Stretch processing of simultaneous, segmented bandwidth linear frequency modulation in coherent ladar
Date of Award
M.S. in Electro-Optics
Department of Electro-Optics and Photonics
Advisor: Joseph Haus
In stretch processing (SP) both the local oscillator (LO) and the transmitted signal are linearly frequency modulated (LFM). A heterodyne detection process is performed using the LO and the received echo signal, which create a detected signal at a single difference-frequency. The frequency is proportional to the distance the received echo signal travels relative to the LO signal, and the range resolution is inversely proportional to the bandwidth making large bandwidth LFM chirps favorable. However, it is difficult to maintain linearity over a lager bandwidth LFM chirp. On the other hand small bandwidth LFM chirps can be easily produced, so the idea of segmenting the transmitted pulse into multiple small non-overlapping frequency LFM chirps was conceived. The extended frequency bandwidth is recovered in post processing. This technique is called multi-frequency stretch processing (MFSP). The procedure outlined is a practical method to achieve greater range resolution using less expensive technology. Another advantage of this technique is the similar modulation noise on each LFM chirp. The multiple signals are processed using an algorithm developed for extracting the additional bandwidth information. The range resolution is related to the time span and bandwidth of the LFM pulses. For n transmitted LFM chirped signals the range resolution is nearly n times longer. Moreover the required detection bandwidth of the echo signal is lower than for other LFM processing systems without a chirped LO signal.
Optical radar, Signal processing, Harmonic oscillators
Copyright 2011, author
Brown, Robert L., "Stretch processing of simultaneous, segmented bandwidth linear frequency modulation in coherent ladar" (2011). Graduate Theses and Dissertations. 360.