Enhancing Dynamic Hand Gesture Recognition using Feature Concatenation via Multi-Input Hybrid Model

Radar-based hand gesture recognition is an important research area that provides suitable support for various applications, such as human-computer interaction and healthcare monitoring. Several deep learning algorithms for gesture recognition using Impulse Radio Ultra-Wide Band (IR-UWB) have been proposed. Most of them focus on achieving high performance, which requires a huge amount of data. The procedure of acquiring and annotating data remains a complex, costly, and time-consuming task. Moreover, processing a large volume of data usually requires a complex model with very large training parameters, high computation, and memory consumption. To overcome these shortcomings, we propose a simple data processing approach along with a lightweight multi-input hybrid model structure to enhance performance. We aim to improve the existing state-of-the-art results obtained using an available IR-UWB gesture dataset consisting of range-time images of dynamic hand gestures. First, these images are extended using the Sobel filter, which generates low-level feature representations for each sample. These represent the gradient images in the x-direction, the y-direction, and both the x- and y-directions. Next, we apply these representations as inputs to a three-input Convolutional Neural Network- Long Short-Term Memory- Support Vector Machine (CNN-LSTM-SVM) model. Each one is provided to a separate CNN branch and then concatenated for further processing by the LSTM. This combination allows for the automatic extraction of richer spatiotemporal features of the target with no manual engineering approach or prior domain knowledge. To select the optimal classifier for our model and achieve a high recognition rate, the SVM hyperparameters are tuned using the Optuna framework. Our proposed multi-input hybrid model achieved high performance on several parameters, including 98.27% accuracy, 98.30% precision, 98.29% recall, and 98.27% F1-score while ensuring low complexity. Experimental results indicate that the proposed approach improves accuracy and prevents the model from overfitting

Low Profile, Wideband and High Power Capable Antennas for Diverse Military Platforms

This thesis presents the analysis, design, and measurements of antennas and antenna systems across three frequency bands with attention to the practical aspects of antenna design and deployment on specific platform of interest. Low profile, wideband support, and high-power operation form the underlying elements that bind all the research areas together. The first research area deals with the design of vehicular HF antenna for use over the 3 MHz to 30 MHz frequency range. Antenna performance for both scaled and full scaled HF antenna models using full wave electromagnetic analysis tools is shown for a vehicular platform of interest. Recent standardization of wideband HF waveforms has pushed the development of electrically small, vehicular HF antennas with 24 kHz tuned bandwidth. The antenna performance specifications are set to be at par or better than the existing vehicular HF antennas. The antenna must support zenith gain better than -20 dBi and bandwidth of better than 24 kHz. Antenna profile is a major motivating factor for this research. Traditional 3 kHz vehicular HF antennas have profiles of 1 m or higher. The design requirement for antenna profile lower than 1 m over the vehicle roof is inspired from the review of existing HF antennas. 3D printing and scaled prototyping is shown to validate the computational modeling and the proposed design process. The second area of research showcased in this work focuses on the design, fabrication and field testing of a full scaled antenna on an actual military platform. Antenna design process developed in the first part is used to develop the full scaled antenna prototype. Special attention is given to practical design of the antenna to ease fabrication and integration on the military platform. The antenna design is approached as a modular kit so that it can be easily reconfigured into different modes of operation. A COTS tuner is interfaced with the antenna and tunability is demonstrated over the HF frequencies. Validation of the developed HF antenna system is achieved through measurement data and link establishment during field tests. The implementation of switched reconfigurable HF antenna with support for all three modes of HF propagation is discussed in the end as an extension of the reconfigurable antenna concept to increase the versatility of the antenna system. The third part of research outlined in this work deals with the integration strategies for isolation improvement in cylindrical RF payloads operating at the millimeter wave frequencies. Cutting the horn antenna at its throat is proposed for ease of fabrication and integration inside a space constrained payload. The antenna performance in case of a realistic air gap at the cut interface between the top and bottom parts of the horn antenna is shown. Following the antenna level analysis, a system level impact of integration strategies on the RF leakage and coupling between the RF front ends in a cylindrical payload is shown. Measurements show the impact of internal RF leakages from components on deterioration in the system level isolation. Use of a conductive mesh as an RF sleeve placed over the component is discussed. Technique for improving system isolation from 65 dB worst case to 95 dB worst case using the proposed RF sleeves, across 18 GHz to 45 GHz is shown through a series of exhaustive measurements. The practical considerations for platform integration of wideband antennas are covered in subsequent appendix sections at the end of the thesis body. The use of a low cost radome is proposed using a COTS Frisbee disc for a planar log-periodic aperture in appendix section A. A spiral helix antenna is considered as a candidate for the study of antenna breakdown under high power conditions in appendix section B. Appendix section C discusses about the inspection of RF components for identification of fabrication artifacts that may lead to RF leakages when assembled in a system.</p