Hawal Marouf Rashid

Performance of the First ALMA Band 5 Production Cartridge

We present performance of the first ALMA Band 5 production cartridge, covering frequencies from 163 to 211 GHz. Atacama Large Millimeter/sub-millimeter Array (ALMA) Band 5 is a dual polarization, sideband separation (2SB) receiver based on all Niobium (Nb) superconductor-insulator-superconductor (SIS) tunnel junction mixers, providing 16 GHz of instantaneous RF bandwidth for astronomy observations. The 2SB mixer for each polarization employs a quadrature configuration. The sideband separation occurs at the output of the IF hybrid that has integrated bias-T for biasing the mixers, and is produced using superconducting thin-film technology. Experimental verification of the Band 5 cold cartridge performed together with warm cartridge assembly, confirms that the system noise temperature is below 45 K over most of the RF band, which is less than 5 photon noise (5 hf/k). This is to our knowledge, the best results reported at these frequencies. The measurement of the sideband rejection indicates that the sideband rejection is better than 10 dB over 90% of the observational band.

Novel Waveguide 3 dB Hybrid With Improved Amplitude Imbalance

We present a new design concept for a 90° waveguide hybrid and its implementation. This novel hybrid design is based on a multiple branch waveguide hybrid. The primary feature of this quadrature waveguide hybrid is the introduction of a controllable ripple in the operational band for achieving a better overall amplitude imbalance. This design concept is verified by implementation of a 90° waveguide hybrid for the 166-208 GHz band and can be used for waveguide hybrids up to several THz. Our simulations indicate that the amplitude imbalance of the designed hybrid is better than 0.11 dB over the most of the 166-208 GHz band with a phase imbalance better than ± 2.3°. Experimental verification of the hybrid shows excellent agreement with simulations with an amplitude imbalance better than 0.15 dB and phase imbalance of ± 2.5° over most of the band being achieved.

Design of Wideband Waveguide Hybrid With Ultra-Low Amplitude Imbalance

We present a design and synthesis procedure for a new 90 ° waveguide hybrid with ultra-low amplitude imbalance. This novel hybrid design is based on Reeds multiple branch waveguide hybrid. The primary feature of this quadrature hybrid design is the introduction of a controllable ripple in the operational band by, firstly changing the heights of the input and output branches and, secondly, by introducing three waveguide-height discontinuity sections placed symmetrically in the main waveguide. This layout allows ultra-low amplitude imbalance over a wide operational band. At the same time, it permits a greater input/output branch height as compared to the Reeds 5-branch waveguide hybrid, which should ease fabrication for short-mm and sub-mm wavelengths. This design concept is demonstrated through a 90 ° waveguide hybrid for the 159-216 GHz band (30% fractional bandwidth). Our simulations indicate that the amplitude imbalance of the hybrid is better than 0.2 dB over the most of the 159-216 GHz band with a phase imbalance better than ±4°. Experimental verification of the hybrid shows excellent agreement with the simulations.

Direct Measurement of Superconducting Tunnel Junction Capacitance

Superconductor-insulator-superconductor (SIS) junction is the key component for millimeter and submillimeter mixers for radio astronomy and environmental science. The capacitance of the SIS mixer determines both the RF and IF performance. Previously, measurements of this capacitance has had high uncertainty. Herein, we determine the SIS junction capacitance at cryogenic temperature ( ~ 4 K) by direct measurement of the SIS junction impedance at microwave frequencies. The proposed calibration method uses only one short-circuit reference. The SIS junction capacitance measurement is realized by biasing the junction at the different parts of its current-voltage characteristic, thus eliminating a separate measurement of short-circuit standard. In order to verify the measurement results, thin-film capacitors with known capacitance were also measured. The capacitance of four SIS junctions with various areas were measured. The absolute uncertainty of the proposed measurement method was found to vary from 5 to 6.8% amongst different junction areas.

SEPIA - a new single pixel receiver at the APEX Telescope

Context: We describe the new SEPIA (Swedish-ESO PI Instrument for APEX) receiver, which was designed and built by the Group for Advanced Receiver Development (GARD), at Onsala Space Observatory (OSO) in collaboration with ESO. It was installed and commissioned at the APEX telescope during 2015 with an ALMA Band 5 receiver channel and updated with a new frequency channel (ALMA Band 9) in February 2016. Aims: This manuscript aims to provide, for observers who use the SEPIA receiver, a reference in terms of the hardware description, optics and performance as well as the commissioning results. Methods: Out of three available receiver cartridge positions in SEPIA, the two current frequency channels, corresponding to ALMA Band 5, the RF band 158--211 GHz, and Band 9, the RF band 600--722 GHz, provide state-of-the-art dual polarization receivers. The Band 5 frequency channel uses 2SB SIS mixers with an average SSB noise temperature around 45K with IF (intermediate frequency) band 4--8 GHz for each sideband providing total 4x4 GHz IF band. The Band 9 frequency channel uses DSB SIS mixers with a noise temperature of 75--125K with IF band 4--12 GHz for each polarization. Results: Both current SEPIA receiver channels are available to all APEX observers.

Frequency Multiplier Based on Distributed Superconducting Tunnel Junctions: Theory, Design, and Characterization

In this paper, we present the analysis, design, and characterization of the first frequency multiplier using distributed superconductor-insulator-superconductor (SIS) junctions. We derived analytical expressions describing the properties of the distributed SIS junction as a frequency multiplier. The modeling of the distributed SIS junctions shows that high conversion efficiency can be achieved when used as the multiplier. The measured output power generated by such multiplier employing the distributed SIS junction at the second harmonic of the input frequency is in good agreement with the model. Furthermore, the frequency multiplier based on the distributed SIS junction for the first time was able to pump an SIS mixer. The multiplication efficiency of the distributed SIS junction is 15-30% for a fractional bandwidth of 10% with excellent spectral line purity. The -3 dB line width of the multiplied signal is 1 Hz, which was limited by the resolution bandwidth of the spectrum analyzer. The results attained in this paper show that the distributed SIS junction frequency multiplier has considerable future potential, and could possibly be used in LO source in single-end and multipixel SIS mixer receivers.

Harmonic and reactive behavior of the quasiparticle tunnel current in SIS junctions

In this paper, we show theoretically and experimentally that the reactive quasiparticle tunnel current of the superconductor tunnel junction could be directly measured at specific bias voltages for the higher harmonics of the quasiparticle tunnel current. We used the theory of quasiparticle tunneling to study the higher harmonics of the quasiparticle tunnel current in superconducting tunnel junction in the presence of rf irradiation. The impact of the reactive current on the harmonic behavior of the quasiparticle tunnel current was carefully studied by implementing a practical model with four parameters to model the dc I-V characteristics of the superconducting tunnel junction. The measured reactive current at the specific bias voltage is in good agreement with our theoretically calculated reactive current through the Kramers-Kronig transform. This study also shows that there is an excellent correspondence between the behavior of the predicted higher harmonics using the previously established theory of quasiparticle tunnel current in superconducting tunnel junctions by J.R. Tucker and M.J. Feldman and the measurements presented in this paper

ALMA Band 5 receiver cartridge - Design, performance, and commissioning

We describe the design, performance, and commissioning results for the new ALMA Band 5 receiver channel, 163–211 GHz, which is in the final stage of full deployment and expected to be available for observations in 2018. This manuscript provides the description of the new ALMA Band 5 receiver cartridge and serves as a reference for observers using the ALMA Band 5 receiver for observations. At the time of writing this paper, the ALMA Band 5 Production Consortium consisting of NOVA Instrumentation group, based in Groningen, NL, and GARD in Sweden have produced and delivered to ALMA Observatory over 60 receiver cartridges. All 60 cartridges fulfil the new more stringent specifications for Band 5 and demonstrate excellent noise temperatures, typically below 45 K single sideband (SSB) at 4 K detector physical temperature and below 35 K SSB at 3.5 K (typical for operation at the ALMA Frontend), providing the average sideband rejection better than 15 dB, and the integrated cross-polarization level better than –25 dB. The 70 warm cartridge assemblies, hosting Band 5 local oscillator and DC bias electronics, have been produced and delivered to ALMA by NRAO. The commissioning results confirm the excellent performance of the receivers.

Dependence of the scatter of the electrical properties on local non-uniformities of the tunnel barrier in Nb/Al-AlOx/Nb junctions

In this paper, we study the effect of the tunnel barrier thickness non-uniformity in Nb/Al-AlOx/Nb tunnel junctions using the measurement results of the junctioncapacitance (C) and the normal resistance (Rn). The local thickness distribution of the AlOx tunnel barrier in Nb/Al-AlOx/Nb trilayer (RnA ∼ 30 Ω μm2) was studied by high resolution transmission electron microscopy. The specific resistance (RnA) values of the measured junctions range from 8.8 to 68 Ω μm2. We observed scatter in both the junction specific resistance and capacitance data, which is considerably higher than the measurement uncertainty. We also observed noticeable scatter in the RnC product, which does not stem from junction area estimation uncertainties. We discuss the possible reasons that contribute to this scatter. We suggest that the local thickness non-uniformity of the tunnel barrier significantly contributes to the scatter in the RnC product. We confirm this conclusion through an illustrative model based on the barrier imaging data, which results in the variation of the RnC data consistent with the measurements in this paper.

THz Frequency Up-Conversion using Superconducting Tunnel Junction

In this letter we present the characterization of the first frequency up-converter using distributed superconducting tunnel junctions. The power of the frequency up-converted signal was large enough to pump an SIS mixer. The efficiency of the distributed superconducting tunnel junction is 11-22 % for a fractional bandwidth of 7% with excellent spectral line purity. The -3 dB line width of the up-converter signal is better than 1 Hz, which was the lowest resolution bandwidth of the spectrum analyzer.