Study of Impedance Matching in Antenna Arrays

Impedance mismatching in antenna arrays is an important issue especially when a huge number of antenna elements are placed side by side. This mismatch is generally blamed to exist because of mutual coupling between antenna elements. The phenomenon of mutual coupling, however, may result due to surface waves, near field radiation or far field radiation. The phenomenon of mismatch, nevertheless, reveals itself strongly when the whole array is set to radiate even in presence of less significant coupling. In this thesis, we focus our work to the effect of total radiation due to far field radiation only. It says that by arraying the antennas the input impedance of each element of the antenna array changes as compared to that of the single element which is not arrayed. In other words, the value of the input impedance of individual antenna elements changes versus antenna number and position. This work further proposes an important aspect of the evaluation of active S-parameters in antenna arrays. It has been shown that the active S-parameters obtained by using the passive scattering matrix do not correspond to the actual values obtained during a simultaneous excitation of all the elements. Finally, this study has taken a step further towards two novel decoupling methods in order to validate the theory of total radiation and evaluation of active S-parameters. Theoretical results are complemented with 3D simulations and measurements.