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This paper reports the test results of our own carbon-fiber cathodes made by using the technique of liquid infiltration in vacuum. The technique is completely different from the conventional adhering techniques that were employed previously in constructing carbon-fiber cathodes. Our technique could be used to precisely control the distribution and pointing direction of the carbon-fiber tips on the cathode surface. In our technique, the carbon-fiber material and the base material (which is usually the metal that we use in making the cathodes) can be well compounded to become a novel composite material. Compared with frequently used metal cathodes, the voltage and current waveforms of our carbon-fiber cathodes were more stable and smooth, their turn-on times were shorter, and their durations were longer. These advantages were especially obvious for generating high-quality electron beams using long-pulse-driven devices. Experiments for producing high-power microwaves have also been done on the reflex triode virtual cathode oscillator using our carbon-fiber cathodes. The peak power of the microwave that was generated using our carbon-fiber cathode was increased by a factor of about 2-3 over the case of a stainless steel cathode under the same experimental conditions.