INJECTION-LOCKING-BASED FREQUENCY- MODULATED CONTINUOUS WAVE GENERATORS FOR SYNTHETIC APERTURE RADAR APPLICATIONS

Abstract

In this thesis, two injection-locking–based architectures for FMCW chirp generation are presented to address the limitations on the bandwidth and frequency linearity of conventional chirp generation techniques. In the first approach, a synthetic bandwidth technique to obtain a wideband chirp was proposed by upconverting a narrowband chirp to different adjacent frequency bands. This is achieved by mixing a narrowband direct digital synthesized (DDS) chirp with a fast-switching subharmonic injection-locked oscillator (SHILO). The use of SHILO allows fast-switching at sub-10 ns and provides better phase noise performance than phase-locked loops due to its much wider loop bandwidth. Wide bandwidth of 2 GHz (43%) was achieved in C-band resulting to a high range resolution of 7.5 cm. The second approach proposes the use of an injection-locked oscillator as a frequency multiplier to a low-frequency chirp. The main advantage of the architecture is the faster locking response to a frequency step, compared to phase-locked loops, which minimizes the frequency errors. Measurements show a precise ranging capability with 71 μm (0.02% of the resolution) standard deviation. Indoor tests demonstrate good SAR imaging capabilities for both architectures.