Microwave Signal Generation and Noise Reduction Using Cascaded MZM for Radar Applications

In a radar system, frequency up and down conversion processes requires higher frequency local oscillators (LO). Advancement in microwave photonics and optical domain made it possible to synthesis high frequency microwave signals. There are variety of microwave generation techniques available in optical domain such as optical heterodyning, optical injection locking, optical phase lock loop, Mach-Zehnder modulator based photonic technique etc. It is known that Mach-Zehnder modulator based microwave signal generation is superior in terms of reduced complexity and noise effects. But this work explores the possibility of reducing noise still further for generating signals in 2-4GHz range (preferred for normal S-band of radar operation). For this purpose single and cascaded Mach-Zehnder configurations are compared and evaluated. An addition of cascaded Mach-Zehnder modulator results in noise reduction. We also propose that the carrier signal filtering is not required in cascaded configuration compared to single Mach-Zehnder modulator which is an additional component in single Mach-Zehnder modulator. The work is also supported with results and its analysis for above configurations.