Broadband slot spiral antenna with external feed and microstrip-to-slotline transition

As the demand for spread spectrum and multifunction RF systems increases, antennas that are capable of wideband/multiband operation are becoming more and more desirable. Spiral antennas with an inherent broadband nature meet the requirements for automotive applications. Recently, slot spiral antennas, with or without a reflecting cavity, have been widely studied. We propose a new design of slot spiral antenna with an external feed, combined with a wideband microstrip-to-slotline transition and backed with a reflecting cavity for unidirectional radiation and gain enhancement. A new approach to identify the active region of the spiral antenna is also presented. The simulation results show that the return loss bandwidth covers from 2.2 GHz to 8 GHz. The gain performance is approximately 3 dBi over 3 GHz to 5 GHz. The active region identification approach is verified by HFSS simulation; it can be used to identify the size reduction ratio of the meandered spiral.