Antenna Mutual Coupling in Near-Field: Insights Using EM Lagrangian Density and Complex Helicity

In this letter, we provide new insights into the mutual coupling between antennas, using spatial distribution of period-averaged electromagnetic (EM) Lagrangian density and magnitude of complex helicity in the near-field. Using method of moments-based MATLAB Antenna Toolbox, we compute the distribution (intensity-maps) of normalized complex helicity magnitude and period-averaged Lagrangian density around two-port antenna systems (with and without nearby scatterers) in the frequency domain, revealing complex near-field interelement interactions. Such visualization of mutual coupling period-averaged EM Lagrangian density and complex helicity can enable antenna array designers to go beyond the traditional
S
-parameter approach, and identify regions containing near-zone non-TEM fields and nonpropagating energy density, which may contribute constructively/destructively to the port-to-port mutual coupling.