ngVLA Reference Design Development & Performance Estimates (October 2018)

 
Preliminary (revB) ngVLA Configuration

A preliminary configuration map for all 244 antennas including the Main Array and the LBA.

The next generation Very Large Array (ngVLA) is  an astronomical observatory  designed to operate in a frequency coverage of ~1.2 -- 116 GHz with up to 20 GHz of instantaneous sampled bandwidth. The observatory will be a non-reconfigurable synthesis radio telescope operating in a phased or interferometric mode. The ngVLA is designed to accommodate a wide variety of scientific observations at centimeter-to-millimeter wavelengths aiming to deliver high sensitivity over a wide range of resolutions. The ngVLA array design includes three fundamental subarrays: the main interferometric array, the short baseline array and the long baseline array. 

Antennas within the main array are distributed over a range of physical scales and with different geometries: (a) a dense core which provides high surface brightness sensitivity at ~ 1,000 mas resolution; (b) a multi-arm spiral capable of high-fidelity imaging at ~ 10 mas scales; (c) longer arms which provide mid-scale baselines for imaging at ~ 1 mas.

The main array will be augmented by a very compact array of smaller antennas (SBA) which will provide sensitivity on larger angular scales, and four antennas of the main array will be equipped to measure total power in order to fill in the center of the (u,v)-plane.  Additionally, a long baseline array (LBA) consisting of several outlying stations will provide intercontinental-scale baselines for achieving resolutions of ~ 0.1 mas. The design of the array configuration is practical, accounting for logistic limitations such as topography, utility access, local RFI sources and land managements/availability.

The first table below provides the current baseline receiver configuration, while the second table gives the key imaging performance. Imaging sensitivity is estimated based on a similar procedure as shown in ngVLA Memo # 16  and provided as a function of angular resolution in the key performance metrics table. The table is by necessity a simplification and the imaging sensitivity will vary from these reported values depending on the quality of the (sculpted) synthesized beam required to support the science use case. 

A sensitivity calculator is currently being developed based on such investigations and will eventually supersede the values included in performance metric table below.

 

ngVLA Baseline Receiver Configuration

Band # Dewar fL
GHz
fM
GHz
fH
GHz
fH:fL BW
GHz
1 A 1.2 2.0 3.5 2.92 2.3
2 B 3.5 6.6 12.3 3.51 8.8
3 B 12.3 15.9 20.5 1.67 8.2
4 B 20.5 26.4 34.0 1.66 13.5
5 B 30.5 39.2 50.5 1.66 20.0
6 B 70.0 90.1 116.0 1.66 46.0

 

 

Next Generation VLA Key Performance Metrics
Parameter [units] 2.4 
GHz

GHz
16
GHz
27
GHz
41
GHz
93
GHz
Notes
Band Lower Frequency, fL [GHz] 1.2 3.5 12.3 20.5 30.5 70.0 a
Band Upper Frequency, fH [GHz] 3.5 12.3 20.5 34.0 50.5 116.0 a
Field of View FWHM [arcmin] 24.3 7.3 3.6 2.2 1.4 0.6 b
Aperture Efficiency [%] 0.77 0.76 0.87 0.85 0.81 0.58 b
Effective Area, Aeff x 103 [m2] 47.8 47.1 53.8 52.6 50.4 36.0 b
System Temp, Tsys [K] 25 27 28 35 56 103 a, f
Max Inst. Bandwidth [GHz] 2.3 8.8 8.2 13.5 20.0 20.0 a
Antenna SEFD [Jy] 372.3 419.1 372.1 485.1 809.0 2080.5 a, b
Resolution of Max. Baseline θmax [mas] 2.91 0.87 0.44 0.26 0.17 0.07 c
 
Naturally Weighted Sensitivity
             
Continuum rms, 1 hr [μJy/beam] 0.38 0.22 0.20 0.21 0.28 0.73 d
Line Width, 10 km/s [kHz] 80.1 266.9 533.7 900.6 1367.6 3102.1  
Line rms, 1 hr, 10 km/s [μJy/beam] 65.0 40.1 25.2 25.2 34.2 58.3 d
Projected Imaging Sensitivity
 
 
Resolution θ1/2 [mas]
1000
 
Continuum rms, 1 hr, Robust [μJy/beam] 0.52 0.34 0.35 0.39 0.59 2.24 e
Line rms 1 hr, 10 km/s Robust [μJy/beam] 88.9 61.1 43.3 47.9 70.9 179.6 e
Brightness Temp (TB) rms continuum, 1 hr, Robust [K] 0.1107 0.0064 0.0017 0.0007 0.0004 0.0003 e
TB rms line, 1 hr, 10 km/s, Robust [K] 18.76 1.16 0.21 0.08 0.05 0.03 e
Resolution θ1/2 [mas]
100
 
Continuum rms, 1 hr, Robust [μJy/beam] 0.50 0.30 0.27 0.28 0.40 1.14 e
Line rms 1 hr, 10 km/s Robust [μJy/beam] 85.0 53.6 33.6 34.8 48.4 91.3 e
Brightness Temp (TB) rms continuum, 1 hr, Robust [K] 10.58 0.56 0.13 0.05 0.03 0.02 e
TB rms line, 1 hr, 10 km/s, Robust [K] 1794.1 101.9 15.9 5.8 3.5 1.3 e
Resolution θ1/2 [mas]
10
 
Continuum rms, 1 hr, Robust [μJy/beam] 0.41 0.27 0.26 0.27 0.38 0.97 e
Line rms 1 hr, 10 km/s Robust [μJy/beam] 69.9 48.3 32.4 33.2 46.3 77.7 e
Brightness Temp (TB) rms continuum, 1 hr, Robust [K] 870.58 50.51 12.42 4.53 2.77 1.36 e
TB rms line, 1 hr, 10 km/s, Robust [K] 1E5 9173 1540 555 335 109 e
Resolution θ1/2 [mas]
1
 
Continuum rms, 1 hr, Robust [μJy/beam] -- 20.87 0.31 0.21 0.29 0.90 e
Line rms 1 hr, 10 km/s Robust [μJy/beam] -- 3789.8 38.2 25.7 34.7 72.0 e
Brightness Temp (TB) rms continuum, 1 hr, Robust [K] -- 4E5 1466 350 207 126 e
TB rms line, 1 hr, 10 km/s, Robust [K] -- 7E7 2E5 42813 25073 10119 e
Resolution θ1/2 [mas]
0.1
 
Continuum rms, 1 hr, Robust [μJy/beam] -- -- -- -- -- 20.96 e
Line rms 1 hr, 10 km/s Robust [μJy/beam] -- -- -- -- -- 1683.2 e
Brightness Temp (TB) rms continuum, 1 hr, Robust [K] -- -- -- -- -- 294732 e
TB rms line, 1 hr, 10 km/s, Robust [K] -- -- -- -- -- 2E7 e
(a)  6-band 'baseline' receiver configuration.
(b) Reference design concept of 244 18m aperture antennas. Unblocked aperture with 160 µm surface.
(c) Current reference design configuration ('Spiral214' + LBA). Resolution in EW axis.
(d) Point source sensitivity using natural imaging weights, dual polarization and all baselines
(e) Using Weights  scaled by frequency.
(f) At the nominal mid-band frequency shown. Assumes 1mm PWV for W-band, 6mm PWV for others; 45 deg elev. on sky for all.