Keilanohjaukseen soveltuvan litteän dielektrisen linssiantennin suunnittelu ja mittaus

In this thesis, flat hemi-elliptic dielectric lens antennas are studied at millimeter wavelengths. The used lens materials are teflon and a commercial plastic called preperm450, developed specifically for high frequency antenna applications. The main focus of this work is in the beam steering properties of the antennas. Proposed antenna structure is suitable for, e.g., automotive radar applications. Two different lens configurations are studied, one based on a dielectric slab waveguide and another based on a parallel plate waveguide. The design process for both antenna types is presented in detail and the antenna structures are simulated using commercial simulation software. Both antennas are fed with a WR-10 waveguide. Four prototype antennas (one of each type, and of both materials) are manufactured using water jet cutting. Manufactured antennas are measured using a planar near-field scanner and the results are compared with the simulated results. In the measurements and simulations beam steering is realized by changing the positioning of the waveguide feed. The measurement results follow the simulation results to a large extent and confirm the suitability of the proposed antenna structure for beam steering applications at millimeter wavelengths. The low relative permittivity of teflon lenses limits the maximum beam steering angle, especially with the dielectric slab extended lens. Preperm450 proves to be a viable option when choosing materials for dielectric lenses and beam steering angles up to 15 degrees can be achieved with small feed offsets.Teknologian nopea kehittyminen on mahdollistanut millimetriaaltoalueen käyttöönoton mm. tiedonsiirrossa ja tutkasovelluksissa, mikä on myös kasvattanut mielenkiintoa dielektrisiä linssiantenneja kohtaan. Millimetriaaltoalueella linssiantennien fyysiset mitat ovat pieniä, mikä mahdollistaa niiden käytön myös liikuteltavissa sovelluksissa. Tässä diplomityössä tutkitaan litteitä dielektrisiä linssiantenneja Etaajuuskaistan(71 – 86 GHz) sovelluksiin. Tutkimuksen suurin mielenkiinnon kohde on antennien keilanohjausominaisuudet, joita tutkitaan syöttöpistettä muuttamalla. Litteä linssiantenni tarjoaa viuhkamaisen keilan, jota keilaamalla voidaan kattaa laajoja alueita. Tämä mahdollistaa tutkitun antennityypin käytön esimerkiksi autotutkissa. Työssä käsitellään kahdenlaisia antennikonfiguraatioita. Ensimmäinen koostuu linssistä, syöttöantennista ja tukirakenteista, kun taas jälkimmäisessä linssi on suljettu kahden metallilevyn väliin. Käytetyt linssimateriaalit ovat teflon ja preperm450, joka on varta vasten korkean taajuuden antennisovelluksiin suunniteltu kaupallinen muovimateriaali. Linssien suunnitteluprosessi on kuvailtu yksityiskohtaisesti ja fyysiset mitat optimoitiin tietokoneohjelmiston avulla. Suunnitelluista antenneista valmistettiin neljä erilaista antenniprototyyppiä, jotka mitattiin lähikenttäskannerin avulla. Mittaustulosten ja tietokonesimulaatioiden vertailu osoittaa, että antenniprototyyppien mitattu toiminta mukailee hyvin simuloitujen linssien toimintaa. Teflonlinsseillä keilanohjausta rajoittaa matala suhteellinen permittiivisyys, mutta preperm450 osoittautuu hyvin soveltuvaksi dielektristen linssien valmistusmateriaaliksi

Instrumentation of a submillimetre wave hologram compact antenna test range

This thesis presents the developed instrumentation and measurement techniques suitable for use in a submillimetre wave compact antenna test range (CATR) for testing high-gain antennas and the quiet-zone quality of the CATR, but also for use in antenna testing with planar near-field scanning at submillimetre wavelengths. The thesis work is focused on improving the phase measurement accuracy and the dynamic range of a commercial submillimetre wave vector network analyser. The full angular scattering properties of radiation absorbing materials (RAM) suitable for the CATR are also analysed in the thesis. A CATR can be used for testing of electrically large antennas at millimetre and submillimetre wavelengths. These high-gain dish antennas are required for spaceborne astronomy and limb sounding of the Earth atmosphere. The most common CATR configuration at millimetre waves uses a reflector as the collimating element. However, the surface accuracy requirement of the reflector becomes very stringent at frequencies over 200 GHz, and the manufacturing of the reflector thus very expensive. An alternative collimator to the reflector is the binary amplitude hologram which is studied in this thesis. The hologram is a planar transmission type device, which is realised as a slot pattern on a metallised dielectric film. The surface (pattern) accuracy requirement of the hologram is less stringent than that of a reflector and it is potentially of lower cost. The amplitude and phase ripples of the CATR quiet-zone field need to be below ± 0.5 dB and ± 5°. The hologram CATR operating at 310 GHz discussed in this thesis is shown to be able to achieve these limits even at submillimetre wavelengths. The amplitude and phase measurement accuracies of a vector network analyser largely depend on the strength of the detected signal. The quiet-zone tests of planned large hologram CATRs require larger dynamic range than is possible with the standard solid-state source configuration, so a phase-lock system for submillimetre wave backward-wave oscillators (BWO) had to be developed. The powerful phase-locked BWO source described in this thesis can improve the dynamic range and the accuracy of the measurement system considerably. The improvement in dynamic range over the standard source based on a frequency-multiplied Gunn oscillator is 16-40 dB over the frequency range of 300-700 GHz. Problems in the phase measurement accuracy arise when the receiver is moved across the quiet-zone area with microwave cables connected to it. The flexing of the cables causes phase errors reaching tens of degrees due to changes in their electrical lengths. The novel phase error measurement and correction system described in this thesis is based on the use of a pilot signal to track changes in the electrical length of a microwave cable. The error analysis shows that phase correction of the detected submillimetre wave signal is possible down to a level of 2° with the constructed system. Accurate operation has also been verified by measurements. The CATR facility needs large quantities of high-performance absorbers. In order to select suitable absorbers, the specular and non-specular reflectivities of several commercially available, state-of-the art absorber materials have been measured between 200-600 GHz. Selected wool and synthetic floor carpet materials were also included in the tests. The results show that specular reflectivities between −40…−50 dB are possible over a considerable angular range when the materials are oriented properly. The best floor carpet materials have reflectivities below −15 dB over a wide angular range and are useful in the less critical areas by reducing backscatter. The published report is the first in the open literature showing the full angular performance of these materials across a wide frequency range.reviewe

Synthesis and design of periodic mm- to nano-scale gratings and their application in antenna systems

This thesis investigates the application of 2D periodic arrays of passive elements for future millimetre and nanometre waves antenna applications, and aims to provide guidelines for researchers dealing with the electromagnetic response of this type of structures in next generation communication systems. Novel configurations are here reported driven by the power requirements at each frequency band, as well as adapted analysis methods for its synthesis and analysis. All-dielectric structures based on form-birefringence and gradient index optics are considered in the first part of this dissertation, for their application to highly di rective circularly polarised antennas for transmission and reception of high power millimetre waves. Higher frequency nanometre waves are the focus of the second part, where the utilisation of 2D arrays of metallic nanoparticles as building blocks for optical leaky wave and magnetic antenna systems is thoroughly studied.Funded by EPSRC (Engineering and Physical Sciences Research Council

Frequency-Selective Surfaces for Microwave and Terahertz Spectra

FREQUENCYselective surfaces (FSSs) made of subwavelength periodic structures have been broadly applied in various electromagnetic applications. Their main function is to tailor the frequency response to incident waves, or to obtain electromagnetic (EM) properties that do not exist in homogeneous natural materials. When increasing the design complexity to enhance performance, however, the computation cost hikes dramatically in analysis and synthesis as additional design variables are introduced. In contrast to such complexity increase, this thesis aims at systematically developing effective and efficient design and optimization approaches for FSS-based structures adopting fundamental unit-cell patterns, such as rectangular patches, rings and grids. Additionally, impedance matching to free space is thoroughly investigated and adapted as a means towards performance improvement in both absorbers and filters. Hereby, multiple designs are demonstrated with realizations from the microwave to the terahertz (THz) frequency spectrum. In spite of their simplicity, the proposed designs outperform the state-of-the-art counterparts in the literature by fully exhausting the potentials of their spatial structures and material attributes. Specifically, Chapter 3 challenges a common belief that adding an impedance matching superstrate to an absorber will broaden its operation bandwidth at the cost of increased total thickness profile. This Chapter proves that it is possible to increase the bandwidth-to-thickness ratio. The concept is firstly demonstrated at the circuit level, and then verified by full-wave simulations. The optimization process can be illustrated with an admittance Smith chart. The distinctive performance of the proposed single- FSS-layer absorber is justified with a figure of merit (FoM) which comprehensively involves the relative bandwidth, the normalized thickness and the level of reflectivity. In Chapter 4, a semi-analytical approach for absorber design is developed by systematically combining analytical, empirical and numerical techniques. The optimization space can be simplified from millions of exhaustive search cases to merely a few hundreds of seed simulations, by exploiting insights into the linearity, scalability and independence regarding the major components of an absorber. For any specified level of absorption and operation bandwidth, the obtained semi-analytical algorithm enables fast synthesis of an absorber with a minimal thickness. Both absorbers proposed in the above chapters have been realized using patterned resistive layers and experimentally validated under oblique angles of incidence for transverse-electric (TE) and transversemagnetic (TM) modes. The design methods can be readily expanded for structures of multiple FSS layers. In the terahertz frequency range, common microfabrication technologies do not accommodate those resistive inks used for silk-printing lossy FSS patterns. As an alternative, a sub-skin-depth metal layer with nanoscale thickness is proposed in Chapter 5 to meet this requirement. The Drude model is adopted to simulate the ultra-thin metallic FSS, as it satisfactorily describes the frequency dependent properties of noble metals. The proposed absorber is robust to dimensional tolerance in fabrication and attains a stable absorption bandwidth under oblique impinging waves. In Chapter 6, a frequency reconfigurable terahertz bandpass filter is proposed and experimentally verified. It includes two identical double-layer FSSs separated by an air spacer which can be mechanically tuned. The filter allows a highly selective transmission sweeping across a wide spectrum. The underlying mechanism can be explained from two perspectives, namely through interpretation as Fabry-Perot resonant cavity and through consideration of the admittance Smith chart. The designed device is insensitive to fabrication tolerances and stable to oblique angle of incidence. The fabricated filter confirms a 40% tuning range and less than 1 dB insertion loss. This design is among the first few practical reconfigurable terahertz bandpass filters reported in the literature. Overall, the research outcomes suggest that developing complicated FSS patterns with a large number of degrees of freedom is unnecessary in many cases if the potential of fundamental geometries is fully exploited through rigorous algorithmic optimization methods. The design approaches illustrated in this thesis are generic to all FSS-based structures and can potentially be extended to multi-FSS layers and impedance surfaces, to satisfy performance requirements in specific applications.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 202

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Optics for Earth Observation Instruments

The optical system is an essential part of every remote sensing instrument used for detecting electromagnetic waves. Careful design, fabrication and characterization is therefore crucial, especially for satellite-borne missions where the possibility of post-launch repairs is highly limited. This thesis presents contributions to a new type of reflector optics and horn antennas for three instruments for Earth observation, which operate at wavelengths between the UV and millimeter-wave regions: Mesospheric Airglow/Aerosol Tomography Spectroscopy (MATS), International Submillimetre Airborne Radiometer (ISMAR) and Stratosphere-Troposphere Exchange And climate Monitor Radiometer (STEAMR).A free-form three-mirror off-axis telescope was developed for the limb instrument on board the MATS satellite. The f/7.3 (D = 35 mm) design achieved diffraction-limited performance (at 270-772 nm) over a wide field (5.67\ub0 7 0.91\ub0) by applying a new design method that corrects for linear astigmatism. Single point diamond turning was used to fabricate the free-form mirrors, which resulted in a telescope with a modulation transfer function of 0.45 at 20 lp/mm. Simulations and measurements were used to assess stray light rejection of the limb instrument. Measurements of a breadboard front baffle with a new type of extremely black coating showed a point source transmittance down to 10-6, which was in excellent agreement with simulations. Detailed modeling predicted a stray light rejection of 10-10-10-4 in the most critical region below the nominal field of view.Two 874 GHz Schottky mixer receivers with integrated low noise amplifiers, spline horns and low-loss dielectric lenses were developed for ISMAR, which exhibited record-low receiver noise temperatures of 2260-2770 K. Radiation patterns were measured between 868.7-880.0 GHz in a setup capable of resolving side lobes down to 25-30 dB below the main peak. The main beam full-width-half-maximum was in good agreement with simulations and well below the required 5\ub0. Spline horn antennas at frequencies 120-340 GHz were also developed. An efficient optimization algorithm based on mode matching in circular waveguides was used for all designs, which exhibited Gaussicity values of 98% over bandwidths up to 19%. Far field radiation patterns were measured using a setup for spherical and planar scanning geometries.A mechanical tolerance analysis was performed for the optical system of STEAMR, which consists of two polarization-separated focal plane arrays, a four-reflector anastigmatic relay optics chain and an off-axis Ritchey-Chretien telescope. Using Monte-Carlo simulations based on ray-tracing and physical optics, an overall reflector alignment accuracy requirement of 100 μm was obtained. Surface distortion analyses of the 1.6 m 7 0.8 m primary reflector highlighted the need for an optical system with small mechanical variations in orbit (<30 μm). A relay optics demonstrator showed that alignment accuracies down to 50 μm could be obtained. In conclusion, the methods for design, manufacturing and characterization presented in this thesis can be used to develop new instruments for Earth observation and related fields

Medical applications of microwave and millimetre-wave Imaging

This thesis presents a feasibility study of using microwave and millimetre wave radiations to assess burn wounds and the potential for monitoring the healing process under dressing materials, without their removal. As interaction of these types of radiations with the human body is almost exclusively with the skin, there is potential in others areas of medicine such as early skin cancer detection and the diagnosis of skin conditions such as eczema and psoriasis. This study involves developments of experimental methodologies, electromagnetic modelling, and measurements conducted on human skin (in vivo from 150 healthy participants), porcine skin samples (ex vivo from 20 fresh samples), and dressing materials (20 samples). Radiometric measurements obtained from the human skin over the frequency band (80-100) GHz show that the emissivity of the skin varies consistently over different regions of the hand and forearm, with gender, ethnicity, body mass index, age, and hydration level of the skin. A half space electromagnetic model of human skin has been developed and simulations using this model indicate that the human skin can be modelled as a single layer over the band 30 GHz to 300 GHz. The model also indicates that the band could be used to detect burns and a range of medical conditions associated with the skin. Experimental data collected from samples (human and porcine) have been measured by passive and active imaging systems and the results analysed in terms of the emissivity and the reflectivity of the skin. The major outcomes of the thesis are that microwave and millimetre wave radiations are capable of discriminating burn-damaged skin from healthy tissue and these measurements can be made through bandages without the sensor making any physical contact with the skin or the bandage

Recent Topics in Electromagnetic Compatibility

Recent Topics in Electromagnetic Compatability discusses several topics in electromagnetic compatibility (EMC) and electromagnetic interference (EMI), including measurements, shielding, emission, interference, biomedical devices, and numerical modeling. Over five sections, chapters address the electromagnetic spectrum of corona discharge, life cycle assessment of flexible electromagnetic shields, EMC requirements for implantable medical devices, analysis and design of absorbers for EMC applications, artificial surfaces, and media for EMC and EMI shielding, and much more