High performance chirped microwave generator for space applications

Photonic generation and transmission of Linearly Chirped Microwave Waveform (LCMW) with a high Time-BandWidth Product (TBWP), of the order of 102 or more, is a widely used approach in Synthetic Aperture Radar (SAR) payloads to realize high range resolution, improving the distinction between two or more targets on the same bearing. In standard payload systems, an electronic approach based on voltage-controlled oscillator or digital signal processing, is used as LCMW generator, with both limited TBWP and operating frequency. In this context, a photonic approach plays a crucial role, ensuring low phase noise, high TBWP and operation frequency of the order of GHz, with a significant reduction of mass and size with respect to the electronic counterparts. Here, we propose the design of a Ka-band photonic LCMW generator, based on a frequency-tuneable Opto-Electronic Oscillator (OEO) and a Recirculating Phase Modulation Loop (RPML), with high spectral purity and high chirp rate in a small footprint. The OEO heart is a one-dimensional photonic crystal ring resonator with an ultra-high Q factor value and an optical delay < 10 μs. A low-frequency optical signal, with a high chirp rate and TBWP values of the order of 102-103, is generated in the RPML section.