Fig. 1. Different types of microwave sources.

Fig. 2. Schematic diagram of the principle of photoconductive microwave generation using wide-bandgap semiconductors.

Fig. 3. Equivalent circuit model of the device^[45].

Fig. 4. Framework diagram of the transient photocurrent model of a 4H-SiC PCSD^[48].

Fig. 5. System architecture of the burst-mode-operation pulse laser, including the schematic diagram of the three-stage all-fiber amplifier^[49] and the second-harmonic generation (SHG) system.

Fig. 6. Typical structure of a 6H-SiC device.

Fig. 7. (a) Optimization of the optical coupling structure. (b), (c) Comparison of the outputs of systems with and without optical coupling^[63].

Fig. 8. (a) Experimental setup of the frequency-adjustable HPM generator based on a linear 6H-SiC PCSD, including (b) the integrated device and (c) the test circuit.

Fig. 9. Experimental results of output waveforms of the SiC device with the 1064-nm pulse laser. (a) The output waveform at a modulated frequency of 1 GHz. (b) The typical normalized spectra of output waveforms with modulated frequencies ranging from 0.5 GHz to 2.5 GHz.

Fig. 10. (a) Breakdown process of the device, (b) optimized electrode structure with the double-sided AZO, and (c) effect of the optimized electrode structure on the lifetime and efficiency^[66].

Fig. 11. Key steps to achieve higher power and higher frequency output.