Bhushan Billade

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.

An SIS Mixer With

We present the design and the performance of a fixed-tuned, all niobium (Nb) Superconductor-Insulator-Superconductor (SIS) mixer covering RF frequencies from 163 to 211 GHz with 4-8 GHz IF bandwidth. The mixer uses two Nb/Al-AlOx/Nb junctions of size 3 μm2 each with the RnA product of 30 Ω·μm 2, in a twin junction configuration. An local oscillator (LO) directional coupler made of superconducting lines with slots in the ground plane is integrated on the SIS mixer chip. The isolated port of the LO coupler is terminated using a wide-band resistive load with a sheet resistance of 12 Ω/□. The SIS tuning circuitry is optimized to achieve best power match between the twin junctions and the embedding circuitry. The measurement of the double sideband mixer noise at 171 GHz shows that the receiver noise temperature is approximately 17 K, which is just 2 hf/k. The estimated noise contribution from the RF loss and the IF chain at 176 GHz LO frequency is 8 K and 7.5 K respectively, resulting in a SIS mixer noise of hf/2k . The mixer noise performance across the entire RF band varies between 19 to 25 K. This is to our knowledge the best reported noise temperature at these frequencies till now.

2hf/k

We report the first experimental off-chip detection of frequency multiplication in a distributed array of superconductor-insulator-superconductor (SIS) junctions. A test device consisting of series array of 68 Nb/Al-AlOx/Nb tunnel junctions was designed to study generation of the second harmonic in the 190-210 GHz band. The SIS array was exited with microwave radiation at 3-mm band using a quasi-optically coupled Gunn oscillator, and the output response of the device was studied using a double-sideband SIS mixer operating in the 163-211 GHz range with 4-8 GHz IF bandwidth. We measured extremely sharp spectral signals, associated with the ×2 frequency multiplication by the SIS array. Single- and multi-photon processes were observed in the response of SIS tunnel junction-array to the applied microwave radiation, confirming device operation in the quantum mode. The output power of the multiplied signal increases linearly with the power of the pumping signal up to certain level and them saturates. In attempt to verify that the device produces noticeable power, the output of the test device was connected to the LO port of the SIS mixer, and an increase of 10%-20% in the SIS mixer dark current was observed. Further development of the demonstrated principle of frequency multiplication may lead to a practical frequency multiplier device.

DSB Noise Temperature at 163–211 GHz Band

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.

Experimental Study of Frequency Multiplication in a Distributed Array of SIS Junctions

A new receiver for the Onsala 20 m antenna with the possibility of being equipped with 3 mm and 4 mm bands has been built and the 3 mm channel has been commissioned during the Spring 2014. For single-dish operation, the receiver uses an innovative on-source/off-source optical switch. In combination with additional optical components and within the same optical layout, the switch provides two calibration loads (for the 3 mm and 4 mm channels), sideband rejection measurement, and tuning possibilities. The optical layout of the receiver employs all cold (4 K) offset elliptical mirrors for both channels, whereas the on-off switch employs flat mirrors only. The 3 mm channel employs a sideband separation (2SB) dual polarization receiver with orthomode transducer (OMT), 4-8 GHz intermediate frequency (IF), x? 2pol x? upper and lower sidebands (USB? +? LSB). The cryostat has four optical windows made of high density polyethylene (HDPE) with anti-reflection corrugations, two for the signal and two for each frequency band cold load. The cryostat uses a two-stage cryocooler produced by Sumitomo HI? RDK? 408D2 with anti-vibration suspension of the cold-head to minimize impact of the vibrations on the receiver stability. The local oscillator (LO) system is based on a Gunn oscillator with aphase lock loop (PLL) and four mechanical tuners for broadband operation, providing independently tunable LO power for each polarization. This paper provides a technical description of the receiver and its technology and could be useful for instrumentation engineers and observers using the Onsala 20 m telescope.

SEPIA - a new single pixel receiver at the APEX Telescope

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.

A new 3 mm band receiver for the Onsala 20 m antenna

ALMA, Atacama Large Millimetre Array, covers the frequency band from 30 GHz to 960 GHz in ten separate frequency bands. We present here the design and performance of the ALMA Band 5 receiver cartridge that covers 163–211 GHz. The Band 5 receiver shows the state-of-the-art performance with the noise temperature below 65K (SSB) and sideband rejection above 12 dB over 80% of the RF band.

Superconducting 4–8 GHz IF Hybrid for Low Noise mm-Wave Sideband Separation SIS Receiver

This paper presents design of a novel coupler for the injection of calibration signal into the RF path of the SKA Band 1 quad-ridged flared horn, covering frequencies from 350–1050 MHz. The coupler is integrated in the feed horn and provides a coupling factor of −35 dB. The calibration signal is injected before the first amplification stage, without any degradation in the noise performance of the room temperature system.

Design and performance of ALMA band 5 receiver cartridge

A new quadruple-ridge flared horn with numerically defined profiles by spline function is proposed for Band B of the Wide Band Single Pixel Feed (WBSPF) Advanced Instrumentation Programme for SKA in the paper. Optimization for high aperture efficiency on the spline-profiles have been carried out, resulting in that the aperture efficiency is higher than 65% over 4.6-20 GHz and reflection coefficient is below -10 dB.

Integrated calibration noise coupler for room temperature SKA band 1 feed system

The Square Kilometre Array (SKA) Project is a global science and engineering project realizing the next-generation radio telescopes operating in the metre and centimetre wavelengths regions. This paper addresses design concepts of the broadband, exceptionally sensitive receivers and reflector antennas deployed in the SKA1-Mid radio telescope to be located in South Africa. SKA1-Mid (350 MHz – 13.8 GHz with an option for an upper limit of ~24 GHz) will consist of 133 reflector antennas using an unblocked aperture, offset Gregorian configuration with an effective diameter of 15 m. Details on the unblocked aperture Gregorian antennas, low noise front ends and advanced direct digitization receivers, are provided from a system design perspective. The unblocked aperture results in increased aperture efficiency and lower side-lobe levels compared to a traditional on-axis configuration. The low side-lobe level reduces the noise contribution due to ground pick-up but also makes the antenna less susceptible to ground-based RFI sources. The addition of extra shielding on the sub-reflector provides a further reduction of ground pick-up. The optical design of the SKA1-Mid reflector antenna has been tweaked using advanced EM simulation tools in combination with sophisticated models for sky, atmospheric and ground noise contributions. This optimal antenna design in combination with very low noise, partially cryogenic, receivers and wide instantaneous bandwidth provide excellent receiving sensitivity in combination with instrumental flexibility to accommodate a wide range of astronomical observation modes.