Indium-antimonide films have been prepared for experiments involving the application of high electric fields to this semiconducting material. The films have been deposited onto a mica substrate. To obtain high mobilities, a multilayer construction with subsequent annealing was used. Measurements of the complex propagation coefficient of a section of waveguide containing the film have been made and the results agree closely with a numerical solution of a theoretical model proposed for the structure. The design of a new type of a pulse generator for these high electric field experiments is described. / Thesis / Master of Engineering (ME)

Abstract In the first part of this study, determination of the dielectric properties of the low loss microwave ceramic material, barium nonatitanate (Ba2Ti9O20), around 1 GHz is discussed. The structures under test were coaxial resonators, the cores of which were made of barium nonatitanate and the metallization was realised by thick film silver. The measured value of the real part of the relative dielectric constant was εr = 37 and that of the loss tangent was tan σ = 0.00014. The change of the resonance frequency of the coaxial resonators with temperature, in the range -20 … +80 C, was 4 ppm/ C. In addition, realisation of compact interdigital and comb-line bandpass filters was demonstrated for the 900 MHz mobile phone band. Besides Ba2Ti9O20, Ba(Sm,Nd)2Ti5O14 ceramic material with a dielectric constant of εr = 78 was also employed in order to improve the miniaturisation. The volume of the smallest filter was 2 cm3 and the weight was 9 g. In the second part of this study, various measurement methods have been demonstrated to determine the real part of the relative permittivity of FR4 fibreglass circuit board. Test structures were straight asymmetric open-circuited strip lines. It was found that the real part of the relative permittivity decreased slightly with frequency. At 0.72 GHz and 4.5 GHz, εr values of 4.3 and 4.1, respectively, were measured. All the characterisation methods used gave consistent values for εr, and electromagnetic simulators were used to verify the results. In the third part of this study, the structures under test were microstrip or strip line transmission lines, the S parameters of which were measured by using on-wafer measurement techniques. It was found that the insertion loss of the 10 mm long etched Cu microstrip was slightly less than that of the Ag microstrips which were manufactured by etching and gravure offset printing techniques, respectively. The performance of the Ag microstrips was, however, similar. In addition, a theoretical basis was established for the determination of εr of the dielectric substrate and the attenuation coefficient of the transmission lines under test. The calculations were based on signal flow diagrams. The method was applied to determine the dielectric and loss properties of a commercial, Kyocera, Japan, LTCC (Low Temperature Cofired Ceramic) material up to 50 GHz. The measured value of the real part of the relative permittivity was εr = 5.7, and the loss tangent was approximately tan σ = 0.003. The essential idea behind the studies reported in this thesis was twofold. First, the studies aimed at characterising dielectric media which find usage in the realisation of UHF, microwave or millimetre wave circuits. Second, the studies aimed to obtain data of immediate value in practical design work. For this reason, the structures under test were transmission lines having extensive usage in practical high frequency circuit design.

Characterization and modeling of devices at high drive levels often requires specialized equipment and measurement techniques. Many large-signal devices will never have traditional nonlinear models because model development is expensive and time-consuming. Due to the complexity of the device or the size of the application market, nonlinear modeling efforts may not be cost effective. Scattering parameters, widely used for small-signal passive and active device characterization, have received only cursory consideration for large-signal nonlinear device characterization due to technical and theoretical issues. We review the theory of S-parameters, active device characterization, and previous efforts to use S-parameters with large-signal nonlinear devices. A robust, calibrated vector-measurement system is used to obtain device scattering parameters as a function of drive level. The unique measurement system architecture allows meaningful scattering parameter measurements of large-signal nonlinear devices, overcoming limitations reported by previous researchers. A three-port S-parameter device model, with a nonlinear reflection coefficient terminating the third port, can be extracted from scattering parameters measured as a function of drive level. This three-port model provides excellent agreement with device measurements across a wide range of drive conditions. The model is used to simulate load-pull data for various drive levels which are compared to measured data. / Master of Science

No description available.

Accurate knowledge of the centimeter- and millimeter-wavelength absorptivity of ammonia is necessary for the interpretation of the emission spectra of the jovian planets. The objective of this research has been to advance the understanding of the centimeter- and millimeter-wavelength opacity spectra of ammonia under jovian conditions using a combination of laboratory measurements and theoretical formulations. As part of this research, over 1000 laboratory measurements of the 2-4 mm-wavelength properties of ammonia under simulated upper and middle tropospheric conditions of the jovian planets, and approximately 1200 laboratory measurements of the 5-20 cm-wavelength properties of ammonia under simulated deep tropospheric conditions of the jovian planets have been performed. Using these and pre-existing measurements, a consistent mathematical formalism has been developed to reconcile the centimeter- and millimeter-wavelength opacity spectra of ammonia. This formalism can be used to estimate the opacity of ammonia in a hydrogen/helium atmosphere in the centimeter-wavelength range at pressures up to 100 bar and temperatures in the 200 to 500 K range and in the millimeter-wavelength range at pressures up to 3 bar and temperatures in the 200 to 300 K range. In addition, a preliminary investigation of the influence of water vapor on the centimeter-wavelength ammonia absorptivity spectra has been conducted. This work addresses the areas of high-sensitivity centimeter- and millimeter-wavelength laboratory measurements, and planetary science, and contributes to the body of knowledge that provides clues into the origin of our solar system. The laboratory measurements and the model developed as part of this doctoral research work can be used for interpreting the emission spectra of jovian atmospheres obtained from ground-based and spacecraft-based observations. The results of the high-pressure ammonia opacity measurements will also be used to support the interpretation of the microwave radiometer (MWR) measurements on board the NASA Juno spacecraft at Jupiter.

The object of this research program has been to provide a baseline for microwave remote sensing of ammonia and water vapor in the atmosphere of Jupiter through laboratory measurements of their microwave absorption properties. Jupiter is not only the largest planet in our solar system, but one of the most interesting and complex. Despite a handful of spacecraft missions and many astronomical measurements, much of Jupiter s atmospheric dynamics and composition remain a mystery. Although constraints have been formed on the amount of certain gases present, the global abundances and distributions of water vapor (H2O) and ammonia (NH3) are relatively unknown. Measurements of H2O and NH3 in the Jovian atmosphere to hundreds of bars of pressure are best accomplished via passive microwave emission measurements. For these measurements to be accurately interpreted, however, the hydrogen and helium pressure-broadened microwave opacities of H2O and NH3 must be well characterized, a task that is very difficult if based solely on theory and limited laboratory measurements. Therefore, accurate laboratory measurements have been taken under a broad range of conditions that mimic those of the Jovian atmosphere. These measurements, performed using a newly redesigned high-accuracy system, and the corresponding models of microwave opacity that have been developed from them comprise the majority of this work. The models allow more accurate retrievals of H2O and NH3 abundances from previous as well as future missions to Jupiter and the outer planets, such as the NASA New Frontiers class Juno mission scheduled for launch in 2011. This information will enable a greater understanding of the concentration and distribution of H2O and NH3 in the Jovian atmosphere, which will reveal much about how Jupiter and our solar system formed and how similar planets could form in other solar systems, even planets that may be hospitable to life.

Les transistors à haute mobilité d’électrons (HEMTs) en nitrure de gallium (GaN) s’affirment comme les candidats prometteurs pour les futurs équipements à micro-ondes - tels que les amplificateurs de puissance à état solide (SSPA), grâce à leurs excellentes performances. Une première démonstration d'émetteur en technologie GaN-MMIC a été développée et embarquée dans la mission spatiale PROBA-V. Mais cette technologie souffre encore des effets de pièges par des défauts présents au sein de la structure. L’objectif de ce travail est donc l'étude d’effets de pièges et des aspects de fiabilité des transistors de puissance GH50 pour des applications en bande C. Un protocole d’investigation des phénomènes de pièges est présenté, qui permet l’étude des dynamiques des effets de pièges du mode de fonctionnement DC au mode de fonctionnement radiofréquence, basé sur la combinaison des mesures IV impulsionnelles, des mesures de transitoires du courant de drain avec des impulsions DC et RF et des mesures de paramètres [S] en basse fréquence. Un modèle de HEMT AlGaN/GaN non-linéaire électrothermique est présenté, incluant un nouveau modèle thermique de pièges restituant le comportement dynamique de ces pièges et leurs variations en température afin de prédire correctement les performances en conditions réelles de fonctionnement RF. Enfin, une méthodologie temporelle pour l’évaluation de la fiabilité et de limites réelles d'utilisation de transistors dans l'amplificateur de puissance RF en régime d’overdrive (très forte compression), basée sur la mesure monitorée de Formes d'Onde Temporelles (FOT), est proposée. / GaN-based high electron mobility transistors (HEMTs) are promising candidates for future microwave equipment, such as new solid state power amplifiers (SSPAs), thanks to their excellent performance. A first demonstration of GaN-MMIC transmitter has been developed and put on board the PROBA-V mission. But this technology still suffers from the trapping phenomena, principally due to lattice defects. Thus, the aim of this research is to investigate the trapping effects and the reliability aspects of the GH50 power transistors for C-band applications. A new trap investigation protocol to obtain a complete overview of trap behavior from DC to radio-frequency operation modes, based on combined pulsed I/V measurements, DC and RF drain current measurements, and low-frequency dispersion measurements, is proposed. Furthermore, a nonlinear electro-thermal AlGaN/GaN model with a new additive thermal-trap model including the dynamic behavior of these trap states and their associated temperature variations is presented, in order to correctly predict the RF performance during real RF operating conditions. Finally, an advanced time-domain methodology is presented in order to investigate the device’s reliability and to determine its safe operating area. This methodology is based on the continual monitoring of the RF waveforms and DC parameters under overdrive conditions in order to assess the degradation of the transistor characteristics in the RF power amplifier.