Radiation Efficiency of an Electrically Small Dual-band UHF Microstrip Patch Antenna Using Wheeler Cap Method

da Silva, W. G.; Campos, A. L. P. S.; Guerra, J. R. F.; da Silva, I. B. T.

Abstract Determining the radiation efficiency of an antenna is a difficult task that becomes challenging when it is about electrically small antennas. This work investigates the applicability of the Wheeler cap method to measure the radiation efficiency of a UHF dual-band compact microstrip patch antenna. An overview of Wheeler method is presented. An adaptation to the original method is suggested to measure the efficiency of a small slitted microstrip patch antenna operating at two frequencies (400 MHz and 431 MHz). A third-order equivalent RLC circuit has been proposed. The measurements were performed using three metal shields of different sizes and shapes. Measured results agreed with the theoretical model. However, the metallic shield significantly interferes in the fringing fields, reducing the accuracy of the method. Despite the inaccuracy observed in the measurements, the method proved to be attractive due to its low cost and ease of measurement. The contribution of this work is to apply the method to an antenna under test with a high degree of miniaturization, low efficiency, and very narrow band, in addition to using a thick substrate. No previous work with this focus has been found in the literature, up to date.

Radiation Efficiency of an Electrically Small Dual-band UHF Microstrip Patch Antenna Using Wheeler Cap Method

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