A Compact Yagi-Uda Type Pattern Diversity Antenna Driven by CPW-Fed Pseudomonopole

This paper presents two end-fed compact Yagi-Udatype pattern diversity antennas, which use a coplanar-waveguide (CPW)-fed printed pseudomonopole antenna (PPMA) as the driver element. The balun-less driver PPMA behaves like a folded strip dipole and adds to its compactness. A common mode/differential mode (CM/DM) decomposition of antenna current on PPMA is carried out to show that the CM current distribution is similar to the current distribution of an asymmetrically fed dipole. The designed three-element Yagi-Uda antenna operates in the 2.4-GHz band with F/B ratio of about 23 dB and gain of 7.3 dBi. The compact pattern diversity antennas are realized by using two Yagi-Uda antennas separated by a common reflector. Two diversity antennas are realized using two different arrangements of Yagi-Uda antennas. The separation between the constituent PPMAs is varied to study its effect on the isolation and element embedded efficiency. The better of the two diversity antennas has overall footprint area of 65 x 58 mm(2) and the separation between two radiating elements is only 34 mm or 0.272 lambda(o). The simulated and measured port isolation (vertical bar S-12 vertical bar) between two diversity branches is about 35 and 27 dB, respectively. The signal envelope correlation is 0.018 and the embedded efficiency is about 93%.