Abstract
A novel and flexible photonics-based scheme is proposed
for generating phase-coded RF pulses suitable for coherent radar systems with
pulse compression techniques. After selecting two modes from a mode-locked
laser (MLL), the technique exploits an optical in-phase/quadrature modulator
driven by a low-sample rate and low-noise direct digital synthesizer to modulate
the phase of only one mode. The two laser modes are then heterodyned in a
photodiode, and the RF pulse is properly filtered out. The scheme is experimentally
validated implementing a 4-bit Barker code and a linear chirp on radar pulses
with a carrier frequency of about 25 GHz, starting from an MLL at about 10
GHz. The measures of phase noise, amplitude- and phase-transients, and autocorrelation
functions confirm the effectiveness of the scheme in producing compressed
radar pulses without affecting the phase stability of the optically generated
high-frequency carriers. An increase in the radar resolution from 150 to 37.5
m is calculated. The proposed scheme is capable of flexibly generating software-defined
phase-modulated RF pulses with high stability, even at very high carrier frequency,
using only a single commercial device with potentials for wideband modulation.
It can therefore allow a new generation of high-resolution coherent radars
with reduced complexity and cost.
© 2012 IEEE
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