Flexible multi-band dual-chirped microwave waveform generator based on a recirculating frequency shifting loop

A photonic method for flexible multi-band dual-chirped microwave waveform generation is proposed using a recirculating frequency shifting loop (RFSL). The RFSL can be used as an optical frequency comb (OFC) generator with adjustable frequency spacing and line numbers. By heterodyning the OFC with a lightwave modulated by a baseband linearly chirped waveform in a balanced photodetector, a flexible multi-band dual-chirped microwave waveform can be generated. The frequency spacing and the number of the sub-bands can be easily adjusted by tuning the frequency shift and the bandwidth of the optical filter in the RFSL. The bandwidth and duration of each sub-band signal can also be tuned by adjusting the baseband linearly chirped waveform. A numerical simulation is conducted to verify the proposed generator. A flat four-band dual-chirped waveform with frequency spacing of 3 GHz and six-band dual-chirped waveform with frequency spacing of 4 GHz are generated successfully. Due to the flexible reconfigurability and high performance, the proposal may have great potential in multi-band radar systems.