Radiation efficiency of printed slot antennas backed by a ground reflector

Although in the literature the back-reflector technique has been extensively used as a means of rendering the slot patterns unidirectional, there is no quantitative information on the effectiveness of this approach. In this work, the use of a back reflector as a means of increasing the efficiency and antenna gain of printed slot antennas is evaluated. For this purpose, the radiation efficiency of reflector-backed printed slot antennas on either electrically thin or thick substrates is thoroughly characterized; both single and twin slot elements are considered. Twin slot elements have been previously proposed for the reduction of the coupling to the dominant surface-wave mode in the case of electrically thick substrates. In this article, twin slot elements are explored as a means of enhancing the radiation efficiency of printed slots backed by a ground reflector. It is shown that in the case of thick substrates, simultaneous partial cancellation of the surface-wave and the parallel-plate TEM modes can be achieved. On the other hand, in the case of thin substrates where the back radiation is severe, the twin slot element can be utilized for the drastic reduction of the parallel-plate TEM mode.