Circularly polarised printed antenna with wide axial-ratio bandwidth using strip dipoles and slots

A circularly polarised series-fed printed-array antenna having a wide axial-ratio bandwidth (for an axial ratio of less than 3 dB) is realised by combining strip dipoles with slots. To form a free-space dipole, i.e. a complementary radiator to a slot, the strip dipole is constructed by modifying the strip radiator of the circularly polarised antenna presented in a previous paper. Several experiments verify that the strip dipole behaves like a free-space dipole. Next, a design procedure of the circularly polarised printed antenna with a wide axial-ratio bandwidth is described. On the basis of the design procedure, two types of the array antenna having different strip-dipole spacings are made and measured at S-band. An axial-ratio bandwidth of about 27% is obtained for the three sets of the radiators, although the actual gain is less than 0 dBi because the impedance matching is neglected.