A Compact Triple bands Receiver System for Millimeter-wave VLBI observations

Transcription

1 EVN symposium 2016 A Compact Triple bands Receiver System for Millimeter-wave VLBI observations Korea Astronomy and Space Science Institute (KASI) Seog-Tae Han and KVN receiver group sthan@kasi.re.kr September 2106, St. Petersburg, Russia

2 I. Motivation Why we need compact receiver optics; - Big optical bench (2.6m x 2.3m) with a lot of optical components - Individual receiver dewars such K-, Q-, W- and D-bands - Not so easy to align the beam among each channels - Difficult both to transport and to install with given limited space - Big cost impact KVN receiver optics 2.6m 2.3m

3 I-1 Conceptual design for simultaneous compact triple bands receiver - Wide band simultaneous observations - Optimal aperture efficiency for wide band [K/Q-band receiving system] 43GHz K Q 430mm Q K LPF 810 [K/Q/W-band receiving system] 580 W Q K 910 mm Height : 300~400mm Height : 300~400mm W Q K - Dewar size and optical bench are strongly depend on antenna specifications and given space of receiver cabin(room)

4 II. Design of Triple Band Optics BEFORE STARTING QUASI-OPTICAL CIRCRUIT DESIGN, WHAT WE HAVE TO DO Simultaneous observation for triple bands - Simple optical circuit with minimum number of optical components - Easy optical alignment among each bands Wide band operation Dual polarization IF band width - K-band : 18~26.5 GHz - Q-band : GHz R/L polarisaions 4 GHz or 8 GHz - W-band : GHzI In order to make optimal antenna aperture efficiency for wide band operation - Frequency Independent Image Beams (Seog-Tae Han and T.S. Chu) - Gaussian Beam Telescope (F. Goldsmith and Seog-Tae Han) were chosen to design the optical circuit Insertion loss and cross polarization - Dicroic filter such LPF(Low Pass Filter) and HPF(High Pass Filter) - Ellipsoidal mirror design Optical circuit and receiver system can be made as possible as compact - Transportation and installation

5 Triple band optical circuit HPF Beam from Sub-reflector Ellips mirror(1) Ellips mirror(4) LPF Ellips mirror(2) W-band K-band Q-band 640 mm Ellips mirror(3) 680 mm

6 LPF Ellipsoidal Mirror Q-band K-band W-band 640mm HPF Cryogenic dewar LPF Q-band horn K-band horn W-band horn Height 300mm~400mm HPF 940mm

7 Radiation patterns of 21m KVN Antenna Obtained by GRASP including triple band optical circuit which are radiated from ideal Gaussian beams. GRASP(General Reflector Antenna Software Package), TICRA, Denmark

8 The Evaluation Results of Quasi-optical Circuit The constant edge taper at sub-reflector are maintained over the wide band Make sure of optimal aperture efficiency given observation frequency range Band Freq. [GHz] Theoretical Values FWHM(arcsec) GRASP Observational Results (By KVN antenna) Theore. Values Side lobe Level [db] Observation Results Beam radius at subreflector[mm] K-band Edge Taper [db] Q-band W-band [Ref.] Seog-Tae Han et al., Korean VLBI Network Receiver Optics for Simultaneous Multifrequency Observation : Evaluation, PASP 125, , (2013).

9 Real triple band optical circuit Under the testing, it will be finished until the end of this year HPF EM4 EM5 LPF EM1 640 mm EM2 EM3

10 3-1. HPF(High Pass Filter) and LPF(Low Pass Filter) : Measured properties - Very much critical component for receiver performance - Losses for all bands : less than 0.2dB, - Cross polarization : lower than 25 db - Developed by QMC, Wales [HPF] [LPF] 33~50GHz Reflection 80~115GHz Transmission 18~26 GHz Transmission 35~50GHz Reflection

11 3-2. Compact and Wide band Circular Polarizers 1) Q-band Polarizer Developed by Dr. Moon-Hee Chung(KASI) 2) W-band Polarizer 3) W-band OMT TE01mode TE10 mode

12 3-3. Compact Spline profile feed horns Developed by Dr. Moon-Hee Chung(KASI) * Compact spline profile feed horns are chosen to reduce size of dewar Reduced the length to 1/2 or 1/3 for conventional corrugated feed horn 128 mm Q-band 3-4. Cryogenic chamber vacuum window for wide band operation K-band Single Teflon sheet Multi-layer dielectric sheet for wide band

13 (built by antenna company in Korea : High Gain Antenna Co.) - 22/43GHz simultaneous observation as KVN does : Radio astronomy * Aperture efficiency : 22GHz : : 54% * Pointing accuracy is good enough to carry out 86GHz observation * Expected aperture efficiency at 86GHz to be more than 50% We are discussing on compact triple band receiver to be installed on that

14 Summary 2300mm 640mm Ellipsoidal Mirror HPF LPF 940mm 2600mm K-band W-band Q-band KVN receiver optics Compact triple band receiver

15 Simultaneous SUPER ultra wide band receiver for VLBI BRAND receiver Triple band receiver LPF Callisto company Q-band K-band W-band Proposed by Dr. Walter Alef HPF 1.5 GHz 15.5GHz 18-27GHz GHz GHz IF chain IF bandwidth : 4 GHz or 8 GHz DBBC 3 (0 ~15.5GHz)

16 Summary-1 Evauation of designed optical circuit has been carried out by GRASP - FWHM, constant edge taper and aperture efficiency as function of frequency Possible to design simultaneous observation for more higher frequency such as GHz/230 GHz/350 GHz - 43 GHz/86 GHz/230 GHz - 86 GHz/230 GHz Optical circuit test - will be finished until the end of this year Somebody has asked me frequently Why didn t you make compact triple band receiver? when KVN project started in 12 years ago

17 Not only I am very much proud of my colleagues and their achievements, But also I would like to really appreciate for their efforts and passions for KVN Thanks for your attention 17