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

A simple approach for radiation pattern reshaping of the third 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 third 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 third mode are reshaped to be omnidirectional or bidirectional, respectively. The effects of parasitic element length, spacing, and position on radiation patterns 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 especially without using lumped elements. 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 third mode are shaped with lower sidelobes and high realized gains. In both the first and third modes, the dipole and slot antennas realize omnidirectional and bidirectional radiations, respectively.