A Theory of Antenna Electromagnetic Near Field—Part II

Analysis of Generic Near-Field Interactions Using the Antenna Current Green's Function

“…Although this agreement in the convergence results with increasing n was proved mathematically in [12] and verified numerically for far-field illumination in [13], they are confirmed here numerically for non-plane wave, i.e., inhomogeneous or evanescent fields, for the first time. Note that since a generic electromagnetic field can always be written as a proper mixture of propagating and evanescent modes [2], the results here provide evidence that the ACGF can be used to compute the response to any excitation field. This is because the basic building blocks of this excitation, namely propagating and evanescent modes, are dealt with successfully using the ACGF method.…”

“…The main advantage in using the special sequence (6) is that it has exactly the same form of the evanescent modes radiated by a point source at the origin [2,5]. As is well known in electromagnetic near field theory, the major difference between far fields and generic fields (for example, near fields, directed beams, scattered fields) is that the latter contain rich and complex mixture evanescent modes in addition to the typical propagating modes [2,5]. Mathematically, a generic near field can be written as E r;R = E pr r;R + E ev r;R ,…”

“…Here,R is a 3D rotation matrix specifying orientation of the local coordinate frame used in deciding the direction of the axis along which the splitting into propagating and evanescent modes is enacted [2]. Consequently, since it is this type of evanescent modes E ev (r;R) that represents the rapid part of generic near field variations, knowledge of the accuracy of the ACGF method in terms of exponentiallydecaying excitations like (6) automatically provides information about how good the ACGF thus obtained in predicting the response of the antenna system to this level of short-wavelength details in the near field.…”

“…In theory, the near field is much more complex than the far fields or waveguide modes. Although it is not completely arbitrary but appears to enjoy a very specific mathematical structure of its own, e.g., see [1][2][3][4], understanding near-zone problems remains challenging compared with other limit cases (examples of the latter include far zone and waveguide-based excitations. ).…”

On the Fundamental Relationship Between the Transmitting and Receiving Modes of General Antenna Systems: A New Approach

“…The radiation of into free space is Mode B and will not be taken into consideration in the present work. 4 We have assumed that the problem is well posed, allowing the operator to be inverted. Since is also linear, it admits a Greens function, denoted by , satisfying .…”