Efficiency enhancement of defect monopole antenna with asymmetry environment

Usually the design of a monopole antenna is with symmetric on a larger ground plane for higher antenna overall efficiency. Unfortunately, in many communication devices, such as Z-wave, the overall size of the device is not only limited but also the geometry of antenna is distorted. In this paper, a monopole antenna is designed for a device with size 65mm × 38.5mm × 85mm at a frequency of 908 MHz .The monopole antenna with various kinds of environments is also simulated and measured. The measured antenna efficiency is 17% without environment matching. By using stub matching, the antenna overall efficiency is improved from 17% to 56%.