Design of a cavity backed 15:1 bandwidth two arm spiral helix antenna

A design of a 15:1 bandwidth single-mode two-arm spiral helix antenna is presented. In order to achieve unidirectional and efficient radiation, the spiral is cavity backed and resistively loaded. A trapezoidal pyramid cavity is implemented for higher gain at the turn on frequency and smoother gain variation at higher frequencies. Numerical simulations are conducted to assess the gain and axial ratio of the spiral helix for different trapezoidal pyramid heights and diameters. By choosing proper cavity parameters, a wideband spiral with VSWR <; 2.5, axial ratio <; 4 dB at elevation angle of 30° and gain > 0 dBic at the turn-on frequency are realized.