Image Rejecting Microwave Photonic Downconverter

摘要

An image rejecting microwave photonic downconverter uses a microwave sub-carrier modulation technique without concern for image frequency interference in the shifted signal, thereby allowing telecommunications systems to downconvert densely multiplexed communications channels into a low frequency band where conventional electronics can perform signal-processing functions. Using the image rejecting microwave photonic downconverter incoming microwave signals can be processed without ambiguity in direction finding applications, allowing remotable, multioctave microwave signal processing for frequency and phase determination. Two lasers providing separate optical carriers that are modulated by separate electro-optic modulators with sinusoidal electrical signals generated by separate local oscillators; are transmitted independently through two polarization-maintaining (PM) optical fibers of arbitrary length to a distant point. There the first modulated optical carrier is converted to an electrical domain and mixed with an input from an ultra-broadband radio frequency (RF) antenna receive-array, shifting the entire RF band to a higher frequency band equal to the original RF plus the modulation frequency of the first optical carrier. This upshifted frequency band is amplified and passed through a band-pass filter to attenuate frequencies outside the up-converted pass-band. The filtered signal is optically mixed with the modulated optical carrier modulated by the second local oscillator and the resulting intermediate frequency (RF) modulated optical carrier is detected using a second photodetector and transmitted to an electrical output port of the system.