Active and passive dielectric rod waveguide components for millimetre wavelengths

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Aalto-yliopiston teknillinen korkeakoulu | Doctoral thesis (monograph)
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Date

2010

Department

Radiotieteen ja -tekniikan laitos
Department of Radio Science and Engineering

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Mcode

Degree programme

Language

en

Pages

Verkkokirja (15455 KB, 205 s.)

Series

TKK radio science and engineering publications, 18

Abstract

In this thesis, active and passive dielectric rod waveguide (DRW) components have been studied and developed for millimetre wavelengths. DRW antennas made of relatively high permittivity materials like silicon and sapphire are designed and simulated with HFSS (a commercial electromagnetic structure simulator based on Finite Element Method) at frequencies up to 325 GHz. A prototype antenna for D band (110-170 GHz) has been fabricated and measured. The location of the phase centre of an antenna is an important parameter in many applications, especially when the antenna is used as a feed for a reflector. This location of the phase centre for the DRW antenna has been studied with different methods from measurement results obtained with a planar scanner at W band. A high-permittivity DRW antenna is an interesting candidate for an antenna array element. According to W-band simulations and measurements the mutual coupling between the elements is relatively low even with the distance of ∼λ ⁄ 2 as the element spacing. This makes the DRW an appealing alternative as an element for densely packed arrays. However, mutual coupling studies for antenna arrays revealed a very strong coupling phenomenon when the distance between the elements is small. At some point the power is transferred completely from the excited waveguide to the neighbouring waveguide. This phenomenon is similar to cross-talk in optical fibres. In that regime cross-talk has been utilised in many applications, e.g. in directional couplers. In this thesis a frequency selective coupler based on that strong coupling has been developed. Frequency selectivity is based on the fact, that the waveguide length required for complete power transfer depends on the frequency. The length that is required for the power to transfer from one waveguide to the other and back is also called as the beat length. A prototype coupler has been simulated, manufactured and measured at W band. The results are very promising for this type of components made of DRWs for millimetre wavelengths. Different types of DRW junctions for power division have also been studied. Such junctions can be used also for monitoring the propagating power in a DRW. Junctions can be designed for both E and H planes depending on the application. Symmetric and asymmetric Y-type junctions have been designed and studied with simulations in both planes. Active components studied in this thesis include a travelling-wave amplifier based on GaAs/AlGaAs heterostructure and a DRW phase shifter designed for ferroelectric varactors fed through Au strips, both designed for W band. A DRW travelling-wave amplifier is based on the interaction between an electron drift and an electromagnetic wave travelling in a periodic structure. Electronic gain of 10 dB/cm at 150 V/cm has been measured at 70-80 GHz. The proposed novel prototype of millimetre-wave phase shifter includes a dielectric rod waveguide with a periodic printed array of electrically small dipoles loaded with ferroelectric varactors. Measurement results of a non-tunable phase shifter prototype show that optimally a phase shift of 60 deg/dB can be obtained at W band.

Description

Supervising professor

Räisänen, Antti, Prof.

Thesis advisor

Lioubtchenko, Dmitri, Doc.

Keywords

dielectric rod waveguide, millimetre wave, antenna, mutual coupling, travelling-wave amplifier

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https://urn.fi/URN:ISBN:978-952-60-3463-8

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[diss] Sähkötekniikan korkeakoulu / ELEC