A Compact Yagi–Uda Antenna With Enhanced Bandwidth

Bandwidth Limitations for Scattering of Higher Order Electromagnetic Spherical Waves With Implications for the Antenna Scattering Matrix

“…This antenna is electrically large, (it has k 0 a = 1. It should be noted that the simulation results in this paper do not perfectly match those from the references [5] and [1]. One reason is that the exact dimensions of the antennas were not clear.…”

“…The higher order static transition matrix elements are not as well-studied; there are, however, a few previous publications, see [25,31,40,42]. A couple of general remarks can also be made: Firstly, note that the magnetostatic transition matrix T [1] vanishes when the scatterer is nonmagnetic. This gives the upper bounds f ν (0; k 0 a) in Figure 2b.…”

“…Consequently, the static transition matrices are crucial to the limitations. For dipoles (l = l = 1), the elements of T [2] and T [1] for an uncharged body are (apart from normalization) equal to the elements of the well-studied static electric and magnetic polarizability dyadics, dened in [23]. The elements of T [2] and T [1] for higher order spherical waves can be seen as generalizations of the polarizability dyadics in spherical coordinates, see Appendix B for details.…”

“…This can lead to sharper bounds in some cases. If, for instance, the antenna is non-magnetic, the bounds for the magnetic spherical waves (TE-modes) are sharpened since the magnetostatic transition matrix T [1] vanishes. Recall, though, that the limitations (3.4) coincide with the corresponding limitations in [29,38] for the simple case of a high contrast sphere.…”

“…As a consequence of the limitations (3.4), such an antenna must be narrowband and/or electrically large. A design of a directive Yagi-Uda antenna recently proposed by Arceo and Balanis in [1] has been simulated here (the specic dimensions labelled C in Table I in [1] was used). It has a maximum directivity of D = 5.7, and the results for the antenna scattering matrix can be found in Figure 8.…”