Dual-Mode Compression of Dipole Antenna by Loading Electrically Small Loop Resonator

This communication presents a dual-mode dipole antenna for impedance bandwidth improvement. In our approach, an electrically small loop (ESL) resonator is properly loaded to compress the operating frequencies of first- and third-order modes. With the existence of ESL, the third-order mode shifts to its first-order mode to obtain a wide bandwidth with stable polarization and radiation patterns, due to the fact that ESL is equivalent to an orthogonal magnetic dipole at the third-order mode. To validate the design strategy, a prototype was fabricated and tested. Omnidirectional radiation pattern in H-plane is achieved over the entire operating band from 2.94 to 3.89 GHz while keeping a smaller size of $0.45\lambda _{0}\times 0.17\lambda _{0} (\lambda _{0}$ is the wavelength in free space at the center frequency). Good agreement has been obtained between measurement and simulation.