Bruce Veidt

Wide-band CMOS low noise amplifier for applications in radio astronomy

A CMOS low noise amplifier (LNA) is proposed for a proof-of-concept design of the square kilometer array (SKA) radio telescope. A novel variation on a well-known source-degenerated LNA topology is introduced that allows tuning of the power match centre frequency independently from the frequency at which the LNAs noise figure approaches its minimum noise. The 0.7-1.4 GHz LNA designed in 0.18mum CMOS achieves better than 11 dB return loss with a noise temperature of 40 K, provides a power gain of 17 dB and IP1dB of -10dBm while consuming 50 mW of power from a 1.8 V supply. The design procedure of the LNA is presented and performance of the LNA is compared with previously published results

Low-Noise Amplifier Design Considerations For Use in Antenna Arrays

This work analyzes the implications of noise coupling in arrays of antennas on the design of low-noise amplifiers (LNAs). To select LNA design parameters in a manner familiar to LNA designers, the effective noise temperatures Teff of LNAs are presented. The effect of beamformer coefficients and antenna coupling on Teff is analyzed in a manner similar to a stand-alone LNA analysis. This leads to the proposed LNA design strategy of selecting LNA Γopt near the reflection coefficient of antenna ports and selecting the largest practical |S11| with a proper phase. This strategy is based on the assumption that the antenna array may be used for various beamforming and nonbeamforming applications, unknown at the time of the design. Numerical simulations of a 38- and 41-element antenna arrays show that a global search of LNA S11 and Γopt, which result in the minimum average beam-equivalent receiver noise temperature Trec, finds nearly identical results to the proposed LNA design strategy. For a 41-element array with high antenna coupling at low frequencies, the proposed method shows as much as 80% improvement in the Trec over conventional LNA design strategies that do not account for the intended use of the amplifier in an array.

The large adaptive reflector: a 200-m diameter wideband centimeter- to meter-wave radio telescope

The Large Adaptive Reflector (LAR) is a concept for a low- cost, large aperture, wideband, radio telescope, designed to operate over the wavelength range from 2 m to 1.4 cm. It consists of a 200-m diameter actuated-surface parabolic reflector with a focal length of 500 m, mounted flat on the ground. The feed is held in place by a tension-structure, consisting of three or more tethers tensioned by the lift of a large, helium-filled aerostat -- a stiff structure that effectively resists wind forces. The telescope is steered by simultaneously changing the lengths of the tethers with winches (thus the position of the feed) and by modifying the shape of the reflector. At all times the reflector configuration is that of an offset parabolic antenna, with the capability to point anywhere in the sky above approximately 15 degree Elevation Angle. At mid-range wavelengths, the feed is a multi-beam prime-focus phased array, about 5 m diameter; at meter wavelengths, it is a single-beam phased array of up to 10 m diameter. Simulations have shown that in operating wind conditions (10 m/s average speed with 2.5 m/s gusts), the position of the feed platform can be stabilized to within a few cm over time scales of approximately 20 s. Research indicates that the telescope concept is feasible and that an order of magnitude improvement in cost per m2 of collecting area over traditional designs of large parabolic antennas can be achieved.

Activites of the Dominion Radio Astrophysical Observatory

The Dominion Radio Astrophysical Observatory (DRAO) carries out world-class research in radio astronomy science and engineering, with a focus on science and technologies relevant to the planned International Square- Kilometre Array (SKA). DRAO staff operate three on-site telescopes, and participate in international science projects, with recognized expertise in the theory and practice of wide-field imaging and polarimetry. Active engineering programs include digital signal processing (correlators and beam-forming), phased-array feeds, and high performance composite reflector antennas.

Feed-reflector design for large adaptive reflector antenna (LAR)

A novel feed-reflector system for large Cassegrain antennas of radio astronomy and deep-space communication applications is investigated. This feed-reflector is used to illuminate a hyperboloid subreflector with a 5-10 m diameter located 500 m above the ground. Because the subreflector is located in the near field of the feed-reflector antenna, a theory based on the near field focusing properties of paraboloid reflectors is established. The focusing at near distance is formed by moving the feed horn away from the focal point of the feed-reflector. In this theory, the properties of axial defocused paraboloid reflectors at near distance are investigated in more detail. By using equivalence path law, the subreflector shape is obtained. It is found that the hyperbola can approximate the subreflector well. A detailed ray tracing is performed on the entire system which reveals that the feed system uses some part of the subreflector three times. The gain, side lobe level, cross polarization, and aperture distribution are calculated for different feed horn locations and taper at the edge of the feed-reflector and also for different sizes and eccentricities of the subreflector. Peak efficiency in excess of 74.8% and side lobe level around -20 dB are obtained for an unshaped system. The performance of the system over the operating band (1-22 GHz) is also studied and shown that the lower-frequency limit is dependent on subreflector and feed-reflector sizes.

Low noise phased-array feed with CMOS LNAs

Phased-array feeds are being developed for expantion of the field-of-view of parabolic reflector antennas. The University of Calgary (UCalgary) and the National Research Council (NRC) of Canada have recently demonstrated a low-noise phased-array feed for possible use in the Square Kilometre Array radio telescope. NRC has made noise measurements of such an array equipped with CMOS low-noise amplifiers (LNAs) designed by the University of Calgary. In the design range from 0.7 GHz to 1.5 GHz, array beam-referred noise measurements, using an ambient load as a hot load and the sky as a cold load, show array beam-referred noise temperatures as low as 20 K. This paper describes the phased-array feed.

Development of a CMOS receiver for a radio-telescope phased-array feed

Next generation radio telescopes will have a very large number of antenna elements. For such systems, ultra-low-noise ambient-temperature integrated CMOS receivers can address some design challenges, such as size, weight, power consumption, and cost. This paper describes the development of one such receiver. Developed in 65-nm TSMC CMOS, it operates between 0.7 and 1.5 GHz and achieves minimum noise temperatures of 16 K at 1.5GHz and power gain of 70 dB, while consuming 265 mW of power.

CryoPAF4: a cryogenic phased array feed design

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.

Characteristics and design of the LAR offset system with feed-reflector

A novel approach for analyzing the quasi-optical offset large adaptive reflector (LAR) Cassegrain system is described. In this system, a feed-reflector is used to illuminate a reconformable hyperboloid subreflector with 5-10 m diameter, located 500 m above the ground. An exact equation for the offset LAR surface is given. To scan the beam up to 60/spl deg/ which is one of the LAR requirements, the concept of the dual offset LAR with feed-reflector is introduced. In this design, the cross polarization is eliminated by a proper orientation of the subreflector. The parameters of the configuration are obtained by utilizing generalized Gauss-Laguerre beam modes and matrix representation of the beam mode transformation factor. The blockage effect due to the feed-reflector is totally removed.

A digital beamformer for the advanced focal array demonstrator (AFAD)

Phased array feeds (PAFs) are an active research area in radio astronomy, as they offer potential advantages over traditional single-pixel feeds. Their key advantage is increased field of view and survey speed, however they also permit tailoring the antenna beam for Ae=Tsys, or other objectives such as attenuating strong radio frequency interference (RFI). A primary research goal is to improve the noise temperature performance of a PAF over comparable single-pixel feeds. In this work we have constructed a small 16-element digital beamformer with 384 MHz of bandwidth to evaluate the performance of NRCs Advanced Focal Array Demonstrator (AFAD) operating from 750 to 1500 MHz. We compare measured sensitivity results to previous measurements made with an analog beamformer. The digital beamformer is implemented using NRCs Kermode platform, a Virtex6-based compute blade. We take a standards-based approach, using the AdvancedTCA (ATCA) form factor for the Kermode board, ANSI/VITA-49.0 framing for all chip-to-chip and chip-to-host communications, and AXI4-Stream format for all internal datapaths. The Kermode system can be expanded with a standard ATCA full-mesh backplane to support up to 128 inputs with over 1 GHz of bandwidth. This expanded capability will ultimately be used to evaluate the performance of the full 96-element AFAD PAF mounted on a re ector antenna. To achieve this goal, we are well into developing a digitizer system that will handle at least 96 elements with up to 1.5 GHz of bandwidth per element. We present an overview of the digitizer system in the context of the PAF beamformer system, and provide an update on the progress to date.