Small-aperture UHF antennas for remote-keyless-entry (RKE) applications can be terminated either as a shorted or open loop within a fob. Depending on how the loop is terminated, its far-field pattern and the antenna’s characteristic impedance will be influenced.

This application note explores antenna theory and design using EZNEC, an easy-to-use antenna simulator. We will measure the antenna’s characteristic impedance through our application board. The results will show the tradeoffs between open and shorted loops, the effects of the ground, and considerations for antenna matching. All this information is a preface to the measurement described in Part II of this application note.