| Popis: |
A counter-intuitive phenomenon of propagation of the electromagnetic waves below a cut-off frequency in a waveguide loaded with the split-ring resonators (SRRs) was reported recently. Detailed analysis of this phenomenon, based on anisotropic property of mu-negative (MNG) metamaterial filling, together with an experimental verification of backward wave propagation and possible applications in waveguide miniaturization has also been proposed so far. Very recently, a dual case of a waveguide filled with anisotropic thin-wire based ENG metamaterial has been reported. This waveguide also supports propagation of the backward waves but it may have lower losses due to non-resonant properties of a thin-wire-based ENG metamaterial. In this contribution, some recent experimental results of possible applications of waveguides with uniaxial single-negative (SNG) filling in antenna technology are discussed. The first group of conducted experiments dealt with open-ended radiators based on the waveguides with anisotropic (thin-wires-based ENG or SRR-based MNG) filling operating in 8 GHz band. It was found that although these waveguides may in principle operate at frequencies arbitrarily lower than cut-off frequency, they do radiate into free space and exhibit radiation pattern and directivity similar to those of equivalent apertures with uniform current distribution. Thus, the anisotropic single– negative (SNG) metamaterial filling cannot beat out the fundamental relations between antenna size and directivity. Recently, it was also shown that that inductive loading of thin wires can substantially decrease the plasma frequency of an ENG metamaterial. The open-ended waveguide radiators based on such an ENG metamaterial operated in 2 GHz were investigated in the second group of experiments. It was found that this type of open-ended waveguide radiator offers both low-loss operation and a high degree of miniaturization. |
