Thomas F. Eibert

Technische Universität München | TUM

According to the electromagnetic uniqueness theorem, the radiation behavior of an antenna under test (AUT) can be recovered from measurements of two tangential components of its radiated fields on an enclosing surface. In practice, measurements conducted in the radiating near-field (NF) of an AUT utilize probe antennas of finite size. Thus, instead...

p>The characterization of unknown antennas under test (AUTs) from measurements of the radiated near field (NF) is commonly performed with known probe antennas. By accounting for the behavior of a given probe in the processing of the NF data, the obtained quantities of interest, e.g., the far-field (FF) behavior of the radiator, are free of biases a...

p>According to the electromagnetic uniqueness theorem, the radiation behavior of an antenna under test (AUT) can be recovered from measurements of two tangential components of its radiated fields on an enclosing surface. In practice, measurements conducted in the radiating near-field (NF) of an AUT utilize probe antennas of finite size. Thus, inste...

The accurate solution of quasi-Helmholtz decomposed electric field integral equations (EFIEs) in the presence of arbitrary excitations is addressed: Depending on the specific excitation, the quasi-Helmholtz components of the induced current density do not have the same asymptotic scaling in frequency, and thus, the current components are solved for...

p>A ray tracing framework based on the utilization of multiple Huygens surfaces is introduced and evaluated. As such, complex propagation environments are divided into smaller subdomains, thereby restricting rays to traverse within a smaller, simpler space. The subdomains are surrounded by the Huygens surfaces and equivalent Huygens sources interco...

p>A ray tracing framework based on the utilization of multiple Huygens surfaces is introduced and evaluated. As such, complex propagation environments are divided into smaller subdomains, thereby restricting rays to traverse within a smaller, simpler space. The subdomains are surrounded by the Huygens surfaces and equivalent Huygens sources interco...

Near-field measurements, which are performed in-situ, may suffer from the fact that the antenna under test (AUT) cannot be accessed to transmit or receive a specifically tailored test signal. In some scenarios, it might also be desired to test the AUT during its real operation state, especially when it comes to the verification of antenna systems....

An interdigital resonator approach for wideband filter applications in ridged-waveguide technology is presented. The interdigital arrangement of the ridged-waveguide resonators ensures stronger coupling between the resonators. As the coupling sections are consequently enlarged by the interdigital arrangement of the resonators, more feasible filter...

Precise position information is important for terrestrial and airborne surveying systems, such as unmanned aerial vehicles (UAVs). Those systems often rely on real-time kinematic (RTK) global navigation satellite systems (GNSSs) for position determination, where the GNSS antenna mounting environment impacts the GNSS position accuracy to a great ext...

The magnetic field surface integral equation for perfect electrically conducting scatterers suffers from accuracy problems when discretized with lowest-order Rao-Wilton-Glisson (RWG) functions. For high-frequency scattering scenarios, one of the various reported countermeasures are hierarchical higher-order (HO) functions. We demonstrate that the a...

p>According to the electromagnetic uniqueness theorem, the radiation behavior of an antenna under test (AUT) can be recovered from measurements of two tangential components of its radiated fields on an enclosing surface. In practice, measurements conducted in the radiating near-field (NF) of an AUT utilize probe antennas of finite size. Thus, inste...

p>According to the electromagnetic uniqueness theorem, the radiation behavior of an antenna under test (AUT) can be recovered from measurements of two tangential components of its radiated fields on an enclosing surface. In practice, measurements conducted in the radiating near-field (NF) of an AUT utilize probe antennas of finite size. Thus, inste...

p>The characterization of unknown antennas under test (AUTs) from measurements of the radiated near field (NF) is commonly performed with known probe antennas. By accounting for the behavior of a given probe in the processing of the NF data, the obtained quantities of interest, e.g., the far-field (FF) behavior of the radiator, are free of biases a...

p>The characterization of unknown antennas under test (AUTs) from measurements of the radiated near field (NF) is commonly performed with known probe antennas. By accounting for the behavior of a given probe in the processing of the NF data, the obtained quantities of interest, e.g., the far-field (FF) behavior of the radiator, are free of biases a...

p>The accurate solution of quasi-Helmholtz decomposed electric field integral equations (EFIEs) in the presence of arbitrary excitations is addressed: Depending on the specific excitation, the quasi-Helmholtz components of the induced current density do not have the same asymptotic scaling in frequency, and thus, the current components are solved f...

p>The accurate solution of quasi-Helmholtz decomposed electric field integral equations (EFIEs) in the presence of arbitrary excitations is addressed: Depending on the specific excitation, the quasi-Helmholtz components of the induced current density do not have the same asymptotic scaling in frequency, and thus, the current components are solved f...

Distributed spherical harmonics expansions are a powerful approach for the efficient solution of inverse source problems. They allow for a relatively accurate representation of the geometric support of the source distribution without the overhead of handling a mesh and mesh-specific basis functions representing the commonly utilized surface current...

Phase retrieval, in particular for the operators arising from near-field measurements, is a non-convex task suffering from a severe lack of reliability due to local minima and false solutions. Approaches to tackle this issue, in turn, suffer from strict and often unrealistic oversampling requirements and possibly unfeasible computational complexiti...

p>Phase retrieval, in particular for the operators arising from near-field measurements, is a non-convex task suffering from a severe lack of reliability due to local minima and false solutions. Approaches to tackle this issue, in turn, suffer from strict and often unrealistic oversampling requirements and possibly unfeasible computational complexi...

p>Distributed spherical harmonics expansions are a powerful approach for the efficient solution of inverse source problems. They allow for a relatively accurate representation of the geometric support of the source distribution without the overhead of handling a mesh and mesh-specific basis functions representing the commonly utilized surface curre...

p>In order to accurately compute scattered and radiated fields in the presence of arbitrary excitations, a low-frequency stable discretization of the right-hand side (RHS) of a quasi-Helmholtz preconditioned electric field integral equation (EFIE) on multiply-connected geometries is introduced, which avoids an ad-hoc extraction of the static contri...

p>In order to accurately compute scattered and radiated fields in the presence of arbitrary excitations, a low-frequency stable discretization of the right-hand side (RHS) of a quasi-Helmholtz preconditioned electric field integral equation (EFIE) on multiply-connected geometries is introduced, which avoids an ad-hoc extraction of the static contri...

Time-harmonic inverse source solutions are commonly working with electric and magnetic surface current densities defined and discretized on appropriately chosen Huygens surfaces. An efficient meshless alternative are spherical harmonics expansions of low order distributed along the chosen Huygens surface, which still possess pretty good spatial loc...

p>Time-harmonic inverse source solutions are commonly working with electric and magnetic surface current densities defined and discretized on appropriately chosen Huygens surfaces. An efficient meshless alternative are spherical harmonics expansions of low order distributed along the chosen Huygens surface, which still possess pretty good spatial l...

The magnetic field surface integral equation for perfect electrically conducting scatterers suffers from accuracy problems when discretized with lowest-order Rao-Wilton-Glisson (RWG) functions. For high-frequency scattering scenarios, one of the various reported countermeasures are hierarchical higher-order (HO) functions. We demonstrate that the a...

p>The magnetic field surface integral equation for perfect electrically conducting scatterers suffers from accuracy problems when discretized with lowest-order Rao-Wilton-Glisson (RWG) functions. For high-frequency scattering scenarios, one of the various reported countermeasures are hierarchical higher-order (HO) functions. We demonstrate that the...

A fully polarimetric frequency-wavenumber domain algorithm for 3-D imaging using the synthetic aperture radar technique with irregular sample locations is introduced. At its core, the algorithm works with a multilevel plane-wave representation and relies on some of the concepts of the multilevel fast multipole method (MLFMM). By utilizing a recursi...

Most methods tackling the phase retrieval problem of magnitude-only antenna measurements suffer from unrealistic sampling requirements, from unfeasible computational complexities, and, most severely, from the lacking reliability of nonlinear and nonconvex formulations. As an alternative, we propose a partially coherent (PC) multi-probe measurement...

Some innovative near-field antenna measurement setups, e.g., UAV-based, have limited capabilites for providing a phase and magnitude reference to the receiver. Phaseless antenna measurements have always been an important topic for such scenarios, but they often suffer from the unreliability of nonconvex phase retrieval algorithms, necessity of extr...

p>Some innovative near-field antenna measurement setups, e.g., UAV-based, have limited capabilites for providing a phase and magnitude reference to the receiver. Phaseless antenna measurements have always been an important topic for such scenarios, but they often suffer from the unreliability of nonconvex phase retrieval algorithms, necessity of ex...

p>Conventional phaseless near-field measurement data is not adequate for reliable transformation into the far field. We tackle this challenge by a formulation working with multifrequency phaseless measurements under the assumption of coherently measured spectra. Such data is, for instance, obtained with a transmitting antenna under test and standar...

p>A non-reciprocal self-mixing receive antenna array is presented. First, the principle of the self-mixing concept is explained and it is found that self-mixing receivers achieve a large gain over a wide angular range, which is in contrast to reciprocity. In the second part, the design of a 4×2 antenna array operating from 34 GHz to 39 GHz includin...

A non-reciprocal self-mixing receive antenna array is presented. First, the principle of the self-mixing concept is explained and it is found that self-mixing receivers achieve a large gain over a wide angular range, which is in contrast to reciprocity. In the second part, the design of a 4×2 antenna array operating from 34 GHz to 39 GHz including...

Starting from the monopolar representation of the Rao-Wilton-Glisson (RWG) functions, an approximate inverse (AI) of the RWG Gram matrix is constructed, where only 3x3 matrices for all individual triangles have to be inverted. The inversion of the Gram matrix is, however, only approximate, since it results as the inverse of a product of singular ma...

The combined source (CS) condition is employed to augment the electric field integral equation (EFIE), whereby the CS condition is implemented as a modification of the weak form Leontovich impedance boundary condition. By doing so, both electric and magnetic surface current densities can be modeled with Rao-Wilton-Glisson (RWG) basis functions. Str...

p> The inverse source problem of near-field antenna measurements is often formulated in terms of unknown equivalent electric and magnetic surface current densities. Exploiting just the constraints for the radiated field exterior to a closed Huygens surface results in ambiguous equivalent sources due to the excitation of non-radiating currents dur...

A novel design of a broadband mm-wave patch antenna for mobile devices is introduced. The proposed antenna element operates around 40 GHz. Through utilizing a multiple resonances patch structure, 9% bandwidth has been obtained. The substrate consists of low cost material and the antenna with its microstrip feed can easily be integrated with fronten...

The accuracy of near-field antenna measurements combined with near-field far-field transformations (NFFFT) is deteriorated if objects are located in close vicinity to the antenna under test (AUT). We compare two equivalent sources based modeling techniques to suppress the influence of structures in the vicinity of the AUT. Simulation results for pe...

The accuracy problem of the classically Rao-Wilton-Glisson (RWG) discretized magnetic field and combined field integral equations originates from the strong singularity of the identity operator. With a novel basis transformation scheme, i.e. two subsequent weak-form rotations of the RWG basis functions, the accuracy of the identity operator discret...

A low-order discretization scheme for the magnetic field integral equation (MFIE) with considerably improved accuracy is discussed and analyzed. The formulation is based on the classical form of the MFIE discretized with Rao-Wilton-Glisson functions and introduces weak-form basis transformations, which have recently been employed with great success...

The electric field integral equation (EFIE) for perfect electrically conducting objects is augmented by a weak form combined source side condition. Thereby, the solution of the resulting combined source integral equation (CSIE) is unique and the interior resonance problem is circumvented. The discretization of electric and magnetic surface current...

Inverse source solutions for field transformations and diagnostics are mostly working with surface current densities on appropriately defined Huygens surfaces around the test object. This gives excellent modeling flexibility, but the handling of the discretized surface current representation requires also substantial computational effort. Distribut...

p>Inverse source solutions for field transformations and diagnostics are mostly working with surface current densities on appropriately defined Huygens surfaces around the test object. This gives excellent modeling flexibility, but the handling of the discretized surface current representation requires also substantial computational effort. Distrib...

p>The electric field integral equation (EFIE) for perfect electrically conducting objects is augmented by a weak form combined source side condition. Thereby, the solution of the resulting combined source integral equation (CSIE) is unique and the interior resonance problem is circumvented. The discretization of electric and magnetic surface curren...

p>A novel design of a broadband mm-wave patch antenna for mobile devices is introduced. The proposed antenna element operates around 40 GHz. Through utilizing a multiple resonances patch structure, 9% bandwidth has been obtained. The substrate consists of low cost material and the antenna with its microstrip feed can easily be integrated with front...

p>The combined source (CS) condition is employed to augment the electric field integral equation (EFIE), whereby the CS condition is implemented as a modification of the weak form Leontovich impedance boundary condition. By doing so, both electric and magnetic surface current densities can be modeled with Rao-Wilton-Glisson (RWG) basis functions. S...

p>The accuracy of near-field antenna measurements combined with near-field far-field transformations (NFFFT) is deteriorated if objects are located in close vicinity to the antenna under test (AUT). We compare two equivalent sources based modeling techniques to suppress the influence of structures in the vicinity of the AUT. Simulation results for...

p>A low-order discretization scheme for the magnetic field integral equation (MFIE) with considerably improved accuracy is discussed and analyzed. The formulation is based on the classical form of the MFIE discretized with Rao-Wilton-Glisson functions and introduces weak-form basis transformations, which have recently been employed with great succe...

p>Starting from the monopolar representation of the Rao-Wilton-Glisson (RWG) functions, an approximate inverse (AI) of the RWG Gram matrix is constructed, where only 3x3 matrices for all individual triangles have to be inverted. The inversion of the Gram matrix is, however, only approximate, since it results as the inverse of a product of singular...

p> The inverse source problem of near-field antenna measurements is often formulated in terms of unknown equivalent electric and magnetic surface current densities. Exploiting just the constraints for the radiated field exterior to a closed Huygens surface results in ambiguous equivalent sources due to the excitation of non-radiating currents dur...

p>The accuracy problem of the classically Rao-Wilton-Glisson (RWG) discretized magnetic field and combined field integral equations originates from the strong singularity of the identity operator. With a novel basis transformation scheme, i.e. two subsequent weak-form rotations of the RWG basis functions, the accuracy of the identity operator discr...

The inverse equivalent source problem related to near-field antenna measurements is typically ill-posed, i.e., the forward operator suffers from non-trivial null spaces. This issue is commonly tackled by pursuing a least-squares solution of the reconstructed near fields. We propose to find a solution of the normal error system of equations which mi...

We present a low-cost and light-weight measurement equipment based on a software-defined radio (SDR) and a radio-frequency over fiber (RFoF) connection. The main purpose of the hardware are near-field antenna measurements, but possible use-cases also include imaging and other inverse-source scenarios. The two features “low-cost” and “light-weight”...

Conventional phaseless near-field measurement data is not adequate for reliable transformation into the far field. We tackle this challenge by a formulation working with multifrequency phaseless measurements under the assumption of coherently measured spectra. Such data is, for instance, obtained with a transmitting antenna under test and standard...

We present a low-cost and light-weight measurement equipment based on a software-defined radio (SDR) and a radio-frequency over fiber (RFoF) connection. The main purpose of the hardware are near-field antenna measurements, but possible use-cases also include imaging and other inverse-source scenarios. The two features “low-cost” and “light-weight”...

The free-space radiation characteristic of an antenna under test (AUT) is determined from measurements in proximity of a scatterer by time gating reconstructed equivalent currents for the AUT and the scatterer. The presented approach effectively combines spatial filtering methods with time domain methods while mitigating their individual drawbacks....

p>Conventional phaseless near-field measurement data is not adequate for reliable transformation into the far field. We tackle this challenge by a formulation working with multifrequency phaseless measurements under the assumption of coherently measured spectra. Such data is, for instance, obtained with a transmitting antenna under test and standar...

p>The free-space radiation characteristic of an antenna under test (AUT) is determined from measurements in proximity of a scatterer by time gating reconstructed equivalent currents for the AUT and the scatterer. The presented approach effectively combines spatial filtering methods with time domain methods while mitigating their individual drawback...

p>The inverse equivalent source problem related to near-field antenna measurements is typically ill-posed, i.e., the forward operator suffers from non-trivial null spaces. This issue is commonly tackled by pursuing a least-squares solution of the reconstructed near fields. We propose to find a solution of the normal error system of equations which...

Reducing near-field measurement times is an important challenge for future antenna measurement systems. We propose to incorporate knowledge about material parameters of the antenna measurement environment within the simulation model. To do so, a method-of-moments code with surface discretization is implemented as a side constraint to the near-field...

p>Reducing near-field measurement times is an important challenge for future antenna measurement systems. We propose to incorporate knowledge about material parameters of the antenna measurement environment within the simulation model. To do so, a method-of-moments code with surface discretization is implemented as a side constraint to the near-fie...

Inverse source solutions for field transformations and diagnostics are mostly working with surface current densities on appropriately defined Huygens surfaces around the test object. This gives excellent modeling flexibility, but thehandling of the discretized surface current representation requires also substantial computational effort. Distribute...

Fully coherent unmanned aerial vehicle (UAV)-based near-field measurements of the S67 parabolic ground station antenna in Weilheim, Germany at 2.06392 GHz are presented. The utilized measurement setup involves a vector network analyzer (VNA), radio frequency optical fiber connections, a laser tracking device (LT), and a specially designed light-wei...

Explicit formulas for converting spherical wave expansions with vector basis functions and scalar expansion coefficients into spherical wave expansions with scalar basis functions and vector expansion coefficients and vice versa are presented. The formulas are given in terms of Wigner-3- j - symbols. The conversion formulas are derived by spheric...

Time-harmonic inverse source solutions are commonly working with electric and magnetic surface current densities defined and discretized on appropriately chosen Huygens surfaces. An efficient meshless alternative are spherical harmonics expansions of low order distributed along the chosen Huygens surface, which still possess pretty good spatial loc...

Background and clutter suppression techniques are important towards the successful application of radar in complex environments. We investigate eigenimage based methodologies such as principal component analysis (PCA) and apply it to frequency modulated continuous wave (FMCW) radar. The designed dynamic principal component analysis (dPCA) algorithm...

A portable fast chirp frequency modulated continuous wave (FMCW) reflectometer is presented to locate and monitor fast varying discontinuities or faults on transmission lines. This frequency-domain reflectometry (FDR) approach exploits and adapts the advantages of the closely related and frequently employed FMCW radar principle to transmission line...

Accurate position information is crucial in antenna measurements. This is especially challenging for unmanned aerial vehicle (UAV)-based antenna measurement systems. UAVs often rely on global navigation satellite systems (GNSSs) for position determination. Hereby, the GNSS antenna mounting environment significantly influences the GNSS position accu...

Most methods tackling the phase retrieval problem of magnitude-only antenna measurements suffer from unrealistic sampling requirements, from unfeasible computational complexities, and, most severely, from the lacking reliability of nonlinear and nonconvex formulations. As an alternative, we propose a partially coherent (PC) multi-probe measurement...

In near-field measurements, the correction of the field probe influence is crucial for achieving high accuracy. With the increasing interest in antenna measurements based on unmanned aerial vehicles (UAVs), probe correction becomes essential also in this field. Here, the actual probe comprises the UAV together with the mounted probe antenna and in...

Propagating plane-wave fast multipole translation operators (TLOPs) convert propagating plane-wave spectra radiated from a source region of finite extent into incident propagating plane-wave spectra at a distant observation region of finite extent. This translation is diagonal, and the received fields in the observation region are obtained by integ...