Development of portable radar systems for short-range localization and life tracking

This dissertation presents the theoretical analysis, system design, and experimental evaluation of portable radar systems for short-range localization and life tracking. A multi-mode continuous wave (CW) radar system, which incorporates the advantages of Doppler radar systems in highly accurate displacement measurement and frequency-modulated continuous-wave (FMCW) radar systems in range detection, has been proposed. The proposed radar system has the capability to obtain both absolute ranges and tiny motions of targets by switching between the FMCW mode and the Doppler mode through an onboard microcontroller. The cost and hardware complexity of the proposed radar system have been reduced by utilizing the audio card of a laptop to sample the baseband signals. Two radar prototypes have been developed. One of them works at C-band and the other one works at K-band. In the FMCW mode of the two prototypes, the operational-amplifier-based sawtooth signal generators are used to control the voltage-controlled oscillators (VCOs) to generate the FMCW signals. In the Doppler mode, a low-intermediate-frequency (low-IF) modulation method is implemented to up-convert the slow vital signs to the pass-band of the audio card. The C-band prototype utilizes off-the-shelf components with customized patch antenna arrays. On the other hand, the K-band prototype utilizes an architecture with a six-port circuit to lower the cost of the system. Several experiments have been performed. Experiments with a glass wall and a human subject showed that the proposed radar systems can easily detect glass, which is usually difficult for camera-based sensors. Also, range-Doppler imaging method has been implemented to isolate moving subjects from surrounding clutters. Moreover, a human-aware algorithm was developed to identify the stationary human target from other targets in a two-dimensional mechanical scanning measurement. In addition, the radar prototypes have also been used for vital sign measurement, human gait/gesture recognition, and wind turbine structure health monitoring, etc. In order to extend the capability of electrical beam steering for the portable radar system without dramatically increasing the cost, a K-band portable FMCW radar transceiver with beamforming array has been proposed. The conventional solutions for K-band FMCW radar systems require high-frequency phase shifters, which have a limited number of manufacturers and are very expensive. In the proposed radar transceiver, a vector controller is implemented on a printed circuit board (PCB) with simple microwave structure and PIN diodes. Each vector controller can simultaneously control the phase and amplitude of the K-band signal. The proposed radar transceiver has four receiver antennas and one transmitter antenna. The beam of the receiver array can be continuously steered in a range of ±45° on the H-plane through an array of vector controllers. The theoretical of the vector controller is analyzed. In order to minimize the influence of fabrication errors and component variations, a calibration method is introduced. Measurement of the beam patterns steering to different directions has been performed. System-level experiments have also been carried out to show the two-dimensional localization capability of the designed portable FMCW radar system. Radar systems with beam steering capability on the H-plane can obtain the directions of the targets. However, they fail to get the three-dimensional locations or the profiles of the targets. Moreover, a large array and complex phase control structures are required for conventional radar systems to achieve high three-dimensional angular resolution. In order to solve these issues, a 24 GHz multiple-input and multiple-output (MIMO) FMCW radar is proposed with 16 transmitters and 16 receivers. This MIMO FMCW radar provides beamforming on both horizontal and vertical planes with 3° angular resolution and 90° field of view. A non-uniformly spaced array is introduced to obtain a high angular resolution with fewer antenna elements. The design principles of the proposed MIMO FMCW are introduced, and a prototype has been built. A calibration procedure was performed to eliminate path delays of different MIMO channels. Experiments of the MIMO FMCW radar prototype reveal its capability in getting the three-dimensional locations of targets.