It is well known that the maximum amount of power in an electrical or electronic system can be transferred to a load when its impedance is the complex conjugate of the source impedance, although, the power transfer efficiency is only 50%. Is this fact true for a radio system, as well? The question has existed for decades. In this article, the equivalent circuits of antenna systems are reexamined. It is demonstrated that classical equivalent circuit models based on the Thévenin and Norton theorems are not suitable for a receiving antenna system since the antenna cannot be simply approximated by a voltage or current source. A constant power source is required but not readily available. Thus, two new general power source models are introduced and examined. It is found that they may be suitable for a transmitting antenna system but not accurate enough for a receiving antenna when the antenna loss is taken into account. A novel special constant power source model is therefore proposed and shown to accurately simulate the behavior of a receiving antenna. When the load impedance is the complex conjugate of the antenna impedance, maximum power is obtained, and the power transfer efficiency is simultaneously maximized (up to 100% if the antenna system is lossless).

中文翻译：

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广义天线系统的等效电路和分析[天线应用角]


众所周知，当电气或电子系统的阻抗为源阻抗的复共轭时，可以将最大功率传输到负载，但功率传输效率仅为 50%。对于无线电系统来说，这一事实也成立吗？这个问题已经存在了几十年。在本文中，重新审视了天线系统的等效电路。事实证明，基于戴维宁和诺顿定理的经典等效电路模型不适用于接收天线系统，因为天线不能简单地用电压或电流源来近似。需要恒定电源，但不易获得。因此，引入并检验了两种新的通用电源模型。人们发现，当考虑到天线损耗时，它们可能适用于发射天线系统，但对于接收天线来说不够准确。因此，提出并展示了一种新颖的特殊恒定电源模型，以准确模拟接收天线的行为。当负载阻抗是天线阻抗的复共轭时，获得最大功率，同时功率传输效率最大化（如果天线系统无损，则高达100%）。