An Electrically Small Planar Loop Antenna with High Efficiency for Mobile Terminal Applications

Abstract

An electrically small loop antenna with complete planar configuration is proposed. The radiator is directly connected with a 50-Ohm coaxial line when it is coupled-fed by a tiny feeding loop. The interdigital capacitor loaded loop has a size of only 0.116λ ₀, where λ ₀ is its operating wavelength, and the measured results show that it can have good radiation efficiency and gain. As the loop is placed coplanar with the ground plane, it has higher radiation efficiency and the impedance bandwidth is nearly doubled compared to its vertical counterpart. Other characteristics of such an electrically small loop like the reduced current on the ground plane, the tunable operating frequency, and potential pattern diversity for MIMO applications implies its promising use in mobile terminal applications. The working mechanism of the antenna is illustrated, with the help of an equivalent circuit and some key parameter study is also given.