Electrically small high-temperature superconducting Y-Ba-Cu-O meander dipole antennas for space-limited applications

摘要

Two sets of electrically small antennas in the form of coplanar meander dipoles have been designed and tested in this study. The meander dipoles are the anti-symmetrical and the symmetrical meander structures. Both sets were based on the 1.0 GHz linear halfwavelength dipole, i.e., all the meander dipole antennas have equal total arm lengths of 150.0 mm. Each set consists of several antennas, with different number of meander sections. The anti-symmetrical meander antennas were fabricated from copper (on RT/duroid substrate) whilst the symmetrical meander antennas were fabricated from copper, thick- and thin-film high temperature superconducting (HTS) materials. The first type of meander antennas was fed from underneath the circuit, through the substrate. The meander antennas are electrically small. However, as the physical size decreases, the frequency of operation increases resulting in an electrical size increase. The antennas were found to be inefficient, which is inherent to their small size. In addition, the far-field radiation pattern was close to that of a short dipole. Although they are inefficient as compared with large antennas, they can potentially have increased gain and increased efficiency with the use of superconducting material. This potential has been demonstrated by the second design, even though they have much smaller electrical and physical size. Coplanar strip (CPS) feeding line was employed to help reduce radiation pattern distortion. No matching network was designed because the antennas are reasonably well-matched to the input. Instead, a quarter-wavelength sleeve balun was incorporated to reduce the feeding loss and stray radiation. It also behaves as a matching network. The HTS symmetrical meander antennas were found to outperform the corresponding copper structures in terms of gain and efficiency. They also exhibit the supergain ratio in the range 10 to 45 over the corresponding copper structures. The symmetrical meander antennas operate at almost the same frequency as that of a linear halfwavelength dipole which has the same track length. This shows that the linear dipole can be miniaturised by meandering its radiating structure, whilst maintaining the frequency of operation. Numerical simulations were also done on all the designed antennas. The suitability of the HTS meander antennas for space-limited applications has been demonstrated.