Phase Noise Measurement Research Of Wideband Microwave Source Based On Microwave Photonics

Microwave source is the key device in modern radar, communication, electronic warfare, and precision metrology systems. In these systems, a low phase noise microwave signal source is always preferred to achieve better performance. With the rapid development of wideband and low-phase-noise oscillators, phase noise measurement system based on conventional electronic technology is becoming more and more limited in many aspects, for example, working bandwidth and sensitivity. Phase noise measurement using photonic delay-line method can obtain high sensitivity, but the operation bandwidth is still limited by electronic devices in the system, e.g., electrical phase shifter and mixer. Thus, it is unable to meet the measurement requirement of microwave signal with a large frequency tuning range. In this paper, on the basis of theoretical analysis, we have proposed and realized phase noise measurement system using microwave photonic phase shifting and microwave photonic frequency mixing technologies. The noise floor of the system is as low as-140 dBc/Hz@10 kHz, and an operating bandwidth as large as 35 GHz(i.e., 5-40 GHz) is also achieved. The main innovative works of this paper are as follows:1. A novel scheme for phase noise measurement using a multifunctional microwave photonic processor is proposed, which can implement the electrical-to-optical conversion, provide a time delay, and control the phase of the microwave signal. This scheme has a compact structure. The requirement for electronic phase shifter is relaxed and a large operation bandwidth can be achieved. The experimental results prove the feasibility and advantages of this solution. The phase noise of a 5–40 GHz microwave source is measured precisely,and the noise floor is as low as-140 dBc/Hz@10 kHz.2. An approach for broadband phase noise measurement based on a microwave photonic frequency down-converter is proposed. The system has a very large operation bandwidth thanks to the frequency conversion in the optical domain, and good phase noise measurement sensitivity can be achieved since the signal degradation caused by electrical amplifiers is avoided. The feasibility of the system is experimentally verified. The phase noise of a 5–40 GHz microwave source is measured precisely. Moreover, phase noise floor as low as-137 dBc/Hz@10 kHz is achieved.3. Comprehend application of microwave phase shifting and microwave down-conversion, a photonic-assisted scheme for phase noise measurement is proposed. In the proposed scheme, all the microwave signal processing(phase shifting, time delay, mixing) are implemented in the optical domain, and the electrical devices that would limit the operation bandwidth and measurement sensitivity are avoided. The phase noise of a 5–40 GHz microwave source is measured precisely without rebuilding the system, and the phase noise floor as low as-140 dBc/Hz@10 kHz is obtained.4. A phase noise measurement instrument is developed and the noise floor of single channel is-140 dBc/Hz@10 kHz. In addition, the phase noise measurement floor is further reduced to below-160 dBc/Hz@10 kHz using two channel cross-correlation technique.