| With the increase demands of multi-functional and integrated wireless electronic equipment, antenna as the converter of guided wave and electromagnetic wave has a develop trend of compact-volume, broadband, multi-band and multi-function. Therefore, this paper mainly studies the compact-size, wide-band and multi-band technologies for antennas from practical applications with abundant theoretical analyses and experimental studies of the antenna prototype.First of all, the research background of compact-size broadband multiband antenna is briefly introduced in this paper, and the research status at domestic and overseas are also analyzed from four aspects of practical applications in order to further clarify the current development requirements. Then the electrical characteristic parameters of antenna are discussed and contradictions between compact-size, broadband and radiation efficiency are elucidated. Moreover, the main technical means of compact-size, broadband and multi-band and their advantages and disadvantages are analyzed proceeding from these contradictions, which provide ideas and methods for the following antenna design.Afterward, a compact-size broadband tri-band antenna based on capacitive coupling is designed. By embedding a parasitic E-shaped radiating element inside the double-C-shaped monopole structure, tri-band characteristic of the antenna is obtained and by the means of etching two quarter-circles in the ground, impedance matching condition of the high operating band is significantly improved. Its overall dimensions are31x21x1.6mm3. Experimental results show that the antenna can work in2.33-2.83GHz,3.27-3.97GHz and4.30-6.67GHz three operating bands, covering all the requirements of WLAN and WiMAX bands. The comparison shows that the proposed antenna has the advantages of easy fabrication, compact size, and showing wide tri-band operating bandwidth and stable radiation patterns, etc. Consequently, the proposed antenna is expected to be having the application prospects for WLAN and WiMAX wireless communication systems.Finally, metamaterials and the advantages and disadvantages of its applications in antenna multi-band and compact-size are briefly discussed. On this basis, a new method to achieve broadband multi-band antenna is proposed by combining metamaterials with monopole structure and making the best of their respective multi-mode and multi-frequency resonance characteristics (merging these resonance frequencies to some extent), which could effectively compensate for the shortcomings of narrow bandwidth of the metamaterials based antenna. A compact-size quad-band antenna based on this method is designed. FR4is used as its substrate and coplanar waveguide (CPW) is used for parallel excitation to the metamaterial unit (Composite Right/Left-Handed Transmission Line unit cell, CRLH-TL unit cell) and meandered monopole unit. Its overall dimensions are31x21x2mm3. Experimental results show that the antenna can work in1.25-1.28GHz,2.44-2.73GHz,3.17-3.82GHz and5.03-6.16GHz four operating bands, covering the requirements of Compass (BeiDou) B3and WiMAX bands. For the problem of poor radiation efficiency in low operating band by using FR4as a substrate, a feasible improvement scheme is also provided. The verification of antenna prototype illustrates the feasibility and correctness of the proposed method in this paper. The comparison shows that the proposed antenna has the advantages of easy fabrication, compact size, and showing wide WiMAX operating bandwidth and stable radiation patterns, etc. Consequently, the proposed antenna is expected to be having the application prospects for Compass and WiMAX wireless communication systems. Presently, the amount of miniaturized multi-band antenna with similar functions is still relatively small. |
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