Through continued innovation and growth, traveling wave tube amplifiers (TWTAs) remains the microwave power amplifiers of choice in a wide range of high power microwave and millimeter-wave applications specifically for aerospace applications with the volume, weight, bandwidth and power constraints. These advances can be credited to device innovation, improved modeling and design and development of advanced materials and construction techniques. This thesis aims at advancing the present technology of TWTs with coupled resonator slow-wave structures (SWSs) by a combination of device innovation, development of enhanced analytical and field analysis codes and understanding gained through improved modeling, simulation and experimentation. In a TWT, the SWS that slows the RF wave velocity down to near the electron beam velocity for interaction with the electron beam primarily determines the microwave performances of the tube. As compared to helix SWS, the coupled resonator SWS is capable of handling high peak and average powers with higher efficiency and TWTs based on these SWS are well suited for air-borne or space-borne radar systems and the major focus of this thesis is on the analysis and design of coupled resonator SWSs. As a part of this thesis, improved analytical codes based on quasi-TEM analysis and equivalent circuit analysis have been developed. The technical formulation is explained and the improvements made for enhanced accuracy and for incorporation of different types of coupled resonator SWSs detailed. Using these models new variants of coupled resonator SWSs have been investigated. The SWSs proposed are the ladder-core inverted slot mode SWS and the inductively loaded inter digital SWS (ILID-SWS). The possibility of achieving both coalesced mode design that gives wide bandwidth and multi beam design that improves the peak power and gain using rectangular ILID-SWS is presented. The properties of these proposed SWSs have been compared with the existing SWSs and found to give superior performance. Also an improved modeling and simulation technique using 3-D electromagnetic codes has been proposed and the conventional cold test measurement procedure has been modified for more accurate results. Numerous illustrative examples are presented throughout the thesis highlighting the analytical model and simulation code validation with experimental results. The experimentations have been carried out on the real SWS model that have been fabricated and assembled. Further, the contribution of the thesis is towards the development of a field analysis model for analysis of a corrugated waveguide SWS, based on the coupled integral equation technique (CIET), which is a combination of mode matching technique (MMT) and method of moments. The technical formulation and computational methodology employed in the model are explained and some of the most important aspects of implementation like the handling of singularities and choice of parameters controlling the accuracy is discussed. The accuracy and speed of the code is demonstrated by comparing CIET with MMT and 3-D electro magnetic simulators based on finite difference time domain (FDTD) method and finite element method (FEM). The CIET code developed is quite faster than the existing numerical methods and helps in solving the convergence problem associated with the MMT.

With the increasing demand of compact and lightweight wireless devices, there is a significant need to miniaturize the antennas, which are one of the largest radiofrequency components. The radiation performance of antennas degrades as their physical size becomes smaller in terms of operating wavelength [1]. The key challenge in antenna design, therefore, lies in the compromise between size and radiation performance. This challenge becomes critical for low frequency antennas such as for the RFID band. The Antenna-in-Package (AiP) concept, where the antenna is realized as part of the package along with the driving electronics, provides some console in terms of size as the antenna does not need any additional space. In this approach, the package becomes a functional module along with its primary job of protecting the components from the environment. This work aims to investigate various miniaturization techniques for a UHF RFID tag on package. Firstly, a dipole is given a 3D shape by carefully folding it over a package, in a manner that the currents on different segments add constructively. Secondly, the package material (which acts as the substrate for the antenna) is chosen to have a dielectric constant of 5.3 which further helps in size reduction. Finally, loading of slow-wave structures, comprising of inductors and capacitors, is used to achieve further miniaturization. The Artificial Transmission Line approach is utilized to determine the required values of the lumped components, and its location is optimized by analyzing the current distribution of the antenna to maintain a good efficiency. The RFID chip with a large capacitive impedance is conjugately matched to the antenna without an external matching network. This is done by carefully selecting the values of the lumped components as well as by adjusting the trace width of the antenna. The package has been realized through a low-loss filament (𝑡𝑎𝑛(𝛿) = 0.004) with the Raise3D Pro2 printer, and the conductor has been realized by copper tape using laser patterning technology with the laser platform PLS6MW. At an operational frequency of 866 MHz, a 𝑘𝑎 of 0.26, a read-range of 2.7 𝑚, and a radiation efficiency of approximately 32% is achieved.

No description available.

Vacuum microwave tubes, such as klystron, traveling-wave tube, gyrotron are high efficiency devices, where the RF interaction structure facilitates efficient energy transfer from the kinetic energy of the high energy electron beam to the electromagnetic wave. Traveling-wave Tube is the most versatile microwave power amplifier widely used for terrestrial communication, radar and aerospace applications. The waveguide based slow-wave structures like Millman, Karp, inter digital, grated waveguide, ring-plane, ring-bar, millitron and folded-waveguide structure gathered importance for application in millimeter-wave traveling-wave tubes. Among these millimeter-wave interaction structures, the folded-waveguide slow-wave structure became the most popular due to its robust structure, high power capability, low RF loss, simpler coupling, reasonably wide bandwidth and ease of fabrication for millimeter-wave to terahertz frequencies. Hence this thesis aims to analyse the folded-waveguide slow-wave structure for broad-banding and efficiency enhancement. The existing approaches for the analysis of cold circuit parameters (dispersion and interaction impedance characteristics) of folded-waveguide slow-wave structure are reinvestigated and found that these have limitation, as the effects of E-plane bend and beam-hole discontinuities are ignored in the parametric analysis. A cascaded matrix equivalent circuit model includes the effect of E-plane and beam-hole discontinuities for the analysis, but reported only for the serpentine folded-waveguide slow-wave structure. The cold test measurement technique was reported only for the dispersion characteristics. Hence the measurement technique has to be extended for the measurement of interaction impedance. The author proposes to orient the present doctoral work to (i) extend the proposed cascaded transmission matrix equivalent model for the analysis of rectangular folded-waveguide slow-wave structure, (ii) develop a non-resonant perturbation technique for the measurement of interaction impedance characteristics of the folded-waveguide slow-wave structure and also to (iii) establish new analysis models for the folded-waveguide slow-wave structure. The effect of E-plane bend and beam-hole discontinuities on the RF characteristics have been considered and simple, yet accurate closed form expressions for the computation of dispersion and interaction impedance characteristics have been established by three different approaches namely: transmission line equivalent circuit model, conformal mapping equivalent circuit model and quasi-TEM approach. The analysis results are benchmarked against 3-D electromagnetic modeling. The non-resonant perturbation theory is developed for the interaction impedance measurement. Typical Ka-band structures are fabricated by wire-EDM process and cold test measurements are carried out to benchmark the analysis approaches. The equivalent circuit models based on lumped circuit model are simpler than the cascaded matrix equivalent circuit model and can give closed form expressions for the prediction of dispersion and interaction impedance characteristics. The quasi-TEM approach can be extended for the complicated structure like ridge-loaded FWG-SWS. Broad-banding of the conventional folded-waveguide slow-wave structure is attempted by ridge-loading on the broad wall of the structure. The ridge-loaded folded-waveguide slow-wave structure is analyzed by parametric approach, cascaded transmission matrix equivalent circuit model and quasi-TEM approach and validated against numerical simulation. The analysis is extended for exploring the efficacy of the ridge-loading on broad-banding of the traveling-wave tube. Finally efficiency enhancement of the folded-waveguide slow-wave structure is attempted by introducing grating on the broad wall of the structure. The analysis is carried out by numerical simulation for exploring the efficacy of the grating on efficiency enhancement of the traveling-wave tube.

No description available.

En esta tesis se realiza un estudio teórico de la interacción luz-sonido en estructuras foxonicas, con las cuales es posible el control de la luz y el sonido a la misma vez. Esta interacción en dichas estructuras se estudia, tanto desde un punto de vista macroscópico (diseño de estructuras para el confinamiento y guiado de ondas electromagnéticas y elásticas) como microscópico (estudio de la interacción fotón-fonón en microcavidades y desarrollo teórico de modelos cuánticos para la comprensión de dicha interacción). / Escalante Fernández, JM. (2013). Theoretical study of light and sound interaction in phoxonic crystal structures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/33754 / TESIS