Spirograph Planar Monopole Antenna (SPMA) Providing Unidirectional Invariant Radiation Patterns by Employing a Broadband Ground Plane

The spirograph planar monopole antenna (SPMA) is combined with the proposed broadband ground plane to achieve unidirectional radiation patterns with enhanced gain and minimal broadside gain variation. The broadband ground plane is a simple structure that consists of a resistive card and a copper sheet in a fixed position. The measured impedance bandwidth for the unidirectional SPMA, with VSWR <; 2 matching criterion, is 1.14-2.90 GHz (87.1% bandwidth). The antenna has a unidirectional radiation pattern that is mostly invariant over the entire frequency range, a single main lobe, and low cross polarization. The measured broadside gain varies from 2.59 to 6.85 dBi within the impedance bandwidth.