development of a Superconductor-Insulator-Superconductor (SIS) junction mixer covering RF frequencies from 163 to 211 GHz, reaching the quantum limited noise performance. The mixer uses an integrated approach, where an LO coupler and a resistive LO termination are fabricated on the same mixer chip.Another part of the thesis describes the work on the design and development of the Band 5 receiver cartridge for the Atacama Large Millimeter Array (ALMA) project. Details on the development of Band 5 receiver cartridge, sideband separation mixer, and a superconducting IF hybrid is presented.Additionally, this thesis presents first ever experimental demonstration of an SIS device as frequency multiplier, and presents successful off-chip detection of the multiplied signal. The experimental frequency multiplier was designed for the 182 to 192 GHz output frequency band, and uses an array of SIS junctions to boost the total output power. Dependence of multiplier output power on the DC bias voltage and pumping power are investigated. The measurements successfully confirm x2 multiplication, where extremely sharp multiplied signal was detected with no observable spurious signals. The SIS multiplier shows no deterioration of the linewidth of the original pumping signal.
This thesis presents the work done in the field of development of low noise instruments for radio astronomy applications, and addresses some of the key components in the receiver. Part of this thesis describes the design and development of a Superconductor-Insulator-Superconductor (SIS) junction mixer covering RF frequencies from 163 to 211 GHz, reaching the quantum limited noise performance. The mixer uses an integrated approach, where an LO coupler and a resistive LO termination are fabricated on the same mixer chip.Another part of the thesis describes the work on the design and development of the Band 5 receiver cartridge for the Atacama Large Millimeter Array (ALMA) project. Details on the development of Band 5 receiver cartridge, sideband separation mixer, and a superconducting IF hybrid is presented.Additionally, this thesis presents first ever experimental demonstration of an SIS device as frequency multiplier, and presents successful off-chip detection of the multiplied signal. The experimental frequency multiplier was designed for the 182 to 192 GHz output frequency band, and uses an array of SIS junctions to boost the total output power. Dependence of multiplier output power on the DC bias voltage and pumping power are investigated. The measurements successfully confirm x2 multiplication, where extremely sharp multiplied signal was detected with no observable spurious signals. The SIS multiplier shows no deterioration of the linewidth of the original pumping signal.
Abstract We developed a low-noise, compact, balanced superconductor–insulator–superconductor (SIS) mixer, operating in the 787–950 GHz radio frequency range. A waveguide mixer block was designed to integrate all the key components, such as a radio frequency (RF) 90° hybrid coupler, two identical SIS mixer chips, bias-tees, and an intermediate frequency power-combiner. The RF waveguide 90° hybrid coupler consists of branch lines with wide slots optimized by numerical simulation, for ease of fabrication. The balanced mixer was installed into a cartridge type receiver, originally developed for the Atacama Large Millimeter/submillimeter Array Band 10 (787–950 GHz). The receiver demonstrated double sideband noise temperatures of approximately 200 K for most of the band, without any correction for loss in front of the receiver. The local oscillator noise rejection ratio was estimated to be more than 15 dB within the measured frequency range.
This thesis focuses on the development of advanced components for the future wideband side band separating and / or multipixel receivers for radio-astronomy with ultimate sensitivity.\nIn this thesis, a novel frequency multiplier based on distributed superconducting tunnel (SIS) junctions has been demonstrated for the first time, taking advantage of the extreme inherent nonlinearity of such device. This practical demonstration is the result of an extensive theoretical exploration and modelling, showing the importance of the reactive quasi-particle tunnel current\nand its impact on the SIS tunnel junction frequency multiplier. In addition, a novel technique\nwas suggested that allows for the first time direct measurement of the reactive quasi-particle tunnel current.\nThis work comprehends the analysis, design and characterisation of the first frequency multiplier using distributed SIS junctions. The measured output power generated by the distributed SIS junction at the second harmonic of the input frequency were in good agreement\nwith the model. Furthermore, the distributed SIS junction as a frequency multiplier were for the first time able to pump an SIS mixer. An efficiency of the distributed SIS junction multiplier of 15-30 % for a fractional bandwidth of 10% with excellent spectral line purity were\ndemonstrated. The -3 dB line width of the multiplied signal is better than 1 Hz, which were the lowest resolution bandwidth of the spectrum analyser. Consequently, the results attained in this work show that the distributed SIS junction frequency multiplier has considerable future potential, and could possibly be used in LO source in single-ended and multi-pixel SIS mixer\nlayouts.\nFurthermore, in order to improve the sideband rejection ratio of cryogenically cooled sideband separating receivers for radio astronomy receivers to more than 15 dB over a wide RF and IF bandwidth, novel wideband RF and IF hybrid couplers have been developed and demonstrated\nwith very low imbalances. More specifically, a 4-8 GHz IF assembly comprising a compact 90° hybrid chip, two bias-T circuits and two transmission line circuits was designed and characterised. The compact size of the hybrid chip allows it to be integrated into virtually any sideband separating (2SB) mixer operating at cryogenic temperatures and is furthermore especially advantageous for multi-pixel 2SB receivers or low noise balanced amplifier layouts.\nThe characterisation of the hybrid assembly was performed at a cryogenic temperature of 4 K and sophisticated calibration and fixture de-embedding procedures were used. To further improve the sideband rejection ratio, a novel design for a RF 90° waveguide hybrid with very\nlow amplitude imbalance over a fractional bandwidth of 30% (159-216 GHz) was demonstrated. Both Hybrids are currently implemented in the ALMA Band 5 receivers, which\nrepresent the state-of-the-art for ultra-low noise sideband separated receivers.\nIn order to allow complete characterisation of the ALMA Band 5 cartridge a highly versatile measurement setup has been built. The measurement setup includes all necessary hardware and achieves automatic measurements for the system noise and sideband rejection with in-built\noptimisation procedures. The measurement setup additionally comprises measurements of the receiver saturation, phase and amplitude stability, as well as optical beam characterisation.
This thesis work covers the development of integrated superconducting balanced mixers for heterodyne (resolution> 10^7) THz focal plane arrays. The aim was to develop on chip integrated balanced superconductor-insulator-superconductor (SIS) mixers at 800-1100 GHz and in addition at the Intermediate Frequency (IF) 4-12 GHz integrated \n180° IF hybrids both for the CHAI (CCAT Heterodyne Array Instrument) receiver for the Cerro Chajnantor Atacama Telescope (CCAT) observatory. A planar 180º hybrid ring \ncoupler, two separate slotline antennas, two separate slotline to CPW transitions to employ for the 800-1100 GHz balanced SIS mixer, based on NbTiN circuitry, were designed and all were integrated on one 6 μm silicon substrate. \nAt the IF side of the integrated balanced mixers, two different configurations of superconducting \nintegrated 180º IF hybrids were designed to combine the two generated IF outputs at either Σ or Δ port depending on the choice of the input port of the hybrid. These 4-12 GHz IF hybrid coupler designs were based on planar lumped elements to miniaturize the size to about 0.5×2.2 μm^2. The designs were simulated for 500 μm and 9 μm silicon substrates. The latter is studied in order to integrate it at a later \nstage with the RF part of the mixer on one substrate. The lithography mask and subsequently the micro-fabrication of the IF hybrids were made. The measurement of the Nb based IF hybrid on a 500 μm silicon with Vector Network Analyzer (VNA) in liquid helium is reported. The measured results are analyzed and compared to the IF hybrid with the implemented superconducting Nb in the simulation. \n \nThese developments and designs will be available and applicable for future receivers of the CCAT-prime observatory. Because the original envisioned CCAT-observatory project was discontinued due to the lack of funding, it was decided that my 800-1100 GHz designs would not be further developed into working mixers for the time being and that other projects would get priority. \n \nMy work continued with the the development of integrated 1.9 THz balanced Hot Electron Bolometer (HEB) mixers. This development is relevant for 1.9 THz focal plane array receivers for the airborne Stratospheric Observatory for the Far Infrared (SOFIA), for which the mixers are developed in our group. The LO power consumption of the array presently limits its usable RF bandwidth. This power consumption could be reduced by a factor of 5 by using integrated balanced mixers. The mixers are based on superconducting NbN HEBs and Au is applied as normal metal to wire the mixers. The development contained design, micro-nanofabrication, DC and cryogenic high frequency measurements. All designed planar elements consisted of an 1 octave broadband 180º RF hybrid-ring coupler, two slotline tapered antennas, two slotline to \nCPW transitions, two or four 120 Ω HEB bridges, two low pass filters (LPFs) and two DC/IF blocking capacitors integrated on one 3 μm silicon substrate and simulated using CST suite. A further integrated 1.9 THz HEB mixer was designed to support the two separate IF outputs at one side of a 3 μm silicon substrate with employing a CPW-CPW crossover. \n \nThe micro-nanofabrication of the 1.9 THz balanced mixers was done in house using E-beam and photo-lithography techniques. Almost all DC measured devices contained HEB bridges that were sufficiently similar in normal state resistance and transition temperature. The average resistance of the devices, in the one available wafer for measurements, was about 17% too low. The transition temperature of the devices was around 7.9 K, in comparison to 8.5 K for our state of the art single pixel mixers. The two machined 1.9 THz balanced waveguide blocks for testing of the devices were machined in the institute's in house workshop. I have tested the transmission of the blocks, and thereby the workmanship, with a THz time Domain Spectrometer, showed about 2.4 dB of loss per mm waveguide length at room temperature, for a split block waveguide made of the oxygen free copper tellurium alloy (CuTe). \n \nThe cryogenic RF measurements showed a very similar LO-power coupling to both mixers in the balanced device, from both input ports of the mixer. By using an in house built Quantum Cascade Laser (QCL) LO as a local oscillator and a severely attenuated Virginia Diode multiplier chain (VDI) LO as a signal source I have shown proper balanced mixer behavior, thereby validating the design. Signal suppression up to 38 dB was shown by inverting the bias voltages on one of the mixers in the balanced device, which added a 180º phase change to the IF of one of the mixers.
This thesis describes the development of low-noise heterodyne receivers at THz frequencies for submillimeter astronomy using Nb-based superconductor-insulator-superconductor (SIS) tunneling junctions. The mixers utilize a quasi-optical configuration which consists of a planar twin-slot antenna and antisymmetrically-fed two-junctions on an antireflection-coated silicon hyperhemispherical lens. On-chip integrated tuning circuits, in the form of microstrip lines, are used to obtain maximum coupling efficiency in the designed frequency band. To reduce the rf losses in the integrated tuning circuits above the superconducting Nb gap frequency (~ 700 GHz), normal-metal Al is used to replace Nb as the tuning circuits. To account the rf losses in the micros trip lines, we calculated the surface impedance of the AI films using the nonlocal anomalous skin effect for finite thickness films. Nb films were calculated using the Mattis-Bardeen theory in the extreme anomalous limit. Our calculations show that the losses of the Al and Nb microstrip lines are about equal at 830 GHz. For Al-wiring and Nb-wiring mixers both optimized at 1050 GHz, the RF coupling efficiency of Al-wiring mixer is higher than that of Nb-wiring one by almost 50%. We have designed both Nb-wiring and Al-wiring mixers below and above the gap frequency. A Fourier transform spectrometer (FTS) has been constructed especially for the study of the frequency response of SIS receivers. This FTS features large aperture size (10 inch) and high frequency resolution (114 MHz). The FTS spectra, obtained using the SIS receivers as direct detectors on the FTS, agree quite well with our theoretical simulations. We have also, for the first time, measured the FTS heterodyne response of an SIS mixer at sufficiently high resolution to resolve the LO and the sidebands. Heterodyne measurements of our SIS receivers with Nb-wiring or Al-wiring have yielded results which arc among the best reported to date for broadband heterodyne receivers. The Nb-wiring mixers, covering 400 - 850 GHz band with four separate fixed-tuned mixers, have uncorrected DSB receiver noise temperature around 5hv/kb to 700 GHz, and better than 540 K at 808 GHz. An Al-wiring mixer designed for 1050 GHz band has an uncorrected DSB receiver noise temperature 840 K at 1042 GHz and 2.5 K bath temperature. Mixer performance analysis shows that Nb junctions can work well up to twice the gap frequency and the major cause of loss above the gap frequency is the rf losses in the microstrip tuning structures. Further advances in THz SIS mixers may be possible using circuits fabricated with higher-gap superconductors such as NbN. However, this will require high-quality films with low RF surface resistance at THz frequencies.
This licentiate is focused on the design and development of Superconductor-Insulator-Superconductor (SIS) junction mixer for ALMA Band 5, one of the ten frequency bands of the Atacama Large Millimeter Array (ALMA) project. ALMA Band 5 is a dual polarisation sideband separation heterodyne receiver covering radio frequencies (RF) from 163 GHz to 211 GHz, with 4-8 GHz intermediate frequency (IF). Amongst the other ALMA bands, Band 5 is the lowest frequency band, which uses all-cold optics. That puts strong constrains on the dimensions of all the receiver components. For the SIS mixer, we employ a MMIC-like approach where most of the DSB mixer components, including LO injection circuitry with novel directional coupler, are integrated on the same crystal quartz substrate. The mixer uses a lumped filter technique to extract the IF frequencies, which is non-traditional for SIS mixers. A custom made superconducting Lange coupler with suspended air bridges to connect the fingers of Lange coupler is used. Experimental measurements of the double sideband mixer show state of the art performance with the receiver noise temperature below 30 Kelvin across the entire band. The noise temperature for sideband separation mixer is below 60 Kelvin with sideband rejection better than 12 dB over most of the band.
We report on the design and experimental results of a fix-tuned Superconductor-Insulator-Superconductor (SIS) mixer for Atacama Large Millimeter/submillimeter Array (ALMA) band 8 (385-500 GHz) receivers. Nb-based SIS junctions of a current density of 10 kA/cm(2) and one micrometer size (fabricated with a two-step lift-off process) are employed to accomplish the ALMA receiver specification, which requires wide frequency coverage as well as low noise temperature. A parallel-connected twin-junction (PCTJ) is designed to resonate at the band center to tune out the junction geometric capacitance. A waveguide-microstrip probe is optimized to have nearly frequency-independent impedance at the probe's feed point, thereby making it easy to match the low-impedance PCTJ over a wide frequency band. The RF embedding impedance is retrieved by fitting the measured pumped I-V curves to confirm good matching between PCTJ and signal source. We demonstrate here a minimum double-sideband receiver noise temperature of 3 times of quantum limits for an intermediate-frequency range of 4-8 GHz. The mixers were measured in band 8 cartridge with a sideband separation scheme. Single-sideband receiver noise below ALMA specification was achieved over the whole band.