Design of electrically small Hilbert fractal NFRP magnetic monopole antennas

ABSTRACT

Electrically small, Hilbert fractal, near-field resonant parasitic (NFRP) antennas are reported and investigated in this paper. This type of electrically small antennas (ESAs) consists of Hilbert fractal curves as the NFRP resonators and small vertical monopoles as the driven elements. By offsetting the driven monopole off the centre position, good impedance matching can be easily realized. The current distributions on the fractal NFRP elements and the driven monopoles manifest that strong electric coupling could excite loop-mode currents along the Hilbert fractal NFRP structures, and thereby horizontal magnetic monopole patterns with broadside radiation property are realized. The results show that the 2nd-step evolution Hilbert fractal NFRP antenna witnesses an electrically size reduction of 25% compared to ka = 0.9622 of the square capacitively loaded loop (CLL) NFRP antenna, while maintaining its original broadside radiation. It is also demonstrated that there is a performance trade-off, i.e. higher fractal iteration orders leading to smaller resonant frequencies, narrower bandwidth and lower radiation efficiencies.

KEYWORDS:

• Electrically small antennas
• near-field resonant parasitic (NFRP) antennas
• Hilbert fractal antennas
• magnetic monopole

Acknowledgements

The authors would also like to thank the anonymous reviewers for their valuable comments and suggestions to improve the quality of the paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Hao Zeng http://orcid.org/0000-0002-1803-9670

Additional information

Funding

This work was supported in part by the National Natural Science Foundation of China under Grants 61471072 and 61701052, in part by Innovation Funds from China Academy of Space Technology under grant no CAST2016021, and in part by the Fundamental Research Funds for the Central Universities under grant no 106112017CDJXY160001 and grant no 2018CDGFTX0014.