Alexander Herschlein

Bio: Alexander Herschlein is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Luneburg lens & Method of moments (statistics). The author has an hindex of 3, co-authored 10 publications receiving 175 citations.

A photonic bandgap (PBG) structure for guiding and suppressing surface waves in millimeter-wave antennas

Abstract: Periodic and regular metal posts, a photonic bandgap (PBG) structure for guiding surface waves in a parallel-plate waveguide is proposed. The isotropic PBG structure is applied to the design of an asymmetric parallel-plate waveguide Luneburg lens (APWLL). The relation between the dimensions of the metal posts and the required refraction index in the lens is derived with transmission-line theory and the transverse resonance method. Different lattices for the entire lens are also investigated. For verification, an antenna for a 76.5 GHz adaptive-cruise control radar is fabricated, consisting of an APWLL, a primary feed, and symmetric corrugated flares to improve the property of the antenna in elevation. Measured results verify the PBG structure design in the APWLL.

Methods for the Evaluation of Regular, Weakly Singular and Strongly Singular Surface Reaction Integrals Arising in Method of Moments

Abstract: : The accurate and fast evaluation of surface reaction integrals for Method of Moments computations is presented. Starting at the classification of the integrals into regular and weakly, strongly and nearly singular integrals, appropriate methods are presented that handle each. A Gauss-Legendre quadrature rule evaluates regular integrals. For singular integrals, the singularity is lifted or weakened by an extraction of the singularity, a transform to polar coordinates or a domain transform. The resulting regular integral is in turn solved by a quadrature rule. The different methods are finally applied to an example, and the resulting accuracy tested against the analytical result. The presented methods are general enough to be used as integration methods for integrals with various degrees of singularity and is not limited to Method of Moments.

A generalized integral equation formulation for mixed dielectric-PEC scatterers

Abstract: [1] The known integral representation of electromagnetic fields is reviewed. Based on the review, a new formulation allows us to model any general case. The formulation of PEC, dielectric, dielectric with metallic surfaces, and dielectric scatterers with dielectric or PEC inclusions is derived. Finally, a new operator notation allows a concise and accurate representation of the integral equation formulations. The electric field integral equation and the magnetic field integral equation are contained in this formulation.

Schutzabstände in der Mobilkommunikation

Abstract: The increasing number of base stations in mobile communications causes considerations about possible adverse health effects. In this paper protective distances for typical GSM 900and GSM 1800-base stations reflecting the German "26. Bundesimmissionsschutzverordnung" (26. BlmSchV) as well as the Swiss 'Verordnung uber den Schutz vor nichtionisierender Strahlung" (NISV) are calculated. The calculation procedures and results are presented. Especially the consequences due to stricter regulations are discussed. Alternative concepts resulting in lower emissions are shortly addressed. A new approach, which also yields reliable values in the near field, is established for the calculation of the power densities in the main beam. The results described in this paper shall support the ongoing discussions by giving concrete numbers for the exposition. Biological and athermal effects are not considered. Fur die Dokumentation EMVU / Schutzabstande / GSM / 26. BlmSchV / NISV / Netzsendeleistung

Offset cylindrical reflector antenna fed by a parallel-plate Luneburg lens for automotive radar applications in mm-wave

Abstract: Using a single offset cylindrical parabolic reflector and an improved parallel-plate Luneburg lens, a novel antenna is developed for automotive radar in the mm-wave range. By adding linearly- or circularly-corrugated extensions to the parallel-plate Luneburg lens, a cylindrical wave illuminates the reflector, and hence good performances are achieved. Using GO, the aperture field of the antenna is found and then far-fields of the entire antenna are derived using the aperture field integration method. Design procedures of the entire antenna are presented. For verification of design rules and simulation, a prototype antenna for an adaptive cruise control (ACC) radar at 76.5 GHz is designed and measured. The antenna has properties of a relatively wide scan angle and multiple beams.

Metallo-dielectric electromagnetic bandgap structures for suppression and isolation of the parallel-plate noise in high-speed circuits

Abstract: A novel approach for the suppression of the parallel-plate waveguide (PPW) noise in high-speed printed circuit boards is presented. In this approach, one of the two conductors forming the PPW is replaced by an electromagnetic bandgap (EBG) surface. The main advantage of the proposed approach over the commonly practiced methods is the omnidirectional noise suppression it provides. For this purpose, two EBG structures are initially designed by utilizing an approximate circuit model. Subsequently, the corresponding band structures are characterized by analytical solutions using the transverse resonance method, as well as full-wave finite-element simulations. The designed EBG surfaces were fabricated and employed in a number of PPW test boards. The corresponding frequency-domain measurements exhibited bandgaps of approximately 2.21 and 3.35 GHz in the frequency range below 6 GHz. More importantly, suppression of the PPW noise by 53% was achieved based on time-domain reflectometry experiments, while maintaining the signal transmission quality within the required specifications for common signaling standards.

Metasurfing: Addressing Waves on Impenetrable Metasurfaces

Abstract: Metasurfaces constitute a class of thin metamaterials, which are used from microwave to optical frequencies to create new antennas and microwave devices. Here, we propose the use of variable-impedance metasurfaces for transforming surface or guided waves into different wavefield configurations with desirable properties. We will shortly refer to this metasurface-driven wavefield transformation as “metasurfing.” Metasurfing can be obtained by an appropriate synthesis of inhomogeneous metasurface reactance that allows a local modification of the dispersion equation and, at constant operating frequency, of the local wave vector. The general effects of metasurface modulation are similar to those obtained in solid (volumetric) inhomogeneous metamaterial as predicted by the transformation optics-namely, readdressing the propagation path of an incident wave. However, significant technological simplicity is gained. Several examples are shown as a proof of concept.

Non-Uniform Metasurface Luneburg Lens Antenna Design

Abstract: A metasurfing concept is demonstrated and applied in the design of Luneburg lens antennas. Using an array of size-varying circular patches on a dielectric substrate inside a parallel-plate waveguide (PPW) structure variable surface impedance is obtained, which realizes an equivalent refraction index as that of a Luneburg lens. The obtained lens has good bandwidth characteristics and significant fabrication advantages with respect to conventional dielectric lenses. Based on this PPW lens, an H-plane antenna has been designed and simulated.

Gain Enhancement of a Microstrip Patch Antenna Using a Cylindrical Electromagnetic Crystal Substrate

Abstract: The performance of a circular microstrip patch antenna is improved using a new cylindrical electromagnetic bandgap (EBG) substrate. The microstrip patch antenna is fed by a coaxial probe and is integrated within a cylindrical electromagnetic bandgap substrate, based on the mushroom-like substrate, to increase the antenna gain. The cylindrical electromagnetic bandgap structure is a combination of two periodic structures with different periods. One is made of metallic rings and the other of grounding vias, which are disposed such as to form a radially and circularly periodic structure. A parametric analysis using a full-wave method was carried out in order to design the EBG structure. With the proposed concept, an antenna prototype was fabricated and tested. The radiation patterns and return loss obtained from measurements show a good impedance matching and a gain enhancement of the proposed antenna.