Electrically small spiral transmission line-connected triple-arm folded monopole antenna

We proposed electrically small spiral transmission line-connected triple-arm monopole antenna of cylindrical geometry with circumscribing sphere of the electrical length ka = 0.44. The diameter of the antenna base is λ₀/10, and the monopole height is λ₀/20. EM simulation and analysis of radiation resistance as a function of number of monopoles is performed. It is shown that factor N² appropriately takes into account increase of input resistance of parallel short monopoles even for their λ₀/10 distance. A prototype has been designed for frequency 3 GHz with ground plane size 1.4 × 1.4 λ₀ and provides relative bandwidth of 0.83 %, and measured efficiency of 81.7 %. Proposed structure is simple, and might be completely produced in single layer microstrip technology with linear vertical vias, potencially with additional air substrate layer to improve bandwidth as we present here.