Stubs-integrated-microstrip antenna design for wide coverage of circularly polarised radiation

A generalised stubs-integrated-microstrip (SIM) antenna with wide coverage circularly polarised (CP) radiation is proposed for radio-frequency energy harvesting applications. The antenna consists of a microstrip patch radiator with four integrated asymmetric/symmetric-stubs and a coaxial feed. Four stubs are integrated at the corners of a square microstrip radiator. The stub lengths or stub gaps from the microstrip radiator are optimised for wide-beam CP radiation. Four different combinations of asymmetric/symmetric based SIM antennas are designed, fabricated, and tested. The proposed antennas are able to cover upper-half area with CP radiation across the 3-dB axial ratio bandwidth.