Oleg Iupikov

An Optimal Beamforming Strategy for Wide-Field Surveys With Phased-Array-Fed Reflector Antennas

An optimal beamforming strategy is proposed for performing large-field surveys with dual-polarized phased-array-fed reflector antennas. This strategy uses signal-processing algorithms that maximize the beam sensitivity and the continuity of a field of view (FOV) that is formed by multiple closely overlapping beams. A mathematical framework and a newly developed numerical approach are described to analyze and optimize a phased array feed (PAF) system. The modeling approach has been applied to an experimental PAF system (APERTIF prototype) that is installed on the Westerbork Synthesis Radio Telescope. The resulting beam shapes, sensitivity, and polarization diversity characteristics (such as the beam orthogonality and the intrinsic cross-polarization ratio) are examined over a large FOV and frequency bandwidth. We consider weighting schemes to achieve a conjugate-field matched situation (max. received power), maximum signal-to-noise ratio (SNR), and a reduced SNR scenario but with constraints on the beam shape. The latter improves the rotational symmetry of the beam and reduces the sensitivity ripple, at a modest maximum sensitivity penalty. The obtained numerical results demonstrate a very good agreement with the measurements performed at the telescope.

Analysis of Large Microstrip-Fed Tapered Slot Antenna Arrays by Combining Electrodynamic and Quasi-Static Field Models

A reduced-order model for large arrays of microstrip-fed tapered slot antennas (TSAs) is presented. The currents on the antenna conductors are modeled by a relatively small number of physics-based macro-domain basis functions through a technique which is known as the characteristic basis function method (CBFM). The array is treated as a metal-only structure, while the wideband microstrip feeds are separately modeled using quasi-static circuit models. It is demonstrated that, even though the dielectric-supported feeds are non-shielded and therefore form an integral part of each radiating antenna element, the feeds can be modeled independently from the strongly coupled antenna elements. Validation of the combined antenna-feed model has been carried out through the measurements of several practically realized TSA arrays, among them a 8 × 7 × 2 dual-polarized array. The results demonstrate good agreement over a large scan range, as well as over a wide frequency band. The polarization-discrimination capabilities of the antenna, when operating in phased-array mode, have been analyzed in the context of radio-astronomical applications.

Improving the Calibration Efficiency of an Array Fed Reflector Antenna Through Constrained Beamforming

Calibrating for the radiation pattern of a multi-beam Phased array feed (PAF) based radio telescope largely depends on the accuracy of the pattern model, and the availability of suitable reference sources to solve for the unknown parameters in the pattern model. It is shown how the efficiency of this pattern calibration for PAF antennas can be improved by conforming the beamformed far field patterns to a two-parameter physics-based analytic reference model through the use of a linearly constrained minimum variance (LCMV) beamformer. Through this approach, which requires only a few calibration measurements, an accurate and simple pattern model is obtained. The effects of the model parameters on the directivity and sidelobe levels of multiple scanned beams are investigated, and these results are used in an example PAF beamformer design for the proposed MeerKAT antenna. Compared to a typically used maximum directivity (MaxDir) beamformer, the proposed constrained beamforming method is able to produce beam patterns over a wide Field-of-View (FoV) that are modeled with a higher degree of accuracy and result in a significant reduction in pattern calibration complexity.

Optimization of the 0.35–1.05 GHz Quad-Ridged Flared Horn and Eleven feeds for the Square Kilometer Array baseline design

Initial optimization results for the wide-band Eleven antenna and Quadruple-Ridged Flared Horn (QRFH), designed to operate as the reflector antenna feeds at 350 - 1050 MHz, are presented and discussed in the context of the next generation radio telescope - the Square Kilometer Array (SKA). First, we describe the procedure that has been developed to carry out time-efficient optimization of the feeds for multiple antenna optics configurations at the system level (so as to maximize the antenna-receiver sensitivity), and then cross-compare the two feed types by assessing the main antenna system characteristics and radio-astronomy performance metrics.

Fast and Accurate Analysis of Reflector Antennas With Phased Array Feeds Including Multiple Reflections Between Feed and Reflector

Several electrically large phased array feed (PAF) reflector systems are modeled to examine the mechanism of multiple reflections between parabolic reflectors and low- and high-scattering feeds giving rise to frequency-dependent patterns and impedance ripples. The PAF current is expanded in physics-based macro domain basis functions (CBFs), while the reflector employs the physical optics (POs) equivalent current. The reflector-feed coupling is systematically accounted for through a multiscattering Jacobi approach. An FFT expands the reflector radiated field in only a few plane waves, and the reflector PO current is computed rapidly through a near-field interpolation technique. The FEKO software is used for several cross validations, and the convergence properties of the hybrid method are studied for several representative examples showing excellent numerical performance. The measured and simulated results for a 121-element Vivaldi PAF, which is installed on the Westerbork Synthesis Radio Telescope, are in very good agreement.

Towards the understanding of the interaction effects between reflector antennas and phased array feeds

A computationally efficient numerical procedure has been developed and used to analyze the mutual interaction effects between an electrically large reflector antenna and a phased array feed (PAF). The complex electromagnetic behavior for such PAF systems is studied through a few simple and didactical examples, among which a single dipole antenna feed, a singly-excited antenna in an array of 20 dipoles, and a fully-excited array. These examples account for the effects of the ground plane, active loading (low noise amplifiers), and beamforming scenario, and are used to illustrate the differences between single-port feeds and PAFs.

Digital-beamforming array antenna technologies for future ocean-observing satellite missions

Existing passive microwave radiometers that are used for ocean observations are limited in spatial resolution and geographic coverage, due to the limitations of traditional antenna technologies using mechanically-scanning reflectors and horn-type feeds. Future ocean observation missions call for new solutions, such as digitally-beamforming array feeds (DBAFs) as well as stationary and more complex reflectors. Our studies demonstrate that DBAFs can overcome the physically fundamental limitations of traditional horn feeds, and are capable of meeting all the challenging requirements for the next-generation instruments.

Feed model for the tapered slot antennas

In this paper we will describe the feed model for the tapered slot antennas (TSAs) and will find one of the important parameter of this model-transformation coefficient.