Compact Orientation Insensitive Dipolar Patch for Metal-Mountable UHF RFID Tag Design

An orientation insensitive dipolar patch antenna, which has a dimension of 30 mm x 30 mm x 1.6 mm (0.0915λx 0.0915λ x 0.0049λ), is proposed for designing a metal mountable tag. It consists of two pairs of orthogonal dipolar patches, which are placed in such a way that their inherent blind spots and null points are all removed. The tag antenna is readable in all directions in the boresight. Highly inductive thin stubs are inserted into the patches, and they are stub shorted to ground for increasing the tuning range of the operating frequency. A simple equivalent circuit model has been derived for visualizing the tag impedance characteristics. The proposed tag antenna can be read in the range of 2.9-3.5 m (at effective isotropic radiated power of 4 W) covering the entire azimuth plane when mounted on a metal plate with a dimension 20 cm x 20 cm. It can also be read from at least 2 m omnidirectionally when used for dielectrics with ε
_r
in the range of 1-12.