No. 1 (2007)
Published:
2007-03-30
ARTICLES FROM THIS ISSUE
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Performance and operation of stressed dual gap RF MEMS varactors
Abstract
The design, fabrication and measurement of a continuously tunable RF MEMS capacitor is described. The capacitor’s dual gap height architecture allows for electrostatic tuning with low resistive loss and a large tuning range. A new dual tuning scheme is introduced for use with two voltage sources. This dual tuning, coupled with a stress-induced bridge, is used to reach further device tuning. Measurements indicate a continuously tunable capacitance range of 6.2:1 with a quality factor over 50 at 30 GHz for 310 fF.
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SiGe HBT wideband amplifier for millimeter wave applications
Abstract
A wideband amplifier up to 50 GHz has been implemented in a 0.25 μm, 200 GHz ft SiGe BiCMOS technology. Die size was 0.7×0.73 mm2. The two-stage design achieves more than 11 dB gain over the whole 20 to 50 GHz band. Gain maximum was 14.2 dB at 47.5 GHz. Noise figure was lower than 9 dB up to 34 GHz and a current of 30 mA was drawn from a 4 V supply. To the author’s best knowledge this is the highest gain bandwidth product of a monolithic SiGe HBT amplifier ever reported.
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A wideband smart antenna employing spatial signal processing
Abstract
A smart antenna with capability of beam steeringin azimuth over a wide frequency band using only spatial sig-nal processing is presented. Filters and tapped-delay networksemployed in conventional wideband linear arrays are avoidedby using a two-dimensional rectangular array structure. Inthis array, only constant real-valued weighting coefficients, re-alized with amplifiers or attenuators, are used to form a de-sired radiation pattern. In order to estimate direction of ar-rival of a wideband signal, the MUSIC algorithm in conjunc-tion with an interpolated array technique is applied. In theinterpolated array technique, a composite covariance matrixis generated, which is a simple addition of covariance matricesof narrowband virtual arrays, being stretched or compressedversions of a nominal array. A working prototype of this wide-band array is presented. Its operation is assessed via full EMsimulations and measurements.
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Optimizing circular polarization within a beam of patch antenna elements
Abstract
The paper presents the results of an investigation into patch antenna elements that would be capable of pro- viding good circular polarization not only in the broadside direction, but also over a wide range of elevation angles.
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Modified monopole ring antennas as a solution for HiperLAN1/2 and IEEE 802.11b/g standard devices
Abstract
A compact planar antenna for multisystem ap- plications has been designed and manufactured. A modified feeding method has been used to meet the requirements of modern telecommunications devices. It has been shown, that by adjusting the size of the rings, required allocation of bands is possible. The proposed antenna is suitable for ISM band devices and gives perspectives for multi-standard operation. The antenna has been simulated using MoM 2.5D software Zeland IE3D, next fabricated and measured.
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Phased array antennas in MIMO receiver
Abstract
In this paper, a computer simulation of a MIMO system comprising phased array antennas (PAA) in all receiving branches is presented. In order to examine the system performance under relatively realistic conditions, a ray-tracing simulator was applied to generate a baseband channel impulse response matrix H. A bit error rate (BER) of two systems utilizing different detection methods: V-BLAST and simple matrix inversion was examined in order to determine phased array antennas applicability. Results of an attempt to determine relationship between BER and properties of particular matrix H realization are also provided.
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X-band coaxial monopole antenna with an additional metal screen
Abstract
The novel coaxial monopole antenna design with an additional metal screen is presented. The radiation char- acteristics of this antenna are investigated depending on a dis- tance between the ground plane and additional metal screens, as well as on a size of the latter. Measured and calculated ra- diation patterns are compared within limits of the operative frequency band and their revealed distinctions are discussed. The antennas characteristics allow pronounce that it can be considered as a promising candidate for various practical ap- plications both a single radiator and a composite element of antenna arrays.
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Analysis and optimization of outputs of high power microwave tubes
Abstract
The subject of this work is optimization of outputs of L-band high power microwave tubes. These outputs are constructed as coaxial-to-waveguide transitions with a vacuum barrier in a form of glass or ceramic cup. The goal of optimization is to obtain sufficiently low reflection loss in the predefined frequency band and to avoid so called hot spots caused by excessive dissipation of microwave power in parts of the cup. Electromagnetic simulator has been applied to model the behavior of the optimized transition and to propose its optimum shape. The proposed solutions were verified by Z.E. Lamina SA in prototypes of high power (pulsed 600 kW) amplitrons and are to be used in manufacturing practice.
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On the ambiguity function for accelerating target in FMCW radar
Abstract
In the paper, we are concerned with FMCWradar detection of an accelerating target, echo of which is buried in an additive white Gaussian noise. We derive and analyze three-dimensional generalized ambiguity function for target range, velocity and acceleration. We interpret known properties of this function and obtain new ones, which allows us to specify resolutions and regions of unambiguity for range, velocity and acceleration. The obtained resolutions we express in terms of corresponding Cramer-Rao bounds.
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Technologies for low cost small satellites
Abstract
Paper presents short description of satellite struc- ture and characterization of its subsystems. Review of tech- nologies used in small satellite missions is presented, consid- ering possible solutions in low cost projects. Three common solutions: the use of commercial off the shelf (COTS) compo- nents, miniaturization, remote testing and integration of sub- systems can be used to significantly reduce cost of the satellite.
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MUPUS insertion device for the Rosetta mission
Abstract
An original mechanical device designed to insert a penetrator into a cometary nucleus in an almost gravityfree environment is described. The device comprises a hammer and a power supply system that stores electrical energy in a capacitor. The accumulated energy is discharged through a coil forming a part of electromagnetic circuit that accelerates the hammer. The efficiency of converting the electrical energy to kinetic energy of the hammer is not very high (amounts to about 25%), but the system is very reliable. Additionally, the hammer energy can be chosen from four power settings, hence adjustment of the stroke’s strength to nucleus hard- ness is possible. The device passed many mechanical, func- tional, thermal and vibration tests and was improved from one model to another. The final, flight model was integrated with the lander Philae and started its space journey to comet Churyumov-Gerasimenko in March 2004.
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Control and reconfiguration of satellite formations by electromagnetic forces
Abstract
Current concept of interferometric missions assume that they employ formations of spacecraft. The cooperation between members of a multisatellite formation is a challenging problem. One of the main difficulties is to implement a reliable system for position control and actuation. A precise control of the position and orientation of each satellite in the array is a key factor in obtaining high quality images of distant objects. The controlling system should frequently collect data about geometry and kinematics of all array elements and use actuators to keep them as close as possible to their nominal positions. Forces that are required for actuation or array reconfiguration in space can be produced by engines of various types. In most cases chemical propulsion is used, with a drawback of limited fuel resources and a danger of polluting optical elements. In our work, we analyze dynamics of satellite formation flight, in which interaction forces result from electromagnetic fields generated by coils with current. We use simple controller equation proposed by members of MIT team to control a formation of two or three aligned satellites rotating around the array’s mass center.
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Interception of a free-rotating satellite: an autonomous rendezvous scenario
Abstract
The spacecraft’s lifetime is often limited by reliability and redundancy of its components. Furthermore, serious restrictions on duration of spacecraft operations are posed by finite amount of fuel or cooling agent. It is also clear that once a satellite is launched, it is extremely difficult to replace/modify its hardware on the orbit. Future spacecraft missions, especially huge planetary orbiters, will require servicing support from autonomous unmanned satellites. In this paper we introduce and analyze a new scenario for interception of a free rotating satellite ion a Keplerian orbit. The scenario is divided into several stages to be executed by the servicing satellite: attitude determination of the target object; own motion planning; determination of the optimal target position and orientation before docking; controlled approach, i.e., decreasing of a range between satellites; orbiting of the servicing satellite around the target satellite; docking, i.e., radial degreasing of the intersatellite range till the satellites contact, while keeping constant the relative orienta- tion between them. The control algorithm for the servicing satellite motion during its maneuvers is described. Finally, a few examples of satellite motion simulations according to the proposed scenario are presented.
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Feasibility study of the space synthetic aperture radar for the SSETI-ESMO project
Abstract
The following paper presents the analysis of the feasibility study of the SAR radar for lunar space missions. The European StudentsMoon Orbiter (ESMO) project is con- ducted by the Students Space Exploration and Technology Initiative (SSETI) association. The phase A of this project is supported by the European Space Agency (ESA).
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Summary of SSETI Express satellite mission – gained experience
Abstract
In the following paper we present the results of our input in the first of SSETI space missions: SSETI Express, the predecessor of ESEO mission, which we are currently working on, the experience we have gained from this project and how it can benefit us during the upcoming ESEO mission.
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Building distributed ground station system with radio amateurs
Abstract
The paper concerns radio amateur satellites that are built by international student teams. For contacting a satellite, a single ground station is usually used. In this configuration and with the satellite on the low Earth orbit (LEO), teams have contact only for about 40 minutes per day. If the satellite has service for radio amateurs, they use it for 20 hours per day. A lot of them have connection to Internet. This is a big difference. In this paper, is shown how they can use the radio amateur transceivers and antenna systems in order to build ground stations network named distributed ground station system (DGSS). Frequencies, types of modulations, calculation of power budge, and the ways to control amateur stations by the Internet are also shown. These are essential procedures, because radio amateurs have their standards and habits. Finally a proposal of implementation dedicated DGSS system for radio amateurs with and without use of APRS network is put forward. Distributed ground station is one of the experiments on PW-Sat satellite, which is being build on the Warsaw University of Technology.
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Microwave radiometry in monitoring and emergency mapping of water seepage and dangerously high groundwaters
Abstract
Detailed and geo-referenced maps identifying the locations of saturated and dry levees can be produced using microwave radiometric measurements from a light aircraft or helicopter, and integrated with GPS for positioning and orientation. The development of synergetic remote sensing technology for raised groundwater and seepage detection by the joint use of microwave and optical data along with GIS databases is an effective and most contemporary way of supporting risk assessment and facilitating disaster prevention and management. In this paper we present a remote sensing microwave technology for monitoring and detection of areas of water seepage through irrigation constructions, levees and dykes as well as for revealing areas with dangerously high groundwater level. The possibility for emergency response mapping, integrated with GPS and GIS data, facilitates the risk assessment and management services. The passive microwave radiometry (PMR) is based on spectral measurements in the millimetre to decimetre range of wavelengths. Compared to other remote sensing techniques, such as colour and infrared photography, thermal images and lidar, PMR is the only technology taking measurements under the earth’s surface and therefore is very well suited for water seepage and underground water monitoring in a fast and reliable way.
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Modeling of mixed traffic for mobile cellular network
Abstract
The most convenient way of presenting one- or two-dimensional offered traffic in a network by Markovian chain to evaluate quality of service (QoS). Pictorial presentation of chain becomes very complicated for three dimensional traffic case, required for voice data integrated service/mixed traffic of mobile cellular network; hence application of cut or node equations become a cumbersome job. This paper proposes a model of three-dimensional traffic in a network for both unlimited and limited user case. Here direct analytical method is introduced instead of Markovian chain to achieve traffic parameters.
