Blindness effects in ground plane-backed TEM horn arrays

Arrays of TEM (transverse electromagnetic) horn antennas are possible candidates for ultrawideband (UWB) applications. Those applications require focused radiation or reception of transient waveforms without dispersion. Previous work showed that the useful bandwidth of TEM horn arrays extended from the grating lobe limit down to that frequency at which the entire antenna is one half wavelength across. However, due to the fact that they are open to free space in both directions, there is considerable back lobe energy. When a ground plane is added to prevent the back robe radiation a scan blindness appears due the presence of a trapped wave mode between the hems and the ground plane. This paper summarizes numerical experiments that characterize this blindness phenomenon.