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 0.28λ × 0.28λ × 0.002λ 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.