Compact, Low-Profile, Planar Filtering Antennas Based on A Novel Coupling Feeding Scheme

The compact, low-profile linearly polarized (LP) and circularly polarized (CP) filtering antennas based on a novel feed scheme are presented. The LP design consists of a patch and an inverted-h-shaped coupling feed probe, which can introduce two radiation nulls at the lower and the upper band edges to realize a quasi-elliptic bandpass filtering response, respectively. This LP design with simple feed structure is also extended to realize the CP function by adding an extra T -shaped feedline operating as a dual-mode resonator, while maintaining the excellent filtering performance and further enhancing the impedance bandwidth. For demonstration, two prototypes of the LP and CP designs were measured. The measured results agree well with the simulated values. In addition, good performance characteristics, i.e., flat passband gain response, excellent roll-off rate, and high out-of-band suppression level, could be well achieved.