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.

FD-TD analysis of Vivaldi flared horn antennas and arrays

Abstract: This paper summarizes a detailed computational study of Vivaldi flared horn antenna designs including single element, double element crossed-pair subarray elements, and linear arrays using the finite-difference time-domain (FD-TD) method. FD-TD, which numerically solves Maxwell's time dependent curl equations, accounts for the complex geometrical and electrical characteristics associated with this antenna design and array implementation. Validations have been made relative to a moment method (MM) model of an electrically large linearly tapered slot antenna. Also, good correlation is shown to exist in the primary features of the antenna patterns between computed and measured data for all cases. This work has achieved a number firsts for the FD-TD methodology. It represents the first "exact" computational model of a single quad Vivaldi slot antenna; the first "exact" computational model of a phased array of Vivaldi quad elements; and the first FD-TD model to demonstrate grating lobes for a phased array antenna of any sort. Lastly, this research represents an extensive study of the largest grid-based antenna models conducted to date. >

Phased-array antenna beam squinting related to frequency dependency of delay circuits

Abstract: Practical time delay circuits do not have a perfectly linear phase-frequency characteristic. When these delay circuits are applied in a phased-array system, this frequency dependency shows up as a frequency dependent beam direction (“beam squinting”). This paper quantifies beam squinting for a linear one-dimensional phased array with equally spaced antenna elements. The analysis is based on a (frequency-dependent) linear approximation of the phase transfer function of the delay circuit. The resulting relation turns out to be invariant for cascaded cells. Also a method is presented to design time-delay circuits to meet a maximum phased-array beam squinting requirement.

Fast Beamforming for Mobile Satellite Receiver Phased Arrays: Theory and Experiment

Abstract: The purpose of this paper is to present a robust and fast beamforming algorithm for the low-cost mobile phased array antennas. The proposed beamforming algorithm uses a sequentially perturbation gradient estimation method to update the control voltages of the phase shifters, with the objective of maximizing the received power by the array. This algorithm does not require either the knowledge of phase shifter characteristics or signal direction-of-arrival. Moreover, in this paper, the algorithm parameters are derived for the stationary and mobile platform configurations. For the stationary array, it is shown how the proper selection of the beamforming parameters limits the noise effects and increases the array output power. For the mobile array, a condition for the fast convergence is derived and the advantage of using nonuniform step size to update the control voltages is illustrated. When phase shifters suffer from the imbalanced insertion loss the proposed beamforming technique perturbs the phase-conjugate condition to increase the total received power. This algorithm has been implemented with the low-cost microwave components and applied to a Ku-band phased array antenna with 34 sub-arrays. The experimental results verify the broadband performance, and the fast convergence of the algorithm for different platform maneuvers.

TerraSAR-X technologies and first results

Abstract: TerraSAR-X is a satellite that is scheduled to be launched in October 2006 and is currently being built in the framework of a public-private partnership between the German Aerospace Centre (DLR) and EADS Astrium GmbH Germany and will carry an X-band synthetic aperture radar (SAR) instrument equipped with an active phased array antenna. Its operational flexibility will allow the use of the instrument for scientific and commercial applications. High amplitude and phase stability of the radar instrument is achieved by a carbon fibre reinforced plastic slotted waveguide radiator and a high precision transmit/receive module. Additionally, internal calibration hardware will allow for determination of the residual drifts. Precise central electronics controls the radar instrument, provides an arbitrary transmit chirp and receives the radar echo with selectable bandwidth and raw data compression ratio. The ground station's multimode SAR processor is supported by a novel satellite steering law to reduce the attitude-dependent mean Doppler shift. This article summarises the EUSAR 2004 TerraSAR-X contributions.

What is the optimum phased array coil design for cardiac and torso magnetic resonance

Abstract: To determine the optimum configuration of a phased array MR coil system for human cardiac applications, the sensitivity of 10 flexible array designs operating under ideal conditions was calculated at 13 points circling the myocardium of a model torso whose geometry was determined from healthy volunteers. The array geometries that were evaluated included continuous strips of 2, 4, 6, and 10 circular coils of diameter equal to half the torso thickness wrapped laterally around the torso, 2 pairs of coils located on the left side of the chest and back, clusters of 3 coils in 2 orientations, clusters of 4 and 6 coils, and a hybrid cross of 6 coils. The 4-, 6-, and 10-coil strip arrays out-performed the other designs for a given number of coils, yielding average theoretical sensitivity improvements of 45%, 53%, and 55% relative to a single flexible coil positioned at the point closest to the anterior myocardium, compared with about 30% for 4- and 6-coil clusters and the 2-pair geometry (P < 0.02). A flexible 4-coil strip array was constructed for a clinical 1.5 T scanner with 15-cm diameter circular surface coils on flexible circuit board. The signal-to-noise ratio (SNR) of this coil at the 13 cardiac locations was measured in 15 normal volunteers and compared with the SNR measured in images acquired with standard commercial MR coils: a body coil, a flexible torso array, a general purpose flexible coil, and, in 4 subjects, a dual array coil. In the prone orientation, the average myocardial SNR improvement of the 4-coil strip array was 650% relative to the whole body coil, compared with 310-340% for the other commercial coils (P < 0.00005). The twofold advantage over the commercial coils persisted in supine studies (P < 0.00005, n = 5). Thus, flexible circumferential phased arrays of strips of surface coils of diameter comparable with the depth of the heart generally out-perform many other standard geometries for a given number of coils, and can yield dramatically improved SNR over coils available for general use in the torso.