Unidirectional Planar Monopole Antenna Using a Quasi-Radiator

A compact wideband planar monopole antenna with unidirectional radiation properties is proposed in this letter. The measured results demonstrate that the antenna has an S11 <; -10 dB bandwidth ranging from 2.3 to 6 GHz with an end-fire radiation pattern with front-to-back ratio (F/B) > 10 dB across the operating frequency range. The antenna is very simple, comprising a slotted-stepped radiating patch attached to the ground plane through a shorting side stub. The antenna has a small size of 20 × 20 mm
²
, good F/B, and does not require cavity-backed structures and ground plane extensions, making it attractive for compact wireless devices. The antenna also possesses stable main lobe directions.