On the Fundamental Resonance of Slot Loop Antenna Inductively Fed by a Coplanar Waveguide

The fundamental resonance of a slot loop antenna inductively fed by a coplanar waveguide (CPW) is examined and designed for operation. The input matching at the fundamental resonance is achieved by using a pair of shunt inductors realized by folded thin strips placed across the coupled slotlines of the feeding CPW. Besides, the higher-order resonances, or the harmonics, are suppressed effectively by narrowing the protruded signal trace of the CPW as well as by adding the shunt inductor pair. For verification, a prototype antenna is designed and fabricated. The simulated and measured results agree excellently. The antenna is well matched at its fundamental resonance (2.5 GHz), and the wideband harmonic suppression of at least up to 20 GHz is achieved. The radiation pattern at resonance is slot-like, and the measured peak gain is 3.6 dBi with a radiation efficiency of 80%.