A New Method for Antenna Efficiency Measurements

天线作为无线电系统中的重要器件，其性能的好坏有许多重要的参数。其中之一是天线辐射效率（即天线效率），其是辐射功率与输入功率的比率。一旦输入功率已知，该参数对于计算辐射功率非常有用。由于天线系统（包括材料）的复杂性，该参数的理论值通常不可靠，因此系统设计（链路预算）和性能评估通常需要测量天线效率。获得该参数的传统方法是1）。辐射方向图积分法耗时且不精确; 2）.惠勒帽方法，该方法准确且廉价，但仅适用于电小天线; 3）。Q因子法也适用于电小天线。第一种方法通常在工作频率相对较高时使用，而另外两种方法在工作频率相对较低时使用。最近，混响室被尝试作为用于测量天线效率的新设施，但是该方法需要具有已知效率的参考天线，并且精度还有待证明。随着无线电系统向宽带、高频方向发展，传统的测量方法已经不能满足要求，例如超宽带天线的超宽带特性使得惠勒帽法不能用于测量。因此，迫切需要一种更好的方法，可以用来有效地和准确地测量这些新的天线。该项目包括理论和实验工作，旨在开发一种新的天线效率测量方法，该方法基于惠勒帽的思想，即利用导电腔。然而，该腔不需要是电小的，并且腔内的谐振模式可以与混响室（其可以被视为具有旋转搅拌器的过模腔）中的谐振模式一样多。在新方法中，被测天线（AUT）被放置在腔内的一些战略位置，以消除谐振的影响和天线的复反射系数S11的测量。然后可以使用这些测量的S11来获得天线效率。需要校准和数据解释软件。与任何现有方法不同，将考虑腔的损失，这在某些情况下可能是显著的。因此，该方法应比现有的方法更准确，它也应该是便宜和方便的惠勒帽的方法。此外，它将适用于各种天线在一个大的频率范围。该方法可用于小型和大型、窄带和宽带天线的测量，满足了工业界的需求，为测量和无线领域提供了一种新的测量方法。

The antenna, as an essential device for radio systems, has a number of important parameters to characterise its performance. One of them is the antenna radiation efficiency (i.e. antenna efficiency) which is the ratio of the radiated power to the input power. This parameter is very useful to calculate the radiated power once the input power is known. Since the theoretical value for this parameter is normally not reliable due to the complexity of the antenna system (including materials), measured antenna efficiency is often required for system design (link budget) and performance evaluation. The traditional methods to obtain this parameter are 1). radiation pattern integration method which is time consuming and not accurate; 2). Wheeler cap method which is accurate and cheap but only suitable for electrically small antennas; 3). the Q factor method which is also just suitable for electrically small antennas. The 1st method was normally used when the operating frequency is relatively high while the other two methods were employed when the operating frequency is relatively low. More recently the reverberation chamber was attempted as a new facility for measuring the antenna efficiency, but this method requires a reference antenna with a known efficiency and the accuracy is yet to be proven. As the trend of radio systems moves towards broader bandwidth and higher frequencies, the traditional methods are no longer adequate, for example, the Wheeler cap method cannot be employed to measure UWB antennas due to the ultra-wide bandwidth nature. There is an urgent need for a better method which can be used to measure these new antennas efficiently and accurately. This project consists of both theoretical and experimental work and is aimed at developing a new antenna efficiency measurement method which is based on the Wheeler cap idea, i.e. utilising a conducting cavity. However, this cavity does not need to be electrically small and the resonant modes inside the cavity can be as many as that in a reverberation chamber (which can be viewed as an over mode cavity with rotating stirrers). In the new method, the antenna under test (AUT) is placed inside the cavity at a number of strategic positions to remove the effects of the resonance and the complex reflection coefficient S11 of the antenna is measured. The antenna efficiency can then be obtained using these measured S11. A calibration and data interpretation software are required. Unlike any existing methods, the loss of the cavity, which could be significant in some cases, will be taken into account. Thus the proposed method should be more accurate than current methods and it should also be cheap and convenient as the Wheeler cap method. Furthermore, It will be suitable for various antennas over a large range of frequency. Thus this innovative method can be used to measure small and large, narrow and wide band antennas, meet the demand from the industry and provide an alternative method to the measurement and wireless community.