Modeling of slow-wave EBG structure for printed-bowtie antenna array

The novel printed antenna array consisting of series-fed bowtie radiators, finite-width conductor-backed coplanar waveguide-to-coplanar stripline (FW-CBCPW-to-CPS) transitions, and slow-wave electromagnetic bandgap (EBG) structure is presented. By controlling the size and the cascaded number of EBG cell, this structure appears as a slow-wave transmission line that can exhibit large phase shift with broad bandwidth for antenna array applications. The equivalent circuit is also established to model the phase shift of EBG cell. Measured results show that the antenna array achieves a 50% frequency bandwidth for 10-dB return-loss criterion and an end-fire radiation pattern with a front-to-back ratio greater than 20 dB. Good agreement among measured, full-wave simulated, and calculated results supports the validity of the phase-shifting model of EBG structure to predict the main beam angle of the antenna array. Compared to the conventional solid-state phase shifters for antenna arrays, the proposed slow-wave EBG structure has the advantages of higher compactness and lower cost and it is easier to integrate in the FW-CBCPW-fed bowtie antenna array with broad-band and end-fire radiation characteristics.