Research On The Marine Small-Scale Receiving Antenna In MW And SW Bands

Maritime radio navigation system based on the spread spectrum system is with the characteristics of high positioning accuracy, wide coverage and good security, which works in the MW and SW bands, utilizes ground wave to range position. It can be used in many different fields, for example military affairs and civilian.However, because of the development of radio navigation technology, there are higher demands to integration level of the receiving equipment brought by the system. Additionally, as the large signal wavelength of the working band, the bulk of receiver antenna is so large that hard to be installed and maintenance. So, it is a very impending and practical subject to develop the adaptive omni antenna works in the MW and SW bands which meets the request of the maritime radio navigation system.According to the idiographic requests, this paper proposes a new-designed miniaturization antenna called angle reflect antenna based on the Hilbert fractal curve. And then, this paper based on the theory designs an omni antenna whose working frequency is 8.8MHz, and height is 63cm.The main works and conclusions of this paper are shown as following:1. Building the Hilbert fractal antenna system mathematics model. In the MW and SW bands, Hilbert fractal antenna is composed by thin lines with the crossing points. Because of the fine structure's micro-diameter and complicated electromagnetic environment of the thin line crossing point, ordinary numerical analysis methods can not build its math model exactly. So, this paper compartmentalizes the antenna structure by gradual Yee cells and builds on the math model of Hilbert fractal antenna based on the FDTD. Pointing to the fine structure's micro-diameter, this paper divides its cross section into four Yee cells, then, infers the component expressions of the electric field and magnetic field which both penetrate the single cell cross section, and gets the time domain description of electric current and magnetic current flowing in the thin line eventually. Pointing to the special electromagnetic environment of the thin line crossing point, this paper provides the interaction relational expression of electric circuit and magnetic circuit which are inside and outside the included angle, and builds on the math model of thin line with the crossing point. Additionally, in condition of neglecting the impact of high-order modes, this paper is also with the coaxial line analysis, provides the electric time domain expression flowing feed point and antenna in the coupling base on coaxial line TEM equation. The above theory research lays the foundation to the antenna character analysis in this paper.2. Based on establishing Hilbert fractal antenna mathematical model, this paper analysis the electromagnetic characteristics of Hilbert fractal antenna, and elaborate that the changes of antenna geometry parameter, for example, size, fractal dimension, fine structure etc, have effect on gain, resonance frequency, standing wave character, direction chart, also proving the theory analysis in this paper through the simulation results. Secondly, this paper which researching on the design method of antenna system totally discuss the changess of antenna geometry factors, for example, feed position from the idiographic angle, medium backboard material and thickness, earth-plate size etc, taking effect on Hilbert fractal antenna character. Through the simulation results, this paper sums up the rules which can be used as basic theory, designing ideology and technology method for the designing of Hilbert fractural antenna.3. Pointing to low gain of Hilbert fractal antenna is hard to be used in the project, this paper proposes a new antenna miniaturization scheme-angle reflector antenna based on the Hilbert fractal. The main idea is that using Hilbert fractal frame in the design of angle reflector antenna. The antenna uses the mental lead board of Hilbert fractal curve frames instead of the reflecting board of angle reflect antenna, forming double Hilbert fractal frames, and feed point is the crossing point of the reflecting boards. Meanwhile, composing the key technology of coaxial line analysis and model of thin line with crossing point algorithm, this paper builds antenna mathematics model using FDTD, analysis the effect to antenna character when angle and geometry index change, propose design method of angle reflector antenna system based on Hilbert fractal, and discuss the character of antenna miniaturization. The simulation result shows that compared to Hilbert fractal antenna, this antenna enhances antenna gain and fulfill the design acquirement that receiver antenna gain higher than 3dB fitting to project application.4. According to the analysis of signal transmission character in the MW and SW bands, the design index of the maritime radio navigation system is given. This paper propose angle reflector antenna whose angle is 180 degree and base on Hilbert fractal antenna as implement scheme, design and develop a physical size as 0.633×0.318×0.0015m3 antenna model machine. Simulation according with actual measurement data prove that developed antenna can work in the MW and SW bands whose center frequency is 8.8MHz, the height is just only 16.7%of original system antenna, the gain reaches 3.65dB at the center frequency, relative bandwidth higher than 8%, and then, it is also with the characteristic of omni. Theory analyses and experiment data indicate that this angle reflector antenna based on Hilbert fractal curve meets the designing requirement of the maritime radio navigation system, can be used in project practice as the marine antenna in the MW and SW bands.