In the 2SB receivers, the rejection ratio is determined, among other factors, by the performance of the quadrature hybrids. We present here the design and characterization of an intermediate frequency (IF) assembly comprising a compact 90° hybrid chip (coupled line coupler – Lange coupler– coupled line coupler), two bias-T circuits in order to bias the Superconductor-Insulator-Superconductor (SIS) mixers. Specifically, the miniaturized 3-section hybrid chip made using thin-film technology utilizes superconducting Niobium (Nb) transmission lines and air bridges to connect the fingers of the Lange coupler (middle section). The assembly is complemented with two bias-T circuits with integrated MIM capacitors. The assembly was designed to have the amplitude and phase imbalance better than 0.6 dB and ±2.5° respectively. Experimental verification of the assembly at 4 K shows good agreement between the measurements and simulations with amplitude imbalance of 0.5 dB and maximum phase imbalance of ±2°.
In the 2SB receivers, the rejection ratio is determined, among other factors, by the performance of the quadrature hybrids. We present here the design and characterization of an intermediate frequency (IF) assembly comprising a compact 90° hybrid chip (coupled line coupler – Lange coupler– coupled line coupler), two bias-T circuits in order to bias the Superconductor-Insulator-Superconductor (SIS) mixers. Specifically, the miniaturized 3-section hybrid chip made using thin-film technology utilizes superconducting Niobium (Nb) transmission lines and air bridges to connect the fingers of the Lange coupler (middle section). The assembly is complemented with two bias-T circuits with integrated MIM capacitors. The assembly was designed to have the amplitude and phase imbalance better than 0.6 dB and ±2.5° respectively. Experimental verification of the assembly at 4 K shows good agreement between the measurements and simulations with amplitude imbalance of 0.5 dB and maximum phase imbalance of ±2°.
We present here the design and characterization of an intermediate frequency (IF) assembly comprising a compact 90° hybrid chip (coupled line coupler - Lange coupler- coupled line coupler), two bias-T circuits for biasing the superconductor-insulator-superconductor (SIS) mixers, and two transmission-line circuits. Specifically, the miniaturized three-section hybrid chip fabricated using thin-film technology utilizes superconducting Niobium (Nb) transmission lines, air bridges to connect the fingers of the Lange coupler (middle section), and is complemented with two bias-T circuits with integrated MIM capacitors. The assembly was designed to ensure amplitude and phase imbalances better than 0.6 dB and ±2°, respectively. Experimental verification of the assembly at 4 K shows good agreement between the measurements and simulations with amplitude imbalance of 0.5 dB and maximum phase imbalance of ±2°. The ALMA band-5 (163-211 GHz) receiver will include such assembly. The receiver tests shows sideband rejection ratio better than 15 dB over the entire RF band, i.e., a systematic improvement of 3-9 dB as compared with the previously reported results.
We present the design and performance of a superconducting 90° hybrid covering a full octave bandwidth from 4 to 8 GHz. The hybrid is designed using the Lange coupler layout. The novel features of this quadrature hybrid include superconducting niobium (Nb) transmission lines, air bridges to connect the fingers of the coupler and a bias-T integrated with the coupler. Our simulations indicate that the amplitude imbalance of the designed hybrid is less than 0.8 dB over the entire 4-8 GHz band with negligible phase imbalance. Experimental verification of the hybrid at 4 K, shows very good agreement between the simulations and the measurement results. The measured amplitude imbalance of the hybrid is less than 0.8 dB over 98% of the band and the maximum phase imbalance is ±4 degrees.
We report the design and cryogenic characterisation of a broadband superconducting 90◦ intermediate-frequency (IF) hybrid covering 4–20 GHz for sideband-separating (2SB) heterodyne receivers. The hybrid is implemented in thin-film niobium using capacitively loaded edge coupled transmission lines, avoiding the air-bridge interconnections required in Lange-coupler layouts while retaining a compact superconducting implementation with low loss and good quadrature balance. Cryogenic measurements using Vector Network Analyser (VNA) show amplitude and phase imbalance better than 0.6 dB and 6◦, respectively, across the full band. When used in a 2SB receiver, this level of IF balance is consistent with the observed image-rejection performance in the 10–20 dB range, for the full receiver. The design supports the development of wide-instantaneous-bandwidth 2SB receivers for millimeter and submillimeter observatories, improving spectral grasp for broadband line surveys and high-redshift line searches.
We report the design and cryogenic characterisation of a broadband superconducting 90deg intermediate-frequency (IF) hybrid covering 4 to 20 GHz for sideband-separating (2SB) heterodyne receivers. The hybrid is implemented in thin-film niobium using capacitively loaded edge coupled transmission lines, avoiding the air-bridge interconnections required in Lange-coupler layouts while retaining a compact superconducting implementation with low loss and good quadrature balance. Cryogenic measurements using Vector Network Analyser (VNA) show amplitude and phase imbalance better than 0.6 dB and 6deg, respectively, across the full band. When used in a 2SB receiver, this level of IF balance is consistent with the observed image-rejection performance in the 10-20 dB range, for the full receiver. The design supports the development of wide-instantaneous-bandwidth 2SB receivers for millimeter and submillimeter observatories, improving spectral grasp for broadband line surveys and high-redshift line searches.
A modular sideband-separating (2SB) receiver for 600-720 GHz has been built and tested. The used modular design allows to characterize all the parts separately, including testing of the superconductor-insulator-superconductor (SIS) junctions individually in a double-sideband mode before building them in to the 2SB assembly. The developed 2SB mixer has a single sideband noise temperature below 380 K in the entire operating band and reaches a level of 200 K in the best point. At the same time, the image rejection ratio (IRR) was demonstrated to be better than 11.5 dB over the entire band. However, we have found a discrepancy between the observed and expected performance. To investigate this problem, we have developed and applied methods to characterize RF and intermediate frequency imbalances of a fully assembled 2SB mixer using the SIS junction properties. As result, the IRR of our mixer was found to be limited by the RF imbalance, which is caused by complex standing waves created by reflections from the SIS junctions, the RF hybrid and the RF absorption load.
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.