Discover a modern approach to the analysis, modeling and design of high sensitivity phased arrays. Network theory, numerical methods and computational electromagnetic simulation techniques are uniquely combined to enable full system analysis and design optimization. Beamforming and array signal processing theory are integrated into the treatment from the start. Digital signal processing methods such as polyphase filtering and RFI mitigation are described, along with technologies for real-time hardware implementation. Key concepts from interferometric imaging used in radio telescopes are also considered. A basic development of theory and modeling techniques is accompanied by problem sets that guide readers in developing modeling codes that retain the simplicity of the classical array factor method while incorporating mutual coupling effects and interactions between elements. Combining current research trends with pedagogical material suitable for a first-year graduate course, this is an invaluable resource for students, teachers, researchers, and practicing RF/microwave and antenna design engineers.

Phased Arrays for Radio Astronomy, Remote Sensing, and Satellite Communications

A continuous-time (CT) radio frequency (RF) antenna array beamformer and analog circuit based on a discrete-space-continuous-time (DSCT) 2-D fan-filter having transfer function HF,A(zx,sct) is derived. The proposed transfer function is based on a 2-D FIR discrete domain fan filter. The discrete domain prototype is converted to the proposed mixed-domain DSCT analog filter by replacing unit sampled delays with CT analog first-order all-pass networks corresponding to the bilinear transform. First-order all-pass network Φ(st) is a poor approximation to a CT delay exp(-sT) . To address this, a novel broadband pre-warping method is proposed to exactly compensate for such “bilinear warping”. A 65 nm CMOS VLSI circuit for Φ(st) is proposed and an example fan filter with axis oriented at θ0=35°, half-fan-angle e = 5° and maximum frequency Fu = 2.6 GHz is simulated employing closed-form expressions, an ABCD parameter based model and 65 nm CMOS simulations in Cadence. A stop-band interference rejection of 38 dB is verified by BSIM4 based simulations. The proposed circuit for Φ(st) operates at 3.7 mA from a 1.2 V supply. The beamfomer is shown to operate correctly in the presence of PVT variations of Φ(st).

RF Analog Beamforming Fan Filters Using CMOS All-Pass Time Delay Approximations

The characteristic basis function method (CBFM) is extended to apply to efficient analysis of dual-polarized connected-patch arrays where neighboring patches are connected via two-wire transmission lines and a groundplane. Comparison with a reference solution shows that the use of tertiary basis functions can significantly improve the CBFM approximation to the array currents and radiation patterns. A simple procedure for estimating the error in the CBFM current is shown to produce good approximations to the true error and therefore may be useful more generally in determining suitable parameters of the CBFM basis. The technique is applied to a prototype phased array feed for a next-generation radio telescope. A thin dielectric supporting the array patches is shown to produce a loading effect that modifies the radiation patterns. Good agreement with the results of other techniques and measured data has been obtained.

Connected Patch Array Analysis Using the Characteristic Basis Function Method

We describe the design and construction of a dual-polarized phased-array feed (PAF) with the purpose of demonstrating this technology as a means of expanding the instantaneous field-of-view of radio telescopes. The PAF beamformer is calibrated with observations of an unpolarized astronomical radio source, the covariance matrix of all receiver channels is calculated, and the two dominant eigenvectors are then used as beamformer weights. We show measurements demonstrating the capabilities of this instrument as a polarimeter, and confirm that the calibration method does produce orthogonally-polarized beams. These results are then analyzed to show the sensitivity to fluctuations in gain and phase in the multiple parallel receiver chains making up the phased-array feed. We also compare the performance of PAFs that beamform all array elements with PAFs that beamform only co-polarized elements.

Demonstration of a Dual-Polarized Phased-Array Feed

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 $T^{eff}$ of LNAs are presented. The effect of beamformer coefficients and antenna coupling on $T^{eff}$ is analyzed in a manner similar to a stand-alone LNA analysis. This leads to the proposed LNA design strategy of selecting LNA $\mathbf{\Gamma_{opt}}$ near the reflection coefficient of antenna ports and selecting the largest practical $\left\vert S_{11}\right\vert$ 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 $\mathbf{S_{11}}$ and $\mathbf{\Gamma_{opt}}$ , which result in the minimum average beam-equivalent receiver noise temperature $T_{rec}$ , 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 $T_{rec}$ over conventional LNA design strategies that do not account for the intended use of the amplifier in an array.

Low-Noise Amplifier Design Considerations For Use in Antenna Arrays

Future radio telescopes will be used by astronomers to make high-sensitivity wide-band and wide-field surveys of the radio sky. A candidate technology to provide these expanded capabilities is to place high-sensitivity phased-arrays at the focal plane of reflector antennas. Since this technology has not been proven yet, we have constructed the PHased-Array feed Demonstrator (PHAD) with the goal of exploring engineering aspects of this new technology. PHAD comprises 180 densely-packed Vivaldi elements operating from 1 to 2 GHz. Each element feeds a low-noise amplifier and a receiver (both commercial integrated circuits), with the outputs digitized and stored. Beamforming is performed off-line using a matrix language, providing great flexibility in diagnostics and algorithm development. PHAD testing began in a near-field range and has progressed to tests on a dedicated 10-m reflector antenna. Early results (with emphasis on calibration) are reported here.

The DRAO Phased Array Feed Demonstrator: Recent results

This paper reports on the world's first CMOS low noise amplifier (LNA) operating successfully on a radio telescope since October 15th, 2010. The radio telescope used in this work is the Synthesis Telescope operated by the Dominion Radio Astrophysical Observatory, NRC, and located near Penticton, BC, Canada. This paper describes the work that led to the installation of the LNA on the telescope and shows measurement results obtained with the telescope.

The first CMOS LNA on a radio telescope

An automated system for measuring the sensitivity of microwave radiometers with a free-space input port is described. The Hot/Cold Test Facility (HCTF) exposes a test radiometer to two free-space loads: a hot load formed by ambient-temperature microwave absorber, and to cold sky to act as a cold load. Automation has been added to this facility to improve repeatability, enable long-term studies, and to minimize operator error. We describe the HCTF, discuss measurement errors, and show typical results.

An Automated System for Measurement of Sensitive Microwave Radiometers

Low-noise phased-array feeds are a new way to expand the field of view of radio telescopes at centimetre wavelengths. First generation engineering demonstrators of this technology have been constructed and tested by several institutes worldwide. The development of second-generation phased-array feeds is now underway. We describe one effort to design and build an astronomy-capable phased-array feed using techniques to reduce front-end noise and increase system bandwidth.

/pdf/development-of-a-low-noise-wide-band-phased-array-feed-1xa34vx9ii.pdf

Development of a low-noise wide-band phased-array feed

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