A novel combination of Vivaldi radiator and embedded diplexing filter (fig. 5) is proposed as radiator for linear and two-dimensional wideband active electrically steerable array (AESA) antennas. The diplexer is made of segments of striplines (fig. 2, 3) and is built into the internal volume of radiator\'s three-layer printed circuit board (PCB). This allows Vivaldi\'s ultra-wide bandwidth being splited on two frequency bands (two channels, one in L-band and one in S-band). Fig. 4 shows SWR, insulation and amplitude transfer function unevenness in operating bands 1.0…1.6 and 2.5…3.5 GHz. Each frequency channel has its own physical input (1, 2 in fig. 5) for AESA TX/RX module connection. Full-duplex operation is possible considering that TX/RX modules have its own front-end filters which further improve band-to-band insulation.
For effective usage of radiator\'s PCB available surface (which is critical for volume-limited in-line H-plane Vivaldi array and 2D dual polarization «egg-crate» configuration), it is proposed to use the diplexer with series load connection. In this configuration (fig. 6) low-pass and high-pass filters (6 and 5) of the diplexer are placed on the opposite sides of radiator\'s slotline and are connected by a stripline 4 in series with each other. That stripline crosses Vivaldi\'s slotline and excites that slotline thus acing both as stripline-to-slotline transition and a part of balun. Series-load fifth-order diplexer was synthesized (fig. 7), its elements\' geometry has been optimized using custom designed software which is based on matrix apparatus of two-port networks. Results of its numerical modeling (fig. 8) indicate SWR better than 1,3 as well as port-to-port insulation over 23 dB in operating frequency bands.
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