Thesis (M.A.)--Eastern Illinois University, 2009. / Includes bibliographical references.

Efficient reconfigurable antennas are highly sought after in all communication applications for the ability to reduce space cost while maintaining the ability to control the frequency, gain, and polarization. The ability to control these parameters allows a single antenna to maximize its performance in a wide range of scenarios to satisfy changing operating requirements. This thesis will describe reconfigurable antennas using liquid-metal alloys that give the system this ability by injecting or retracting the liquid metal from various channels. After simulations were performed in an electromagnetic simulation software, proof-of-concept models were built, tested, and compared to the simulations to verify the results. / Master of Science / Antennas that can change the tuned center frequency and/or the direction they are pointing are needed in many different applications. Antenna adaptability allows the system to maximize the physical dimensions of the antenna to satisfy a wide range of situations without losing performance. This thesis describes antennas using a liquid-metal alloy that can make physical adaptations for the need at hand. After simulations were performed using computer software, proof-of-concept models were constructed and empirically validated to verify the simulation models.

International Telemetering Conference Proceedings / October 13-16, 1986 / Riviera Hotel, Las Vegas, Nevada / In Aerospace missions it is often required to have a flexible telemetry system for carrying out flight test on aircraft, in which the bit rate, sampling rate and the number of channels can be programmed. This enables the pilot of the aircraft to reconfigure the telemetry system to suit any particular test missions. An L-Band PCM/FM Telemetry System containing a Stored Programme Multiplexer, 12 bit ADC and other digital interfaces for carrying out the measurements on Speed, Events, etc has been developed as a flight instrumentation telemetry for HAL, India. This paper not only presents complete details of the system, which was qualified to meet MIL-5422 levels but also the performance of the system during actual aircraft missions.

This dissertation addresses the design of monolithically integrated phase shifters at S- and L- frequency bands using a commercially available GaAs process from Triquint. The focus of the design is to operate over a wide bandwidth with full 360° phase shift capability, 50 Ω input/output impedance match and low RMS phase and gain errors. The first version of the design is based on passive all-pass phase shifters integrated with wideband amplifiers to compensate for insertion loss. This design uses a 4-bit system to achieve the required phase shift and each bit consists of 3 sections of all-pass filters designed at separate frequencies within the 0.8 – 3 GHz band. Simulation results show a complete 360° phase shift with RMS gain error of less than 0.6 dB and RMS phase error of less than 2.5°. The system is also shown to achieve good input and output impedance matching characteristics. However, the fabricated prototype fails to perform with full functionality due to the excessive number of passive inductors in the design and the resulting mutual coupling. The mutual coupling issue could be solved by spacing out the layout to allow more separation among the inductors. Unfortunately, in the S- and L-bands, this is not an option for this research work as the fabricated design already uses the maximum allowed chip size as determined by the foundry. In addition, larger chip sizes considerably increase the cost in practical applications. To address the challenging needs of small size, wide bandwidth and low frequency applicability, the second design introduced in this dissertation proposes a novel phase shifter implementation that utilizes tunable active differential inductors within all-pass networks. The inductor tuning is used to achieve phase shifts up to 180⁰. A switchable active balanced to unbalanced transition circuit (balun) is included in front of the all-pass network to complement its phase shift capability by another 180°. In addition, the all-pass network is followed by a variable gain amplifier (VGA) to correct for gain variations among the phase shifting states and act as an output buffer. Although active inductors have been previously used in the design of various components, to the best of our knowledge, this is the first time that they have been used in an all-pass phase shifter. The approach is demonstrated with an on-chip design and implementation exhibiting wideband performance for S and L band applications by utilizing the 0.5 µm TriQuint pHEMT GaAs MMIC process. Specifically, the presented phase shifter exhibits 1 × 3.95 mm2 die area and operates within the 1.5 GHz to 3 GHz band (i.e. 2:1 bandwidth) with 10 dB gain, less than 1.5 dB RMS gain error and less than 9° RMS phase error. Comparison with the state-of-the-art MMIC phase shifters operating in S and L bands demonstrates that the presented phase shifter exhibits a remarkable bandwidth performance from a very compact footprint with low power consumption. Consequently, it presents an important alternative for implementation of wideband phase shifters where all-passive implementations will consume expensive die real estate.

Recent developments in the field of phased array feeds for radio astronomical reflector antennas, have opened a new frontier for array signal processing for radio astronomy observations. The goal is to replace single horn feeds with a phased array feed, so as to enable astronomers to cover more sky area in less time. The development of digital backend signal processing systems has been a major area of concentration for the development of science-ready phased array feeds for radio astronomers. This thesis focuses on the development of analog down-converter receivers and an FPGA-based digital backend for real-time data processing and analysis support for phased array feeds. Experiments were conducted with new receiver boards and both single-polarization and dual-polarization phased array feeds at the Arecibo Observatory, Puerto Rico and at the 20-meter telescope at Green Bank, WV, and results were analyzed. The experiments were performed as a part of a feasibility study for phased array feeds. The new receiver boards were developed as an upgrade to the earlier connectorized receivers as the number of input channels increased from 19 to 38 and space constraints arose due to the large size of the earlier receivers. Each receiver card has four independent channels on it. The receiver cards were found to have lower cross-coupling between the channels in comparison to the earlier receivers. The development of a FPGA-based real time digital backend focused on a real-time spectrometer, beamformer and a correlator for all the 64-channels using a x64 ADC card and ROACH FPGA boards. The backend can plot results in real time and can stream and store the data on the computers for purpose of post-processing and data analysis. The design process uses libraries and blocks provided by the Center for Astronomy Signal Processing and Electronics Research (CASPER) community.

Radio astronomy is the science of observing the universe at radio frequencies. In recent years, radio astronomy has faced a growing interference problem as radio frequency (RF) bandwidth has become an increasingly scarce commodity. Communication systems such as Earth orbiting communication satellites creates severe interference to the radio telescopes. This thesis proposes an algorithm to mitigate the radio frequency interference (RFI) from the Iridium satellite system. A technique is presented here to detect the downlink signal of Iridium, estimate the parameters of the signal, synthesize the noise-free version of the signal and finally subtract the recreated signal from the radio telescope output. Using both simulated and real data captured by a radio telescope testbed, we demonstrate that for Iridium bursts with 20 dB signal to noise power ratio (SNR), the proposed algorithm achieves more than 15 dB cancellation. The method proposed here can be implemented using present-day digital signal processing hardware and software. A performance analysis of this proposed cancellation scheme in the radio astronomy RFI mitigation regime is presented. / Master of Science

Accurate measurement of soil moisture (SM) has a significant impact on agricultural production, hydrological modeling, forestry, horticulture, waste management, and other environmental fields. Particularly in precision agriculture (PA), high spatiotemporal resolution information about surface SM is crucial. However, the use of invasive SM probes and other sensors is expensive and requires extensive manpower. Moreover, these intrusive techniques provide point measurements and are unsuitable for large agricultural fields. As an alternative, this dissertation explores the remote sensing of surface SM by utilizing the surface reflectivity estimated from global navigation satellite systems reflectometry (GNSS-R) data acquired through smartphones and off-the-shelf, cost-effective U-blox global navigation satellite systems (GNSS) receivers. To estimate surface reflectivity, the GNSS receivers are attached underneath a small unmanned aircraft system (UAS), which flies over agricultural fields. Additionally, this dissertation investigates a fully custom UAS-based dual-polarized L-band microwave radiometric measurement technique over agricultural areas to estimate surface brightness temperature (����). The radiometer measures surface emissivity as ����, allowing for the estimation of surface SM while considering the detection and removal of radio frequency interference (RFI) from the radiometric measurements. This radiometer processes the data in near real-time onboard the UAS, collecting raw in-phase and quadratic (I&Q) signals across the study field. This feature mitigates the RFI onboard and significantly reduces post-processing time. In summary, this study highlights the utilization of smartphones and semi-custom GNSS receivers in conjunction with UAS-based GNSS-R techniques and UAS-based L-band microwave radiometry for the estimation of surface reflectivity and ����. The radiometric measurement of surface emissivity is related to surface reflectivity through the relationship (Emissivity = 1 -Reflectivity).

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / Embedded "Card-Based" receivers are one of the latest innovations in telemetry reception. These products provide substantial power and flexibility in a small form factor (one slot, PC or VME). In many applications they are a cost effective alternative to conventional telemetry receivers. This paper analyzes currently available products with regard to their features, capabilities, and performance, as well as highlighting typical applications.

This work is focused on design of L band power amplifier. First, the design of the amplifier is substantiated by necessary theoretical basics of RF power amplifiers. Then, after comparsion of availible RF power amplifiers concepts, the doherty power amplifier is chosen as a suitable type. Design of the amplifier is focused on the linearity and efficiency. AWR design program is used for simulation of the amplifier. Amplifier is then realized and parameters are measured. Measured results are then discussed and evaluated. This work proposes design of the linear doherty amplifier for modern communications systems.

Aquarius/SAC-D is a joint NASA/CONAE (Argentine Space Agency) Earth Sciences satellite mission to measure global sea surface salinity (SSS), using an L-band radiometer that measures ocean brightness temperature (Tb). The application of L-band radiometry to retrieve SSS is a difficult task, and therefore, precise Tb corrections are necessary to obtain accurate measurements. One of the major error sources is the effect of ocean roughness that "warms" the ocean Tb. The Aquarius (AQ) instrument (L-band radiometer/scatterometer) baseline approach uses the radar scatterometer to provide this ocean roughness correction, through the correlation of radar backscatter with the excess ocean emissivity. In contrast, this dissertation develops an ocean roughness correction for AQ measurements using the MicroWave Radiometer (MWR) instrument Tb measurements at Ka-band to remove the errors that are caused by ocean wind speed and direction. The new ocean emissivity radiative transfer model was tuned using one year (2012) of on-orbit combined data from the MWR and the AQ instruments that are collocated in space and time. The roughness correction in this paper is a theoretical Radiative Transfer Model (RTM) driven by numerical weather forecast model surface winds, combined with ancillary satellite data from WindSat and SSMIS, and environmental parameters from NCEP. This RTM provides an alternative approach for estimating the scatterometer-derived roughness correction, which is independent. The theoretical basis of the algorithm is described and results are compared with the AQ baseline scatterometer method. Also results are presented for a comparison of AQ SSS retrievals using both roughness corrections.