Design of a defected ground beam forming network

This text presents the design of a novel, wideband beam forming network (BFN) realized by defected ground structure (DGS). The BFN is a corporate one with equi-phase and magnitude output ports. In a regular microstrip BFN design, non-standard, thin-and-thick lines are used together with the standard-width (50 Ω) lines for matching purposes. However, in this design, the BFN is implemented by using standard-width microstrip lines, and rectangular defects at the ground with a 0.508 mm-thick Rogers RO4003C substrate in between. Results of the simulation show that the designed structure is a wideband, equi-phase, and equi-magnitude BFN with at most 0.4 dB magnitude difference, and 4° phase difference in the 5.6 GHz-11.1 GHz band. The resulting structure is in a compact form with constant width line lengths on the upper side, and defects on the ground side. In order to avoid the radiation effects from the defect, another substrate of the same dielectric is also placed beneath the DGS.