Shinichiro Asayama

Ultra-Low Noise Photonic Local Oscillator at 100 GHz

Noise at millimeter wavelengths from a photonic local oscillator (LO) is compared with that from a Gunn oscillator using a low-noise superconductor-insulator-superconductor (SIS) receiver. No significant additional noise is added to the receiver by the photonic LO in the frequency range of 96–110 GHz.

A 385-500 GHz Low Noise Superconductor-Insulator- Superconductor Mixer for ALMA Band 8

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 probes 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.

Numerical Matrix Analysis for Performances of Wideband 100GHz Branch-Line Couplers

The wideband waveguide 3-dB branch-line coupler suitable for use in SSB heterodyne receivers in radio astronomy is designed and its performances are reported. The coupler is designed by a numerical analytical method by using matrices based on the circuit theory and has good performances in the range of frequencies from 84GHz to 116GHz.The numerical analytical method presented in this manuscript enables quick calculations for performances of RF components and possesses advantages over electromagnetic simulation software in common use.

A Fixed-Tuned W-Band Waveguide SIS Mixer with 4.0-7.5 GHz IF

The design and performance of a fixed-tuned W-band SIS mixer with a wide band IF of 4.0-7.5 GHz is presented. Waveguide-to-stripline transition of the SIS mixer is designed using the lumped-gap-source port provided by HFSSTM. Measured receiver noise temperature is less than 25 K in the frequency range of 95-120 GHz, with a minimum value of around 19 K achieved. Mixer noise temperature is determined to be about 8.5 K, which is around twice the quantum limit (i.e., 2hw/k). In spite of the high IF frequencies (f0 = 6 GHz), the performance of the SIS receiver is comparable or even superior to those of the best mechanically-tunable waveguide SIS receivers at low IF frequencies (f0 = 1.5 GHz). This result suggests that it is easy to design waveguide-to-stripline transitions without scale-model measurements.

Design and Development of a Hybrid-Coupled Waveguide Multiplexer for a Multiband Receiver

This paper describes a waveguide hybrid-coupled multiplexer for frequencies around 400 GHz. The designed multiplexer has three bands with 25-GHz bandwidth and no frequency gap between channels. The multiplexer is composed of two identical waveguide branch-line quadrature hybrid couplers and two identical bandpass filters based on waveguide inductive iris windows. In order to find the critical element of the multiplexer, network analysis was carried out using signal flow graphs. The multiplexer was fabricated based on direct machining technology with machining accuracy in the order of a few microns. S-parameters measured with a vector network analyzer show excellent agreement with simulations.

Reconfigurable Near-Field Beam Pattern Measurement System From 0.03 to 1.6 THz

With the discovery and utilization of great observation sites, on-ground radio astronomical observations have been extended from the millimeter-wave (mm-wave) range to around 1.6 THz. The radiation collected by the telescope reflector antenna is coupled to the receiver by means of the receiver optics. These optics must be designed to match the in-coming fields from the telescope and properly characterized by amplitude and phase measurements. This paper presents a reconfigurable near-field beam pattern measurement system which can characterize magnitude and phase patterns of antennas and optics from the mm-wave to the THz region. Measurements at 900 GHz and 1.37 THz are presented for two different configurations, using different phase-lock components, and measured under cryogenic and room-temperature conditions, respectively.

ALMA band 10 (787-950 GHz): summary of the production of 73 receivers and first light results

This paper summarizes the performance of all the 73 ALMA band 10 cartridges in terms of noise performance and/or optical efficiencies compared to the required ALMA specifications. In particular, the measured optical performance is compared with the results of novel statistical Monte Carlo analyses carried out before receiver production. Some of the technical difficulties encountered during production are briefly described. Finally, some of the first light results of the first receivers used in Chile are presented.

ALMA array element astronomical verification

The Atacama Large Millimeter/submillimeter Array (ALMA) will consist of at least 54 twelve-meter antennas and 12 seven-meter antennas operating as an aperture synthesis array in the (sub)millimeter wavelength range. The ALMA System Integration Science Team (SIST) is a group of scientists and data analysts whose primary task is to verify and characterize the astronomical performance of array elements as single dish and interferometric systems. The full set of tasks is required for the initial construction phase verification of every array element, and these can be divided roughly into fundamental antenna performance tests (verification of antenna surface accuracy, basic tracking, switching, and on-the-fly rastering) and astronomical radio verification tasks (radio pointing, focus, basic interferometry, and end-to-end spectroscopic verification). These activities occur both at the Operations Support Facility (just below 3000 m elevation) and at the Array Operations Site at 5000 m.

Exploration of Southern Sky with Atacama Submillimeter Telescope Experiment (ASTE)

The Atacama Submillimeter Telescope Experiment (ASTE) is a joint project between Japan and Chile to install and operate a 10 m high precision telescope for exploration of the Southern sky at submillimeter wavelengths. Due to the excellent atmospheric conditions at the site, Pampa la Bola (4800 m) in the Atacama desert in northern Chile, ASTE offers an unique opportunity to make extensive submillimeter observations. We successfully started scientific observations in August 2003 at 800, 500, and 350 GHz bands.

275–500 GHz Waveguide Diplexer to Combine Local Oscillators for Different Frequency Bands

Development of local oscillator (LO) sources based on amplifier multiplier chains (AMC) have steadily progressed in recent years, with more power and more bandwidth available at mm and sub-mm wavelengths. Recent radio astronomy receiver projects are, however, aiming at duplicating the RF bandwidth, with fractional bandwidth around 60%, even at frequencies as high as 500 GHz. In particular, National Astronomical Observatory of Japan (NAOJ) is developing wideband SIS mixers for a combined Atacama Large Millimeter/Submillimeter Array (ALMA) band 7 and 8 receiver, extending from 275 to 500 GHz. Currently, LO sources are not available for such a wide frequency band. To solve this problem, we have developed a waveguide diplexer to combine the output power of two different LO sources for ALMA band 7 (275–373 GHz) and band 8 (385–500 GHz). The proposed waveguide diplexer is based on hybrid couplers and waveguide filters. Two units of the designed component have been fabricated and S-parameters have been measured with good agreement with simulations. Initial tests to combine the LO power of band 7 and 8, LO sources at cryogenic temperature to pump a wideband 275–500 GHz SIS mixer have been successful.