A polarization-insensitive planar patch antenna, which has a large embedded serial capacitance, is proposed for constructing a metal mountable tag by using merely a single radiator. The proposed antenna structure itself contains two flaps of patches, which are very closely overlapped, for generating a large capacitive reactance for reducing the resonant frequency of the tag. It has been found that the surface currents in the overlapped region are in the reverse direction as the large capacitance is virtually placed in series. This feature has been tactfully employed for producing a pair of orthogonal currents for designing the polarization-insensitive tag antenna and it can generate orthogonal fields in a unique way, making it readable from almost all directions at all points above the metal surface. For analyzing the impedance properties, an equivalent circuit was also constructed. This tag antenna is compact, and it can be read from ~ 15 m with 4W EIRP. Furthermore, the tag resonant frequency is shown to be unaffected much by its backing material. The proposed tag antenna is polarization-insensitve as it can be accessible from almost all directions on the metal.
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