Parveen Wahid

Deposition and x-ray photoelectron spectroscopy studies on sputtered cerium dioxide thin films

Cerium dioxide is a rare earth oxide material that can be useful in various optical and electronic applications because of its high refractive index and its dielectric constant. The purpose of this study was to conduct an x-ray photoelectron spectroscopy analysis of sputtered cerium dioxide thin films. The thin films were deposited onto glass substrates using rf magnetron sputtering. A cerium dioxide target was used and various oxygen–argon gas flow ratios under different sputtering power levels were used for deposition. The results presented here characterize the properties of the rf sputtered cerium dioxide thin films under different deposition conditions.

Characterization and optimization of cerium dioxide films deposited by r.f. magnetron sputtering

Abstract Cerium dioxide (CeO2) films were deposited on glass substrates by an r.f. magnetron sputtering process. The deposition rates were studied as a function of the molar fraction of oxygen in the system for various input power levels. The deposition conditions were optimized to obtain good quality films for optical transmission.

A Wideband, Dual-Polarized, Substrate-Integrated Cavity-Backed Slot Antenna

A new technique for designing wideband dual-polarized slot antennas is presented. The proposed structure is in the form of a differentially fed cross-slot antenna backed by a shallow substrate-integrated cavity with a depth of approximately λ0/10 . This technique takes advantage of a double-resonance observed in off-center microstrip-fed slot antennas to enhance its bandwidth to double that of typical cavity-backed cross-slot antennas of the same size. Experimental results demonstrate a bandwidth of 19%, average gain of 5.3 dBi, isolation better than 28 dB, and wideband polarization purity.

FDTD speedups obtained in distributed computing on a Linux workstation cluster

The project investigated various aspects of parallel FDTD implementation on a workstation cluster. The computation grid was divided among nodes. For a fixed size problem, as the number of processor increases, the speedup saturates. This happens because each processor spends less time computing but essentially the same time communicating with its neighbors. To take advantage of the parallel algorithm, the problem size must be sufficiently large compared with the number of processors. For very large problems, we can efficiently employ a large number of processors to obtain a linear speedup. In this work, the message passing interface (MPI) parallel implementation was integrated with POSIX threads using the pthreads library. This was required because each node in the cluster was equipped with two processors. On each node, each process contained two threads that executed in parallel. As expected, for sufficiently large problems the speedup was increased by almost a factor of two when using threads.

A high efficiency L-band microstrip antenna

The design of a high efficiency circularly polarized nearly square patch antenna at L-band is presented. One way to improve the efficiency of the inherently low efficiency microstrip antennas is to use substrates with a low permittivity. A low permittivity substrate with /spl epsi//sub r/=1.1028 was obtained by using a combination of Rogers RT/Duroid 5880 and Rohacell hard foam. The effect of a 5 mils thick Rogers RT/Duroid 5880 superstrate on the efficiency was also studied. Results of the antenna efficiency and bandwidth for both the low dielectric substrate and superstrate are presented. The results were obtained using the 1E3D software package and compared with measured results. Efficiencies of the order of 85% for a single patch element were obtained.

Third order nonlinear distortion of SAW duplexers in UMTS system

Nonlinearity distortion characterization and accurate modeling techniques for leaky surface acoustic wave (LSAW) devices have been desired in the recently years due to the applications of the Radio Frequency (RF) SAW duplexers in the third-generation (3G) telecommunication system, such as Universal Mobile Telecommunications System (UMTS). In the work, we first discuss the approaches to measure and characterize the 3rd order harmonic generation of the resonators on lithium tantalate YXl42° wafer and YXl48° wafer, with resonance frequency of 800MHz to 900 MHz; Second, we present an effective nonlinear Butterworth-van-Dyke (BVD) model to simulate the multi-tone 3rd order intermodulation effects of a band 5 duplexer; simulation result vs. measurement of 3rd order harmonic generation, 3rd order intermodulation (IMD3) and triple beat are presented.

Hexagonal fractal multiband antenna

With the increased interest in wireless multiband operation, there is a renewed search for multiband antennas. The Sierpinski gasket antenna is a prime example of applying fractal geometry to produce multibandwidth behavior. Since the Sierpinski gasket has proven itself to be an excellent multiband antenna, other multiband antennas have been investigated using fractal geometry. This paper examines the input characteristics of one such fractal design based on the hexagon and evaluates its suitability for multiband usage.

A reconfigurable Yagi array for wireless applications

The reconfigurable antenna is a revolutionary new type of antenna that controls the radiation pattern by dynamically adjusting its aperture. It provides a unique way to cover different frequency bands and, in an array, provides a beam steering capability. There is therefore a great demand for reconfigurable antennas in the field of wireless communications, satellite communications, radar etc. We present a reconfigurable Yagi to work at both the 5.78 GHz and 2.4 GHz frequencies. It is intended for use in the transition period when wireless communication shifts to the 5.78 GHz band. Preliminary results for this reconfigurable antenna are presented.

Two-branch space and polarization diversity schemes for dipoles

The performance of two-branch space and polarization diversity schemes for linearly polarized signals is evaluated. An antenna system must be designed to reduce multipath fading, interference and polarization mismatch. Space diversity is the most common technique used to reduce multipath fading. Recently, polarization diversity has been used since its performance is comparable to that of space diversity and in addition the size of the antenna array can be reduced. Adaptive arrays are also used to cancel multipath components or combine them coherently to enhance the desired signal while nulling the interference signals from different directions. The results for the performance of two-branch horizontal space diversity, H/V polarization diversity and /spl plusmn/45/spl deg/ slanted polarization schemes for arbitrary polarized signals are presented here. Although the performance of the adaptive array depends on the environment, the results show that when polarization diversity is combined with horizontal space diversity, the two-branch /spl plusmn/45/spl deg/ slanted polarization scheme performs better than the H/V polarization scheme.

Analysis of frequency selective surfaces with ferrite substrates

The spectral domain Greens function for the problem of frequency selective surfaces (FSS) with ferrite substrates is developed and presented. Several results are presented to show the tunability of frequency selective surface with ferrite substrates as a function of the applied dc bias. Other unique characteristics of the FSS on ferrite substrates are also presented and discussed.