Theoretical and Experimental Validation of a Generalized Wheeler Cap Method

Although Wheeler´s method has been reported as being one of the most accurate for the measurement of the radiation efficiency of antennas, its limitations are also known: it assumes that the antenna can be modelled as a RLC circuit; the losses resistance must appear in series with the radiation resistance; no cavity resonances can be present within the bandwidth to be measured. To overcome these limitations, an improved method, that treats the antenna as a two-port network, is thoroughly investigated here by electromagnetic simulation. After the method is validated, two cylindrical cavities, meant to be used in the measurement of the radiation efficiency of small printed antennas, are designed, fabricated and tested. Two different aspects of the cavities are investigated: the presence of cavity resonances and the cavity quality factor.