Defect modes in electromagnetic bandgap structures for micro- and millimetre waves

In the previous decades, the investigation of the optical properties of materials has lead to a number of important developments like the laser, optical fibre cables and high precision spectrometers. In 1987, Yablonovich and John suggested a possibility to tailor the optical properties of a material in a way that the flow of electromagnetic waves could be controlled by the creation of a band structure for allowed and forbidden states: the so called "electromagnetic bandgap". It was found out that such structures could exhibit improved properties that could not be achieved with conventional treatment of light waves, for example higher quality factors, low radiation losses in sharp bends in waveguides, low dispersion waveguiding and frequency selective substrates. Another feature of EBG materials was that their properties could be scaled to an arbitrary frequency range by rescaling the lattice constant of the dielectric lattice. This scalability makes them interesting for possible applications in the frequency range in between the microwave and optical ranges, the so called "Terahertz gap". In the frame of this work, the suitability of electromagnetic bandgap structures for possible applications as integrated passive element in circuits from the microwave up to the millimetre wave range has been investigated. It has been taken advantage from the scalability of the EBG properties, which makes it possible to investigate structures at low frequencies where fabrication, assembly and measurement are relatively easy and to scale up the results that have been found. In the first part of this work, a theoretical description of the behavior of electromagnetic waves in periodic dielectric media is given, and thus the basic properties of EBG structures are derived from the appropriate solutions of Maxwell's equations. A number of EBG lattice structures are presented, and described by band structure calculations. Furthermore the behavior of point and line defects in the lattice, is investigated, and a slab structure that can provide a three dimensional confinement is presented. In the second part, a number of fabrication schemes for EBG structures from microwave up to millimetre wave frequencies are presented, which have been investigated in the frame of this work, in collaboration with partners. Different ways of fabricating have been investigated such as mechanical treatment, moulding techniques and microfabrication techniques (laser machining and Silicon etching) and different material systems are employed. In the third part of this work, the simulated and fabricated structures have been investigated experimentally at frequencies of 10, 20, 30 and 100 GHz with respect to a possible application as passive transmission line elements and high quality factor resonant structures. For frequencies of 10 GHz, it has been shown that in a 2D EBG structure for TM waves the strength of the coupling to a defect resonance could be tuned and optimised by size variation of adjacent lattice elements to yield low insertion loss. Furthermore, a broadband waveguiding with little reflection by line defects with a width of one and three lattice periods could be shown. A three dimensional confinement of modes has been demonstrated in both simulation and experiment for a 3D EBG structure with a band gap at 20 GHz. For frequencies around 30 GHz, the creation of a band gap in a 2D EBG structure that was prepared by a ceramic moulding technique with a band gap for TM waves has been demonstrated and a resonant cavity mode with moderate quality factor could be observed. Two different structures with band gaps at frequencies around 100 GHz were investigated and it was shown that a 2D interconnected structure could exhibit a band gap for TM waves and provide a high mechanical stability without the need for a backfilling material. A 2D slab structure could provide a three dimensional confinement of defect modes by a combination of both band gap guiding and index guiding. A broadband waveguiding by a line defect mode in this slab structure was shown, and it was demonstrated that a localised mode in a point defect could act as a high quality factor cavity in both band pass and band reject configuration.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2005

Author dc:creator

• Schuster, Michael

Contributors dc:contributor

• Klein, Norbert

• info:eu-repo/classification/ddc/530
• Photonischer Kristall
• Mikrowelle
• Physik
• hf electronics
• dielectrics
• electromagnetic bandgap
• millimetre waves
• microwaves

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-121525%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:59771