Variations in input characteristics of Quadrifilar Helix Antenna due to finite metallic plain structures

In this work, input characteristics of Quadrifilar Helix Antenna (QHA) are investigated for variations in height in the presence of finite metallic structures of varying sizes. It is noticed that the input characteristics such as conductance, susceptance and reflection coefficient are affected as height of QHA above these finite metallic ground planes varies. Rapid variations are observed if QHA is placed below 0.2 λ above ground plane. Conductance, susceptance and reflection coefficient of input feed point are inversely proportional to the distance between QHA and ground plane. If the height of QHA is greater than 0.2 λ above ground plane, these parameters are relatively insensitive with respect to changes in height. Larger sizes of ground planes severely affect conductance and susceptance while the effects of smaller sizes of ground planes on input reflection coefficient are significant. Deployment above 0.2 λ at decks of LEO satellites, aerial drones and handheld mobile devices results in stable input characteristics of QHA that eventually conclude to better performance.