Wideband Circularly Polarized Reflectionless Filtenna

The manuscript presents the implementation of a reflectionless wideband filtenna, with circular polarization and high gain characteristics from 1 to 2.5 GHz. The antenna front-end interface comprises: i) a reflectionless filter which consists of a two-stage λg/4 coupled line (defined at the mid-band frequency, fo= 1.75 GHz) and a stepped impedance open-circuited stub and ii) a balun that is used to feed a self-complementary log spiral antenna. The balun consists of two sections: a microstrip line on the input side and a parallel stripline on the output side, connected to the antenna feed point. The transition between the two sections is achieved using a Chebyshev tapering geometry. For the implementation of the wideband antenna, a cavity-backed logarithmic spiral antenna with non-uniform widths was used. The proposed front-end filtenna system exhibits an axial ratio less than 3 dB in the entire 1-2.5 GHz band and a gain that varies between 5 and 9 dBi.