An Ultra Wideband Antenna Based on Tightly Coupled Effect with Practical Compact Balun

An ultra wideband low-profile antenna array based on tightly coupled effect is presented. The proposed antenna array consists of tightly coupled dipoles, the size of an element is
$4\text{cm}\times 4\text{cm}\times 10\text{cm}$
. A compact balun of microstrip line gradual changing to parallel double-strip line at both sides is designed, providing unbalanced to balanced transformation and impedance transformation. With resistive frequency select surface, the proposed antenna achieves a wide operating bandwith of 0.5GHz∼11.5GHz with
$\text{VSWR} < 2.5$
. To avoid cutoff effect, extra no-feeding elements are added in each row of the array.