Researches On VHF/UHF Antennas Based On Ferrite Magneto-dielectrics

The antenna is a key component in wireless communication systems.With the development of wireless communication devices towards miniaturization,integration and intelligence,there are increasing requirements for the miniaturization of antenna size and performance improvement.The development of antennas with miniaturization,broadband and excellent radiation performance has become the focus of research in the field of wireless communication.In particular,the miniaturization and broadband research of antennas are of great importance for the lower communication bands of ultra-high frequency(UHF),very high frequency(VHF)and below.In recent years,as a technology combined with the application of new microwave materials,ferrite magneto-dielectrics have received great attention in the development of miniaturized and wideband antennas.Ferrite magneto-dielectrics can have both high dielectric and magnetic properties over a wide frequency band,both of which are important factors in regulating electromagnetic waves and antenna performance.Compared with the usual non-magnetic microwave dielectric materials,ferrite magneto-dielectrics increase the new design freedom of magnetic properties,which can effectively regulate the antenna operating frequency,bandwidth,gain,size and other properties.In this thesis,In this paper,we propose several VHF/UHF miniaturized broadband antennas by combining the new high-performance ferrite magneto-dielectric developed by our laboratory,and the influence of ferrite on antenna performance and the regulation mechanism are systematically studied.The main research contents of this thesis are as follows:1.A miniaturized broadband antenna in UHF frequency band loaded with ferrite is designed,and the structural parameters of the antenna are systematically optimized and analyzed.The impedance matching performance of the antenna is improved by loading ferrite on the bowtie dipole antenna.Finally,a miniaturized antenna with a wide frequency band and high gain is realized,with an impedance bandwidth of 320-790 MHz,a relative bandwidth of 84.7%,and an in-band gain of 3.4-5.9 d Bi.The electrical size of the antenna is only 0.32λ_L×0.32λ_L×0.09λ_L,whereλ_L is the wavelength of the electromagnetic wave at the lowest operating frequency.In order to further improve the radiation gain of the antenna,based on the above antenna,a 1×4 antenna array is designed by using the microstrip power divider to feed,and the peak gain of the array is increased to 10.4 d Bi.The proposed antenna array shows a wide impedance bandwidth from 298 to 804 MHz,with a fractional bandwidth of 92%.2.For the application of VHF/UHF band,a miniaturized broadband antenna covering part of VHF and UHF bands is proposed.The antenna is composed of a top radiating part and a bottom reflective ground plane.The effect of antenna height on the impedance matching performance is analysed.It is proposed to load ferrite to improve the impedance matching bandwidth of the antenna and reduce the electrical size of the antenna,and the mechanism of ferrite in the antenna is studied.The electrical size of the antenna is only0.27λ_L×0.27λ_L×0.07λ_L.The-10 d B impedance matching bandwidth is 146-500MHz,corresponding to a fractional bandwidth of 109.6%,and the gain of 146-400MHz is4.2-7.3d Bi.3.A dual-polarized antenna covering part of the UHF frequency band is designed.The dual polarization performance is achieved by two orthogonal dipoles.By loading high-performance low-loss ferrite,the impedance matching bandwidth and radiation gain of the antenna are significantly improved.The structural parameters of the antenna were optimized and the mechanism of the effect of ferrite on the antenna performance was investigated.Then,an antenna prototype was fabricated and measured.The results show that the measurement and simulation of the antenna have good consistency in various performance parameters.The-10 d B impedance bandwidth of the antenna is 290-442MHz,corresponding to a fractional bandwidth of 41.5%,and the radiation gain is from 2.4 to 5.1d Bi.The electrical dimension of the antenna is only 0.34λ_L×0.34λ_L×0.03λ_L.The above research work shows that the introduction of ferrite magneto-dielectric provides a new idea for the realization of new miniaturized broadband antennas.It fully illustrates the outstanding advantages of ferrite magneto-dielectrics in realizing miniaturized and high-performance antennas in the VHF/UHF band.These VHF/UHF miniaturised broadband antennas based on ferrite magneto-dielectrics proposed in this thesis have a large potential for applications in vehicular communications,marine communication,aerospace communications,radar systems,etc.