Simulations of Dipole Surface Current Distributions and Radiation Patterns
Authors
Sørensen, Patrick Bøgsted ; Thomsen, Jes Lydholm
Term
4. term (FYS10)
Education
Publication year
2018
Submitted on
2018-06-01
Pages
80
Abstract
Denne afhandling anvender momentmetoden (en numerisk integralligningsmetode) til at modellere de overfladestrømme, der induceres på metalliske antenner monteret på et halvleder-substrat. Formålet er at understøtte modellering af fotokonduktive antenner til terahertz (THz) generering. Vi opstiller den elektriske feltintegralligning og den dyadiske Green-tensor for en plan grænseflade mellem isotrope materialer, som tilsammen beskriver, hvordan et indfaldende felt inducerer strømme, og hvordan felter udbreder sig over substratgrænsen. Med udgangspunkt i disse formuleringer anvendes momentmetoden til at beregne elektriske overfladestrømme på en perfekt elektrisk leder (PEC) exciteret af et givet indfaldende felt og derfra de spredte felter. Der er udviklet et MATLAB-script, som beregner den inducerede strøm på vilkårlige tredimensionelle PEC-geometrier og deres spredte elektriske felt samt fjernfeltets strålingsmønster for antenner placeret på et halvleder-substrat. En observeret begrænsning ved planbølgeexcitation er en variation i den tværsnitsvise overfladestrøm. Som alternativ præsenteres en spændingsfødet excitationsmetode. Med denne metode blev der opnået strålingsmønstre for antennearrays på et substrat med forskellige indbyrdes afstande, og en mulig optimal mellemafstand foreslås.
This thesis uses the method of moments (a numerical integral-equation technique) to model the surface currents induced on metal antennas mounted on a semiconductor substrate. The goal is to support the modeling of photoconductive antennas for terahertz (THz) generation. We formulate the electric field integral equation and the dyadic Green’s tensor for a flat interface between isotropic materials. Together, these describe how an incident field induces currents and how fields propagate across the substrate boundary. Using these formulations, the method of moments is applied to compute electric surface currents on a perfect electric conductor (PEC) excited by a given incident field and, from these currents, the scattered fields. A MATLAB script was developed to compute the induced current on arbitrary three-dimensional PEC geometries and their scattered electric field, as well as the far-field radiation pattern for antennas placed on a semiconductor substrate. A limitation observed with plane-wave excitation is a variation of the surface current across the conductor cross section. As an alternative, a voltage-feed excitation method is presented. With this approach, radiation patterns were obtained for antenna arrays on a substrate with different inter-antenna spacings, and a possible optimal spacing is proposed.
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