Low-Profile Compact Circularly Polarized Slot-Etched PIFA Using Even and Odd Modes

In this communication, a novel dual-fed slot-etched planar inverted-F antenna (PIFA) is proposed for the miniaturization of wideband circularly polarized (CP) antenna. By applying in-phase feeding and out-of-phase feeding at two ports of the antenna, the PIFA (even mode) and open-slot (odd mode) modes can be excited, respectively, with orthogonal polarizations. A simple approach is used to deduce the required phases at the two ports to generating a 90° phase shift between even and odd modes. The λ/4 resonant property and shared-aperture configuration of even and odd modes fulfill the proposed size-reduction scheme for a CP radiation. A prototype was simulated, fabricated, and measured to verify the performance. The measured results show that an overlapping fractional bandwidth of 14.7% with S
₁₁
<; -10 dB, axial ratio <; 3 dB, and gain variation <; 3 dB is achieved within a compact volume of 0.3 × 0.23 × 0.032 λ
₀
³
. The excellent features of the proposed design, such as its simple feeding strategy, low profile, compact size, low cost, and wide bandwidth, make it applicable for universal radio frequency identification readers.