Research On Broadband Microwave Narrow Pulse Modulator

Pulse modulator is widely used in radar system, seeker, measurement and calibration for radio frequency system,microwave communication transceiver system,particle accelerator,electronic warfare, high power microwave source,electromagnetic environmental effects research and other fields which needs to produce a specific pulse width, repetitive frequency microwave signal. In the microwave-induced thermo-acoustic tomography systems, the microwave pulse width directly determines the resolution of the ultrasonic imaging. Especially in the narrow-band high power microwave electromagnetic environment experiments, the narrow microwave pulse modulator combined with the broadband power amplifier is the most combination of microwave effect source. Some commercial microwave signal generator , such as the source products of Keysight technology, can provide a minimum pulse width of 20ns for narrow pulse modulator options, but the price is very high, and need to purchase or upgrade the series microwave signal generator's kit to supporting the use. But the update kits option is always incompatible with the earlier instrument. In this application background,the paper provides a flexible, low-cost broadband microwave ns-class narrow pulse modulator to achieve the program, in the S-band and X-band modulator output the narrowest pulse width of up to 10ns, pulse rising / falling edge is less than 4ns, pulse minimum period of 40ns, pulse on/off ratio is better than 65dB.In this paper, we first introduce the parameters of pulse, microwave switch and the principle of switch for pulse modulation , mixer and mixer modulation principle.and then,based on the past pulse modulator is commonly used PIN diode or control Vacuum tube to produce the microwave pulse ,introduced a kind of pulse modulator which is designed by RF stitch and mixer,that can solve the problem of using the PIN diode to make the microwave switch to realize the pulse modulator or control the traveling wave tube to produce the narrow pulse of the microwave and so on. The design of the microwave pulse modulator can take into account the modulation pulse response time and off isolation and vacuum tube bulky, difficult to cool and other issues.The test results show that the design of the S-band microwave narrow pulse modulator's frequency is operating in 1.6GHz to 5.9GHz, and the maximum pulse modulation output power is greater than 15dBm, and have less than 5ns of the modulation pulse narrowest modulation pulse width,modulation pulse rise / fall time is less than 4ns , the harmonic ratio is less than 20dB and the modulation pulse on/off ratio is 65-70dB,the package size is 90×86×16 mm3.and the power consumption is less than 1W. The designed frequency range of the X-band microwave narrow pulse modulator is 7.5GHz-13GHz, the maximum output power of the modulation pulse is more than 10dBm,and the narrowest modulation pulse width is less than 10ns , and the modulation pulse rise / fall time is less than 5ns, the on/off ratio is more than 45 dB,the package size is 60×90×15 mm3.Input and output are used SMA interface, and the power consumption is less than 1W.The narrow pulse modulator designed in this paper has been applied to the S-band relativistic magnetron high-power microwave output detector narrow pulse calibration test and S-band injection effect experiment.