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Wideband phased arrays require very tight element spacing to permit wide angle scanning of the main beam over the wide bandwidth. The consequence of tight spacing is very high mutual coupling among the elements in the array. Previous efforts by Virginia Tech Antenna Group has shown that the strong coupling can be utilized in arrays to obtain broadband frequency response while maintaining a small element spacing. However, mutual coupling between elements in a tightly coupled array can sometimes dramatically change the operating frequency, bandwidth, and radiation pattern from that of the single isolated element. Thus, there are some fundamental questions that remain regarding the effective operation of highly coupled arrays for beam forming, beam scanning, and aperture reconfiguration. Existing antenna pattern analysis techniques including the active element pattern method are inadequate for the application in highly coupled arrays. This dissertation focuses on the development of a new antenna array analysis technique. The presented method is based on the scattering parameter network descriptions of the array elements, associated feed network and the active element patterns. The developed model is general. It can be applied to an array of any size and configuration. The model can be utilized to determine directivity, gain and realized gain of arrays as well as their radiation efficiency and impedance mismatch. Using the network model, the relationship between radiation pattern characteristics and the input impedance characteristics of the array antennas becomes clear. Three types of source impedance matching conditions for array antennas are investigated using the model. A numerically simulated array of strip dipole array is used to investigate the effects of various impedance matching methods on the radiation pattern and impedance bandwidth. An application of network analysis is presented on an experimental investigation of $3\times 3$ Foursquare array test bed to further verify the concepts. / Ph. D.

In airborne communication systems such as airborne cell-extender repeaters the receiver faces the challenge of demodulating the signal of interest (SOI) in the presence of excessive amounts of Co-Channel Interference (CCI) from a large number of sources. This results in the overloaded environment where the number of near-equal power co-channel interferers exceeds the number of antenna array elements. This thesis first analyzes the interference environment experienced by an airborne cellular repeater flying at high altitudes. Link budget analysis using a two-ray propagation model shows that the antenna array mounted on an airborne receiver has to recover the SOI out of hundreds of co-channel interfering signals. This necessitates use of complex overloaded array signal processing techniques. An extensive literature survey on narrowband signal extraction algorithms shows that joint detection schemes, coupled with antenna arrays, provide a solution for narrowband overloaded array problem where as traditional beamforming techniques fail. Simulation results in this thesis investigates three "promising" overloaded array processing algorithms, Multi-User Decision Feedback Equalizer (MU-DFE), Iterative Least Squares with Projection (ILSP), and Iterative Least Squares with Enumeration (ILSE). ILSE is a non-linear joint maximum-likelihood detector, is shown to demodulate many more signals than elements even when the users are closely spaced and the channel is blindly estimated. Multi-user time delay estimation is one of the most important aspects of channel estimation for overloaded array processing. The final chapter of the thesis proposes a low-complexity data-aided time-delay estimation structure for embedding in a Per Survivor Processing (PSP) trellis for overloaded array processing. An extensive analysis proves that the multi-user delay estimation is separable, which leads to the proposed multi-user algorithm that estimates the user delays with a bank of simple data-aided synchronization loops to reduce the complexity. This thesis shows simulation results for the single-user case where the low-complexity Delay Locked Loop (DLL) structure, working at a low oversampling rate of 2 samples per symbol, estimates and compensates for any integer or non-integer sample delay within ±Tsym(symbol period). Two extensions to this technique are proposed to provide efficient multi-user delay estimation. The first multi-user structure employs a bank of DLLs, which compensate for the timing offset of each user simultaneously. This multi-user algorithm is suitable for CDMA-type applications, where each user has a distinct PN-code with good auto- and cross-correlation properties. We show that for spreading gain of 31, the presence of an interpolator enables us to reduce the oversampling factor from 4 to 2 samples per chip. Thus, the requirements of the A/D converter are relaxed without sacrificing system performance. Furthermore, we show that the proposed scheme meets the requirements of multi-user interference cancellation techniques for residual worst-case timing errors, i.e., residual timing error < 0.2 Tc, as reported in [200]. Finally, the thesis recommends a similar multi-user structure for narrowband TDMA-type system, which is based on bank of DLLs with whitening pre-filters at the front end of each branch. / Master of Science

An antenna array is overloaded when the number of cochannel signals in its operating environment exceeds the number of elements. Conventional space-time array processing for narrow-band signals fails in overloaded environments. Overloaded array processing (OAP) is most difficult when signals impinging on the array are near equal power, have tight excess bandwidth, and are of identical signal type. In this thesis, we first demonstrate how OAP is theoretically possible with the joint maximum likelihood (JML) receiver. However, for even a modest number of interfering signals, the JML receiverà ­s computational complexity quickly exceeds the real-time ability of any computer. This thesis proposes an iterative joint detection technique, Spatially Reduced Search Joint Detection, (SRSJD), which approximates the JML receiver while reducing its computational complexity by several orders of magnitude. This complexity reduction is achieved by first exploiting spatial separation between interfering signals with a linear pre-processing stage, and second, performing iterative joint detection with a (possibly) tail-biting and time"-varying trellis. The algorithm is sub-optimal but is demonstrated to well approximate the optimum receiver in modest signal to interference ratios. SRSJD is shown to demodulate over 2M zero excess bandwidth synchronous QPSK signals with an M element array. Also, this thesis investigates a temporal processing technique similar to SRSJD, Temporally Reduced Search Joint Detection (TRSJD), that separates co-channel, asynchronous, partial response signals. The technique is demonstrated to separate two near equal power QPSK signals with r= .35 root raised-cosine pulse shapes." / Master of Science

This work investigates the ideal distribution of sensors in networked arrays. MATLAB models these arrays and simulates the results these networks obtain using active and passive sonar. These results determine the ideal sensor placement for optimal parameter detection and estimation of targets. This work's first part focuses on active sonar networks with a fixed number of sensors in a differing number of arrays. MATLAB simulates the data of these sensors taking into account the geometries and velocities of the arrays and targets, then estimates the parameters of the targets using an elliptical filter, a conventional beamformer, a matched filter and one of three fusion methods. This work compares the performance of each network and fusion method. This work shows that the adding more arrays, regardless of size, enhances the overall performance of the network. It also shows the larger arrays obtain more robust parameter estimation. The second part of this work investigates the effects of uncertainty of the array position and orientation using passive sonar. Two networks, one with 2 32-channel arrays and one with 8 2-channel arrays, estimate a sound source's location using a conventional beamformer. MATLAB simulates the data taking into account the geometries of the arrays and the sound source. The results of these simulations show that when uncertainty of position and orientation increases, the better the smaller arrays estimate the location of the sound source compared to the larger arrays. / Master of Science

Yes / This paper presents a new optimization algorithm based on the behavior of the fungi kingdom expansion (FKE) to optimize the radiation pattern of the array antenna. The immobile mass ex-pansion of the fungi is mimicked in this work as a chaotic behavior with a sinusoidal map func-tion, while the mobile mass expansion is realized by a linear function. In addition, the random germination of the spores is utilized for randomly distributing the variables that are far away from the best solution. The proposed FKE algorithm is applied to optimize the radiation pattern of the antenna array, and then its performance is compared with that of some well-known algo-rithms. The MATLAB simulation results verify the superiority of the proposed algorithm in solving 20-element antenna array problems such as sidelobe reduction with sidelobe ratio (SLR = 25.6 dB), flat-top pattern with SLR = 23.5 dB, rectangular pattern with SLR = 19 dB, and an-ti-jamming systems. The algorithm also results in a 100% success rate for all of the mentioned antenna array problems

Antenna arrays offer notable superiority over a single antenna element. By weighting the signals before combining them, antenna arrays offer several enhanced features such as beam steering or beam switching without physically moving the aperture. While in general the array platform can take any given shape, cylindrical arrays offer many advantages compared to linear and planar arrays due to their azimuthal symmetry, and as such find numerous applications in radar, sonar, etc.. This research proposes a Wi-Fi band cylindrical switched beam array that is capable of full azimuthal beam switching for direction finding applications. Six microstrip patch antennas are arranged in a hexagonal platform to create a cylindrical array. The antenna beam is switched electronically using a SP6T RF switch providing azimuthal coverage with 60-degree resolution. Multiple antennas and arrays were designed, analyzed, and fabricated. The devices and the full array system were measured, and their RF performance was characterized. The experimental results validate the feasibility and practicality of the proposed design, and demonstrate a high-speed array platform for direction finding that can be used for search and rescue operations in emergency situations.

ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / This research article reports a design of a wide band multilayer microstrip patch antenna (MSPA). Positions of a coaxial probe feed to main patch of the multilayer MSPA, widths and lengths of main and parasitic patches, and height of a Rohacell foam layer in the multilayer MSPA were optimized to achieve desired performance in L-band. The work also reports a design of a two-by-two array of multilayer MSPA. We present results on antenna radiation patterns and return loss obtained with full wave finite element simulations with Ansoft HFSS software and measurements with a vector network analyzer.

International Telemetering Conference Proceedings / October 17-20, 1988 / Riviera Hotel, Las Vegas, Nevada / The Goddard Space Flight Center Mission Operations and Data Systems Directorate has developed a Packet Processor card utilizing semi-custom very large scale integration (VLSI) devices, microprocessors, and programmable gate arrays to support the implementation of multi-channel telemetry data capture systems. This card will receive synchronized error corrected telemetry transfer frames and output annotated application packets derived from this data. An adaptable format capability is provided by the programmability of three microprocessors while the throughput capability of the Packet Processor is achieved by a data pipeline consisting of two separate RAM systems controlled by specially designed semi-custom VLSI logic.

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