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Leaky-waves have been a topic of increasing interest in the last years, with diverse practical applications in many different engineering fields. From periodic, FSS, EBG or even metamaterial leaky-wave based antennas to waveguide filters and higher efficiency energy guiding, they all share a common base structure: a travelling-wave propagating within a metal encapsulation, that can be open or closed, and altered by a planar metallization of periodic nature, from which the energy may radiate. Due to the fact that these antennas are usually electrically large and the periodic printed circuit requires a certain grade of complexity, 3D commercial software is prohibitively time consuming. Also, the homebrew methods developed up to this day are either not rigorous and accurate enough or unable to deal with complex periodic geometries. At this point, the evolution of leaky-wave antennas needs a solid, efficient and versatile tool where to base the future design research on. In this work a novel simulation tool for waveguide embedded leaky-wave antennas is presented. It is based on a full-wave Method of Moments applied to the spectral domain Green Functions for a rigorous modal analysis of the finite structure. The use of Subdomain basis functions allows the software to model complex periodic geometries, overcoming a main limitation, and the analytical nature of the method combined with its 2.5D approach, results in a significant computing time reduction. It is built on a modular coding philosophy and provided with a user-friendly graphical interface, and an intuitive working procedure, making the program not only fast and accurate, but also easy to use and extend to new geometries. Finally, it is remarkable the educational potential of this new analysis software, since it identifies higher order effects as bandgaps and multi-harmonic radiation from a complete and simple modal approach.

Higher-order basis functions are widely used to model currents and fields in numerical simulations of electromagnetics problems because of the greater accuracy and computational efficiency they can provide. Different problem formulations, such as method of moments (MoM) and the finite element method (FEM) require different constraints on basis functions for optimal performance, such as normal or tangential continuity between cells. In this thesis, a method of automatically generating bases that satisfy the desired basis constraints is applied to a MoM formulation for scattering problems using surface integral equations. Numerical results demonstrate the accuracy of this approach, and show good system matrix conditioning when compared to other higher-order bases.

The research performed throughout this dissertation aims at implementing quantitative methods in order to assess economic and technological performances of firms, i.e. it tries to assess the impacts of the determinants of technological activity on the results of this activity. For this purpose, a representative sample of the most important R&D firms in the world is constituted. The micro-economic nature of the analysis, as well as its international dimension are two main features of this research at the empirical level. The second chapter illustrates the importance of R&D investments, patenting activities and other measures of technological activities performed by firms over the last 10 years. The third chapter describes the main features as well as the construction of the database. The raw data sample consists of comparable detailed micro-level data on 2676 large manufacturing firms from several countries. These firms have reported important R&D expenditures over the period 1980-1994. The fourth chapter explores the dynamic structure of the patent-R&D relationship by considering the number of patent applications as a function of present and lagged levels of R&D expenditures. R&D spillovers as well as technological and geographical opportunities are taken into account as additional determinants in order to explain patenting behaviours. The estimates are based on recently developed econometric techniques that deal with the discrete non-negative nature of the dependent patent variable as well as the simultaneity that can arise between the R&D decisions and patenting. The results show evidence of a rather contemporaneous impact of R&D activities on patenting. As far as R&D spillovers are concerned, these externalities have a significantly higher impact on patenting than own R&D. Furthermore, these effects appear to take more time, three years on average, to show up in patents. The fifth chapter explores the contribution of own stock of R&D capital to productivity performance of firms. To this end the usual productivity residual methodology is implemented. The empirical section presents a first set of results which replicate the analysis of previous studies and tries to assess the robustness of the findings with regard to the above issues. Then, further results, based on different sub samples of the data set, investigate to what extent the R&D contribution on productivity differs across firms of different industries and geographic areas or between small and large firms and low and high-tech firms. The last section explores more carefully the simultaneity issue. On the whole, the estimates indicate that R&D has a positive impact on productivity performances. Yet, this contribution is far from being homogeneous across the different dimensions of data or according to the various assumptions retained in the productivity model. The last empirical chapter goes deeper into the analysis of firms' productivity increases, by considering besides own R&D activities the impact of technological spillovers. The chapter begins by surveying the alternative ways proposed in the literature in order to asses the effect of R&D spillovers on productivity. The main findings reported by some studies at the micro level are then outlined. Then, the framework to formalize technological externalities and other technological determinants is exposed. This framework is based on a positioning of firms into a technological space using their patent distribution across technological fields. The question of whether the externalities generated by the technological and geographic neighbours are different on the recipient's productivity is also addressed by splitting the spillover variable into a local and national component. Then, alternative measures of technological proximity are examined. Some interesting observations emerge from the empirical results. First, the impact of spillovers on productivity increases is positive and much more important than the contribution of own R&D. Second, spillover effects are not the same according to whether they emanate from firms specialized in similar technological fields or firms more distant in the technological space. Finally, the magnitude and direction of these effects are radically different within and between the pillars of the Triad. While European firms do not appear to particularly benefit from both national and international sources of spillovers, US firms are mainly receptive to their national stock and Japanese firms take advantage from the international stock.

This thesis studies different aspects of firm decisions by using a dynamic model. I estimate a dynamic model of the firm based on the trade-off theory of capital structure that endogenizes investment, leverage, and payout decisions. For the estimation of the model I use Efficient Method of Moments (EMM), which allows me to recover the structural parameters that best replicate the characteristics of the data. I start analyzing the question of whether target leverage varies over time. While this is a central issue in finance, there is no consensus in the literature on this point. I propose an explanation that reconciles some of the seemingly contradictory empirical evidence. The dynamic model generates a target leverage that changes over time and consistently reproduces the results of Lemmon, Roberts, and Zender (2008). These findings suggest that the time-varying target leverage assumption of the big bulk of the previous literature is not incompatible with the evidence presented by Lemmon, Roberts, and Zender (2008). Then I study how corporate income tax payments vary with the corporate income tax rate. The dynamic model produces a bell-shaped relationship between tax revenue and the tax rate that is consistent with the notion of the Laffer curve. The dynamic model generates the maximum tax revenue for a tax rate between 36% and 41%. Finally, I investigate the impact of financial constraints on investment decisions by firms. Model results show that investment-cash flow sensitivity is higher for less financially constrained firms. This result is consistent with Kaplan and Zingales (1997). The dynamic model also rationalizes why large and mature firms have a positive and significant investment-cash flow sensitivity.

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The relationship between politicians and firms has attracted a considerable amount of research, especially in developing countries, where firms' political links are a widespread phenomenon. However, existing literature offers contradicting views about this relationship, espicially regarding the impact of firms' political connections on firms' market-performance. Furthermore, there is limited evidence on the impact of firms' political connections on some of the important corporate decisions, including firms' investment- and dividend-policies. Therefore, this thesis seeks to fill these gaps by offering three empirical essays with Jordan as a case study. The first essay examines the impact of firms' political links on their values by controlling for macroeconomic conditions. Also, in the extended models, by specifying three major events which occurred after 2008, namely, the establishment of the Anti-Corruption Commission (ACC), the Global Financial Crisis, and the Arab Uprisings, we investigate the effects of these events on the relationship between firms' political ties and their value. The findings of this essay indicate that politically-connected firms have higher values compared to their non-connected counterparts in Jordan. Moreover, it is found that firms with stronger political-ties have higher values than firms with weaker ties. Furthermore, the positive effect of political connections continues, even after controlling for the macroeconomic conditions, though the latter are considered to be more important than political connections for firm valuation due to their impact on the share price. Interestingly, findings show that the events occurring after 2008 do not seem to have affected the relationship between political connections and firm value since the significant positive impact of political-ties on firm value persists during the post-event period. The second empirical essay studies the role of political connections in mitigating firms' financing-constraints. Moreover, it investigates the effect of the strength of political connections in alleviating these constraints. Finally, it looks at the impact of the above-mentioned three events which occurred after 2008, notwithstanding the new banking Corporate Governance Code issued in 2007. Findings of this essay reveal that firms' political connections are important in mitigating their financing-constraints. Furthermore, the results show that stronger political connections seem to reduce financing-constraints more than weaker connections. Finally, findings show that the impact of firms' political connections has diminished during the post-event period (2008 - 2014). The third essay examines how a firm's political connections can affect its dividend-policy. It also considers the impact of the strength of political connections on dividend-policy. Finally, we extend the empirical analysis by investigating any shift in the relationship between political connections and dividends due to the events of the Global Financial Crisis, the Arab Uprisings, and the adoption of the International Financial Reporting Standards (IFRS). Results of this essay reveal that a firm's political connections have a significant positive impact on both the propensity to pay dividends and the dividend-payout ratio. Regarding the impact of the strength of political connections on dividends, it is found that firms with weaker political connections pay out more in dividends than firms with stronger connections. In terms of the impact of the events which occurred after 2008 on the relationship between political connections and dividends, the findings show that the impact of these connections on dividends is eliminated.

This study examines the impact of fiscal deficits on economic growth in developing countries. Based on deduction from the relevant theoretical and empirical literature, the study tests the following hypotheses regarding the impact of fiscal deficits on economic growth. First, fiscal deficits have significant positive or negative impact on economic growth in developing countries. Second, the impact of fiscal deficits on economic growth depends on the size of deficits as a percentage of GDP - that is, there is a non-linear relationship between fiscal deficits and economic growth. Third, the impact of fiscal deficits on economic growth depends on the ways in which deficits are financed. Fourth, the impact of fiscal deficits on economic growth depends on what deficit financing is used for. The study also examines whether there are any significant regional differences in terms of the relationship between fiscal deficits and economic growth in developing countries. The study uses panel data for thirty-one developing countries covering the period 1972- 2001, which is analysed based on the econometric estimation of a dynamic growth model using the Arellano and Bond (1991) generalised method of moments (GMM) technique. Overall, the results suggest the following. First, fiscal deficits per se have no any significant positive or negative impact on economic growth. Second, by contrast, when the deficit is substituted by domestic and foreign financing, we find that both domestic and foreign financing of fiscal deficits exerts a negative and statistically significant impact on economic growth with a lag. Third, we find that both categories of economic classification of government expenditure, namely, capital and current expenditure, have no significant impact on economic growth. When government expenditure is disaggregated on the basis of a functional classification, the results suggest that spending on education, defence and economic services have positive but insignificant impact on growth, while spending on health and general public services have positive and significant impact. Fourth, in terms of regional differences with regard to the estimated relationships, the study finds that, while there are some regional differences between the four different regions represented in our sample of thirty-one developing countries - namely, Asia and the Pacific, Latin America and the Caribbean, Middle East and North Africa, and Sub-Saharan Africa - these differences are not statistically significant. On the basis of these findings, the study concludes that fiscal deficits per se are not necessarily good or bad for economic growth in developing countries; how the deficits are financed and what they are used for matters. In addition, the study concludes that there are no statistically significant regional differences in terms of the relationship between fiscal deficits and economic growth in developing countries.

In this paper, the precorrected-FFT method is used to solve the electromagnetic scattering from two-dimensional cavities of arbitrary shape. The integral equation is discretized by the method of moments and the resultant matrix equation is solved iteratively by the generalized conjugate residual method. Instead of directly computing the matrix-vector multiplication, which requires N² operations, this approach reduces the computation complexity to O(N log N) as well as avoids the storage of large matrices. At the same time, a technique known as the complexifying k is applied to accelerate the convergence of the iterative method in solving this resonance problem. Some examples are considered and excellent agreements of radar cross sections between these computed using the present method and those from the direct solution are observed, demonstrating the feasibility and efficiency of the present method. / Singapore-MIT Alliance (SMA)