The 45-m telescope is one of the most important millimeter wave single dish telescope in the ALMA era. The 45-m telescope has undergone a major upgrade, with an installation of three new 100-GHz band receivers (Nakajima et al. 2008; 2012), an intermediate frequency (IF) transmission system, an Analogue-to-Digital Converter (ADC) with a sampling rate of 4 GHz, and a new 32 GHz wide spectrometer (Kamazaki et al. 2012). These instruments are called "new observation system".
The 100-GHz band SIS receivers are the most important ones for this telescope, because they cover the highest frequency range of this telescope and also there are fundamental transitions of carbon-monoxide (CO) line in this band. Two type SIS receivers in 100-GHz band are operated in the old observation system. One is S80/S100, which is single-beam, one-polarization, and single-sideband (SSB) operation mode. Another one is BEARS (SIS 25-BEam Array Receiver System). This receiver is 25 multi-beam, one-polarization, and double-sideband (DSB) operation mode (Sunada et al. 2000; Yamaguchi et al. 2000). However, both of the receivers were developed more than 10 years ago, thus the receiver noise temperatures are higher than the other receivers in 100 GHz band in the world. Therefore, we are developing three type new sideband separating (2SB) SIS receivers in new observation system. The single-beam receiver named T100, the 2-beam receiver named TZ, and new multi-beam array receiver named FOREST (FOur-beam REceiver System for the 45-m Telescope).
We have developed a new multi-beam waveguide-type dual-polarization sideband-separating SIS receiver system in 100 GHz band on the 45-m radio telescope at the Nobeyama Radio Observatory, Japan. This receiver has four (=2×2) beams, with about 16" of the HPBWs at 100 GHz. It has 44" of beam separation and allows on-the-fly (OTF) mapping observation. The receiver of each beam is composed of an OMT and two 2SB mixers, both of which are based on a waveguide technique, and has four intermediate frequency bands of 4.0-8.0 GHz for LSB and 4.0-12.0 GHz for USB. The SSB receiver noise temperatures of each sideband were measured to be lower than approximately 50 K over an RF frequency range of 85-115 GHz. The new receiver system was installed in the telescope, and we successfully observed a 12CO (J=1-0) emission line toward a IRC+10216 on May 19, 2011.
Development of a New Multi-Beam Array
Reference
Nakajima, T. et al., "Development of a New Multi-Beam Array 2SB Receiver in 100 GHz Band for the NRO 45-m Radio Telescope", Proc. of the 23rd International Symposium on Space Terahertz Technology, P-12, 2012
Minamidani, T. et al., "Development of the New Multi-Beam 100 GHz Band SIS Receiver FOREST for the Nobeyama 45-m Telescope", Proc. of SPIE 9914, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VIII, 99141Z (07/2016)