DESIGN AND IMPLEMENTATION OF A PHASED ARRAY ANTENNA FOR MULTI-MISSION APPLICATIONS

Multifunction Phased Array Radar (MPAR) was defined to investigate the feasibility of integrating weather observation and air surveillance radars into a single network. Weather radars require dual polarization capability which may be also beneficial to aircraft characterization. Research activities have begun to identify challenges, mitigate risk, and demonstrate polarimetric technologies. Ten-panel, developed by MIT’s Lincoln Laboratory, was the first dual-polarized planar phased array demonstrator. Alternatively, a cylindrical polarimetric phased array radar (CPPAR) was developed at the Advanced Radar Research Center of the University of Oklahoma to resolve the intrinsic limitations of planar arrays in making accurate polarimetric measurements. The current CPPAR employs a frequency scanning patch array antenna. Since the radar’s performance would be the most important driver, the future operational CPPAR, suitable for long-range weather measurement, will utilize a new antenna with higher performance. It is the purpose of this research to propose a new dual-polarized phased array antenna for MPAR application. A crossed dipole antenna with sufficient operational frequency bandwidth is designed. A high polarization purity is achieved by using a group of efficient techniques in element scale. This element was modified to obtain a higher match between copolar beams. The modified element is utilized as an embedded element to form a cylindrical and a planar array antenna. It is demonstrated that suppressed azimuthal surface wave and consequently highly matched copolar beams can be achieved in a cylindrical array of proposed crossed dipole. In order to compensate for the electrical and geometrical asymmetry of the element, an imaged arrangement of the elements with respect to the center of the array is utilized. It is shown that a planar array of the modified crossed dipole, arranged in a specific configuration, proposes zero cross-polarization in the principal planes without increased side lobe problem. The experimental verification demonstrates that the proposed phased array antennas are promising candidates for multi-mission applications

Ultra-low cross polarization antenna architectures for multi-function planar phased arrays

For over thirty years, single-beam mechanically steered radars have dominated the field of atmospheric observations, and since then, newer improved technologies have emerged that could provide a replacement for aging radars. Phased array radar technology offers meteorologists and scientists a unique opportunity to enhance weather forecasting through rapid electronic adaptive scans. Multiple array geometries exist for phased array radars (i.e., spherical, cylindrical, and planar); however, this work concentrates on enhancing the performance of planar antenna architectures. Planar phased array radar antennas have been under scrutiny due to the challenges posed when trying to satisfy all polarimetric weather requirements met by conventional parabolic dish reflectors (e.g., co-polarized beam mismatch under 0.1 dB, input isolation higher than 40 dB, cross-polarized radiation under -40 dB). This dissertation takes a fresh look into the electromagnetic characteristics of traditional antennas used in planar phased array geometries and provides mathematical insight to prove their performance, limitations, and advantages. The metrics used to evaluate essential performance characteristics were bandwidth, scanning range, polarization, co-polarized beam match, cross-polarization, isolation, and intrinsic cross-polarization (IXR). The antennas presented in this work (i.e., Horus, Polarimetric Atmospheric Imaging Radar (PAIR), and Horus-ONR) were validated by comparing the results of predictive simulating tools against physical antenna measurements. The Horus antenna was made using aperture coupling feeding technique with stacked microstrip patches. It achieved a fractional bandwidth of 15.4%, a co-polarized beam mismatch of 0.08 dB, and scanned cross-polarization levels of -29 dB, based on Ludwig’s third definition of polarization for θ = ± 45°. The PAIR antenna was made using balanced probe-fed stacked microstrip patches and it totaled fractional bandwidths of 7.7%, co-polarized beam mismatch of 0.21 dB, and -40 dB cross-polarization within the required imaging field of view. Lastly, the Horus-ONR antenna. Its design follows Horus guidelines for manufacturing but improves bandwidths up to 24.8% by trading the scanned co-polarized beam mismatch and cross-polarization required for weather missions. Other antenna architectures proposed for future phased array radar developments are the ultra-low cross-polarization microstrip patch (ULCP-MPA) and a dielectric covered slot antenna (ULCP-DCSA). The ULCP-MPA and the ULCP-DCSA can achieve cross-polarization levels of -40 dB for θ = ± 45°. The antenna designs presented in this dissertation show the lowest scanned cross-polarizations with highly calibratable polarization and might be the best planar radiating elements present in literature so far, despite not achieving all polarimetric weather requirements for multi-function phased array radars. Microstrip patch antennas offer a scalable, low profile solution with excellent polarization diversity and reasonable scanned bandwidths for multi-function, planar phased array radar platforms of the future

Quantitative Analysis of Rapid-Scan Phased Array Weather Radar Benefits and Data Quality Under Various Scan Conditions

Currently, NEXRAD provides weather radar coverage for the contiguous United States. It is believed that a replacement system for NEXRAD will be in place by the year 2040, where a major goal of such a system is to provide improved temporal resolution compared to the 5-10-min updates of NEXRAD. In this dissertation, multiple projects are undertaken to help achieve the goals of improved temporal resolution, and to understand possible scanning strategies and radar designs that can meet the goal of improved temporal resolution while either maintaining (or improving) data quality. Chapter 2 of this dissertation uses a radar simulator to simulate the effect of various scanning strategies on data quality. It is found that while simply reducing the number of pulses per radial decreases data quality, other methods such as beam multiplexing and radar imaging/digital beamforming offer significant promise for improving data quality and/or temporal resolution. Beam multiplexing is found to offer a speedup factor of 1.7-2.9, while transmit beam spoiling by 10 degrees in azimuth can offer speedup factors up to ~4 in some regions. Due to various limitations, it is recommended that these two methods be used judiciously for rapid-scan applications. Chapter 3 attempts to quantify the benefits of a rapid-scan weather radar system for tornado detection. The first goal of Chapter 3 is to track the development of a common tornado signature (tornadic debris signature, or TDS) and relate it to developments in tornado strength. This is the first study to analyze the evolution of common tornado signatures at very high temporal resolution (6 s updates) by using a storm-scale tornado model and a radar emulator. This study finds that the areal extent of the TDS is correlated with both debris availability and with tornado strength. We also find that significant changes in the radar moment variables occur on short (sub-1-min) timescales. Chapter 3 also shows that the calculated improvement in tornado detection latency time (137-207 s) is greater than that provided by theory alone (107 s). Together, the two results from Chapter 3 emphasize the need for sub-1-min updates in some applications such as tornado detection. The ability to achieve these rapid updates in certain situations will likely require a combination of advanced scanning strategies (such as those mentioned in Chapter 2) and adaptive scanning. Chapter 4 creates an optimization-based model to adaptively reallocate radar resources for the purpose of improving data quality. This model is primarily meant as a proof of concept to be expanded to other applications in the future. The result from applying this model to two real-world cases is that data quality is successfully improved in multiple areas of enhanced interest, at the expense of worsening data quality in regions where data quality is not as important. This model shows promise for using adaptive scanning in future radar applications. Together, these results can help the meteorological community understand the needs, challenges, and possible solutions to designing a replacement system for NEXRAD. All of the techniques studied herein either rely upon (or are most easily achieved by) phased array radar (PAR), which further emphasizes the utility of PAR for achieving rapid updates with sufficient data quality. It is hoped that the results in this dissertation will help guide future decisions about requirements and design specifications for the replacement system for NEXRAD

Advanced Signal Processing For Multi-Mission Airborne Radar

With the technological advancement of the 21st century, functions of different radars are being merged. A multi-functional system brings the technology of remote sensing to a wide array of applications while at the same time reduces costs of implementation and operation. Ground-based multi-mission radars have been studied in the past. The airborne counterpart deserves a through study with additional and stringent requirements of cost, size, weight, and power.In this dissertation, multi-mission functions in an airborne radar is performed using modular, software-based architecture. The software-based solution is chosen instead of proposing new hardware, primarily because evaluation, validation, and certification of new hardware is onerous and time consuming. The system implementations are validated using simulations as well as field measurements. The simulations are carried out using Mathworks® Phased Array System Toolbox. The field measurements are performed using an enhanced commercial airborne radar system called Polarimetric Airborne Radar Operating at X-band Version 1 (PARADOX1), which is an X-band, vertically polarized, solid state, pulsed radar.The shortcomings of PARADOX1 originate from small aperture size and low power. Various signal processing algorithms are developed and applied to PARADOX1 data to enhance the data quality. Super-resolution algorithms in range, angle, and Doppler domains, for example, have proven to effectively enhance the spatial resolution. An end-to-end study of single-polarized weather measurements is performed using PARADOX1 measurements. The results are compared with well established ground-based radars. The similarities, differences as well as limitations (of such comparisons) are discussed. Sense and Avoid (SAA) tracking is considered as a core functionality and presented in the context of safe integration of Unmanned Aerial Vehicles (UAV) in national airspace. A "nearly" constant acceleration motion model is used in conjunction with Kalman Filter and Joint Probabilistic Data Association (JPDA) to perform tracking operations. The basic SAA tracking function is validated through simulations as well as field measurements.The field-validations show that a modular, software-based enhancement to an existing radar system is a viable solution in realizing multi-mission functionalities in an airborne radar. The SAA tracking is validated in ground-based tests using an x86 based PC with a generic Linux operating system. The weather measurements from PARADOX1 and the subsequent data quality enhancements show that PARADOX1 data products are comparable to those of existing ground based radars