Due to the recent interest in broadband antennas a microstrip patch antenna was developed to meet the need for a cheap, low profile, broadband antenna. This antenna could be used in a wide range of applications such as in the communications industry for cell phones or satellite communication. Particle Swarm Optimization was used to design the dual-linear polarization broadband microstrip antenna and impedance matching network. This optimization method greatly reduced the time needed to find viable antenna parameters. A dual input patch antenna with over 30% bandwidth in the X-band was simulated using Ansoft's High Frequency Structural Simulator (HFSS) in conjunction with Particle Swarm Optimization. A single input and a dual input antenna was then fabricated. The fabricated antennas were composed of stacked microstrip patches over a set of bowtie apertures in the ground plane that were perpendicular to one another. A dual offset microstrip feedline was used to feed the aperture. Two different layers were used for the microstrip feedline of each polarization. The resulting measured impedance bandwidth was even wider than predicted. The antenna pattern was measured at several frequencies over the antenna bandwidth and was found to have good gain, consistent antenna patterns and low cross polarization.

This dissertation reports on three different yet related topics in light scattering computation, radiative transfer simulation, and remote sensing implementation, regarding the cloud properties and the retrieval of cloud properties from satellite-based infrared radiometric measurements. First, the errors associated with the use of circular cylinders as surrogates for hexagonal columns in computing the optical properties of pristine ice crystals at infrared (8-12 µm) wavelengths are investigated. It is found that the differences between the results for circular cylinders and hexagonal columns are on the order of a few percent at infrared wavelengths. Second, investigated in this dissertation are the outgoing broadband longwave and window channel radiances at the top-of-atmosphere under clear-sky conditions on the basis of the data acquired by the Cloud and the Earth's Radiant Energy System (CERES) instrument onboard the NASA Terra satellite platform. Based on the comparison of the observed broadband radiances with those obtained from rigorous radiative transfer simulations, it is found that the theoretical results tend to be larger than their measured counterparts. Extensive sensitivity studies regarding the uncertainties of various parameters were carried out. Within the considered uncertainties of various factors, the computed radiances are still larger than the observed radiances if thin cirrus clouds are excluded. Thus, a potential cause for the differences could be associated with the presence of thin cirrus clouds whose visible optical thickness is smaller than approximately 0.3. Third, presented in this dissertation is an illustration of the application of hyperspectral infrared channel observations to the retrieval of the cloud properties. Specifically, the hyperspectral measurements acquired from the Atmospheric Infrared Sounder (AIRS) aboard the NASA Aqua platform are used to infer cloud top pressure, effective cloud amount, cloud thermodynamic phase, cloud optical thickness, and the effective size of cloud particles. The AIRS-based retrievals are compared with the counterparts of the operational cloud products derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). The two retrievals agree reasonably well except for the retrieved cloud effective particle size. Furthermore, the diurnal and seasonal contrasts of cloud properties are also investigated on the basis of the cloud properties retrieved from the AIRS data.

A fully-differential base-band transimpedance low-pass filter is designed for use in a direct conversion wireless receiver. Existing base-band transimpedance amplifiers (TIA) often utilize single-pole filters which do not provide good stop-band rejection and may even allow the filter to saturate in the presence of large interferers near the edge of the pass-band. The designed filter is placed in parallel with an existing single-pole TIA filter and diverts stop-band current signals away from the existing filter, providing added rejection and safeguarding the filter from saturating. The presented filter has a bandwidth of 10 MHz, achieves 35 dB rejection at 50 MHz (25 dB in post-layout simulations), and can process interferers as large as 10 mA. The circuit is designed in Jazz 0.18 m CMOS technology, and it is shown, using macromodels, that the design is scalable to smaller, faster technologies.

Accelerated growth in wireless communications in recent years has led to the emergence of portable devices that employ several wireless communication standards to provide multiple functionality such as cellular communication, wireless data communication and connectivity, entertainment and navigation, within the same device. Industry drive is towards reduction of the number of radio frequency (RF) front-end receivers required to cater to the various standards/bands within a single device to reduce cost, size and power consumption. The current trend is to use broadband/multi-standard or reconfigurable RF front-ends to cater to two or three standards at a time for cost-effective RF front-end solutions. The direct conversion receiver architecture has become attractive as it offers a full on-chip front-end solution without the need for expensive external components. Passive current-mode mixers are used in these receivers to eliminate mixer flicker noise. The in-band current signals are typically in the micro-amp range after mixer downconversion. Transimpedance amplifiers are used to convert the downconverted current signals to voltage, and they provide amplification in the process. Because of the co-existence of multiple-radios within each device, large blocker currents downconvert close to the channel bandwidth after the mixer. Conventionally, single-pole transimpedance amplifier (TIA) filters are used to provide out-of-band (OOB) signal filtering. This requires high resolution analog-to-digital converters (ADCs) later in the receiver chain for signal processing. Providing higher order filtering before the ADC relaxes its specifications and this reduces the ADC and ADC calibration cost and complexity. Typically, an extra filtering stage is provided in the form of a cascaded filtering block after the single-pole TIA. In this work, higher order filtering is embedded within the TIA in the form of active feedback. In addition to relaxing the ADC specifications, this proposed TIA provides improved large signal linearity such as P1dB compression point. Furthermore, since the extra-circuitry is not in the signal path, in-band flicker noise and linearity are not degraded. The proposed TIA filter has been designed in IBM 90nm technology with a supply voltage of 1.2V. It can tolerate close-in blocker magnitudes of 4.5mA at 60MHz and higher before in-band 1dB compression is reached.

The main purpose of this thesis is to estimate the direct path in dense multipath Ultra Wide-Band (UWB) environment. The time-of-arrival (ToA) estimation algorithm used is based on Generalized Maximum-Likelihood (GML) algorithm. Nevertheless, GML algorithm is so time-consuming that the results usually take a very long period of time, and sometimes fail to converge. Hence, the schemes that would improve the algorithm are investigated. In the schemes, the search was executed in sequential form. Two threshold parameters are to be determined¡Xone is about the arrival time of the estimation path while the other is the fading amplitude of the estimation path. The thresholds are determined in order to terminate the sequential algorithm. The determination of thresholds is based on error analysis, including the probability of error and root-mean-square error. The analysis of the probability of error is subject to the probability of false alarm and the probability of miss. However, a trade-off problem on the probability of false alarm and the probability of miss exists in the process of determining thresholds. The thresholds are determined according to the requirement of the probability of error. We propose an improvement scheme for determining the two thresholds. In the proposed scheme, candidate pairs are evaluated within an appropriate range. The root-mean-square error value for each pair of thresholds is calculated. The smallest error, corresponding to the desired thresholds, is chosen for use in ToA estimation. From the simulation results, it is seen that, when SNR falls between -4dB and 16dB, the improvement proposed scheme results has the smaller estimation error.

The atomic arrangements and electronic structures of [0001] oriented GaN nanowires with different side surfaces have been studied by the first-principles molecular dynamics (MD) method and the conventional first-principles electronic structure calculation method. It is found that due to the dangling bond effects, the Ga-N bonds on the side surfaces of the nanowire tilt with Ga surface atoms moving inward. The radius of the nanowire is found to be reduced with respect to the wire truncated from a bulk GaN solid, which can be attributed to the surface tension effect. Due to the large ratio between the numbers of surface atoms and bulk atoms, the electronic structures of these nanowires are very different from those of bulk and films due to the large number of surface atoms or dangling-bond states, so that a bulk-like energy gap can not be clearly defined.

The first part of this thesis proposes a method to synthesize the T- and £S-prototype of band-pass filters using the two reflection zeros and the rolloff rate. According to the characteristics of passive components embedded in different substrates, £S-prototype band-pass filter is suitable for implementation on LTCC substrate, while T-prototype band-pass filter is suitable for implementation on organic substrate. The second part of this thesis employs the £S-prototype to design the LTCC band-pass filters. It has been found that mutual coupling and feedback elements can be used to create the multiple transmission zeros. With these synthesized transmission zeros, the stopband attenuation can be enhanced at several specific frequencies. For demonstration, this thesis implements the LTCC band-pass filters in 2.4 GHz ISM band and 3.5 GHz WiMAX band. The measured results show that insertion loss and return loss in the passband for these LTCC filters is less than 2 dB and more than 10 dB, respectively. In addition, these filters have the additional transmission zeros for enhancing the stopband attenuation. Moreover, miniaturization is also a key issue in implementing these LTCC filters. The 2.4 GHz and 3.5 GHz LTCC filter can meet the standard 1608 size and 2520 size, respectively, which are the smallest compared to the other LTCC filters reported for similar applications in the current literature and commercial media.

In this work we apply the finite element method to analyze the wave transmission property of solid/fluid composite medium, phononic crystal. The sound attenuation spectrum is obtained to show the forbidden bands of the band gap. First, we construct the finite element model for a two-dimensional phononic crystal, studied by Sánchez-Pérez etc. with PWE and experimentally, constituted of a rectangular array of parallel circular stainless steel cylinders in air. It has demonstrated that our simulation work was feasible; then, we performed the experimental measurements and simulations by using the narrow and wide frequencies. The results show agreement between the experiments and the simulations. We also simulated the crystal samples of filling fraction 5 % and 10 % for square and hexagon lattice, respectively, in both the [100] and [110] direction. The full band gaps are determined from the combination of the results. We have investigated the finite element simulation for the solid/fluid phononic crystal successfully. Both work the results of experiment in the reference and in this work are compared with the FEM simulation. It demonstrates that the finite element method is a good tool for the design of phononic crystal in application to new type sound absorption (isolation) material.

In this thesis, we investigate the single-pumped L-band (1570-1610 nm) amplified spontaneous emission fiber source by employing 1480 nm single pumping configuration. Using the 1480 nm-pumped laser, we chose the adequate fiber length and adjusted the pump power to optimize the characteristics of the ASE source. The characteristics are experimentally examined and compared in terms of the output power, mean wavelength, spectral linewidth, and pumping conversion efficiency in four configurations with single-pass forward (SPF), single-pass backward (SPB), double-pass forward (DPF), and double-pass backward (DPB) structures. Among them, the DPF configuration with low mirror reflectance of 8% is the better one to be an L-band ASE fiber source with output power of 13.8 mW, mean wavelength of 1585.7 nm, spectral linewidth of 40.9 nm and pumping efficiency of 13.8%.

Because of the huge bandwidth of Ultra-Wideband (UWB) systems, in-band narrowband interference may hinder receiver performance. In this dissertation, sources of potential narrowband interference that lie within the IEEE 802.15.3a UWB bandwidth are presented, and a solution is proposed. To combat interference in Multi-Band OFDM (MB-OFDM) UWB systems, an analog notch filter is designed to be included in the UWB receive chain. The architecture of the filter is based on feed-forward subtraction of the interference, and includes a Least Means Squared (LMS) tuning scheme to maximize attenuation. The filter uses the Fast Fourier Transform (FFT) result for interference detection and discrete center frequency tuning of the filter. It was fabricated in a 0.18 µm process, and experimental results are provided. This is the first study of potential in-band interference sources for UWB. The proposed filter offers a practical means for ensuring reliable UWB communication in the presense of such interference. The Operational Transconductance Amplifier (OTA) is the predominant building block in the design of the notch filter. In many cases, OTAs must handle input signals with large common mode swings. A new scheme for achieving rail-to-rail input to an OTA is introduced. Constant gm is obtained by using tunable level shifters and a single differential pair. Feedback circuitry controls the level shifters in a manner that fixes the common mode input of the differential pair, resulting in consistent and stable operation for rail-to-rail inputs. As the new technique avoids using complimentary input differential pairs, this method overcomes problems such as Common Mode Rejection Ratio (CMRR) and Gain Bandwidth (GBW) product degradation that exist in many other designs. The circuit was fabricated in a 0.5µm process. The resulting differential pair had a constant transconductance that varied by only ±0.35% for rail-to-rail input common mode levels. The input common mode range extended well past the supply levels of ±1.5V, resulting in only ±1% fluctuation in gm for input common modes from -2V to 2V.