Printed Filtering Dipole Antenna With Compact Size and High Selectivity
Xiyao Liu, Ken Ning, Shuangmei Xue, Lei Ge, Kwok Wa Leung, Junfa Mao
Abstract
A compact filtering dipole antenna that requires no extra circuits is investigated. It consists of two folded arms and one additional extended arm, which are all printed on a single-layer substrate. Two independently tunable radiation nulls are produced near the edges of the passband, giving filtering responses without the need of any filtering circuits. It has omnidirectional radiation patterns. Its measured −10-dB impedance bandwidth and average realized gain are 15.5% and 2.0 dBi, respectively. It has a high selectivity with a suppression level of over 20 dB across the stopband. This basic design is extended to an electrically small filtering dipole antenna by using meander-line structures. Without greatly sacrificing the filtering effects, the antenna dimension can be reduced from about half wavelength ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5\lambda _{0}$ </tex-math></inline-formula> ) to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.3\lambda _{0}$ </tex-math></inline-formula> . To verify the idea, a prototype was fabricated and tested, with reasonable agreement between the measured and simulated results. The antenna is electrically small (ka = 0.96) with a bandwidth of 10.8%. Its out-of-band suppression level is over 15.5 dB across the stopband with a high-frequency selectivity.