Advanced Overmoded Circuits for Gyro-Amplifiers

To solve the narrow-bandwidth problem associated with cavity-related gyro-amplifiers, a new interaction circuit, containing clustered cavities is considered. In particular, the use of a cluster of cavities in frequency multiplying gyro-amplifiers is described. An analytical theory of a simple frequency multiplying device has been developed, and compared with numerical simulations using the Maryland Gyrotron Code (MAGY). The analytical results and MAGY code simulations are in good agreement. In the small signal regime, the bandwidth of a cluster-cavity device (with two cavities in the cluster) is twice that of a single cavity device, while both have the same peak bunching. We also investigate the effect of coupling between the cavities of a cluster, and the performance of a three-cavity cluster. A four-cavity cluster has been employed as a second harmonic buncher in a new type of Ka band, three-stage, harmonic-multiplying gyro-amplifier, which consists of a fundamental gyro-TWT input and second harmonic gyro-TWT output sections. This amplifier achieved 80 kW output power centered at 33.6 GHz with a bandwidth of 0.3 %, efficiency of 16 % and gain of 36 dB in the high order TE04 mode. MAGY simulations have been carried out and compared with the experimental data. Mode competition is a principal issue in high-power gyrotron research and development. A vaned TE0n mode converter has been proven to be effective in converting one designated TE0n mode into another designated TE0m mode while suppressing unwanted modes. A quasi-analytical theory has been developed to describe the electromagnetic field in the mode converter, and different modes have been calculated. By using a mode matching technique, the nonsymmetric field was incorporated in the MAGY code. This modification is a significant extension of MAGY capabilities. The results of scattering calculations for a vaned mode converter from the modified MAGY agree with the High Frequency Structure Simulator (HFSS) simulation to with 2%. This thesis consists of the following parts: 1. a review of gyrotron oscillator and amplifier research and development; 2. the concept, theory and experimental study of cluster cavities; and, 3. a study of a vaned TE0n mode converter. It is hoped that this research will improve the understanding of gyro-amplifiers using clustered cavities and/or TE0n mode converter structures, and advance research on gyro-amplifiers

Optimisation studies for a high gradient proton Linac for application in proton imaging:ProBE: Proton Boosting Linac for imaging and therapy

Proton beam therapy is an alternative to traditional X-ray radiotherapy utilised especially for paediatric malignancies and radio-resistant tumours; it allows a precise tumour irradiation, but is currently limited by knowledge of the patient density and thus the particle range. Typically X-ray computed tomography (CT) is used for treatment planning but CT scans require conversion from Hounsfield units to estimate the proton stopping power (PSP), which has limited accuracy. Proton CT measures PSP directly and can improve imaging and treatment accuracy. The Christie Hospital will use a \SI{250}{MeV} cyclotron for proton therapy, but \SI{330}{MeV} protons are needed to image the largest adult. In this thesis the feasibility of a pulsed linac upgrade to provide \SI{100}{MeV} acceleration in a cyclinac set up is studied. Space constraints require a compact, high gradient (HG) solution that is reliable and affordable. An overview of accelerator physics and beam dynamics are presented alongside the phenomenology of breakdown in high gradient RF structures. Both a small and large aperture solution are investigated. The small aperture option aims to keep the beam size to a minimum using focussing magnets between cavities and accelerate with a very high gradient. The large aperture solution aims to occupy more of the available space with accelerating structures and less with focussing magnets. This way the optics are simpler and the beam size is larger throughout the linac. The small aperture optimisation investigated S-, C- and X-band cavities. Firstly with simple pill-box structures then looking at the effect of nose cones on RF efficiency and breakdown limits. Multi-cell structures are then investigated employing side-coupling for standing wave (SW) cavities and various different magnetic coupling slots for backward travelling wave structures (bTW). Limited by 100~MW/m a 15~cm bTW solution was proposed with a calculated gradient of 65~MV/m. Unfortunately to be used with a cyclotron, which typically have large emittance, infeasibly strong magnets would be required. The large aperture optimisation only considers S- and C-band structures as they exhibit higher shunt impedance with larger apertures than X-band cavities. Side-coupled SW structures and magnetically coupled bTW structures are re-optimised for a larger aperture. An S-band side-coupled SW structure is subsequently identified as being the optimum for this energy range. A full 11-cell structure design with input coupler and end cells is presented calculated to reach 54~MV/m. A beam dynamics study is also presented considering both the small and large aperture schemes. For the large aperture scheme a particle tracking study is also presented. Mechanical engineering considerations are presented with a novel disk design manufacturing each individual cell from two machined copper disks. Thermal analysis of the temperature distribution inside the cavity is presented alongside heat transfer calculations for the cavity cooling system. Finally the conditioning and high power test of a similar S-band medical structure is presented with comparison made to the prototype structure designed in this study

Wideband and UWB antennas for wireless applications. A comprehensive review

A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems

Proceedings of the Mobile Satellite Conference

A satellite-based mobile communications system provides voice and data communications to mobile users over a vast geographic area. The technical and service characteristics of mobile satellite systems (MSSs) are presented and form an in-depth view of the current MSS status at the system and subsystem levels. Major emphasis is placed on developments, current and future, in the following critical MSS technology areas: vehicle antennas, networking, modulation and coding, speech compression, channel characterization, space segment technology and MSS experiments. Also, the mobile satellite communications needs of government agencies are addressed, as is the MSS potential to fulfill them

Study of advanced communications satellite systems based on SS-FDMA

A satellite communication system based on the use of a multiple, contiguous beam satellite antenna and frequency division multiple access (FDMA) is studied. Emphasis is on the evaluation of the feasibility of SS (satellite switching) FDMA technology, particularly the multiple, contiguous beam antenna, the onboard switch and channelization, and on methods to overcome the effects of severe Ka band fading caused by precipitation. This technology is evaluated and plans for technology development and evaluation are given. The application of SS-FDMA to domestic satellite communications is also evaluated. Due to the potentially low cost Earth stations, SS-FDMA is particularly attractive for thin route applications up to several hundred kilobits per second, and offers the potential for competing with terrestrial facilities at low data rates and over short routes. The onboard switch also provides added route flexibility for heavy route systems. The key beneficial SS-FDMA strategy is to simplify and thus reduce the cost of the direct access Earth station at the expense of increased satellite complexity

Autonomous Vehicles: MMW Radar Backscattering Modeling of Traffic Environment, Vehicular Communication Modeling, and Antenna Designs

77 GHz Millimeter-wave (mmWave) radar serves as an essential component among many sensors required for autonomous navigation. High-fidelity simulation is indispensable for nowadays’ development of advanced automotive radar systems because radar simulation can accelerate the design and testing process and help people to better understand and process the radar data. The main challenge in automotive radar simulation is to simulate the complex scattering behavior of various targets in real time, which is required for sensor fusion with other sensory simulation, e.g. optical image simulation. In this thesis, an asymptotic method based on a fast-wideband physical optics (PO) calculation is developed and applied to get high fidelity radar response of traffic scenes and generate the corresponding radar images from traffic targets. The targets include pedestrians, vehicles, and other stationary targets. To further accelerate the simulation into real time, a physics-based statistical approach is developed. The RCS of targets are fit into statistical distributions, and then the statistical parameters are summarized as functions of range and aspect angles, and other attributes of the targets. For advanced radar with multiple transmitters and receivers, pixelated-scatterer statistical RCS models are developed to represent objects as extend targets and relax the requirement for far-field condition. A real-time radar scene simulation software, which will be referred to as Michigan Automotive Radar Scene Simulator (MARSS), based on the statistical models are developed and integrated with a physical 3D scene generation software (Unreal Engine 4). One of the major challenges in radar signal processing is to detect the angle of arrival (AOA) of multiple targets. A new analytic multiple-sources AOA estimation algorithm that outperforms many well-known AOA estimation algorithms is developed and verified by experiments. Moreover, the statistical parameters of RCS from targets and radar images are used in target classification approaches based on machine learning methods. In realistic road traffic environment, foliage is commonly encountered that can potentially block the line-of-sight link. In the second part of the thesis, a non-line-of-sight (NLoS) vehicular propagation channel model for tree trunks at two vehicular communication bands (5.9 GHz and 60 GHz) is proposed. Both near-field and far-field scattering models from tree trunk are developed based on modal expansion and surface current integral method. To make the results fast accessible and retractable, a macro model based on artificial neural network (ANN) is proposed to fit the path loss calculated from the complex electromagnetic (EM) based methods. In the third part of the thesis, two broadband (bandwidth > 50%) omnidirectional antenna designs are discussed to enable polarization diversity for next-generation communication systems. The first design is a compact horizontally polarized (HP) antenna, which contains four folded dipole radiators and utilizing their mutual coupling to enhance the bandwidth. The second one is a circularly polarized (CP) antenna. It is composed of one ultra-wide-band (UWB) monopole, the compact HP antenna, and a dedicatedly designed asymmetric power divider based feeding network. It has about 53% overlapping bandwidth for both impedance and axial ratio with peak RHCP gain of 0.9 dBi.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163001/1/caixz_1.pd