A High Out-of-Band Suppressed Compact Wideband Filtering Dipole Antenna With a Dual-Mode Compressed Parasitic Folded Dipole

This article presents a design of a high out-of-band suppressed compact wideband filtering dipole antenna with a dual-mode compressed parasitic folded dipole. The proposed antenna consists of a half-wavelength dipole and a compressed parasitic folded dipole. The half-wavelength mode and the one and a half-wavelength mode of the parasitic folded dipole are excited simultaneously. A capacitive load is utilized to tune the resonance of the half-wavelength mode of the parasitic folded dipole to make it come close to the resonant frequency of the one and a half-wavelength mode. Then, the parasitic element and the driven dipole couple with each other to achieve a wide bandwidth. Moreover, mixed coupling is observed between the driven dipole and the parasitic folded dipole, which results in the radiation nulls at the lower and the upper band, respectively. The antenna is fabricated and measured. The measurements reveal that a wide bandwidth of 37.9% is attained with an omnidirectional radiation pattern. Three radiation nulls can be observed at 580, 990, and 1545 MHz. The level of the out-of-band suppression achieves 15.1 dB. Only two resonators are utilized in this design, which makes the proposed antenna simple and compact.