Development of Digitally Reconfigurable Radar for Short-Range Sensing

Multimode continuous wave (CW) radar systems are being investigated for a wide range of applications. These systems are adept at measuring a target’s velocity by analyzing the frequency response of the return signal. Target distances can be determined by introducing modulation to the transmitted CW signal, such as frequency modulation (FMCW) or phase modulation (PMCW). Of the modulated CW radar system families, PMCW radar systems have been less explored compared to FMCW radar systems. The need for high-accuracy time-domain analysis, fast phase shifting, high data load, and system complexity has limited PMCW radar design compared to FMCW radar design. Despite these hurdles, simulations of PMCW radar systems show promise in addressing the increasingly cluttered frequency spectrum. Radar-to-radar interference, an issue faced by all modulated CW radar systems, can be reduced by implementing orthogonal PMCW modulation schemes. Joint radar-communication (JRC) systems capable of radar-to-radar communication can also be realized with PMCW waveforms. These informational advantages come at the cost of system and processing complexity. As such, the prevalent approaches to commercialized radar design focus on the integrated circuit (IC) design. These ICs can be manufactured for multimode operation but are not ideal solutions for rapid radar design due to their cost, complexity, and fabrication time. With the speed at which digital systems are improving, such as working with faster clock speeds, improved field programable gate arrays (FPGA), and more accurate signal acquisition, IC radar design must consider current and emerging technologies along with existing design costs. A more flexible approach to the prototyping and verification of digital signal integration into radio frequency (RF) systems is to use the advantages of existing ICs with PCB microwave structures. With access to faster semiconductor technologies, embedded chip solutions, and improved PCB techniques, PMCW radars can be realized on a portable board-level system that is more flexible for prototyping and continued technological growth. Integrating existing RFICs and digital systems opens the door to PMCW radar system exploration. This dissertation presents the theoretical analysis, component design, and experimental evaluation of a low-cost, portable, reconfigurable radar system implementing digital communication techniques for short-range sensing. As opposed to emerging PMCW radar IC designs with integrated FPGAs, the proposed K-band radar system can implement CW Doppler, PMCW, and FMCW operation modes using a digital modulation source that can be upgraded and reprogrammed without needing to refabricate the system. A voltage-controlled oscillator (VCO) controls the frequency of the carrier and implements the FMCW modes. High-frequency phase shifter ICs are commonly designed to support multi-bit phase shifting over a limited bandwidth, resulting in radar integration challenges and high costs. The PMCW mode for the proposed system only requires one-bit modulation, which is used for a high signal-to-noise ratio (SNR) and improved time-domain analysis of the radar response signal. As opposed to integrating a phase shifter IC, a wideband binary phase shifter (BPS) is implemented on a PCB utilizing fast-switching PIN diodes and conventional microwave structures. This BPS is vital for implementing PMCW operation, where its three-state system controls amplitude and phase modulation of the carrier signal. The bandwidth dependence of the BPS is explored as well, and an ultra-wideband BPS is evaluated theoretically and experimentally. The proposed radar system also uses microwave structure-based balanced mixers to downconvert the received high-frequency signal to a low-frequency baseband signal containing the target information and phase modulation. This approach further lowers the cost of the radar system while accounting for potential target response nulls by using in-phase and quadrature (I/Q) signals. To verify the system’s PMCW performance, short-range human responses are measured. A demodulation algorithm is used to recover the subject information. Experimental results from the radar demonstrate the system feasibility and differences between CW and PMCW modes when measuring the respiration rate of a human subject and in gesture detection.