Wideband integrated feeding system for a dual polarisation sinuous antenna

The objective of this work is to demonstrate the achievability of integrating a feeding system to the radiating part of a wideband dual polarised antenna. To reach this objective, a wideband microstrip-to-coplanar stripline (CPS) balun has been developed. This balun configuration is suitable for integration with planar balanced antennas in a compact form. The performance of this balun is investigated over a wide frequency range by comparison between measured and simulation results. The measured return and insertion loss of the balun in back-to-back configuration exhibit a wideband performance between 3 and 8 GHz. In order to validate the proposed balun potentiality, it has been employed to feed a wideband single polarised sinuous antenna in a compact configuration. A measured return loss better than 10 dB from 2.5 to 5.6 GHz was observed with a sinuous antenna in single polarisation mode. The radiation patterns show a good symmetrical directivity in the E- and H-planes and a cross polarisation level better than 10 dB in the frequency bandwidth. Finally, a wideband dual polarised CPS-fed antenna with an integrated configuration has been designed. Although the impedance bandwidth obtained for the dual polarised sinuous geometry (measured return loss better 10 dB from 3.7 to 7.3 GHz) was larger than the single polarisation, the radiation patterns were not symmetrical in the entire frequency bandwidth and some small distortions were observed. In conclusion, the authors have demonstrated that it is possible to integrate a feeding system very close to the radiating part of a wideband dual polarised antenna.