Novel compact design of CPW-fed circular patch antenna

Due to low radiation leakages and easily integrated with active devices in the same side of the planar substrate, several related designs of CPW-fed microstrip antenna with different coupling slots have been studied. However, very few designs for a compact microstrip antenna with a CPW-fed line have been published in the open literature. The only compact design with CPW-fed line that has been proposed uses meandered slots in the antenna´s ground plane. We demonstrate that by increasing the vertical arm´s length of the U-shaped coupling slot connected with coplanar waveguide (CPW) feed line, the fundamental resonant frequency of the circular microstrip antenna can significantly be lowered. Moreover, by perpendicularly bending a vertical portion of the U-shaped coupling slot back to back, which can be considered as a pair of introduced rectangular slots connected with the vertical portion of the U-shaped slot, a modified U-shaped slot is presented in this study. It is found that the proposed design causes more significantly lowering of the antenna´s fundamental resonant frequency. Prototypes of the proposed design have been successfully implemented, and experimental results are described in detail.