Abstract :
Magneto-dielectric materials, having both relative permeability and permittivity greater than unity, can provide more flexibility to miniaturize antennas (G. H. Mosallaei and K. Sarabandi, IEEE Trans. Antennas Propagat., vol. 52, no. 6, pp. 1558–1567, June 2004). For this purpose, several magneto-dielectric materials with promising value of permeability and permittivity have been developed in Temasek Laboratories at NUS through different ferrite ceramics process ( L. B. Kong et al, J. Am. Ceram. Soc., vol. 90, no. 7, pp. 2104–2112, July 2007; L. B. Kong et al, IEEE Trans. Magn., vol. 44, no. 5, pp. 559–656, May 2008). We have applied these newly developed electromagnetic materials to design an electrically small magneto-dielectric coated VHF monopole antenna with its height of 250 mm, which can operate at 71.14 MHz with good matching to 50 O SMA connector (C. F. Wang et al, “Electrically small magneto-dielectric coated VHF monopole antenna,” IEEE AP-S Int. Symp. Dig., IF25.7, 2012). Antenna height reduction factor achieved is less than 1/4. The effectiveness of the newly developed magneto-dielectric material is quite promising. To further shift its resonant frequency to HF band, we introduced several PEC thin wire posts as parasitic elements uniformly distributed around the magneto-dielectric cylinder. The resonant frequency was further shifted to 27.0 MHz if we put four PEC posts uniformly distributed around the magneto-dielectric cylinder. The antenna height reduction factor was about 0.094 (less than 1/10) (C. F. Wang et al, “Electrically small magneto-dielectric coated monopole antenna at HF band,” Asia-Pacific Conf. Antennas Propagat. (APCAP), pp. 78–79, 2012). To make those two magneto-dielectric coated monopole antennas work at both HF and VHF bands, we carefully study their resonant behavior and found that introducing proper capacitive and inductive components can make the magneto-dielectric coated monopole work at both HF and VHF bands with good matching to 50 Ω SMA connector. The capacitive and inductive components can be realized through a combination of wire posts and thin copper sheet sleeve. The measured input impedance of the designed antenna clearly shows that its impedance is about (37.03-j0.4045) Ω at 26 MHz and (89.01-j8.582) Ω at 74 MHz. The designed dual-band HF/VHF antenna works reasonably well at 26 MHz and 74 MHz with matching to standard 50 Ω SMA connector. Detailed discussion on the design principle and results will be presented at the conference.
