Pattern Reshaping of the Third Resonant Mode of Dipole and Slot Using Parasitic Elements

Abstract

A simple approach for radiation pattern reshaping of the 3rd mode of dipole and slot antennas is proposed. Short parasitic strips or slots are added to both sides of the dipole or slot antenna. In the 3rd mode, the reversed current or E-field will destroy the omnidirectivity or bidirectivity of these two antennas. But, the induced current or E-field on the parasitic elements is opposite to that on the original antenna canceling the effect of the reversed current or E-field. As a result, the radiation patterns of the dipole and slot in the 3rd mode are reshaped to be omnidirectional or bidirectional, respectively. The effects of parasitic element length, spacing and position on radiation pattern have also been studied. Besides, it is proved that parasitic loops have the same effect. For simplifying impedance matching, a novel feeding method for slot antenna is designed specially without using lumped element. Two prototypes, dipole and slot antennas with parasitic elements, were fabricated and tested to validate the concept. The measured results are in good agreement with the simulated ones. The measured patterns of the 3rd mode are shaped with lower sidelobes and high realized gains. In both the 1st and 3rd modes, the dipole and slot antennas realize omnidirectional and bidirectional radiations, respectively.