Highly stable signal generation in microwave interferometer using PLLs

摘要

The microwave interferometer is a device that works in the millimeter-wave frequency range, and it is used to measure the plasma density. The instability in the frequency source at the transmitter section of the interferometer affects the accuracy of the phase measurement in the receiver section. The phase-locked loop (PLL) circuit is a substantial unit in the generation of highly stable frequency. This paper proposes a highly stable frequency source generator for the D-band Microwave interferometer.The design, development, and analysis of the PLL system with the frequency signal of 6.9 GHz and 7.0 is presented in this paper. Two alternate approaches using the dielectric resonator oscillator (DRO) and Frequency synthesizer are presented to design the PLL circuit. The stability is achieved using a 7 GHz DRO in the transmitter section, which is phase-locked with a 6.9 GHz voltage controlled oscillator (VCO) at the receiver section in the proposed first design and a frequency synthesizer is used instead of DRO in the proposed second design.The developed circuit is analysed in terms of parameters like phase noise performance, output power level, development cost, design complexity, and operating frequency range. The PLL in the receiver section is configured using FPGA to analyze the circuit performance at various frequency offset. DRO generates the power of 17.62 dB m at a frequency of 7.0 GHz. The DRO and synthesizer circuit provides excellent phase noise performance of -120 dBc/Hz and -93 dBc/Hz, respectively, at the transmitter section and -94.12 dBc/Hz at the receiver section.Indigenous methods have been made for the development of PLLs. It will be used to develop a D-band microwave interferometer to measure the electron density of fusion plasma at the Institute for plasma research (IPR)-Government of India.