With the popularization of broadcasting networks, telecommunication networks, and Internet triple play services, broadband requirements have been proposed for transceivers in wireless communication systems. Frequency source is an important part of the RF transceiver, which is usually chosen as the source of the transceiver frequency reference source. Therefore, the development of ultra-wideband, high stability, low phase noise, and low spurious performance of the frequency synthesizer is of great significance. This paper firstly analyzed the transmission process of noise in phase-locked loop by establishing a linear mathematical model of phase locking loop (PLL), and then studied the main factors affecting the phase noise and spurious performance in the application design. In order to meet the demand of triple-miniaturized RF front end, an integrated phase-locked chip is used to design a frequency synthesizer, where the output frequency of the two channels ranges from 137.5 MHz to 4.4 GHz. In order to meet the engineering application requirements, the frequency synthesizer is designed with a host computer to achieve the programmable control of the output frequency and output power. Finally, the optimized design of a wideband frequency synthesizer is provided to make up for the lack of performance of the integrated phase-locked chip design, of which the output frequency range is 31.25 MHz ~8 GHz, including basic PLL module circuit, power control module circuit, and frequency expansion module circuit.

In the face of increasingly complex application scenarios, there is an urgent need for (Radio Frequency Identification) RFID systems that are capable of accurately identifying microwave signals of different frequency bands. Based on the acumen detection characteristics of microwave signals by lithium niobate electro-optic modulators, applying large-bandwidth thin-film lithium niobate electro-optic modulation to RFID systems can achieve efficient operation across multiple frequency bands. This study discusses, in detail, the design, simulation, fabrication, and testing process of the electro-optic modulator to obtain a high-performance, large-bandwidth lithium niobate electro-optic modulator. By using multilayer lithography techniques to prepare thick traveling-wave electrodes, the problem of irregular cross-sections during the fabrication of thick electrodes has been successfully reduced, improving the stability and controllability of the device. Test results show that the insertion loss of the electro-optic modulator is about 6 dB, the extinction ratio is 36.5 dB, the optical waveguide mode field is 1 μm, the full-band characteristic impedance is 50 Ω, the test bandwidth is 50 GHz, and the half-wave voltage is 1.8 V. Compared with existing optimization schemes, this design not only achieves a large bandwidth and a small half-wave voltage, but also proposes a new fabrication process scheme, optimizing the process and resulting in samples with stable performance.

By leveraging the high sensitivity of acousto-optic modulators to microwave signals, their integration into RFID systems can significantly improve the detection of faint microwave signals. Traditional acousto-optic modulators, which use bidirectional uniform comb transducers (IDTs), suffer from a 50% microwave signal loss due to the diffraction efficiency being less than 50%, complicating the accurate identification of already weak signals. This paper presents a solution to the 50% loss issue by replacing the IDT with a floating electrode unidirectional transducer (FEUDT), a key structure in detecting microwave signals. The resulting samples exhibited an optical waveguide insertion loss of 8.73 dB, a mode field diameter of 6.48 $\mathsf{\mu }$m, an operating frequency of 141.2 MHz, and a diffraction efficiency of 61.72%, and required only 0.57 W of driving power. Comparative empirical tests with traditional transducers under identical conditions demonstrated that the FEUDT-based acousto-optic modulator surpassed the 50% diffraction efficiency limit of conventional modulators, which facilitated the detection of weak microwave signals.