User:Antennaeff

The Wheeler cap method is developed from the work of Harold A. Wheeler and is a method of measuring antenna efficency of electrically small antennas. Over time Wheeler's work has yielded multiple modified methods of accurately and easily measuring antenna efficiency.

Wheeler’s initial research introduced the concept of a radiansphere defined as a virtual sphere with a radius of $$\frac{\lambda}{2\pi}$$  surrounding the electrically small antenna under test (AUT). This distance was called the radian length and the idea of the radiansphere was used to separate the near and far field regions of the antenna. He further expanded upon this concept to show that by enclosing an electrically small antenna by a spherical conducting surface (or cap) at the radian length, and placing the AUT on a ground plane, the antenna’s radiation resistance (RR) would be removed. Therefore, by taking measurements of input impedance (Zin) with this cap in place, only the loss resistance (RL) would remain. Taking another measurement without a cap with the antenna radiating in free space results in the total resistance i.e. the sum of the radiation resistance and loss resistance (RR + RL). Using these two values, the efficiency of the antenna could be determined using the IEEE standardized definition for radiation efficiency as follows:

$$\eta=\frac{R_R}{R_R+R_L}$$

The test apparatus for applying the Wheeler cap method would resemble that of figure 1, with the applicable AUT and correct radian length applied.

done.