ABSTRACT This study investigates optimal three dimensional antennas for adaptive applications. Th... more ABSTRACT This study investigates optimal three dimensional antennas for adaptive applications. The choice of the antenna element distribution on the spherical surface is governed by the desire to maintain a nearby constant pattern. Spherical arrays provide wide scan coverage with low grating lobe levels. We calculate the uniform distribution of a set of antennas on a sphere. Based on formulas of the spherical trigonometry, we show all the possible exact uniform distributions. It is astonishing, that only five possible solutions can be found. In this paper, the co-ordinates and the figures of these regular polyhedrons are shown. Because the number of possible uniform spherical distributions is limited, the number of elements that can be placed uniformly without approximation on a spherical surface is also limited to 20
A channel measurement campaign, done with a system from the University of Kassel, is reported. Wi... more A channel measurement campaign, done with a system from the University of Kassel, is reported. With very high bandwidth (600 MHz), a large room has been measured at 1.8 GHz with a moving antenna, forming a synthetic aperture. The transformation from the transfer function in the frequency-domain to the time-domain received signal, with the training sequence included, is explained. On
IEE Proceedings - Microwaves, Antennas and Propagation, 2004
ABSTRACT The design and realisation of a dodecahedral antenna is investigated. The three-dimensio... more ABSTRACT The design and realisation of a dodecahedral antenna is investigated. The three-dimensional design with pentagonally shaped faces is described. The simulation program NEC2 (numerical electromagnetics code, version 2) is used to simulate the proposed design. This dodecahedral antenna configuration is optimised for all pertinent parameters, according to the coupling constraints and the radiation pattern. The coupling values and the radiation pattern are measured and compared with the simulated values.
Proceedings of the 5th European Conference on Antennas and Propagation, Apr 11, 2011
The principal effects that have been investigated are the attenuation due to shadowing and the oc... more The principal effects that have been investigated are the attenuation due to shadowing and the occurrence of false echoes in a radar system. For a communication system, the attenuation due to the presence of the turbine and the modulation due to the movement of the blades and nacelle have been investigated. Some agencies (most Air Navigation Service Providers, for instance) require very large distances to be maintained from their installations, to allow them to follow all air traffic clearly. For special applications however, it is possible to install turbines much closer to the RF installations than one might expect from general rules. The first aspect that has to be noted is that the near-field radar cross section (RCS) (1) of a turbine is much smaller than the far-field formulas (2). Indeed, the far-field of a turbine is only reached when the turbine is out of view of the installations due to the curvature of the earth. So, the interaction with the turbine happens in the Fresnel zone of the turbine. Approximated formulas for turbines in the far-field of the RF system have already been published in (3). In this paper, we will investigate a turbine which is even closer namely in the Fresnel zone of an RF system antenna, which has not yet been investigated up to now.
The instability of the electric field integral equation at low frequencies is studied. The source... more The instability of the electric field integral equation at low frequencies is studied. The source of this instability is identified, both in mathematical and physical terms, and an alternative, possibly stable form of the integral equation is suggested. Implementation details for this alternative are then discussed, touching on the selection of basis function and the handling of the singular kernel.
An alternate form of the EFIE, depending on both current and charge, has been implemented and ver... more An alternate form of the EFIE, depending on both current and charge, has been implemented and verified. A brief overview of the underlying theory will be given, and the deriva- tion of an implementable form will be discussed. Techniques and formulas for handling the singularities have been worked out. The stability of an implementation has then been examined and found
For the simulation of large ATM networks abackground load must be offered to the networkin order ... more For the simulation of large ATM networks abackground load must be offered to the networkin order to obtain useful information. Howeverthe generation of this network load is extremelyresource demanding, because ATM cells must begenerated and discarded at a high rate. This pa-per proposes a source/destination model that al-lows efficient traffic generation: the backgroundload is generated at the ATM layer and
IEEE Benelux Chapter on Vehicular Technology and Communications. Symposium on Communications and Vehicular Technology. SCVT-2000. Proceedings (Cat. No.00EX465), 2000
ABSTRACT This study investigates optimal three dimensional antennas for adaptive applications. Th... more ABSTRACT This study investigates optimal three dimensional antennas for adaptive applications. The choice of the antenna element distribution on the spherical surface is governed by the desire to maintain a nearby constant pattern. Spherical arrays provide wide scan coverage with low grating lobe levels. We calculate the uniform distribution of a set of antennas on a sphere. Based on formulas of the spherical trigonometry, we show all the possible exact uniform distributions. It is astonishing, that only five possible solutions can be found. In this paper, the co-ordinates and the figures of these regular polyhedrons are shown. Because the number of possible uniform spherical distributions is limited, the number of elements that can be placed uniformly without approximation on a spherical surface is also limited to 20
2011 XXXth URSI General Assembly and Scientific Symposium, 2011
ABSTRACT The main effects of wind turbines on radars have been described in previous papers [1-3]... more ABSTRACT The main effects of wind turbines on radars have been described in previous papers [1-3]. They include shadowing by the larger parts and generation of false echoes. Previous studies have been focusing on the influence of moving objects, such as wind turbines, on aeronautical and maritime radars, usually working in the L/S band and in the X-band respectively. Here, we will not only take into account terrain properties, but also compute systems very close to each other and at lower frequencies, where UTD is not valid any more. Also, particular attention will be paid to the computations of systems that are in the near-field of the antenna.
2011 XXXth URSI General Assembly and Scientific Symposium, 2011
ABSTRACT The Method of Moments (MoM, also referred to as the Boundary Element Method outside of e... more ABSTRACT The Method of Moments (MoM, also referred to as the Boundary Element Method outside of electromagnetics [1]) is a well-known and oft-used technique for complex electromagnetics simulations based on a numerical approach to Maxwell's equations. Results can be very accurate, but as it requires solving a dense matrix equation it is very computationally intensive. MoM has traditionally been used for narrow-band antenna simulations, but thanks to advances in processing power and in the technique itself, it is slowly becoming feasible to perform simulations of electrically large objects and of diverse scenarios over a broad frequency band.
A channel measurement campaign, done with a system from the University of Kassel, is reported. Wi... more A channel measurement campaign, done with a system from the University of Kassel, is reported. With very high bandwidth (600 MHz), a large room has been measured at 1.8 GHz with a moving antenna, forming a synthetic aperture. The transformation from the transfer function in the frequency-domain to the time-domain received signal, with the training sequence included, is explained. On
ABSTRACT This study investigates optimal three dimensional antennas for adaptive applications. Th... more ABSTRACT This study investigates optimal three dimensional antennas for adaptive applications. The choice of the antenna element distribution on the spherical surface is governed by the desire to maintain a nearby constant pattern. Spherical arrays provide wide scan coverage with low grating lobe levels. We calculate the uniform distribution of a set of antennas on a sphere. Based on formulas of the spherical trigonometry, we show all the possible exact uniform distributions. It is astonishing, that only five possible solutions can be found. In this paper, the co-ordinates and the figures of these regular polyhedrons are shown. Because the number of possible uniform spherical distributions is limited, the number of elements that can be placed uniformly without approximation on a spherical surface is also limited to 20
A channel measurement campaign, done with a system from the University of Kassel, is reported. Wi... more A channel measurement campaign, done with a system from the University of Kassel, is reported. With very high bandwidth (600 MHz), a large room has been measured at 1.8 GHz with a moving antenna, forming a synthetic aperture. The transformation from the transfer function in the frequency-domain to the time-domain received signal, with the training sequence included, is explained. On
IEE Proceedings - Microwaves, Antennas and Propagation, 2004
ABSTRACT The design and realisation of a dodecahedral antenna is investigated. The three-dimensio... more ABSTRACT The design and realisation of a dodecahedral antenna is investigated. The three-dimensional design with pentagonally shaped faces is described. The simulation program NEC2 (numerical electromagnetics code, version 2) is used to simulate the proposed design. This dodecahedral antenna configuration is optimised for all pertinent parameters, according to the coupling constraints and the radiation pattern. The coupling values and the radiation pattern are measured and compared with the simulated values.
Proceedings of the 5th European Conference on Antennas and Propagation, Apr 11, 2011
The principal effects that have been investigated are the attenuation due to shadowing and the oc... more The principal effects that have been investigated are the attenuation due to shadowing and the occurrence of false echoes in a radar system. For a communication system, the attenuation due to the presence of the turbine and the modulation due to the movement of the blades and nacelle have been investigated. Some agencies (most Air Navigation Service Providers, for instance) require very large distances to be maintained from their installations, to allow them to follow all air traffic clearly. For special applications however, it is possible to install turbines much closer to the RF installations than one might expect from general rules. The first aspect that has to be noted is that the near-field radar cross section (RCS) (1) of a turbine is much smaller than the far-field formulas (2). Indeed, the far-field of a turbine is only reached when the turbine is out of view of the installations due to the curvature of the earth. So, the interaction with the turbine happens in the Fresnel zone of the turbine. Approximated formulas for turbines in the far-field of the RF system have already been published in (3). In this paper, we will investigate a turbine which is even closer namely in the Fresnel zone of an RF system antenna, which has not yet been investigated up to now.
The instability of the electric field integral equation at low frequencies is studied. The source... more The instability of the electric field integral equation at low frequencies is studied. The source of this instability is identified, both in mathematical and physical terms, and an alternative, possibly stable form of the integral equation is suggested. Implementation details for this alternative are then discussed, touching on the selection of basis function and the handling of the singular kernel.
An alternate form of the EFIE, depending on both current and charge, has been implemented and ver... more An alternate form of the EFIE, depending on both current and charge, has been implemented and verified. A brief overview of the underlying theory will be given, and the deriva- tion of an implementable form will be discussed. Techniques and formulas for handling the singularities have been worked out. The stability of an implementation has then been examined and found
For the simulation of large ATM networks abackground load must be offered to the networkin order ... more For the simulation of large ATM networks abackground load must be offered to the networkin order to obtain useful information. Howeverthe generation of this network load is extremelyresource demanding, because ATM cells must begenerated and discarded at a high rate. This pa-per proposes a source/destination model that al-lows efficient traffic generation: the backgroundload is generated at the ATM layer and
IEEE Benelux Chapter on Vehicular Technology and Communications. Symposium on Communications and Vehicular Technology. SCVT-2000. Proceedings (Cat. No.00EX465), 2000
ABSTRACT This study investigates optimal three dimensional antennas for adaptive applications. Th... more ABSTRACT This study investigates optimal three dimensional antennas for adaptive applications. The choice of the antenna element distribution on the spherical surface is governed by the desire to maintain a nearby constant pattern. Spherical arrays provide wide scan coverage with low grating lobe levels. We calculate the uniform distribution of a set of antennas on a sphere. Based on formulas of the spherical trigonometry, we show all the possible exact uniform distributions. It is astonishing, that only five possible solutions can be found. In this paper, the co-ordinates and the figures of these regular polyhedrons are shown. Because the number of possible uniform spherical distributions is limited, the number of elements that can be placed uniformly without approximation on a spherical surface is also limited to 20
2011 XXXth URSI General Assembly and Scientific Symposium, 2011
ABSTRACT The main effects of wind turbines on radars have been described in previous papers [1-3]... more ABSTRACT The main effects of wind turbines on radars have been described in previous papers [1-3]. They include shadowing by the larger parts and generation of false echoes. Previous studies have been focusing on the influence of moving objects, such as wind turbines, on aeronautical and maritime radars, usually working in the L/S band and in the X-band respectively. Here, we will not only take into account terrain properties, but also compute systems very close to each other and at lower frequencies, where UTD is not valid any more. Also, particular attention will be paid to the computations of systems that are in the near-field of the antenna.
2011 XXXth URSI General Assembly and Scientific Symposium, 2011
ABSTRACT The Method of Moments (MoM, also referred to as the Boundary Element Method outside of e... more ABSTRACT The Method of Moments (MoM, also referred to as the Boundary Element Method outside of electromagnetics [1]) is a well-known and oft-used technique for complex electromagnetics simulations based on a numerical approach to Maxwell's equations. Results can be very accurate, but as it requires solving a dense matrix equation it is very computationally intensive. MoM has traditionally been used for narrow-band antenna simulations, but thanks to advances in processing power and in the technique itself, it is slowly becoming feasible to perform simulations of electrically large objects and of diverse scenarios over a broad frequency band.
A channel measurement campaign, done with a system from the University of Kassel, is reported. Wi... more A channel measurement campaign, done with a system from the University of Kassel, is reported. With very high bandwidth (600 MHz), a large room has been measured at 1.8 GHz with a moving antenna, forming a synthetic aperture. The transformation from the transfer function in the frequency-domain to the time-domain received signal, with the training sequence included, is explained. On
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Papers by Emmanuel Van Lil