The Next Generation Very Large Array (ngVLA) project to replace the VLA telescope in New Mexico is just beginning. As a part of the initial Community Studies phase, we have contributed the concept design of a 15m feed-low wheel and track design. This telescope, the Next Generation Dish Verification Antenna 15m (ngDVA-15) follows on from the DVA-1 and DVA-2 antennas developed at the Dominion Radio Astrophysical Observatory (DRAO) between 2012 and the present day. This paper will concentrate on the design and optimization process for the ngDVA-15 back-up structure. Topology and free-size optimization were used to develop the initial design concepts. Both methods helped to steer the back-up structure in the initial design phase, but ultimately engineering intuition also played a role. Topology optimization can lead directly to useful solutions in some cases but hardware and software limitations still limit the physical size of the model. Also, topological routines cannot yet correctly model truss-type networks with no moment transfer at the joints, and optimizing structures with only gravitational loads proved to be challenging for the current generation of optimization routines. Size optimization was also used once the design was sufficiently refined. The initial stage of design involved minimization of reflector surface deflections under gravitational loads only. FEA modelling of surface deflections together with in-house developed fitting algorithms were used to determine primary surface accuracy. Surface accuracies of better than 80 microns RMS were achieved which met the initial design goal for telescope operation at 120GHz.
Dish Verification Antennae (DVA)–1 demonstrates excellent performance at L-band and can operate reasonably up to 10 GHz. However, with recent technological advances, there is a push towards the development of high frequency radio telescopes up to Q-Band and more. As an attempt to demonstrate the capabilities of the composite radio telescopes at higher frequency range (up to Q-Band), a DVA–2 is currently under construction. In this article the authors will elaborate the design path towards the improved carbon based secondary dish support structure (SDSS) for the DVA–2. In DVA–1, the secondary support structure was directly connected to the secondary reflector at four points. At various gravity loads, it is observed in finite element analysis (FEA) that the distortion from the feed platform and adjacent structures are directly transferred into the secondary rim and eventually on to the surface. To separate the effects, a ring made out of carbon composite was placed between the support structure and the secondary reflector. To investigate the size of the ring and especially the layup of the composite, a topology optimization and free-size optimization was performed. A further improvement was achieved by carefully investigating the deformations in the ring and locally stiffening the connection points of the landing tubes on the ring. All these changes in the SDSS resulted in a 96% reduction in RMS residual error for the worst case condition at 15° elevation angle. A combination of careful analyses and application of optimization techniques was paramount to achieve 50GHz performance.
DVA1 (Dish Verification Antenna 1) is a highly innovative rim-supported single-piece composite-material dish radio telescope developed at the National Research Council Canada (NRC). It has a feed-high offset Gregorian optical design with a primary effective diameter of 15 m. DVA1 has been undergoing mechanical and astronomical system tests since 2014. Astronomical measurements were made in L band using a prototype front end developed for MeerKAT by EMSS Antennas (South Africa), including aperture efficiency, beam profiles, sensitivity, and tipping curves. The clean shaped optics, careful attention to feed design, and high sensitivity of the L band receiver (Trx ~ 6 K) yield a system with high aperture efficiency (~ 0.8), excellent sensitivity (~ 9 m2/K), and low spillover (~ 4 K). Observations of 21 cm atomic hydrogen lines towards standard sources demonstrate the low stray radiation pickup of the antenna. Ku band holography has measured the effective surface accuracy and stability of the dual-reflector antenna. The effective RMS of ~ 0.85 mm implies a Ruze efficiency of ~ 0.88 at 10 GHz and ~ 0.60 at 20 GHz. The surface is stable (~ 10% variation in surface RMS) over the limited range of environmental conditions tested. Testing continues for characterization of pointing, low frequency performance (< 1 GHz), and polarimetric performance. NRC is developing a successor antenna, DVA3, which will have a more accurate surface and be usable at frequencies at least up to Q band (30 – 50 GHz).
The Dish Verification Antenna 1 (DVA-1) is a 15m aperture offset Gregorian radio telescope featuring a rim-supported single piece molded composite primary reflector on an altitude-azimuth pedestal mount. Vibration measurements of the DVA-1 telescope were conducted over three days in October 2014 by NSI Herzberg engineers. The purpose of these tests was to measure the first several natural frequencies of the DVA-1 telescope. This paper describes the experimental approach, in particular the step-release method, and summarizes some interesting results, including unexpectedly high damping of the first mode over a narrow range of zenith angles.
Phased array feed (PAF) receivers used on radio astronomy telescopes offer the promise of increased fields of view
while maintaining the superlative performance attained with traditional single pixel feeds (SPFs). However, the much
higher noise temperatures of room temperature PAFs compared to cryogenically-cooled SPFs have prevented their
general adoption. Here we describe a conceptual design for a cryogenically cooled 2.8 – 5.18 GHz dual linear
polarization PAF with estimated receiver temperature of 11 K. The cryogenic PAF receiver will comprise a 140 element
Vivaldi antenna array and low-noise amplifiers housed in a 480 mm diameter cylindrical dewar covered with a RF
transparent radome. A broadband two-section coaxial feed is integrated within each metal antenna element to withstand
the cryogenic environment and to provide a 50 ohm impedance for connection to the rest of the receiver. The planned
digital beamformer performs digitization, frequency band selection, beam forming and array covariance matrix
calibration. Coupling to a 15 m offset Gregorian dual-reflector telescope, cryoPAF4 can expect to form 18 overlapping
beams increasing the field of view by a factor of ~8x compared to a single pixel receiver of equal system temperature.