Modeling and measuring of antenna array s-parameters and radiation efficiency

The S-parameters of an electrically small antenna, modeled as a 2-port device can be calculated using specifically sized Wheeler caps. However, having antenna S-parameters are not sufficient for modeling S-parameters of an array of antennas as that does not model mutual antenna coupling. This paper proposes a model, which accounts for mutual coupling, and permits the calculation of array S-parameters. It is achieved by modeling mutual coupling as a 2-port device connecting the antenna element 2-port devices. In this paper, a two-element antenna array was used to demonstrate the operation of the model. Signal flow diagram of the model is presented and equations to calculate the radiation efficiency were derived. A two-element antenna array prototype was fabricated with two identical monopoles positioned greater than λ/2 apart at all frequencies of interest. The proposed model was verified using experimental outcomes and simulations for four frequency points. Derived equations can be applied directly to determine the radiation efficiency of a two-element antenna array. This model can be extended to a larger antenna arrays as well.