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Professor Jungwon Kim has developed an ultra-low noise microwave frequency synthesizer that can be used for X-band radar with optical fiber optic technology.

Radar is used in a wide range of civil and military applications ranging from autonomous vehicles to meteorological observations, astronomical research, air traffic control, and military detection. In order to implement high performance radar, it is necessary to lower the phase noise of radar transmission signals It is essential. This is especially important for speed detection, improved imaging resolution, and improved communication and signal processing capabilities. Excellent frequency switching and modulation performance is also an important requirement for radar sources. However, microwave frequency synthesizers with very low phase noise are expensive and often require export licensing or special permission as export licensing (EL) items.

Professor Kim and his colleagues use optical fiber optic technology and DDS components that are reliable and cost-competitive, and do not use special technologies that are difficult to use in expensive or specially manufactured devices. They have developed a microwave frequency synthesizer capable of frequency modulation and switching with noise level.

First, frequency locking of a low-noise mode-locked laser to a Michelson fiber-optic interferometer based stabilization device results in very small time errors of one femtosecond (one thousandth of a second) can generate an optical pulse train and then convert this low-noise optical signal into an ultra-low-noise 10-GHz microwave signal using a fiber optics based opto-microwave converter. Finally, a DDS circuit was used to implement a frequency-tunable microwave source operating in the 9-11 GHz range. The measured phase noise performance of the 10-GHz microwave signal exhibits excellent phase noise performance over the entire offset frequency range over the phase noise of conventional commercialized highest performance crystal oscillator (OCXO) based frequency synthesizers.

They have also demonstrated that it is also possible to have fast frequency switching times of less than microseconds and various frequency modulation functions.

Another advantage of this system is that it can generate microwave signals as well as optical pulse pulses with very low timing noise, unlike conventional microwave frequency synthesizers. This low-noise optical pulse train can also be used for high-resolution analog-to-digital converters (ADCs) and up-conversion / down-conversion of signals received from radar receivers, New signal conversion and analysis functions can also be provided. In this study, we presented an X-band (8-12 GHz) signal source, but using any of the frequencies that are an integral multiple of the laser repetition rate, we can use the same principle to achieve even higher frequency W-band (75-110 GHz) You can make it happen.

“Fiber-optic interferometer-based timing stabilization system” and “optical-microwave phase detector and phase lock device”, which are the most important constituent technologies of this system, have already been filed and registered in domestic and foreign patents. Localization through technology transfer is also expected to be possible. In particular, the study is more meaningful as a high-performance radar, including the recent THAAD radar, and as a signal source operating in the X-band, which is gaining in importance in space communications.