Multi-Band RF Downconversion Over Fiber With a Single Modulator

Abstract

We present the theory for an experimental verification of a new technique to combine multiple microwave signals populating a wide spectrum into a single, small band for further relay or processing. The method is an extension of well-known RF-over-fiber downconversion techniques but with multiple local oscillators (LOs) to translate widely spaced signals to intermediate frequencies that are within a single, narrower, spectral band. One dual-drive Mach–Zehnder modulator is used as two parallel phase modulators with the LOs presented to one RF drive and the signals to the other. This parallel arrangement adds, rather than multiplies, the LO tones and signals, eliminating a number of cross-modulation spurs that could otherwise make it very difficult to receive only the signals of interest. We verify the link’s performance by downconverting two widely spaced $K$ -band signals to $C$ -band while simultaneously relaying an existing $C$ -band signal on the same link and demodulating all three signals.