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Phased array

About: Phased array is a research topic. Over the lifetime, 19428 publications have been published within this topic receiving 229231 citations. The topic is also known as: Phased Array Radar, PAR.


Papers
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Journal ArticleDOI
TL;DR: This work proposes an operational optical phased array antenna fed by seven lasers, featuring high transmit power and redundance, applicable for spaceborne laser communications.
Abstract: The feasibility of an optical phased array antenna applicable for spaceborne laser communications was experimentally demonstrated. Heterodyne optical phase-locked loops provide for a defined phase relationship between the collimated output beams of three single-mode fibers. In the far field the beams interfere with a measured efficiency of 99%. The main lobe of the interference pattern can be moved by phase shifting the subaperture output beams. The setup permitted agile beam steering within an angular range of 1 mr and a response time of 0.7 ms. We propose an operational optical phased array antenna fed by seven lasers, featuring high transmit power and redundance.

55 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed a wave-type decomposition method to estimate the propagation characteristics of different seismic phases at regional distances by testing a range of characteristics of the three-component records, and then classifying much of the seismogram in terms of wave type and direction.
Abstract: Both phased array techniques for single-component sensors and vectorial analysis of three-component recordings can provide estimates of the azimuth and slowness of seismic phases. However, a combination of these approaches provides a more powerful tool to estimate the propagation characteristics of different seismic phases at regional distances. Conventional approaches to the analysis of three-component seismic records endeavor to exploit the apparent angles of propagation in horizontal and vertical planes as well as the polarization of the waves. The basic assumption is that for a given time window there is a dominant wavetype (e.g., a P wave) traveling in a particular direction arriving at the seismic station. By testing a range of characteristics of the three-component records, a set of rules can be established for classifying much of the seismogram in terms of wavetype and direction. It is, however, difficult to recognize SH waves in the presence of other wavetypes. Problems also arise when more than one signal (in either wavetype or direction) arrive in the same window. The stability and robustness of the classification scheme is much improved when records from an array of three-component sensors are combined. For a set of three-component instruments forming part of a larger array, it is possible to estimate the slowness and azimuth of arrivals from the main array and then extract the relative proportions of the current P -, SV -, and SH -wave contributions to the seismogram. This form of wavetype decomposition depends on a model of near-surface propagation. A convenient choice for hard-rock sites is to include just the effect of the free surface, which generates a frequency-independent operation on the three-component seismograms and which is not very sensitive to surface velocities. This approach generates good estimates of the character of the S wavefield, because the phase distortion of SV induced by the free surface can be removed. The method has been successfully applied to regional seismograms recorded at the medium aperture Warramunga array in northern Australia, and the two small arrays NORESS and ARCESS in Norway, which were designed for studies of regional phases. The new wavefield decomposition scheme provides results in which the relative proportions of P, SV , and SH waves as a function of time can be compared without the distortion imposed by free surface amplification. Such information can provide a useful adjunct to existing measures of signal character used in source discrimination.

55 citations

Journal ArticleDOI
TL;DR: In this paper, a new approach for reducing mutual coupling between planar inverted-F antennas (PIFAs) is proposed, which consists of placing a resonator in between the PIFAs.
Abstract: A new approach for reducing mutual coupling between planar inverted-F antennas (PIFAs) is proposed. The approach consists of placing a resonator in between the PIFAs. The signal from the first antenna is scattered by the resonator and couples to the second antenna creating another path for mutual coupling, the phase and amplitude of which may be varied to suppress the existing coupling between the antennas. The simulation and experimental studies show that the proposed technique is able to reduce mutual coupling to about −25 dB from −3.5 dB when the antennas are placed as close as λ/11. Reduced mutual coupling between closely spaced antennas may find applications in MIMO, multi-antenna systems and phased arrays.

55 citations

Journal ArticleDOI
TL;DR: In this paper, the authors discuss the sky noise limited design of the antenna system and present a novel technique to obtain the ratio of effective area and system temperature directly from the calibration results, despite the presence of multiple sources within the 2π sr field of view of the antennas.
Abstract: The low frequency array (LOFAR) is a phased array radio telescope that is currently being built in The Netherlands with extensions throughout Europe. It was officially opened on June 12, 2010 and is an important pathfinder for the square kilometre array. The Dutch LOFAR system will consist of 36 stations covering the 10-250 MHz frequency range. In this paper we discuss the sky noise limited design of the antenna system and present a novel technique to obtain the ratio of effective area and system temperature directly from the calibration results, despite the presence of multiple sources within the 2π sr field of view of the antennas. This ratio is the key sensitivity parameter for radio telescopes. The presented technique allows in situ performance evaluation using astronomical calibration sources, i.e., without the use of reference sources, a controlled environment or lab equipment. We use this technique to evaluate the performance of some of the already available LOFAR hardware and demonstrate that LOFAR has the desired sky noise dominated performance.

55 citations

Patent
07 Dec 2004
TL;DR: In this article, a method for calibrating a phase array antenna comprises performing initial measurements of array antenna elements to ensure that calibration measurements are within the linear dynamic range of receive elements contained within the array.
Abstract: A method for calibrating a phase array antenna comprises performing initial measurements of array antenna elements to ensure that calibration measurements are within the linear dynamic range of receive elements contained within the array. The method includes deriving calibration coefficients from a direct measurement of a forced out of phase condition and detection of deep nulls through adjustment of amplitude and phase settings over a range of frequencies of interest.

55 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023373
20221,052
2021661
2020979
20191,266
20181,066