Optical heterodyning in microwave photonic receiver for radar applications

Microwave photonic receiver for radar applications comprising a continuous wave laser together with amplitude modulators and narrow-band optical filters and converting radar signal to low (envelope) frequencies is considered. Possible characteristics of the receiver are estimated and different modes of its operation are discussed. It is shown that homodyne as well as heterodyne methods for transformation of the spectrum of the input microwave signal into the low frequency region can be used, and linearity of the transformation for these methods is studied. Also, the regime of the optical carrier suppression in modulators is considered. In this case, it is not necessary to use narrow-band optical filters in the scheme. It is shown that, for modern optical elements, signal-to-noise ratio at the output of the system can be 60–70 db and more for a microwave signal with a carrier frequency of tens of gigahertz and a frequency bandwidth of 100 MHz and more.