(Antenna) 2018 @
Effelsberg 100m Greenbank 100m Arecibo 300m Telescope 2
The Very Large Array (VLA) [2011, K. Jansky VLA] 3
( ) (Frontend) (Backend) 4
Instrument to transform guided wave in transmission line to free space wave Feed horn Electric circuits I E Instrument to transform free space wave to guided wave 5
Dipole Monopole Yagi Helix Patch Horn Parabolic 6
( : KVN 21m ) Main Reflector Panels Quadrupod Subreflector Vertex Window Az Bearing Back Up Structure Receiver Cabin Yoke Arm Yoke Base Pedestal 7
. (sub-reflector) a + b = -> : a + b +c = -> : ( ) 포물면은원형파를평면파로 ( 혹은그반대로 ) 바꿔주는역할을함. (main reflector) 쌍곡면 ( 또는타원면 ) 은초점을 2 차초점으로이동시켜주는역할을함. 8
( ) Each point on a primary wave front can be considered as a new source of a secondary wave Screen Slit (Aperture) d = slit size, mono-chromatic plane wave Θ = first zero position sinθ = λ d 9
-1 10
-2 (Far field) voltage pattern is a FFT of current distribution on aperture 11
- 3 ( ) - - Sidelobe 12
Shaped Cassegrain Cassegrain Feed horn Current Gaussian. Sidelobe Shaped Cassegrain Uniform Current ( ), Sidelobe KVN, JVLA, ATCA ( ) 13
Ω A = P n (θ, ϕ)dω G = 4π Ω A : Beam Solid Angle : Directivity Gain Ω MB = MB P n (θ, ϕ)dω : Main Beam Solid Angle η MB = Ω MB Ω A : Beam Efficiency 14
T A : W v = 1 2 A eff P n (θ, ϕ)i v (θ, ϕ)dω = kt A I v = 2kT b λ 2 : Rayleigh-Jeans Approx. Ω A = P n (θ, ϕ)dω : T b, T A = T b T A = P n(θ, ϕ)t b (θ, ϕ)dω P n (θ, ϕ)dω A eff Ω A = λ 2 15
(Aperture Efficiency ) -1 W v = 1 2 A eff S v S v : f lux density (W/m 2 /Hz) η A = W v received W v incident = A eff A p < 1 η A = η sf η taper η block η spill η l 16
(Aperture Efficiency ) -2 (Surface Accuracy) * Ruze s expression η sf = e (4πσ/λ)2 σ = r.m.s of surface error For σ = λ/16, η sf = 0.5. -> σ(el) -> η(el) -> G(EL) 17
- Photogrametry Swing Template Theodolite Photogrametry Radio Holography 18
Radio Holography Complex Voltage Beam Pattern FFT => Current => SRAO 6m Holography ( ) ( ) - 2003 19
Homology Design Active Surface Control / : Homology ( ) Design ) Effelsberg 100m, IRAM 30m Active Surface Control Actuator Actuator Laser Ranging, ) GBT 100m, SHAO 65m 20
Gain Curve of GBT at 20GHz from R.N. Prestage + 21
Beam Shapes of GBT at 20GHz from R.N. Prestage + 22
Radome 과 Membrane 햇빛, 바람에 의한 변형으로 부터 보호 경면 정밀도 / 포인팅 TRAO 14m JCMT 15m 전파겨울학교 2018 @ 울산대학교 23
Prime Focus Feed Horn Cassegrain Focus ( ) 24
Offset Type no blockages low sidelobe level Naysmith & Beam Wave Guide 25
22GHz Beam from subreflector 43GHz 129GHz 86GHz
WSRT Beam Rotation on the Sky 27
,,, / 28
Pointing Accuracy Example : Pointing Observation Results of SRAO Blue : pointing > pointing model Red : pointing model 29
(Pointing Model) A encoder = A cmd + A, E encoder = E cmd + E A = IA + CA sec(e) + NPAE tan(e) + AN tan(e) sin(a) AW tan(e) cos(a) + A obs sec(e) E = IE + GF cos(e) + AN cos(a) + AW sin(a) + R(P s,t s,rh,e) + E obs Multiplicative effect on Azimuth Elevation AN Az axis misalignment in N-S tan(e) sin(a) cos(a) AW Az axis misalignment in E-W -tan(e) cos(a) sin(a) NPAE Non-perpendicularity btw. Az & El axes tan(e) 0 CA Collimation error of RF axis sec(e) 0 IA Az encoder zero offset 1 0 IE El encoder zero offset 0 1 GF Gravitational Flexure correction at horizon 0 cos(e) 30
Servo [ KVN ] Tracking Accuracy [<1 arcsec] Slewing Speed [3 deg/s] Acceleration / Deceleration Rate [3 deg/s^2] Lowest Resonance Frequency (Stiff Structure) [2Hz] Settling Time (control loop) Operational Wind Speed [10m/s] OFF ON 31
Slewing Speed KVN 21m NRO45m 32
(Hexapod) X Y Z 33
Z (FOCUS) (Z) 34
- KVN X,Y,Z,Tilt,Tip Otf ( Five / Cross) 35
Cross Scan - KVN ------------------------------------------------------------ X Y Z Tip Tilt El ------------------------------------------------------------ -1200-2000 -200-1100 -70 68.2-1200 -500-200 -800-70 68.2-1200 +1000-200 -500-70 68.3-1200 +2500-200 -200-70 68.3-1200 +4000-200 +100-70 68.3 ------------------------------------------------------------ AzOff ElOff AzBw ElBw AzPk ElPk AzPc ElPc ------------------------------------------------------------ +3.15 +2.32 31.65 33.50 7.90 7.76 8.01 7.97 +2.38 +2.36 31.83 32.48 8.48 8.40 8.60 8.53 +0.57 +0.73 32.59 33.31 8.70 8.78 8.71 8.79-0.73-0.57 32.70 33.96 8.21 8.18 8.22 8.19-1.27-0.34 32.18 33.43 7.39 7.58 7.39 7.61 ------------------------------------------------------------ 36
, XModelCor = Xcoeff[0] YModelCor = YCoeff[0] + YCoeff[1] sin(el) + YCoeff[2] cos(el) (Ycoeff[1] = 0, 2 ) ZModelCor = ZCoeff[0] + ZCoeff[1] sin(el) + ZCoeff[2] cos(el) (Zcoeff[2] = 0, 2 ) TiltModelCor = TiltCoeff[0] TipModelCor = TipCoeff[0] + TipCoeff[1] sin(el)+ TipCoeff[2] cos(el) (Tipcoeff[1] = 0, 2 ) ElModelCor = ElCoeff[0] YModelCor + ElCoeff[1] TipModelCor 37
- KVN (Normalized Gain Curve) KVN ( ) 22GHz 43GHz 86GHz 129GHz (deg) 38
H 2 O O 2 O 2 H 2 O H 2 O and O 2 T A = T source e τ + T atm (1 e τ ) + T rx (> 230GHz) (> 2km) - Scale height of H 2 O ~ 2 km No H2O - Scale hight of O 2 ~ 7 km ν < ν Plasma. ν Plasma ~ 11 MHz at daytime (Radio Frequency Interference) 39
The Five-hundred-meter Aperture Spherical Telescope: FAST 0.07-3 GHz RFI 40
Atacama Large Millimeter Array (ALMA) - Operation Frequency ~ 1THz (λ=0.3mm) - Chile s Atacama desert at altitude of 5km above sea level 전파겨울학교 2018 @ 울산대학교 41
The Square Kilometer Array : SKA SKA-low in Australia 130,000 dipoles, 65km 50 350MHz SKA-mid in South Africa 200 dishes, 150km 0.35-1.8 / 4.8-13.8GHz 42
/ / / 43
Tools of Radio Astronomy, T.L. Wilson, K. Rohlfs, and S. Hüttemeister Introduction to VLBI Systems, Tetsuo Sasao and Andrė B. Fletcher The Primary Antenna Elements, in Synthesis Imaging in Radio Astronomy, Napier, P.J. (1989) 44