Broadband planar circularly polarised antenna for ultra‐high frequency applications

A broadband circularly polarised (CP) antenna employing a deformed square loop radiator in combination with two spiraled monopoles is presented, for use in multiple ultra‐high frequency applications. This combination of radiators provides a broad impedance matching bandwidth which is not accessible using any of these techniques alone. The antenna employs a uniplanar structure that is fed using a coplanar waveguide for simplicity of fabrication. A dual‐resonance response is achieved by introducing two spiraled monopoles in combination with a square loop radiator. Subsequently, circular polarisation is achieved by introducing three conducting rectangles into the periphery of the square loop, forming a deformed loop radiator. The increase in the electrical length caused by the introduction of the three rectangles also improves the impedance matching of the antenna, providing a wide impedance bandwidth. The antenna exhibits a 45% (556–882 MHz) −10 dB impedance bandwidth, and a 21% (715–880 MHz) 3 dB axial ratio bandwidth. It has a compact size of 0.28 λ × 0.28 λ × 0.002 λ at 582 MHz, which is the lowest resonant frequency of the antenna. Throughout the operating bands, the gain and radiation efficiency vary from 3.6 to 6.4 dBi and 85 to 90%, respectively.