Switching Performance of a 12 GHz p-i-n Phase Shifter/Driver Module for Satellite Communication Phased Array

The design and implementation of a high-speed, lowpower, and TTL-compatible driver for a 12 GHz digital p-i-n phase shifter are shown. The switching performance of the phase shifter, combined with its driver in a compact module, is presented. Measurements of 40 phase shifter/driver modules show that the longest time required to change phase states (switching time) is under 8 ns. The maximum driving power consumption is 36 mW at a phase switching repetition rate of 1 MHz. Each module can handle 800 mW of CW RF power. The performance and compactness of the phase shifter/driver make this module especially attractive for satellite and airborne applications.     

A smart repair embedded memetic algorithm for 2D shape matching problems

Shape representation plays a major role in any shape optimization exercise. The ability to identify a shape with good performance is dependent on both the flexibility of the shape representation scheme and the efficiency of the optimization algorithm. In this article, a memetic algorithm is presented for 2D shape matching problems. The shape is represented using B-splines, in which the control points representing the shape are repaired and subsequently evolved within the optimization framework. The underlying memetic algorithm is a multi-feature hybrid that combines the strength of a real coded genetic algorithm, differential evolution and a local search. The efficiency of the proposed algorithm is illustrated using three test problems, wherein the shapes were identified using a mere 5000 function evaluations. Extension of the approach to deal with problems of unknown shape complexity is also presented in the article.     

Optical fiber up-tapers with high beam expansion ratios forcomponent fabrication

Optical fibre up-tapers with beam expansion ratios of 10, about twice the previously achieved value for the same taper outer diameter, have been fabricated and characterized. The increased beam expansion is achieved with a near step-index profile for the core of the taper. The excess coupling loss between two tapers is less than 0.1 dB. A lateral offset of more than 20 μm or an axial displacement of 4 mm between tapers caused an excess loss of 1 dB. The angular tolerance for this loss is a manageable 0.3°. These tapers permit, for a given beam expansion ratio, the manufacture of smaller outer diameter, more compact structures of self-aligned beam expansion. They also permit the insertion of optical elements into the expanded beam for the fabrication of inline single-mode passive fiber components     

Compensation of spherical reflector aberrations by planar array feeds

The feasibility of correcting phase aberrations of spherical reflector antennas with planar array feeds has been investigated. This type of feed seems to be particularly attractive for applications requiring several closely spaced beams. A synthesis procedure for the array excitation has been developed which minimizes the mean-square error with respect to a prescribed reflector illumination. This method was applied to the analysis of a spherical reflector antenna with a642lambdadiameter and an effectiveFnumber of 0.9.     

On energy conservation and the method of moments in scattering problems

Electromagnetic scattering problems, including waveguide discontinuity, phased array, and scattering (exterior type) problems, are frequently described by integral equations that can be solved by the Ritz-Galerkin or generalized method of moments. Under appropriate conditions, it has been shown that reciprocity and variational properties are, in fact, preserved in the approximate solutions. It is shown here that in the Ritz-Galerkin method, energy is also conserved under certain conditions, even in those scattering problems where reciprocity does not exist. Hence energy conservation cannot serve as a check for accuracy of a numerical solution obtained by the Ritz method or other related methods.     

Narrow multibeam satellite ground station antenna employing a linear array with a geosynchronous arc coverage of 60°, part II: Antenna design

A dually polarized narrow (< 0.5deg) beam antenna which provides a geosynchronous arc coverage of60degis proposed and analyzed. To track the geosynchronous arc accurately, the properly oriented antenna produces a conically scanned beam by means of a linear array of feed horns with bias cut apertures illuminating a pair of parabolic cylinder reflectors in an imaging arrangement. This design, with reduced size array and singly carved reflectors, is relatively simple to construct. Calculations for a0.35degbeamwidthKuband earth station antenna show a0.05degpointing accuracy with scan loss due to aberrations less than 1 dB and little pattern degradation throughout the scan region. For multiple beam capability, a Rotman lens is proposed and analyzed as a means of exciting the feed array. It allows communication with multiple satellites spaced as close as1deg.     

Polarization matching of wide angle conically scanned phased array beams

Multisatellite communication may require coverage of a segment of the geosynchronous arc as large as60deg. A properly oriented ground station antenna can cover the above segment by means of a beam whose axis traces a conical surface (i.e., conically scanned beam). The antenna consists of two linear arrays feeding an imaging reflector arrangement through a polarization diplexer. This diplexer separates the incoming wave into two orthogonal polarizations without loss. In general, the polarization of the wave reflected by the diplexer does not remain the same as that corresponding to the feed array as the beam is scanned (polarization mismatch). This mismatch can cause an appreciable degradation of the antenna gain when the feed array is scanned in certain directions. For example, a ground station located at Seattle, WA could experience 3.6 dB reduction in gain due to polarization mismatch when the antenna beam is scanned along a60degsegment of the geosynchronous satellite arc. The above polarization mismatch loss can be substantially reduced by the use of two properly inclined polarization rotators. These devices are sufficiently broadband to cover the entire 12/14 GHz satellite communication band. Design formulas for the inclination angle between the polarization rotators are presented. Applying these formulas we have reduced the above-mentioned polarization mismatch loss to less than 0.01 dB.     

Measurement-based estimates of bit-error-rate performance in urbanLOS microcells at 900 MHz

Cumulative distribution estimates are presented for the one-second-average bit-error-rate (BER) which would be experienced on UHF links in a microcellular environment. It is assumed that users (subscribers) are moving at speeds ranging from quasi-stationary to 96 km/h. The authors concentrate on lineal microcells, in which there is always a line-of-sight path between the microcell and subscriber antennas, in addition to road-reflected and/or building-reflected rays. Using extensive UHF data collected in Manhattan, the signal and interference levels are characterized, point-by-point, for a subscriber moving in a lineal microcell. Combining these measurement-based characterizations with a mathematical model of modem performance, the cumulative distribution of the BER is computed. For moving subscribers, simple diversity reception gives large benefits in grade-of-service (percentage of time that the BER is below a specified threshold value) and uplink and downlink transmission qualities tend to be similar, with the latter being somewhat better. Performance estimates based on a multiray model are generally similar to those based on measured data and tend to be conservative     

Load control on a dynamically pitching finite span wind turbine blade using synthetic jets

The feasibility of active flow control, via arrays of synthetic jet actuators, to mitigate hysteresis was investigated experimentally on a dynamically pitching finite span S809 blade. In the present work, a six‐component load cell was used to measure the unsteady lift, drag and pitching moment. Stereoscopic Particle Image Velocimetry (SPIV) measurements were also performed to understand the effects of synthetic jets on flow separation during dynamic pitch and to correlate these effects with the forces and moment measurements. It was shown that active flow control could significantly reduce the hysteresis in lift, drag and pitching moment coefficients during dynamic pitching conditions. This effect was further enhanced when the synthetic jets were pulsed modulated. Furthermore, additional reduction in the unsteady load oscillations can be observed in post‐stall conditions during dynamic motions. This reduction in the unsteady aerodynamic loading can potentially lead to prolonged life of wind turbine blades. Copyright © 2014 John Wiley & Sons, Ltd.