A Stacked Circularly Polarized Filtering Antenna With Crossed Slot

This letter presents a stacked patch antenna for circularly polarized (CP) filtering without any additional filtering structures. The lower patches consist of a square patch with truncated corners, two sets of parasitic patches, and a 50 Ω microstrip line with a quarter-wavelength impedance matching line at the front end. The upper patch consists of a square patch with corner-truncated and etched crossed slots. Two CP antenna axial ratio (AR) minima are generated by the stacked patches with corner-truncated and crossed slot, respectively. Three radiation nulls are generated by the parasitic patches on both sides of the lower main patch, crossed slot, and parasitic patches on both sides of the quarter-wavelength impedance matching line, respectively. The proposed antenna allows for independently controllable radiation nulls. The fabricated antenna has been measured, and the measurement results indicate that the impedance bandwidth is 17.72% (2.16–2.58 GHz), the AR bandwidth is 9.32% (2.25–2.47 GHz), and the peak gain is approximately 7.07 dBi.