• Journal of Astronomy and Space Sciences
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• v.23 no.1
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• pp.19-28
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• 2006

The noise temperature of existing millimeter-wave receivers is already within two or three times quantum noise limit. One of practical ways to increase the observation speed of single dish radio telescope without longer integration time is use of multi-beam focal plane array receiver as demonstrated in several large single dish radio telescopes. In this context the TRAO (Taeduk Radio Astronomy Observatory), which operates a 143n Cassegrain radio telescope, is planning to develop a 4 x 4 beams focal plane array SIS receiver system for 86-115 GHz band. Even though millimeter-wave HEMT LNA-based receivers approach the noise temperature comparable to the SIS receiver at W-band, it is believed that the receiver based on SIS mixer seems to offer a bit more advantages. The critical part of the multi-beam array receiver will be sideband separating SIS mixers. Employing such a type of SIS mixer makes it possible to simplify the quasi-optics of receiver. Otherwise, an SSB filter should be used in front of the mixer or some sophisticated post-processing of observation data is needed. In this paper we will present a preliminary design concept and components needed for the development of a new 3 mm band multi-beam focal plane array receiver.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.6
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• pp.90-98
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• 1996

We have evaluated the theoretical conversion loss and noise temperature of mixer using the quantum mixer theory and the method to determine the embedding impedance of waveguide-type mixer mount. At fixed backshort position of the mixer, the calculated SSB mixer conversion loss and mixer noise temperature are 5 dB and 10K within frequency range form 85 GHz to 115 GHz, respectively. The SIS mixer has been developed by using through on the calculated rsutls to observe cosmic radio waves. SIS junction of mixer is Nb/Al-AlOx/Nb and it consists of four series array. Area of each of junction is about 2.5${\mu}m^{2}$. The average receiver noise temperature of manufactured receiver with this mixer is about 30 K(DSB). The receiver noise temperature is much lower than that of receiver with a mixer using mechanical tuning backshort.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.737-743
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• 2004

A fixed-tuned SIS(Superconductor-Insulator-Superconductor) mixer across 120∼180 GHz band has been developed. This mixer employs an SIS chip fabricated by Nobeyama radio observatory which consists of a series array of 6 Nb/Al-Al$_2$O$_3$/Nb junctions in a microstrip line on a fused quartz substrate. The SIS chip is placed at the center of the half-height waveguide mixer mount to have a good incoming signal coupling over the whole frequency band. No mechanical tuner was used in the SIS mixer and the RF signal and local oscillator power are injected to the mixer via a cooled cross-guide coupler. In order to prevent the IF signal loss, the If output impedance of the SIS mixer was matched to the 50 $\Omega$ input impedance of the IF chain. Measured double sideband noise temperatures of a receiver using the SIS mixer are 32∼131 K over 120∼180 GHz band. The developed SIS mixer is now in use for radio astronomical observations on the TRAO 14 m radio telescope.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.413-414
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• 1996

A 230 GHz SIS tunnel junction receiver has been being developed for radio astronomy in Nagoya University. In this heterodyne receiver, we use a $\~$1/3 reduced hight rectangular waveguide SIS mixer with two tuning elements as front end. The mixer block with SIS junction was cooled to 4K with a closed cycle He-gas refrigerator. So far, a double sideband receiver noise temperature lower than l00K in 222-237 GHz is obtained. The receiver exhibits a best DSB noise temperature of 69K at 236 GHz as well as 228 GHz.

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.9-9
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• 2004

• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.10
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• pp.12-19
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• 1993

Because of their high sensitivity and moderate bandwidth, superconducting receivers with SIS (Superconductor Insulator Superconductor) tunnel junction mixer are now widely used for millimeter wave radio astronomy. In this paper we have introduced how to determine the parameters of SIS tunnel junction which have to be optimized to achieve a good mixer performance. From these results of optimized junction parameters determined by this methods, SIS junctions which consist of a series array of four Nb/Al-AlOx/Nb junctions with each area 3.4${\mu}m^{2}$ have been fabricated by SNEP (Selective Niobium Etching Process) and RIE (Reactive Ion Eching). Also we have tested their DC current-voltage characteristics. These SIS junctions will be used as a mixer for 100GHz band cosmic waves receiver.

• Publications of The Korean Astronomical Society
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• v.27 no.3
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• pp.71-80
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• 2012

We have developed superconducting mixer receivers for 129 GHz VLBI observation in Korean VLBI Network (KVN). The developed mixer has a radial waveguide probe with simple transmission line L-C transformer as a tuning circuit to its 5 series-connected junctions, which can have 125 - 165 GHz as the operation radio frequency (RF). For intermediate frequency (IF) signal path a high impedance quarter-wavelength line connects the probe to one end of symmetric RF chokes. The double side band (DSB) receiver noise of the mixer was about 40 K over 4 - 6 GHz IF band, whereas we achieved the uncorrected single side band (SSB) noise temperature of about 70 K and better than 10 dB image rejection ratio in 2SB configuration with 8 - 10 GHz IF band. Insert-type receiver cartridges employing the mixers have been under commission for KVN stations.

• Journal of The Korean Astronomical Society
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• v.36 no.1
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• pp.43-48
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• 2003

We introduce and describe performance of the 6-meter telescope of Seoul Radio Astronomy Observatory (SRAO). All the softwares and instruments except the antenna structure and its driving system are developed for ourselves. The SIS mixer type receiver resulted in the receiver noise temperature less than 50 K (DSB) over the whole 3-mm radio window. An autocorrelation spectrometer, developed first in Korea, provides maximum 50 MHz band width over 1024 channels. Antenna surface is measured and adjusted using template method and radio holography which resulted in a superb surface accuracy bet-ter than 30${\mu}m$. Accordingly, the aperture and beam efficiences amount to $70\%$ and $75\%$, respectively, largely independent of frequency in the 85 - 115 GHz range. It is also found that telescope pointing errors are less than 10" in both azimuth and elevation and that antenna gain is almost constant against elevation greater than $20^{\circ}$, without adjusting sub-reflector position. The SRAO 6-meter telescope is now fully operational and all these characteristics verify that observations are carried out with high precision and fidelity.

• Journal of The Korean Astronomical Society
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• v.47 no.6
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• pp.319-325
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• 2014

We map two molecular clouds located in the exact anticenter region emitting in the (J = 1-0) transition of $^{12}CO$ and $^{13}CO$ using the 3-mm SIS mixer receiver on the 14-m radio telescope at Taeduk Radio Astronomy Observatory. The target clouds with anomalous velocities of $V_{LSR}{\sim}-20km\;s^{-1}$ are distinguished from other clouds in this direction. In addition, they are located in the interarm region between the Orion Arm and the Perseus Arm. Sizes of the clouds are estimated to be about 8.6 and 10.8 pc, respectively. The total mass is estimated to be about $4{\times}10^3$ $M_{\odot}$ using CO luminosity of the clouds. Several cores are detected, but no sign of star formation is found according to the IRAS point sources. Their larger linewidths, anomalous velocities, and their location at the interarm region make these clouds more distinguished, though their physical properties are similar to the dark clouds in the solar neighborhood in terms of mass and size.