Effects on scan blindnesses of an absorbing layer covering the ground plane in a triangular grid single-polarized tapered-slot array

Tapered-slot phased arrays can be capable of wide-band and wide-scan performance, and are therefore useful in numerous applications. Some applications require the antenna to have a low radar cross section. However, a single-polarized tapered-slot antenna will have a strong backscattered field for an orthogonally polarized wave due to the ground plane. To reduce the backscattered field an absorber can be positioned above the ground plane. The effect of the absorber is small compared to elements for which the ground plane distance is an important design parameter. Single-polarized tapered-slot antennas form a parallel plate waveguide structure where the cutoff frequency is determined by the H-plane spacing and substrate thickness. The cutoff frequency condition is approximately the same as the condition for a grating lobe free antenna, which requires a H-plane spacing that is less than lambda/2. Therefore, for a wide-scan array, waves with the same polarization as the elements are cutoff by the parallel plate structure for the operational frequencies and the absorbing layer will have almost no affect on the performance. The parallel plate structure can support surface waves and these waves will lead to scan blindness in the E-plane [1, 2, 3]. The blindness described in [3] occurs in triangular grid arrays when they are scanned in the E-plane and moves the field intensity towards the ground plane where the absorbing layer can reduce the backscattered field. Therefore, the absorber mainly alters the performance when the element does not function as intended.