脉冲调制射频功率测量中的标定及FFT分析方法研究

Studies on calibration method and FFT analysis in power measurement of pulse-modulated RF signal

利用电压/电流探头和数字示波器实现了脉冲调制射频功率测量。电压/电流探头输出的电压、电流信号由数字示波器采集存储,电压、电流的幅值及相位差由FFT分析得到。在不同频率下,对电压、电流幅值及相位差进行标定,获得计算射频功率的标定参数。分析表明电压、电流相位差是影响标定系数的主要因素,FFT方法处理非稳态调幅电压、电流时存在问题,只有在零无功功率处才能获得可信的吸收功率。

The capability of a commercial-available voltage/current probe, intended to monitor steady or slowly-varying RF signals, is improved to measure pulse-modulated RF signals. The improvement is realized by means of combination of voltage/current probe sensor and a digital oscilloscope. The outputs of voltage/current probes are acquired with the digital oscilloscope, and their amplitudes and phase difference are obtained with FFT. Under different frequencies, current/voltage amplitude and phase difference are calibrated in order to calculate RF power. The phase difference between voltage and current is the key factor influencing calibration coefficients. Results show the calibrated current/voltage probe can provide reliable and repetitive measurements. FFT method is problematic in analyzing nonstationary amplitude-modulated voltage and current signals, and the pulsed RF power can be only reliably calculated at time when reactive power is zero.