An Injection-Locked-Based FMCW Transmitter With Synthetic Bandwidth Technique

An injection-locked-based frequency-modulated continuous-wave (FMCW) transmitter using a synthetic bandwidth technique is presented. A wideband chirp is synthesized by combining the up-converted narrowband chirp with different adjacent carrier frequencies. This is achieved by mixing a narrowband direct digital synthesis 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. The key idea is demonstrated at 4 GHz by generating two subband chirps with about 300-MHz bandwidth each, achieving a synthetic bandwidth of 600 MHz. The measured impulse response shows a resolution of 32 cm (Hamming) with a sidelobe level of -25 dBc and very accurate range estimates with accuracy of +/- 0.5 cm.