Circularly Polarized UWB Antenna Based on a Single-Folded Substrate

This letter presents a low-profile ultrawideband (UWB) antenna of circular polarization. Four off-axis arranged monopole radiating elements and a feeding network for sequentially rotated excitation are combined to achieve UWB circularly polarized (CP) radiation. The 90 degrees phase shifters required for the sequentially rotated excitation are moved to the vertical parts of the antenna, which effectively reduces its lateral size. Four stubs and a metallic patch are introduced to further improve the antenna's axial ratio performance. The proposed antenna can be easily fabricated as it only uses one substrate. The complete antenna is constructed by folding the substrate twice. To verify the design, a prototype of the designed UWB CP antenna is fabricated and measured. The measured impedance bandwidth and 3 dB axial ratio bandwidth are 2.16 similar to 6.98 GHz (105.4%) and 2.2 similar to 6.9 GHz (103.2%), respectively. Its peak realized gain is 7.6 dBi, and the overall size is only 0.27 lambda(L) x 0.27 lambda(L) x 0.08 lambda(L) with lambda(L) being the free-space wavelength at the lowest operating frequency.