Polarization-Reconfigurable Compact Monopole Antenna With Wide Effective Bandwidth

This letter presents a simple microstrip-line-fed wideband polarization-reconfigurable antenna (PRA). A circular metal ring with gaps and modified ground plane is first designed for wideband circular polarization (CP). Two p-i-n diodes are then introduced to control the polarization states. Left-hand CP, right-hand CP, and linear polarization (LP) can be obtained by controlling the biasing state of the diodes. A prototype antenna is fabricated and tested for a C-band application. Measured results show that the antenna achieves a wide effective bandwidth over 3.79-7.82 GHz (both |S11| ≤ -10 dB and axial ratio ≤ 3 dB) for the CP. However, it decreases to 4.1-6.98 GHz for the LP. Nevertheless, a comparison with previously published PRAs shows that it has the widest effective bandwidth and minimum occupying area.