A Magnetic Yagi-Uda Antenna With Vertically Polarized Endfire Radiation in Millimeter-Wave Band Applying Higher Order Mode

A magnetic Yagi-Uda antenna applying higher order mode in millimeter-wave (mm-Wave) band with vertically polarized endfire radiation is proposed in this article. Surface wave mode analysis is applied to spot TE mode for magnetic Yagi-Uda antenna in contrast to TM mode for electric Yagi-Uda antenna. A modified structure evolved from conventional U-shaped cavity is used to address the reversed current issue for higher order mode, which exhibits a more uniform phase distribution at the Yagi-Uda array end. Then, a composite end-feeding structure with reflector integrated is further introduced to minimize its parasitic effects for practical antenna design in mm-Wave band. To validate the design, a prototype with a size of 2.7
$\lambda _{\mathbf {0}}\times1.25\lambda _{\mathbf {0}}\times0.088\lambda _{\mathbf {0}}$
is fabricated and tested. It can achieve anendfiregain of 8–11 dBi within 24–26 GHz with –10 dB impedance band covering an even wider frequency range. The measured front-to-back ratio (FBR) is larger than 16.1 dB. Vertically polarized radiation is realized with cross-polarization level lower than –20 dB atendfiredirection.