Broadband microstrip-CPW fed circularly polarised slot antenna with inverted configuration for L-band applications

A broadband circularly polarised antenna with a compact structure is proposed based on a microstrip-coplanar waveguide (CPW) fed rectangular slot antenna. The wideband feeding network power divider (PD) consists of a Wilkinson PD and a 90 degrees phase difference comparator. The even modes of four CPW feed lines are generated to provide equal amplitudes but in phase quadrature. Circular polarisations can be excited over a very broad frequency band. A reflector is added to the antenna structure to improve the antenna gains. The inverted configuration, which places the reflector in the slot side, is ultilised to enhance the impedance matching. The measured impedance bandwidth for |S-11|<-10dB is 74.4%. A broad 3-dB axial ratio bandwidth of 70.8% is also obtained. The measured 3-dB gain bandwidth is 53.65% with the peak gain of 7.4dBic.