A Directive Circularly Polarized Planar Yagi Array Antenna

A directive low profile planar Yagi array antenna with circular polarization (CP) is proposed. Each element of the Yagi array is based on a quarter-wavelength shorted patch connected with two printed strips, working as a combination of electric and slot dipole structures. The proposed antenna exhibits a CP radiation with single feed based on an inherent phase difference of about 90° for the two kinds of dipole. Two coupling patches are added between the driven element and the first director element to strength the coupling, therefore a strong CP radiation towards end-fire direction has been obtained. Measured results show that the antenna has an impedance bandwidth of 5.2% and AR bandwidth of 5%. The measured peak gain is around 7.8 dBi.