Closely Arranged Broadband Isolated Monopole Pair Array Antenna by Using U-Shaped Resonator

A closely arranged broadband isolated monopole pair (MP) array antenna using a U-shaped resonator is presented. In the design, the MP element is closely arranged with a short distance of only 6 mm for a compact size. To achieve a broadband isolation in the MP element, a U-shaped resonator is introduced for improving both isolation and impedance performances. Different from the traditional decoupling method using connection lines, the introduced U-shaped resonator works as a shunt-resonated coupling neutralizer. It cannot only neutralize the original coupling in both lower and upper frequency bands for a broadband isolation but also improve the input impedance for a broad impedance bandwidth. Finally, a prototype of the four-pair MP array was fabricated and measured for performance demonstration. The detailed measured results prove that the developed array can have an overlapped bandwidth of 3.2–4.45 GHz (32.7%) for both impedance and isolation. In addition, the envelope correlation coefficient of less than 0.11 and high total efficiency of higher than 80% are achieved for wireless terminal applications.