A Type of Dual/Circularly Polarized Filtering Dipole Antenna Design Based on Coupled Lines

In this letter, a broadband dual linearly polarized (LP) and a circularly polarized (CP) filtering antenna are proposed. These two antennas are designed based on the same approach by incorporating the coupled meander-line and split-ring line into the crossed-dipole antenna. By coupling a pair of meander-lines to the cross-dipole arms, specific controllable radiation nulls are generated. To ensure a high frequency selectivity level, a split-ring line is then coupled to the L-shaped balun feeding structure. This design method is first applied in a dual LP antenna, which realizes an impedance bandwidth of about 46.3% [(1.69 to 2.71) GHz], an average realized gain of about 7.5 dBi and a more than 30 dB suppression level. Then, this method is deployed to design a CP dipole antenna that achieves an overlapping bandwidth (impedance and axial ratio bandwidth) of about 44.2% [(1.5 to 2.35) GHz], an average realized gain of about 7.4 dBic and a more than 18 dB suppression level. These coupled lines are inserted into the antenna structure without increasing the antenna overall size and height. This work presents a general method for base-station antenna designers to develop filtering dipole antennas, which could be useful for Antenna and Propagation Society.