A Compact Wideband Filtering Omnidirectional Dipole Antenna Without Extra Circuits

This article presents a design of a compact wideband filtering dipole antenna with an omnidirectional radiation pattern. We analyze the radiation of three kinds of half-wavelength dipoles (strip, U-shaped strip, and folded strip). It is found that these three diploes produce omnidirectional radiation patterns when they work on half-wavelength mode. In the proposed design, we make these three dipoles couple with each other to achieve wide bandwidth. In addition, both electric coupling and magnetic coupling are observed at the lower band and the upper band, respectively. Therefore, two radiation nulls can be achieved without any extra circuit, which makes the proposed antenna filtering property and compact. A prototype is fabricated and measured to verify our idea. The results show that the proposed antenna has a 10 dB bandwidth of 42.51%, an in-band gain of ~2.4 dBi, and an out-of-band radiation suppression of more than 10 dB with a total size of
${0.4}{ {\lambda }}_{{0}}\,\,{\times }\,\, 0.06{ {\lambda }}_{{0}}$
. The above advantages of wide bandwidth, filtering property, small size, and easy fabrication make the proposed antenna have potential applications on various wireless communication systems.