Antenna mutual impedance computation using measured or computed element fields

Date

2023-9

Author

Öztürk, Mehmet Ali

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This thesis presents a comprehensive study of mutual coupling between two identical radiators in cases of small element spacing. To calculate the mutual coupling, we utilize spherical harmonics and the reaction theorem. However, for closely spaced antennas, a challenge arises when the minimum spheres enclosing the antennas overlap, leading to issues with the convergence of spherical wave expansions on the surface separating the antennas. To overcome this problem, our proposed method relies on addition theorems to translate the spherical wave expansions to a different center, effectively redefining the minimum spheres and convergence regions. We validate our method by analyzing the coupling of two half-wave dipoles in a side-by-side configuration. The results show excellent agreement with those obtained from the induced EMF method. Additionally, we conduct experimental tests using a printed dipole antenna, obtaining its spherical harmonic coefficients through spherical near-field measurement, and calculate the mutual impedance of two such dipoles using our method. The computed results for different element spacings in a side-by-side configuration are compared to those obtained from s-parameter measurements and full-wave simulations. To address the mutual impedance of two infinitely thin half-wave dipoles, we employ the plane wave spectrum and the reaction theorem. Through asymptotic evaluation, we establish a relationship between the spectrum and the far-field pattern function of an infinitely thin dipole. This relationship and the analiticity of the spectrum enable to compute the near fields of the dipole using its known far-field pattern function. By utilizing the computed near fields, we determine the mutual impedance of dipoles in a side-by-side configuration and compare the calculated results for different separation distances with those obtained from the induced EMF method.

Subject Keywords

Mutual coupling, Vector spherical harmonic expansion, Rotation and translation of spherical waves, Addition theorem, Reaction theorem

URI

https://hdl.handle.net/11511/105460

Collections

Graduate School of Natural and Applied Sciences, Thesis