Recently, Ground-penetrating Radar (GPR) has been used more than ever to detectlandmines, tunnels, utilities, buried archaeological artifacts, and so on. The antennas in GPR must be ultra-wideband and high-gain to achieve high imaging resolution. Additionally, the antennas need to be small and lightweight in order to fit within a compact radar system alongside other electronic components. However, fundamental limitations make it challenging to design an electrically compact antenna having a wide bandwidth and high gain. This dissertation focuses on the design, optimization, analysis, and system-level implementation of several novel compact ultra-wideband antennas for the ground-penetrating radar imaging system. The demonstrated antennas in this dissertation possess electrical dimensions smaller than half a wavelength, qualifying them as "electrically compact"; a few designs are close to 10% of a wavelength. The antennas display substantial gain performance (6–12 dBi) and ultrawideband characteristics covering a bandwidth from 360 MHz to 20 GHz with miniaturized dimensions compared to conventional antennas. Other antenna characteristics, such as group delay, isolation, radar cross section, etc., are also satisfactory. The system-level implementation of these antennas in underground imaging systems has shown great promise. It is expected that the theory, analysis, and experimentation on antennas presented in this dissertation will pave the way for further innovative designs that will remarkably enhance the imaging performance of ultrawideband radar systems in future.