End-fire radiation characteristics and high gain performance of a miniaturized printed monopole antenna based on theory of characteristic modes

This article aims to address how to study unidirectional radiation of a printed antenna using characteristic mode analysis (CMA). Two designs are used for the study and analysis. Firstly, the modal analysis of the radiator of the antenna is studied in omnidirectional state when the unidirectional technique has not been employed. Secondly, the unidirectional technique which involves using a shorted radiator-ground and a parasitic conductor is also employed its modal analysis is again studied. The modal currents show more uniform distribution for the omnidirectional antenna but for directional antenna, it exhibits high coupling currents in one single direction which indicates that a high gain end-fire radiation pattern can be realized. A simple microstrip feedline is used to excite the significant modes and end-fire radiation is indeed achieved through excitation. The presented antenna has an S11 bandwidth of 2.3 - 6.4 GHz (94.5%), high front to back ratio across the bandwidth, and high peak gain of 10 dBi.