Aly E. Fathy

Frequency-reconfigurable antennas for multiradio wireless platforms

Looking to increase the functionality of current wireless platforms and to improve their quality of service, we have explored the merits of using frequency-reconfigurable antennas as an alternative for multiband antennas. Our study included an analysis of various reconfigurable and multiband structures such as patches, wires, and combinations. Switches, such as radio-frequency microelectromechanical systems (RFMEMS) and p-i-n diodes, were also studied and directly incorporated onto antenna structures to successfully form frequency-reconfigurable antennas.

Investigation of High-Accuracy Indoor 3-D Positioning Using UWB Technology

There are many challenges in building an ultra-wideband (UWB) indoor local positioning system for high-accuracy applications. These challenges include reduced accuracy due to multipath interference, sampling rate limitations, tag synchronization, and antenna phase-center variation. Each of these factors must be addressed to achieve millimeter or sub-millimeter accuracy. The developed system architecture is presented where a 300-ps Gaussian pulse modulates an 8-GHz carrier signal and is transmitted through an omni-directional UWB antenna. Receiver-side peak detection, a low-cost subsequential-sampling mixer utilizing a direct digital synthesizer, high fidelity 10-MHz crystals, and Vivaldi phase-center calibration are utilized to mitigate these challenging problems. Synchronized and unsynchronized experimental results validated with a sub-millimeter accurate optical tracking system are presented with a detailed discussion of various system errors.

Real-Time Noncoherent UWB Positioning Radar With Millimeter Range Accuracy: Theory and Experiment

In this paper, we propose a novel architecture for ultra-wideband (UWB) positioning systems, which combines the architectures of carrier-based UWB systems and traditional energy detection-based UWB systems. By implementing the novel architecture, we have successfully developed a standalone noncoherent system for positioning both static and dynamic targets in an indoor environment with approximately 2 and 5 mm of 3-D accuracy, respectively. The results are considered a great milestone in developing such technology. 1-D and 3-D experiments have been carried out and validated using an optical reference system, which provides better than 0.3-mm 3-D accuracy. This type of indoor high-accuracy wireless localization system has many unique applications including robot control, surgical navigation, sensitive material monitoring, and asset tracking.

Development of a Novel UWB Vivaldi Antenna Array Using SIW Technology

A compact Vivaldi antenna array printed on thick substrate and fed by a Substrate Integrated Waveguides (SIW) structure has been developed. The antenna array utilizes a compact SIW binary divider to significantly minimize the feed structure insertion losses. The low-loss SIW binary divider has a common novel Grounded Coplanar Waveguide (GCPW) feed to provide a wideband transition to the SIW and to sustain a good input match while preventing higher order modes excitation. The antenna array was designed, fabricated, and thoroughly investigated. Detailed simulations of the antenna and its feed, in addition to its relevant measurements, will be presented in this paper.

Development and Implementation of a Real-Time See-Through-Wall Radar System Based on FPGA

This paper presents the development of a low-cost real-time ultrawideband (UWB) see-through-wall (STW) imaging radar system. The designs of the microwave front end, the UWB data acquisition, and the system integration are discussed in detail. As for the most challenging task, the UWB data acquisition, we introduce a custom low-cost module based on commercial field-programmable gate array (FPGA) boards and low-speed analog-to-digital converters. The introduced module does not require a custom implementation of high-speed wideband mixed-signal circuitry but only depends on the FPGA firmware design, which favors a rapid system prototyping. The data acquisition module accomplishes a 100-ps equivalent-time sampling resolution at 100-Msamples/s real-time rate, while the developed STW system provides a 2-D real-time view of motion with a 1.5-ms speed behind walls. The system allows for an easy reconfiguration to support multiple operating frequency ranges, pulse sampling resolutions, and array deployments, thus providing a tremendous experimental flexibility. Our studies indicate that utilizing available technologies and off-the-shelf components could produce a practical stand-alone STW system at reasonable design effort and cost, which will lead to a better understanding of the challenging problems associated with STW technology.

See-through-wall imaging using ultra wideband short-pulse radar system

See-through-wall imaging radar is a unique application of ultra wideband communication that can provide soldiers and law enforcement officers with an enhanced situation awareness. We have developed an ultra-wideband high-resolution short pulse imaging radar system operating around 10 GHz, where two essential considerations are addressed: the effect of penetrating the walls; the pulse fidelity through the UWB components and antennas of the radar. Modeled and measured wall parameters, and the effect of antenna types on signal fidelity are discussed in detail.

A simplified design approach for radial power combiners

It is known that a radial power combiner is very effective in combining a large number of power amplifiers, where high efficiency (greater than 90%) over a relatively wide band can be achieved. However, its current use is limited due to its design complexity. In this paper, we develop a step-by-step design procedure, including both the initial approximate design formulas and suitable models for final accurate design optimization purposes. Based on three-dimensional electromagnetic modeling, predicted results were in excellent agreement with those measured. Practical issues related to the radial-combiner efficiency, its graceful degradation, and the effects of higher order package resonances are discussed here in detail

CW and Pulse–Doppler Radar Processing Based on FPGA for Human Sensing Applications

In this paper, we discuss using field-programmable gate arrays (FPGAs) to process either time- or frequency-domain signals in human sensing radar applications. One example will be given for a continuous-wave (CW) Doppler radar and another for an ultrawideband (UWB) pulse–Doppler (PD) radar. The example for the CW Doppler radar utilizes a novel superheterodyne receiver to suppress low-frequency noise and includes a digital downconverter module implemented in an FPGA. Meanwhile, the UWB PD radar employs a carrier-based transceiver and a novel equivalent time sampling scheme based on FPGA for narrow pulse digitization. Highly integrated compact data acquisition hardware has been implemented and exploited in both radar prototypes. Typically, the CW Doppler radar is a low-cost option for single human activity monitoring, vital sign detection, etc., where target range information is not required. Meanwhile, the UWB PD radar is more advanced in through-wall sensing, multiple-object detection, real-time target tracking, and so on, where a high-resolution range profile is acquired together with a micro-Doppler signature. Design challenges, performance comparison, pros, and cons will be discussed in detail.

Substrate-Integrated Waveguide Ku-Band Cavity-Backed 2

A Ku-band cavity-backed microstrip patch 2 x 2 antenna array has been implemented using the substrate-integrated waveguide (SIW) technology-a low-cost multilayer printed circuit board (PCB) process. Cavities are emulated using vias, and the patches are fed using microstrip lines that are centrally fed by a shielded coaxial probe feed line. Simple design guidelines for the cavity, patch, and substrate selection are presented. The array was fabricated, and its measured results agreed very well with theoretical predictions and indicated a relatively high efficiency and wide bandwidth of greater than 70% and 9%, respectively.

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We report on an innovative reconfigurable antenna concept with significant practical relevance based on the dynamic definition of metal-like conductive plasma channels in high-resistivity silicon that are activated by the injection of DC current. The plasma channels are precisely formed and addressed using current high-resolution silicon fabrication technology. These dynamically defined plasma-reconfigurable antennas enable frequency hopping, beam shaping, and steering without the complexity of RF feed structures. This concept shows promise for delivering the performance and capabilities of a phased array, but at a reduced cost. However, challenges such as p-i-n biasing circuit complexity and their nonlinearities, as well as antenna efficiency, would still require further investigations.