Numerical modeling of the beams generated from an ultra-wide bandwidth pulse-driven dipole array is considered. Several multi-derivative systems are simulated with these numerical results. The analytic performance bounds on energy, intensity, and beam width of the pulsed beams generated by the pulse driven array are derived. Numerical comparisons are made between the pulsed beams generated by driving the dipole array with monochromatic continuous waves with two distinctive amplitude tapers, Gaussian pulses with two distinctive amplitude tapers, and three types of localized waves. The specific localized waves used include the modified power spectrum pulse and the 1/2 and 3/2 superluminal pulses. The energy pattern of the pulse-driven dipole array is studied for each of these cases. The effect of element density on these energy patterns is also examined. The results obtained show that the modified power spectrum pulse truly outperforms the monochromatic continuous wave by a wide margin for multi-derivative systems.

A method to predict appropriate dielectric constants and thicknesses for double dielectric substrate microstrip structures to minimize forward crosstalk is presented. Ratios of the elements in the capacitance matrix are compared to those in the inductance matrix to determine if forward crosstalk will be minimized. Curves showing C(rat) where C(rat) is the ratio of the C₁₁ element to the C₁₂ element, as a function of the relative permitivity, εᵣ and SPICE simulations are presented for particular geometries. The method accurately predicts combinations of dielectrics that will produce a structure exhibiting greatly reduced crosstalk.

Asymptotic expressions are obtained for the electric field due to a current propagating on a horizontal semi-infinite wire above the earth. First, exact integral representations are derived for the electric field due to a current on a semi-infinite wire in a general multi-layered medium. The resulting integral expressions are then specialized for the problem of a semi-infinite wire above the earth. The resulting expressions involve a semi-infinite integration over an integrand containing the incomplete Lipschitz-Hankel integrals. The steepest descent technique is applied to the direct and reflected terms separately, thereby providing a far-zone approximation for the field (E α r⁻¹). A recurrence relationship is then developed which allows the r⁻² term in the asymptotic expansion to be computed from the previously computed r⁻¹ term. A numerical comparison between the following three methods is carried out: numerical integration, one-term (1/r) approximation, and two-term (1/r²) approximation. It is shown that two-term solution yields more accurate results than that of the one-term solution, especially when the problem of a finite length wire above the earth is considered. The two-term expansion provides accurate results for the fields when 0.1 λ < r < ∞ and it consumes much less computation time than the numerical integration solution.

The effect of neutron irradiation on power metal-oxide-semiconductor field effect transistors (power MOSFETs) breakdown voltage has been investigated. Power MOSFETs of both n- and p-channel with manufacturer's rated breakdown voltage between 100 to 500V were radiated up to accumulated neutron fluence of 5x10¹⁴ neutron/cm² Considerable increase in the breakdown voltages were observed in n-type MOSFETs after 10¹³ neutron/cm² and to p-type MOSFETs after 10¹² neutron/cm² The increase in breakdown voltages is due to the decrease in the mean free path caused by the neutron-irradiation-induced defects. The effect of positive trapped charge oxide and the termination structure to the breakdown voltage were considered. S-PISCES 2B device simulation was used to investigate the change in the b coefficient of Chynoweth's law that relates to the mean free path. Two empirical models are presented: one predicts the power MOSFET breakdown voltage after a certain amount of neutron fluence and the other considers the change in the b coefficient after some amount of neutron radiation to predict the change of breakdown voltage in a device simulation.

A method to reduce Electromagnetic Interference (EMI) of multiple switching waveforms by harmonic cancellation is presented. The waveforms considered are input currents generated by 'n' Discontinuous Mode (DCM) Flyback Switched Mode Power Supplies (SMPS) that share a common source. The waveforms are modeled as ideal triangular waveforms and a Fourier analysis is performed to determine the phase relationship, θ, that minimizes the EMI. The combined EMI is minimum when θ=360°/n and maximum when θ=0°. A system of two DCM Flyback SMPS is designed in such a way that both 0° and 180° phase shifts between input current waveforms are possible. In both cases EMI filters are designed to meet EMI standard MIL-STD-461. The system is simulated and constructed and the experimental results are presented. These results demonstrate the accuracy of the modeled waveform and the reduction of conducted EMI when optimal phasing is achieved.

The design of a digital focus servo control system for an optical disk tester is presented. A total focus misregistration budget is established for three primary disturbances: disk runout, shock, and system noise. The design of an analog servo system is established first to determine the required bandwidth. The analog design is transformed into a digital representation using pole/zero mapping techniques. The transformation to the digital domain includes the effects of the control law computation time, the D/A sample and hold, and the anti-aliasing filter. Modeling and simulation of the digital system in the frequency and time domain are used to obtain the phase margin and the transient response. The transient response overshoot is larger than that obtained from a second order model. The larger overshoot is a result of the additional phase delay produced in the digital system that reduces the gain margin drastically compared to the analog case.

Dielectric and magnetic structures which inhibit the propagation of light for a given frequency range at any angle of incidence are said to have a photonic band gap (PBG). By placing defects inside of these PBG structures, useful devices can be constructed including micro-cavity lasers and nanometer scale waveguides. This thesis is concerned with the evaluation of these PBGs in order to obtain an understanding of how they work, as well as developing new methods to evaluate them. The photonic band gap configurations are modeled with the Finite Difference Time Domain (FDTD) method in one and two dimensions. By modeling these structures in the time domain, the finite amount of time that it takes to establish the photonic band gaps may be observed. Also, methods using the Fast Fourier Transform in combination with the FDTD algorithm are capable of determining the frequency spectrum of a structure with little computation time.

This thesis presents a novel spatial spectrum estimation technique, ∂-MUSIC, for discriminating between two closely spaced sources which are highly correlated. The ∂-MUSIC algorithm is tested, modified, and compared to the MUSIC algorithm using a point source simulation. Various power levels, samples sizes and angle separations are used on a linear and a planar array for correlated and uncorrelated sources. The algorithm is found to be relatively insensitive to correlation and can separate targets to one-half of the angular separation threshold of ∂-MUSIC. The ∂-MUSIC algorithm is tested using a simulation that generated terrain scattered interference representative of a propagation scenario involving multiple paths. The simulation shows that ∂-MUSIC is able to resolve the direct path and image at less than one-fourth of a beam width, with a ten degree angle to the surface, whereas MUSIC finds a single angle which is biased toward the image.

This work contains a discussion of symbolic analysis techniques, symbolic and numerical analysis results, and loosely structured analog design methodologies that one can use in the development of high frequency, low distortion bipolar amplifiers. Central to this purpose is the development of simplified, yet informative symbolic expressions for harmonic distortion by applying power and Volterra series expansions. Instead of analyzing complete and complex amplifiers, critical bipolar amplifier subcircuits are examined to provide design-oriented insight into the root causes of distortion. In each case we determine low frequency distortion, and where it is most appropriate, frequency dependent distortion. We also address common and uncommon distortion reduction schemes like global feedback, bootstrapping, and feedforward error correction.

<p> Energy and security are becoming increasingly important in the design of future wireless communication systems. This thesis focuses on these two main aspects of wireless networks and studies their tradeoffs with other performance metrics such as throughput and delay.</p><p> The first part of the thesis deals with the energy aspect of wireless networks in which we present several novel joint-physical network layer techniques and either evaluate their energy efficiency or study the energy/delay/throughput tradeoffs. First, we study the energy/delay tradeoffs for the problem of reliable packet transmission over a wireless time-varying fading link and also investigate the effect of having Channel State Information on the resulting tradeoff . Then, we extend the model to a single-hop multicast time varying wireless network. We address energy/delay/throughput tradeoffs by considering the problem of streaming a real time file with a fixed delay and energy constraints where the objective is to maximize the number of packets received by the destinations. Again, the effect of having Channel State Information is studied. Also, the effect of using Random Network Coding as a transmission scheme is studied and compared to traditional transmission schemes such as simple ARQ. Next, we consider the effect of cooperation on the energy efficiency of wireless transmissions in which we propose several joint physical-network layer cooperation techniques. Also, the effect of Random Network Coding is investigated in the context of cooperation in which Random Network Coding based cooperation techniques are investigated and compared to cooperation techniques that rely on simple ARQ solely or combined with superposition Alamouti space-time codes. We then consider the particular case of cellular systems in which we design rate allocation technique that minimizes the consumption energy in a Macro cell. This technique takes into account sleep mode configuration of current base stations.</p><p> In the second part of the thesis, we focus on security and in particular on privacy. We also study the tradeoff between securing wireless transmissions and the energy/delay overhead due to security by considering the problem of information exchange among adjacent wireless node in the presence of an eavesdropper. The nodes are required to exchange their information while keeping it secret from the eavesdropper. The nodes can choose to transmit either through public channel or though more costly private channels. We express the cost of using the private channels in terms of the extra energy or delay required to transmit through the private channel. We then minimize the security cost subject to a target security level. Also this part presents a deterministic Network Coding based transmission scheme and investigates its effect on the achieved performance.</p><p> Last, we introduce the problem of minimum energy scheduling of a group of base stations and compare this problem to the standard minimum length scheduling problem. We also discuss the complications and the challenges associated with solving the minimum energy scheduling problem.</p>