This thesis presents the theoretical and experimental framework for the development of accurate on-wafer S-parameter and noise parameter measurements of silicon devices in the upper millimetre-wave frequency range between 70 GHz and 300 GHz. Novel integrated noise parameter test setups were developed for nanoscale MOSFETs and SiGe HBTs and validated up to 170 GHz. In the absence of accurate foundry models in this frequency range, the experimental findings of this thesis have been employed by other graduate students to design the first noise and input impedance matched W- and D-band low-noise amplifiers in nanoscale CMOS and SiGe BiCMOS technologies. The results of the D-band S-parameter characterization techniques and of the new Y-parameter based noise model have been used by STMicroelectronics to optimize the SiGe HBT structure for applications in the D-band. In the first half of the thesis, theoretical analysis indicates that, for current silicon devices, distributive effects in test structure parasitics will become significant only beyond 300 GHz. This conclusion is supported by experiments which compare the lumped-element based open-short and the transmission line based split-thru de-embedding techniques to the multiline thru-reflect-line (TRL) network analyzer calibration algorithm. Electromagnetic simulations and measurements up to 170 GHz demonstrate that, for microstrip transmission lines with metal ground plane placed above the silicon substrate, the line capacitance per unit length remains a weak function of frequency. Based on this observation, the multiline TRL algorithm has been modified to include a dummy short de-embedding structure. This allowed for the first time to perform single step calibration and de-embedding of silicon devices using on-silicon calibration standards. The usefulness of the proposed method was demonstrated on the extraction of the difficult-to-measure SiGe HBT and nanoscale MOSFET model parameters, including transcondutance delay, tau, gate resistance, source resistance, drain-source capacitance, and channel resistance, Ri. Building on the small-signal characterization technique developed in the first half, a new Y-parameter based noise model for SiGe HBTs, that includes the correlation between the base and collector shot noise currents, is proposed in the second half of the thesis along with a method to extract the noise transit time parameter. With this model, the high frequency noise parameters of a SiGe HBT can be calculated from the measured Y-parameters, without requiring any noise figure measurements. Finally, to validate the proposed noise model, the first on-wafer integrated noise parameter measurement systems were designed and measured in the W- and D-bands. The systems enable millimetre-wave noise parameter measurements with the multi-impedance method by integrating the impedance tuner and an entire millimetre-wave noise receiver on the same die as the device-under-test. Good agreement was obtained between the noise parameters calculated from the Y-parameter measurements and those obtained from direct noise figure measurements with the integrated systems. The results indicate that the minimum noise figure of state-of-the-art advanced SiGe HBTs remains below 5 dB throughout the D-band, making them suitable for a variety of commercial products in this frequency range.

This thesis presents the theoretical and experimental framework for the development of accurate on-wafer S-parameter and noise parameter measurements of silicon devices in the upper millimetre-wave frequency range between 70 GHz and 300 GHz. Novel integrated noise parameter test setups were developed for nanoscale MOSFETs and SiGe HBTs and validated up to 170 GHz. In the absence of accurate foundry models in this frequency range, the experimental findings of this thesis have been employed by other graduate students to design the first noise and input impedance matched W- and D-band low-noise amplifiers in nanoscale CMOS and SiGe BiCMOS technologies. The results of the D-band S-parameter characterization techniques and of the new Y-parameter based noise model have been used by STMicroelectronics to optimize the SiGe HBT structure for applications in the D-band. In the first half of the thesis, theoretical analysis indicates that, for current silicon devices, distributive effects in test structure parasitics will become significant only beyond 300 GHz. This conclusion is supported by experiments which compare the lumped-element based open-short and the transmission line based split-thru de-embedding techniques to the multiline thru-reflect-line (TRL) network analyzer calibration algorithm. Electromagnetic simulations and measurements up to 170 GHz demonstrate that, for microstrip transmission lines with metal ground plane placed above the silicon substrate, the line capacitance per unit length remains a weak function of frequency. Based on this observation, the multiline TRL algorithm has been modified to include a dummy short de-embedding structure. This allowed for the first time to perform single step calibration and de-embedding of silicon devices using on-silicon calibration standards. The usefulness of the proposed method was demonstrated on the extraction of the difficult-to-measure SiGe HBT and nanoscale MOSFET model parameters, including transcondutance delay, tau, gate resistance, source resistance, drain-source capacitance, and channel resistance, Ri. Building on the small-signal characterization technique developed in the first half, a new Y-parameter based noise model for SiGe HBTs, that includes the correlation between the base and collector shot noise currents, is proposed in the second half of the thesis along with a method to extract the noise transit time parameter. With this model, the high frequency noise parameters of a SiGe HBT can be calculated from the measured Y-parameters, without requiring any noise figure measurements. Finally, to validate the proposed noise model, the first on-wafer integrated noise parameter measurement systems were designed and measured in the W- and D-bands. The systems enable millimetre-wave noise parameter measurements with the multi-impedance method by integrating the impedance tuner and an entire millimetre-wave noise receiver on the same die as the device-under-test. Good agreement was obtained between the noise parameters calculated from the Y-parameter measurements and those obtained from direct noise figure measurements with the integrated systems. The results indicate that the minimum noise figure of state-of-the-art advanced SiGe HBTs remains below 5 dB throughout the D-band, making them suitable for a variety of commercial products in this frequency range.

The advantages offered by Super High Frequency (SHF) and Extremely High Frequency (EHF) bands such as large bandwidth, small antenna size, and easy installation or deployment have motivated the interest of researchers to study those factors that prevent optimum utilization of these bands. Under precipitation conditions, factors such as clouds, hail, fog, snow, ice crystals and rain degrade link performance. Rain fade, however, remains the dominant factor in the signal loss or signal fading over satellite and terrestrial links especially in the tropical and sub-tropical regions within which South Africa falls. At millimetre-wave frequencies the signal wavelength approaches the size of the raindrops, adversely impacting on radio links through signal scattering and absorption. In this work factors that may hinder the effective use of the super high frequency and extremely high frequency bands in the Southern African region are investigated. Rainfall constitutes the most serious impairment to short wavelength signal propagation in the region under study. In order to quantify the degree of impairment that may arise as a result of signal propagation through rain, the raindrops scattering amplitude functions were calculated by assuming the falling raindrops to be oblate spheroidal in shape. A comparison is made between the performance of the models that assume raindrops to be oblate spheroidal and those that assume them to be spherical. Raindrops sizes are measured using the Joss-Waldvogel RD-80 Distrometer. The study then proposes various expressions for models of raindrops size distributions for four types of rainfall in the Southern Africa region. Rainfall rates in the provinces in South Africa are measured and the result of the cumulative distribution of the rainfall rates is presented. Using the information obtained from the above, an extensive calculation of specific attenuation and phase shift in the region of Southern Africa is carried out. The results obtained are compared with the ITU-R and those obtained from earlier campaigns in the West African sub region. Finally, this work also attempts to determine and characterize the scattering process and micro-physical properties of raindrops for sub-tropical regions like South Africa. Data collected through a raindrop size measurement campaign in Durban is used to compare and validate the developed models. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2014.

Thesis (MScEng (Electrical and Electronic Engineering))--Univerity of Stellenbosch, 2011. / ENGLISH ABSTRACT: The design and simulation of hot electron bolometer sensors for the detection of millimeter and terahertz wave radiation is presented. These devices can be used for the formation of images or for spectroscopy in these frequency ranges. Many molecules resonate and have absorption spectra over these ranges, allowing for the identi cation, non-destructively and at a distance, of the constitution of many di erent materials. The penetrating ability of the radiation makes mm-wave and THz wave detectors ideal for security imaging. The design and simulation of these devices predicts performance as mixers and as interferometers. Manufacturing processes used while fabricating these thin lm devices are outlined and experimental results are reported. / AFRIKAANSE OPSOMMING: Hierdie tesis bespreek die ontwerp en simulasie van warm-elektron bolometers vir die waarneming van millimetergolf- en terahertz-straling. Sodanige toestelle kan in bogenoemde frekwensiebereike gebruik word vir beeldvorming of spektroskopie. Aangesien heelwat molekules binne hierdie bande resoneer, kan die samestelling van 'n verskeidenheid materiale oor 'n afstand en op 'n nie-vernietigende wyse gedenti seer word. Die deurdringingsvermo van millimetergolf- en terahertz-straling maak sulke detektors ideaal vir beeldvorming in veiligheidstoepassings. Met die ontwerp en simulasie van hierdie toestelle word gewys wat hul werkverrigting as mengers en interferometers kan wees. Die prosesse wat gebruik is om hierdie dun lmtoestelle mee te vervaardig word ook bespreek en eksperimentele resultate word aangebied.

This thesis describes work on the theoretical modelling and experimental measurement of the complex permittivity of dielectrics. The main focus of research has been into the characterisation of permittivity of planar and layered samples within the millimetre wave band. The measurement method is based on the free-space measurement of the transmission and reflection coefficients of samples. A novel analytical method of determining the transmission and reflection coefficients as functions of frequency arising from a generalised structure of planar dielectric layers is also described and validated. The analytical method is based on signal flow techniques. The measurement and analytical techniques have been applied in two main areas: firstly, the acquisition of new data on human skin in the band 57 to 100GHz and secondly, the detection and location of defects in composite materials for which a band of 90 to 100GHz was used. Measurements have been made on the complex permittivity of a single sample of excised human skin fixed in formaldehyde. The experimental results have been corrected to account for the fixing process in formaldehyde and are projected to body temperature. This data is, to the best of the author’s knowledge, the first of its kind to be published. Predicted skin permittivity based on various relaxation models varies widely and only partially fits the measured data. The experimental results have been used to determine the parameters of a Cole-Cole function which gives the best fit to the measured data. The measured skin data has also been used to calculate power deposition in skin exposed to millimetre wave radiation. This work concludes that a skin surface temperature rise of only 0.20C results from a thirty second exposure to signals of 100W/m2. Experimental work with fibreglass composite samples has shown that defects such as delaminations, voids, matrix cracks and improper cure result in resolvable differences in the dielectric properties of the samples at 90 – 100GHz. The measurement technique is particularly sensitive to the detection of cracks and its spatial resolution is 20mm or better. Whilst confirming the general conclusions of previously published work, the specific findings of this study are novel.

This thesis describes work on the theoretical modelling and experimental measurement of the complex permittivity of dielectrics. The main focus of research has been into the characterisation of permittivity of planar and layered samples within the millimetre wave band. The measurement method is based on the free-space measurement of the transmission and reflection coefficients of samples. A novel analytical method of determining the transmission and reflection coefficients as functions of frequency arising from a generalised structure of planar dielectric layers is also described and validated. The analytical method is based on signal flow techniques. The measurement and analytical techniques have been applied in two main areas: firstly, the acquisition of new data on human skin in the band 57 to 100GHz and secondly, the detection and location of defects in composite materials for which a band of 90 to 100GHz was used. Measurements have been made on the complex permittivity of a single sample of excised human skin fixed in formaldehyde. The experimental results have been corrected to account for the fixing process in formaldehyde and are projected to body temperature. This data is, to the best of the author’s knowledge, the first of its kind to be published. Predicted skin permittivity based on various relaxation models varies widely and only partially fits the measured data. The experimental results have been used to determine the parameters of a Cole-Cole function which gives the best fit to the measured data. The measured skin data has also been used to calculate power deposition in skin exposed to millimetre wave radiation. This work concludes that a skin surface temperature rise of only 0.20C results from a thirty second exposure to signals of 100W/m2. Experimental work with fibreglass composite samples has shown that defects such as delaminations, voids, matrix cracks and improper cure result in resolvable differences in the dielectric properties of the samples at 90 – 100GHz. The measurement technique is particularly sensitive to the detection of cracks and its spatial resolution is 20mm or better. Whilst confirming the general conclusions of previously published work, the specific findings of this study are novel.

In this work  high gain antennas are investigated for the 60 GHz frequency. The goal is to produce a high bandwidth point-to-point wireless network that could enable improved and new features in embedded systems used to detect particles in high energy physics. A literature study was performed aiming at simple, high gain, highly polarised antennas. Complex designs were grouped into three different groups: flat antenna design, build-up design and multi-antenna design. The multi-antenna design was found to have the simplest design and manufacturing but also feature larger antenna area. Three different designs were produced and tested, standard patch antenna, long patch antenna and a Vivaldi antenna. Manufacturing of a 4-patch antenna was also tested. All three demonstrated expected properties, the Vivaldi shows the best gain while the long patch antenna is slightly below the standard patch antenna. A forth design implementation was also tested using a 3D-printed lens. A lens can increase gain and allow changing beam direction. A lens was design and tested, the results showed an increased gain but with varying results at angels. Antennas were designed and manufactured using simple etching technique showing that further research can be done using simple and easily accessible techniques. Both antenna and lens show good properties and should be further investigated and validated. / I det här arbetet har antenner med hög förstärkning vid frekvensen 60 GHz undersökts. Målet är att utveckla punkt-till-punkt nätverk med hög bandbredd för detektorer i partikelkolliderare. Idag används trådade nätvärk i detektorn, genom att byta till trådlös dataöverföring kan onödig massa minskas och kvalitet förbättras. En litteraturstudie genomfördes med inriktning mot enkla, starkt förstärkande och kraftigt polariserad antenner. Tre olika typer defineras: platta designer, uppbygda designer och antenngrupper. Antenngrupper var de med enklaste design och tillverkning men också de med störst area relativt de andra. Tre olika antenner tillverkades och testades: patchantenn, lång patchantenn och Vivaldiantenn. Även en 4-patch antenn tillverkades. Produktionen av alla antenner höll hög kvalitet och de testade egenskaperna var förväntade. Vivaldiantennen hade starkast förstärkning av de testade antennerna, den långa patchantennen presterade strax under standard patchantennen. Även tester av en antenngrupp bestående av en patch antenn oc hen antennlins gjordes. Genom att använda en lins kan förstärkningen ökas och riktningen ändras. En lins designades och tillverkades med en 3D-skrivare. Resultat från tester visade på en ökad förstärkning men med varierande resultat vid vinklar. Antenner designades och tillverkades med en enkel etsningsmetod, detta visar att forsatta undersökningar kan utnyttja enkel och lättilgänlig teknik. Goda resultat uppvisades med både antenner och lins. Framtida studier kan utföras för att vidarutveckla och validera konceptet.

This thesis concerns methods to enhance current and explore future radiometric imaging systems for security screening. Its main focus is on the test and calibration procedures for the BorderWatch system – an established 33 GHz passive millimetre-wave imager developed by QinetiQ PLC as an outdoor security scanning portal for soft-sided heavy goods vehicles at ports of entry. The effects of the limited size of the sky background reflector of the operational system are addressed and modifications to mitigate these effects are proposed. Systematic diurnal and seasonal variations in the receiver output powers are characterised and strongly linked with variations in the physical temperature of the RF components. The proposed BorderWatch temperature calibration subsystem requires a reliable cold sky temperature reference point; the aim being to reduce the level of fixed pattern noise in present-day imagery and allow for post-processing methods requiring absolute temperature values. Cost considerations rule out independent millimetre-wave radiometers at each site so a proposed alternative is to use infra-red measurements as a proxy. A literature investigation is made into the millimetre-wave and infrared atmospheric opacities for a variety of meteorological conditions. The design, calibration and operation of a 35 GHz switching radiometer is described together with a comparison of the millimetre-wave radiometric brightness temperature measurements against the data from a low cost commercial infra-red sensor and from a nearby meteorological station. The results show an excellent correlation between the zenith sky temperatures in the infrared and millimetre-wave bands but only in clear sky conditions – as anticipated the presence of clouds affects the infra-red brightness distribution much more strongly than that of the millimetre-wave. Future security imagers may well incorporate interferometric arrays. An extensive simulation programme has been carried out to explore appropriate numbers of antennas and whether radio astronomy configurations and post-processing techniques can offer cost-effective routes to high image fidelity. The results of a quantitative analysis are promising and array configurations and techniques appropriate for potential future security imagers are suggested.

Various physical mechanisms that affect radiowave propagation at millimetre wavelengths are considered. Current modelling weaknesses are highlighted and new improved models or more appropriate modelling approaches are suggested. Interference and resonance phenomena in the scattering of spherical ice and water particles are reviewed. The long standing problem of the numerous resonances observed in the scattering diagrams of dielectric spheres is answered. The spatial structure and the physical characteristics of non-precipitable ice and water clouds are reviewed. Extinction and back scattering calculations for a wide variety of cloud models over the entire millimetre frequency spectrum are given. Multiple scattering and the effects of super-large drops in clouds are also dealt with. The potential of a spaceborne instrument in deducing information about the vertical structure of various cloud types is examined. Attenuation and reflectivity profiles resulting from various cloud types are calculated for a nadir pointing fixed beam millimetre wave radar operating at 94 GHz. The physics and application of the equation of radiative transfer to millimetre wave propagation in the earth's atmosphere are given and also is the solution of this equation for a typical millimetre wave remote sensing application. The theory of gaseous absorption at millimetre wavelengths is presented and an improved modelling approach is proposed for the calculation of the absorption and dispersion spectra of atmospheric gases. The effects of trace gases on communication systems operating at high altitudes are for the first time reported. Finally the use of the 60 GHz oxygen absorption band for top-side air traffic control/navigation and broadband transmission purposes is studied.

The Asymmetric Spacer layer Tunnel (ASPAT) diode is a new diode invented in the early 90s as an alternative to the Schottky barrier diode (SBD) technology for microwave detector applications due to its highly stable temperature characteristics. The ASPAT features a strong non-linear I-V characteristic as a result of tunnelling through a thin barrier, which enables RF detection at zero bias from microwaves up to submillimetre wave frequencies. In this work, two heavily doped GaAs contact layer on top and bottom layers adjacent to lightly doped GaAs intermediate layers, enclose undoped GaAs spacers with different lengths sandwiching an undoped AlAs layer that acts as a tunnel barrier. The ultimate ambition of this work was to develop a MMIC detector as well as a frequency source based on optimized ASPAT diodes for millimetre wave (100GHz) applications. The effect of material parameter and dimensions on the ASPAT source performances was described using an empirical model for the first time. Since this is a new device, keys challenges in this work were to improve DC and RF characteristic as well as to develop a repeatable, reproducible, and ultimately manufacturable fabrication process flow. This was investigated using two approaches namely air-bridge and dielectric-bridge fabrication process flows. Through this work, it was found that the GaAs/AlAs heterostructures ASPAT diode are more amenable to the dielectric-bridge technique as large-scale fabrication of mesa area up to 4×4Âμm2 with device yields exceeding 80% routinely produced. The fabrication of the ASPAT using i-line optical lithography which has the capability to reduce emitter area to 4×4Âμm2 to lower down the device capacitance for millimetre wave application has been made feasible in this work. The former challenge was extensively studied through materials and structural characterisations by a SILVACO physical modelling and confirmed by comparison with experimental data. The I-V characteristic of the fabricated ASPAT demonstrated outstanding scalability, demonstrating robust processing. A fair comparison has been made between ASPAT and SBD fabricated in-house; indicating ASPAT is extremely stable to the temperature. The RF characterisations were carried out with the aid of Keysight ADS software. The DC characteristic from fabricated GaAs/AlAs ASPAT diodes were absorbed into an ADS simulation tool and utilized to demonstrate the performance of MMIC 100GHz detector as well as 20GHz/40GHz signal generators. Zero bias ASPAT with mesa area of 4×4Âμm2 with video resistance of 90KΩ, junction capacitance of 23fF and curvature coefficient of 23V-1 has demonstrated detector voltage sensitivity above 2000V/W, while the signal source conversion loss and conversion efficiency are 28dB and 0.3% respectively. An estimate noise equivalent power (NEP) for this particular device is 18.8pW/Hz1/2.