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微波功率晶体管目前有了很大发展,在微波功率放大器、振荡器和倍频器中得到广泛的应用。在应用中除了要知道微波晶体管的直流参数(如击穿电压等)和功率增益(Kp)以外,尚需知道管子的动态阻抗,即晶体管在大讯号状态下的输入阻抗和最佳收集极负载阻抗,这样才能进行阻抗匹配网络的设计计算,使晶体管达到最佳的性能。 在小信号条件下,晶体管的输入、输出阻抗的测量已较成熟。例如,在频率较低时(一般在500兆赫以下),晶体管的H、Y、Z参量可用阻抗(导纳)电桥进行测量;频率更高时,则采用S参量比较方便,可用相应的S参数测量仪或网络分析仪进行测量。 但是,上述晶体管小讯号参量和大讯号参量在数值上是不同的。这是因为晶体管在大讯号下参量的数值是随功率电平而变的,而且在微波功率放大器中除考虑基波频率分量以外,还必须考虑到谐波频率分量,这是和小讯号放大器不同的。 晶体管的大讯号阻抗(动态阻抗),在微波频率下计算起来很困难,所以一般用实验测量的方法来确定。这里,我们介绍一下用测量线对微波管动态阻抗进行测量的原理和
Microwave power transistors have greatly developed at present, and are widely used in microwave power amplifiers, oscillators and frequency multipliers. In addition to knowing the DC parameters of the microwave transistor (such as breakdown voltage) and power gain (Kp), it is necessary to know the dynamic impedance of the tube, that is, the input impedance of the transistor in the large signal state and the optimum collector load Impedance, in order to make the impedance matching network design and calculation, the transistor to achieve the best performance. In small signal conditions, the transistor input and output impedance measurements have been more mature. For example, at low frequencies (typically below 500 MHz) the H, Y, Z parameters of the transistor can be measured with an impedance (admittance) bridge; at higher frequencies, the S parameter is more convenient and the corresponding S Parameter meter or network analyzer to measure. However, the small transistor signal parameters and large signal parameters are different in value. This is because the value of the transistor under large signal changes with the power level, and in the microwave power amplifier in addition to considering the fundamental frequency component, but also must take into account the harmonic frequency component, which is different from the small signal amplifier of. The large signal impedance (dynamic impedance) of a transistor is difficult to calculate at microwave frequencies, so it is generally determined experimentally. Here, we introduce the principle of using the measurement line to measure the dynamic impedance of the microwave tube