SwePub - sökning: WFRF:(Iupikov Oleg 1983)

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1.	Bärring, Maja, 1988, et al. (författare) Factory Radio Design of a 5G Network in Offline Mode 2021 Ingår i: IEEE Access. - 2169-3536 .- 2169-3536. ; 9, s. 23095-23109 Tidskriftsartikel (refereegranskat)abstract The manufacturing industry is connecting people and equipment with new digital technologies, enabling a more continuous stream of data to represent processes. With more things connected, the interest in a connectivity solution that can support communication with high reliability and availability will increase. The fifth generation of telecommunication, i.e., 5G has promising features to deliver this, but the factory environment introduces new challenges to ensure reliable radio coverage. This will require efficient ways to plan the Factory Radio Design prior to installation. 3D laser scanning is used at an ever-increasing rate for capturing the spatial geometry in a virtual representation to perform layout planning of factories. This paper presents how to combine 3D laser scanning and physical optics (PO) for planning the Factory Radio Design of a cellular Long-Term Evolution (LTE) network (5G) in a virtual environment. 3D laser scanning is applied to obtain the spatial data of the factory and the virtual representation serves as the environment where PO computation techniques can be performed. The simulation result is validated in this paper by comparison to measurements of the installed network and empirical propagation models. The results of the study show promising opportunities to simulate the radio coverage in a virtual representation of a factory environment.
2.	Iupikov, Oleg, 1983, et al. (författare) A Cavity-Backed Patch Antenna with Distributed Multi-Port Feeding, Enabling Efficient Integration with Doherty Power Amplifier and Band-Pass Filter 2021 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 69:8, s. 4412-4422 Tidskriftsartikel (refereegranskat)abstract A joint design approach for co-integrated antenna and power amplifier (PA), employing a high-efficiency Doherty PA (DPA) architecture and including a band-pass RF filter, is proposed. This design is realized through the optimally distributed and balanced multi-port feeding of the cavity-backed patch antenna element that provides the desired (unique) loading conditions for the main and auxiliary PA branches and tailored power combining. A novelty and advantage of this feeding solution is that each pair of feeding points form a virtual common feeding centre of the radiating element; as a result, the radiation pattern remains power invariant when the port excitations change. A joint optimization of the integrated antenna-DPA transmitter is carried out to enhance the overall performance and maximize the bandwidth. This optimization is demonstrated through an example design for the sub-6 GHz telecommunication applications that target high power-efficiency (>50%) at the 6dB backed-off power levels and require RF-filtering in a compact integrated design. The latter challenge leads to a non-conventional implementation, which generally does not require the filter to be inserted between the antenna and the final output stage of the PA, and can be embedded in the topology with complex-valued source/load impedance values. Results of numerical studies are supported by measurements obtained with the antenna-DPA-filter prototype system.
3.	Bressner, Thomas A.H., et al. (författare) Cell Partitioning Antenna System Performance in Multi-User Scenarios for mmWave Communications 2021 Ingår i: IEEE Access. - 2169-3536 .- 2169-3536. ; 9, s. 127141-127149 Tidskriftsartikel (refereegranskat)abstract Fixed-beam, high-gain antenna systems can be used for a finer partitioning of the currently used cell-sectoring. This partitioning has the benefit of reducing the number of users seen per antenna beam, which reduces interference. Furthermore, the high antenna gain allows for a high effective isotropic radiated power while keeping the transmit power low. In this paper, we study the performance of such a fixed-beam, high gain antenna system design for millimeter-wave mobile communications. The antenna system is designed to keep the inter-sector interference in a multi-site scenario low. The performance is analyzed for single- and multi-user environments. In single-input single-output mode, the 50th percentile of the signal-to-interference-plus-noise ratio lies between 12.5 dB to 39.7 dB if 3 to 0 interferers are present, respectively. For multiple-input multiple-output transmission using zero-forcing, the signal-to-interference-plus-noise ratio increases and the 50th percentile ranges from 36.1 dB to 43.3 dB if 3 to 0 interferes are present, respectively. By using maximum ratio transmission, the best performance is achieved with no interferers present, while a plunge in performance is observed with interferers. Furthermore, the study revealed that the narrow beam antenna system can also provide a clear signal separation for small spatial separations. In the given example, the signal-to-interference-plus-noise ratio is larger than 32.1 dB with 11 active antenna elements, where 2.8 meters separate the users. Hence, the paper shows that the cell-partitioning antenna systems provide coverage in the desired area while keeping the inter-sector interference low, and the considered transmission techniques can be used for situation optimized mobile communication links.
4.	Cappellin, C., et al. (författare) Design of a Push-Broom Multi-Beam Radiometer for Future Ocean Observations 2015 Ingår i: 9th European Conference on Antennas and Propagation, EuCAP 2015, Lisbon, Portugal, 13-17 May 2015. - 9788890701856 Konferensbidrag (refereegranskat)abstract The design of a push-broom multi-beam radiometer for future ocean observations is described. The radiometer provides a sensitivity one order of magnitude higher than a traditional conical scanning radiometer, and has the big advantage of being fully stationary relative to the satellite platform. Thanks to a dense focal plane array and a dedicated optimization procedure, the instrument can accurately measure in C, X and Ku band and as close as 15 km to the coast line.
5.	Cappellin, C., et al. (författare) Feed array breadboard for future passive microwave radiometer antennas 2018 Ingår i: IET Conference Publications. ; 2018:CP741 Konferensbidrag (refereegranskat)abstract The pattern of a 265 mm x 200 mm breadboard made of 35 x-polarized and 32 y-polarized Vivaldi antennas located above a finite ground plane is computed and measured at 6.9 GHz. The breadboard constitutes the feed array illuminating a 5 m conical scan antenna working at 6.9 GHz for next generation microwave radiometers for ocean observation. The analysis is done including mutual coupling between the elements, and in two commercial software, the MoM add-on to GRASP and CST. The breadboard is measured at the Spherical Near-Field Antenna Test Facility at the Technical University of Denmark.
6.	Cappellin, Cecilia, et al. (författare) Focal Plane Array Breadboard For Advanced Multiple Beam Radiometer Antennas 2017 Ingår i: 38th ESA Antenna Workshop on Innovative Antenna Systems and Technologies for Future Space Missions. ; , s. 1-8 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract The detailed design and RF analysis of a breadboard made by 35 x-polarized and 32 y-polarized Vivaldi antennas, placed 0.67 wavelength from each other and located above a finite ground plane, are described. The breadboard constitutes a representative part of the feed array illuminating a conical scan or push-broom antenna for next generation microwave radiometers for ocean observation. The analysis are done at 6.9 GHz including mutual coupling between the elements, and in two commercial software, i.e. CST and the MoM add-on to GRASP.
7.	Cappellin, C., et al. (författare) Novel multi-beam radiometers for accurate ocean surveillance 2014 Ingår i: 8th European Conference on Antennas and Propagation, EuCAP 2014. - 9788890701849 ; , s. 3531-3535 Konferensbidrag (refereegranskat)abstract Novel antenna architectures for real aperture multi-beam radiometers providing high resolution and high sensitivity for accurate sea surface temperature (SST) and ocean vector wind (OVW) measurements are investigated. On the basis of the radiometer requirements set for future SST/OVW missions, conical scanners and push-broom antennas are compared. The comparison will cover reflector optics and focal plane array configuration.
8.	de lasson, Jakob R., et al. (författare) Innovative Multi-Feed-Per-Beam Reflector Antenna for Space-Borne Conical-Scan Radiometers 2018 Ingår i: 2018 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETING. - 1522-3965. - 9781538671023 - 9781538671023 ; , s. 1729-1730 Konferensbidrag (refereegranskat)abstract We present an antenna for use on conical-scan space-borne radiometers in C band and demonstrate that stringent radiometric requirements can be met. The antenna consists of a 5 m offset reflector fed by a focal plane array in a multi-feed-per-beam configuration, so far never used in ocean observation missions. We use distinct element beams and two optimization routines for obtaining element excitation amplitudes and phases, and with either routine, and in both x- and y-polarization, compliant beams, with footprint < 20 km, distance to coast < 20 km and accuracy < 0:25 K, are obtained. These results may pave the way for use of focal plane arrays with digital beamforming in future radiometric ocean observation missions.
9.	Elsakka, Amr, 1984, et al. (författare) A Design Concept of Power Efficient, High Gain Antenna System for mm-Waves Base Stations 2021 Ingår i: 2021 15TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). - 2164-3342. Konferensbidrag (refereegranskat)abstract A design concept for a phased-array-fed reflector antenna system intended for millimeter-wave base stations is presented. This concept is motivated by the need for efficient beamforming antenna systems with reduced power consumption as compared to the presently considered fully-populated large-scale MIMO arrays. The main idea is to use a high-gain reflector antenna to maximize the effective isotropic radiated power. That in turn, allows minimizing the number of active antenna elements of the phased-array feed, and hence limit the total supplied power. The proposed reflector antenna system is based on a torus reflector which is illuminated by an offset phased-array feed. We show how to determine the antenna design parameters to achieve the desired cell coverage.
10.	Elsakka, Amr, et al. (författare) A mm-Wave Phased-Array Fed Torus Reflector Antenna with ±30° Scan Range for Massive-MIMO Base-Station Applications 2022 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 70:5, s. 3398-3410 Tidskriftsartikel (refereegranskat)abstract A phased-array fed reflector antenna system is presented which can be used for mm-wave base station applications. The proposed system is designed to support massive-Multi-Input-Multi-Output (MIMO) scenarios within a wide coverage (±30°) in the azimuth plane and a limited coverage at the elevation plane. A design and characterization methodology has been established to optimize the system for the operation in various line-of-sight conditions by adopting the maximum-ratio-transmission (MRT) and zero-forcing (ZF) MIMO algorithms. A two-user MIMO case study has been considered for the evaluation of the key system performance metrics, i.e. the effective isotropic radiated power, power consumption, signal-to-noise-ratio (SNR), and signal-to-interference-plus-noise-ratio (SINR). This study demonstrates that the phased-array fed reflector concept has a major advantage over traditional direct-radiating phased array (DRPA) antennas to reduce energy consumption. In the present example, it requires 12–14 dB less transmitted power as compared to the MRT-beamformed DRPAs for the same SNR, and 26–27 dB less transmitted power relatively to ZF-beamformed DRPA systems for the same SINR. A prototype, employing a 55 cm diameter torus reflector and operating at 28 GHz-band, has been manufactured and tested. The measurement results agree well with simulations.
11.	Glazunov, Andres Alayon, 1969, et al. (författare) Emulating Rician distributed channels in a hybrid chamber for OTA measurements 2021 Ingår i: 2020 International Symposium on Antennas and Propagation, ISAP 2020. ; , s. 549-550 Konferensbidrag (refereegranskat)abstract It has been shown by means of simulations that the rich isotropic multipath and the random line-of-sight channels and other Rician channels in-between can be successfully generated in the same over-the-air hybrid measurement chamber without the use of additional static or moving scatterers.
12.	Glazunov, Andres Alayon, 1969, et al. (författare) Multipath Rician Channel Simulation in the Test Zone of a Hybrid OTA Chamber 2021 Ingår i: 15th European Conference on Antennas and Propagation, EuCAP 2021. Konferensbidrag (refereegranskat)abstract Multipath fields with ascribed Rician distribution parameters have been simulated in a novel hybrid chamber for over the air characterization of antenna systems and wireless devices. Simulations are based on waveguide mode summations representing a combination of the half-space rich isotropic multipath component and the on-axis line-of-sight component. It has been shown that the Rician distributed channels can be emulated without the use of additional static or moving scatterers.
13.	Iupikov, Oleg, 1983, et al. (författare) A Dual-Fed PIFA Antenna Element With Nonsymmetric Impedance Matrix for High-Efficiency Doherty Transmitters: Integrated Design and OTA-Characterization 2020 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 68:1, s. 21-32 Tidskriftsartikel (refereegranskat)abstract A single planar inverted F-antenna is proposed employing two input ports to optimally power-combine the output signals of two nonlinear power amplifiers inside the metal-only low-loss antenna structure. High power-added efficiency (PAE) at back-off power levels is reached through a Doherty combiner architecture, where the optimal power combination is seen to generally require the synthesis of a nonsymmetric antenna input impedance matrix. The dual-fed antenna is compact and exhibits close to single-mode radiation properties; it has a relatively stable gain pattern despite the nonequal Doherty power amplifier (PA) output powers. An integrated active prototype has been designed, fabricated, and characterized over-the-air in both an anechoic and a reverberation chamber. Good agreement is observed and an uncertainty analysis is performed. The Doherty transmitter features a max-PAE of 58 at 2.14 GHz and a 6 dB back-off PAE of 52; a minimum system power gain of 9.5 dB (max 12 dB); and a maximum system output power of 43.5 dBm.
14.	Iupikov, Oleg, 1983, et al. (författare) A Plane Wave Approximation in the Computation of Multiscattering Effects in Reflector Systems 2013 Ingår i: 7th European Conference on Antennas and Propagation, EuCAP 2013, Gothenburg, Sweden, 8-12 April 2013. - 2164-3342. - 9781467321877 ; , s. 3828-3832 Konferensbidrag (refereegranskat)abstract A hybrid MoM/PO method for the analysis of multiple scattering effects between reflector and large feeds, such as dense multibeam phased array feeds or multifrequency front-ends (MFFEs) in which higher frequency feeds operate in the vicinity of an extended metal structure, has been presented and studied. This paper evaluates the accuracy and computational efficiency for the MoM/PO method with and without using a uniform plane wave approximation of the reflector scattered field.
15.	Iupikov, Oleg, 1983, et al. (författare) An Optimal Beamforming Algorithm for Phased-Array Antennas Used in Multi-Beam Spaceborne Radiometers 2015 Ingår i: 9th European Conference on Antennas and Propagation, EuCAP 2015, Lisbon, Portugal, 13-17 May 2015. - 9788890701856 Konferensbidrag (refereegranskat)abstract Strict requirements for future spaceborne ocean missions using multi-beam radiometers call for new antenna technologies, such as digital beamforming phased arrays. In this paper, we present an optimal beamforming algorithm for phasedarray antenna systems designed to operate as focal plane arrays (FPA) in push-broom radiometers. This algorithm is formulated as an optimization procedure that maximizes the beam efficiency, while minimizing the side-lobe and cross- Polarization power inthe area of Earth, subject to a constraint on the beamformer dynamic range. The proposed algorithm is applied to a FPA feeding a torus reflector antenna (designed under the contract with the European Space Agency) and tested for multiple beams. The results demonstrate an improved performance in terms of the optimized beam characteristics, yielding much higher spatial and radiometric resolution as well as much closer distance to coast, as compared to the present-day systems.
16.	Iupikov, Oleg, 1983, et al. (författare) Dense focal plane arrays for pushbroom satellite radiometers 2014 Ingår i: 8th European Conference on Antennas and Propagation, EuCAP 2014; The Hague; Netherlands; 6 April 2014 through 11 April 2014. - 9788890701849 ; , s. 3536-3540 Konferensbidrag (refereegranskat)abstract Performance of a dense focal plane array feeding an offset toroidal reflector antenna system is studied and discussed in the context of a potential application in multi-beam radiometers for ocean surveillance. We present a preliminary design of the array feed for the 5-m diameter antenna at X-band. This array is optimized to realize high antenna beam efficiency (∼ 95%) over a wide scan range (±20°) with very low side-lobe and cross-polarization levels.
17.	Iupikov, Oleg, 1983, et al. (författare) Digital-beamforming array antenna technologies for future ocean-observing satellite missions 2016 Ingår i: 2016 IEEE Antennas and Propagation Society International Symposium, APSURSI 2016, Fajardo, Puerto Rico, 26 June - 1 July 2016. - 9781509028863 ; , s. 1377-1378 Konferensbidrag (refereegranskat)abstract 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.
18.	Iupikov, Oleg, 1983 (författare) Digital Beamforming Focal Plane Arrays for Radio Astronomy and Space-Borne Passive Remote Sensing 2017 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Dense Phased Array Feeds (PAFs) for reflector antennas have numerous advantages over traditional cluster feeds of horns in a one-horn-per-beam configuration, especially in RF-imaging applications which require multiple simultaneously formed and closely overlapping beams. However, the accurate analysis and design of such PAF systems represents a challenging problem, both from an EM-modeling and beamforming optimization point of view. The current work addresses some of these challenges and consists of two main parts.In the first part the mutual interaction effects that exist between a PAF consisting of many densely packed antenna elements and an electrically large reflector antenna are investigated. For that purpose the iterative CBFM-PO method has been developed. This method not only allows one to tackle this problem in a time-efficient and accurate manner, but also provides physical insight into the feed-reflector coupling mechanism and allows to quantify its effect on the antenna impedance and radiation characteristics. Numerous numerical examples of large reflector antennas with various representative feeds (e.g. a single dipole feed and complex PAFs of hundreds of elements) are also presented and some of them are validated experimentally. In order to analyze electrically large feeds efficiently, a domain-decomposition approach to Krylov subspace iteration, where macro basis functions (or characteristic basis functions) on each subdomain are naturally constructed from the different segments of the generating vectors, is also proposed.The second part of the thesis is devoted to the optimization of PAF beamformers and covers two application examples: (i) microwave satellite radiometers for accurate ocean surveillance; and (ii) radio telescopes for wide field-of-view sky surveys. Based on the initial requirements for future antenna systems, which are currently being formulated for these applications, we propose various figures-of-merits and describe the corresponding optimal beamforming algorithms that have been developed. Studies into these numerical examples demonstrate how optimal beamforming strategies can help to greatly improve the antenna system characteristics (e.g. beam efficiency, side-lobe level and sensitivity in the presence of the noise) as well as to reduce the complexity of the beam calibration models and overall phased array feed design.
19.	Iupikov, Oleg, 1983, et al. (författare) Domain-Decomposition Approach to Krylov Subspace Iteration 2016 Ingår i: IEEE Antennas and Wireless Propagation Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1548-5757 .- 1536-1225. ; 15, s. 1414-1417 Tidskriftsartikel (refereegranskat)abstract Krylov subspace iterative techniques consist of finding the solution of a scattering problem as a linear combination of "generating vectors" obtained through successive matrix-vector multiplications. This letter extends this approach to domain-decomposition. Here, on each subdomain, a subspace is obtained by constructing the segments of each generating vector associated with the subdomain and by weighting these segments independently, which provides more degrees of freedom. The method is tested for scattering by a sphere and a rectangular plate, as well as radiation from connected arrays with strongly coupled antenna elements. It is shown that substantial computational savings can be obtained for the sphere and the array. This opens up new perspectives for faster solutions of multiscaled problems.
20.	Iupikov, Oleg, 1983, et al. (författare) Fast and Accurate Analysis of Reflector Antennas with Phased Array Feeds Including Multiple Reflections between Feed and Reflector 2014 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 62:7, s. 3450 - 3462 Tidskriftsartikel (refereegranskat)abstract 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.
21.	Iupikov, Oleg, 1983, et al. (författare) Hybrid OTA Chamber for Multi-Directional Testing of Wireless Devices: Plane Wave Spectrum Generator Design and Experimental Demonstration 2022 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 70:11, s. 10974-10987 Tidskriftsartikel (refereegranskat)abstract This paper investigates practical implementation aspects of a novel hybrid chamber concept that has been recently introduced for over-the-air testing of wireless devices. The chamber allows to synthesize a spectrum of plane waves (PWs) incident on a device under test from a wide range of angles-of-arrival (AoAs) through exploiting multiple field scattering inside the overmoded waveguide chamber. An optimal design approach for the plane wave spectrum generator (PWSG) array inside the chamber is presented considering: (i) array antenna impedance matching for the desired test zone (TZ) quality and AoAs range; (ii) an operational frequency bandwidth of the test environment and an instantaneous signal bandwidth; and (iii) the impact of the PWSG excitation errors. A robust linearly constrained minimum variance (LCMV) beamformer is formulated to realize the desired test environment over a wide frequency band, while accounting for the varying number of the waveguide propagating modes as excited by the PWSG array. Numerical simulations and measurements with the first prototype of the hybrid chamber for FR1 frequency band (~3.5 GHz) are presented. This prototype includes a 7 × 7 bowtie antenna element PWSG array, a 1.00 × 1.25 × 1.75 m metal waveguide chamber, an off-line optimal array beamforming setup, and a planar scanner for the TZ characterization.
22.	Iupikov, Oleg, 1983, et al. (författare) Indoor Received Power Prediction Based on Physical Optics (PO): Simulations and Experimental Validation in Industrial Environment 2019 Ingår i: 13th European Conference on Antennas and Propagation, EuCAP 2019. Konferensbidrag (refereegranskat)abstract This study presents an approach based on Physical Optics computations to predict the receive signal power in an indoor environment. The application in focus pertains the development of highly reliable manufacturing industry processes where wireless communications plays a key role. Our proposed numerical method shows a good agreement with measurement data. It is therefore suggested that Electromagnetic modelling based on computationally efficient Physical Optics algorithms can be used as a complement, an alternative or even a replacement for empirical models requiring time consuming measurement campaigns.
23.	Iupikov, Oleg, 1983, et al. (författare) Multi-Beam Focal Plane Arrays with Digital Beamforming for High Precision Space-Borne Remote Sensing 2017 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. Tidskriftsartikel (refereegranskat)abstract The present-day ocean remote sensing instruments that operate at low microwave frequencies are limited in spatial resolution and do not allow for monitoring of the coastal waters.This is due the difficulties of employing a large reflector antenna on a satellite platform, and generating high-quality pencil beams at multiple frequencies. Recent advances in digital beamforming focal-plane-arrays (FPAs) have been exploited in the current work to overcome the above problems. A holistic design procedure for such novel multi-beam radiometers has been developed, where (i) the antenna system specifications are derived directly from the requirements to oceanographic surveys for future satellite missions; and (ii) the numbers of FPA elements/receivers are determined through a dedicated optimum beamforming procedure minimizing the distance to coast.This approach has been applied to synthesize FPAs for two alternative radiometer systems: a conical scanner with an off-set parabolic reflector, and stationary wide-scan torus reflector system; each operating at C, X and Ku bands. Numerical results predict excellent beam performance for both systems with as low as 0.14% total received power over the land.
24.	Iupikov, Oleg, 1983, et al. (författare) Multibeam Focal Plane Arrays with Digital Beamforming for High Precision Space-Borne Ocean Remote Sensing 2018 Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 66:2, s. 737-748 Tidskriftsartikel (refereegranskat)abstract The present-day ocean remote sensing instruments that operate at low microwave frequencies are limited in spatial resolution and do not allow for monitoring of the coastal waters. This is due to the difficulties of employing a large reflector antenna on a satellite platform, and generating high-quality pencil beams at multiple frequencies. Recent advances in digital beamforming focal-plane arrays (FPAs) have been exploited in this paper to overcome the above problems. A holistic design procedure for such novel multibeam radiometers has been developed, where: 1) the antenna system specifications are derived directly from the requirements to oceanographic surveys for future satellite missions and 2) the numbers of FPA elements/receivers are determined through a dedicated optimum beamforming procedure minimizing the distance to coast. This approach has been applied to synthesize FPAs for two alternative radiometer systems: a conical scanner with an offset parabolic reflector and a stationary wide-scan torus reflector system, each operating at C -, X-, and Ku-bands. Numerical results predict excellent beam performance for both systems with as low as 0.14% total received power over the land.
25.	Iupikov, Oleg, 1983 (författare) Phased-Array-Fed Reflector Antenna Systems for Radio Astronomy and Earth Observations 2014 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract Dense Phased Array Feeds (PAFs) for reflector antennas have numerous advantages over traditional cluster feeds of horns in a one-horn-per-beam configuration, especially in RF-imaging applications which require multiple simultaneously formed and closely overlapped beams. However, the accurate analysis and design of such PAF systems represents a challenging problem, both from an EM-modeling and beamforming optimization point of view. The current work addresses some of these challenges and consists of two main parts. In the first part the mutual interaction effects that exist between a PAF consisting of many densely packed antenna elements and an electrically large reflector antenna are investigated. For that purpose the iterative CBFM-PO method has been developed. This method not only allows one to tackle this problem in a time-efficient and accurate manner, but also provides physical insight into the feed-reflector coupling mechanism and allows to quantify its effect on the antenna impedance and radiation characteristics. Numerous numerical examples of large reflector antennas with various representative feeds (e.g. a single dipole feed and complex PAFs of hundreds of elements) are also presented and some of them are validated experimentally. The second part of the thesis is devoted to the optimization of PAF beamformers and covers two application examples: (i) microwave satellite radiometers for accurate ocean surveillance; and (ii) radio telescopes for wide field-of-view sky surveys. Based on the initial requirements for future antenna systems, which are currently being formulated for these applications, we propose various figures-of-merit and describe the corresponding optimal beamforming algorithms that have been developed. Studies into these numerical examples demonstrate how optimal beamforming strategies can help to greatly improve the antenna system characteristics (e.g. beam efficiency, side-lobe level and sensitivity in the presence of the noise) as well as to reduce the complexity of the beam calibration models and overall phased array feed design.

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