| With the development of wireless mobile communication technology,the communication equipment with the characters of miniaturization,integration and intelligence has been paid much attention.Moreover,as the front part of the mobile communication system,the performance of the entire communication system could be affected by the antenna's electrical performance.Therefore,it is of great significance to develop antennas with superior electrical performance.Based on the the engineering projects and the research hotspots about current antennas,a low-profile broadband omidirectional antennas with modified bend line balun-fed has been invested.The main aspects of this dissertation are as follow:1.Research on Low Profile Broadband omnidirectional antenna Feeded by an New?-shaped Structure.Based on the needs of modern mobile communication systems,several low-profile broadband omnidirectional antennas with ?-shaped feeding structure are designed.A wide-band omnidirectional antenna with quarter-wavelength branch is designed.An omnidirectional antenna with built-in coupling matcher is proposed.A broadband low-profile antenna with coplanar coupled parasitic capacitance is designed,a)Design of a broadband omnidirectional antenna loaded with a quarter-wavelength branch in a symmetrical ?-shaped feed structure:Firstly,the symmetrical ?-shaped feed structure is introduced.By the symmetry of the feeding structure,the stray radiation of the lateral current can be effectively suppressed.Thereby,the cross-polarization level can be reduced.Secondly,a pair of quarter-wave impedance matching branches are introduced into the symmetrical ?-shaped feeding structure,which greatly expands the impedance bandwidth of the antenna.Finally,.The patch radiator is shorted to the ground through four pins locating at the corners of the patch.The shorting pins neither reduce the dimension nor improve the operating bandwidth,b)Design of broadband omnidirectional antenna with built-in feed coupling:Firstly,a built-in coupling line is integrated on the structure to improves the impedance of the proposed antenna,.Secondly,due to the introduction of the symmetrical ?-shaped feeding structure,a stable radiation pattern in a wide frequency band is obtained.In addition,a small-sized broadband omnidirectional antenna is obtained by using a method of multi-short-column loading at the edge of the radiator,c)Design of broadband low profile omnidirectional antenna with coplanar coupled parasitic element loading:In this section,a ?-shaped feeding structure with low profile characteristics is introduced,and the impedance bandwidth of the antenna is broadened by combining the"L" shaped impedance line with the ?-shaped structure.Secondly,owing to the introduction of the coplanar coupled parasitic element,the lateral radiation can be eliminated.Therefore,a vertical polarization omnidirectional radiation antenna withlow cross-polarization and additional resonance frequency are obtained.d)?-shaped low profile monopole antenna design.The original monopole is folded by 90° for the reduction of antenna height,which causes a ?-shape and is referred to as ?-shaped monopole antenna.Meanwhile,With the help of the tight coupling technique,a ring array antenna is formed with the adjacent ?-shaped monopole antennas,which close to each other.2.Wideband directional antenna with improved meander line balun feeding structure.For the application of wideband antennas in modern mobile communication systems,three wideband directional antennas are designed in this dissertation:Bending line balun feed broadband folded vibrator antenna,symmetric dual-element vibrator antenna and short-circuit probe loaded symmetric double-loop antenna.a)The broadband folded antenna fed by meander line balun.With the stepped bend line balun structure,the impedance bandwidth of the antenna can be improved.b)Symmetrical dual-folded antenna.In order to reduce the cross-polarization of the proposed antenna,two identical folded vibrators are connected in parallel to obtain a binary folded antenna with symmetrical characteristics.The stray radiation in the far field is mutually suppressed by the symmetric structures.Meanwhile,a dual-folded antenna with broadband,low cross polarization is obtained.c)Gain enhancement of broadband symmetrical dual-loop antenna using shorting pins:a broadband symmetrical dual-loop antenna with enhanced gain is proposed.It is comprised of a symmetrical dual-loop radiator,a pair of magneto-electric feeding structures,two metal shorting pins,and a metal ground plane.To simultaneously broaden its impedance bandwidth and improve its radiation patterns,a symmetrical dual-loop radiator excited by a pair of magneto-electric feeding structures is introduced.By loading shorting pins between the radiator and the ground plane,the peak gain can be significantly enhanced over the band of operation.3.Research on Miniaturization Technology of Broadband array antenna.Based on the array antenna design method of tight coupling technology,a miniaturized wideband array antenna is designed in this dissertation.a)Design of a slot-coupled feed patch antenna.Using the gap coupling technique,a wideband splitter with differential characteristics is designed.Meanwhile,the radiating patch is differentially fed through the feed probe.Therefore,a directional radiation antenna with wide frequency band and low cross polarization is obtained,b)Designed of a ±45°dual-polarized patch antenna.The antenna consists of a radiation patch and a feed loop.The patch can be thought of as a parallel RLC resonant circuit,and the feed loop can be approximated as a series resonator.Using a tuned loop with multi-order matching characteristics,the impedance bandwidth of the antenna can be effectively extended.The signal is fed to the coupling slot through the tuning loop,and the complementary magnetoelectric coupling feed is formed by the coupling slit-thereby obtaining a good differential feeding mode and a broadband directional radiation antenna.Meanwhile,Two tuned loop coupling feed structures are placed orthogonally,thus a ±45° dual-polarized antenna unit is achieved.c)A 1×10 miniaturized broadband linear array is designed.Firstly,The basic principle and design method of the array antenna are studied.According to the tight coupling effect between the array antenna elements,a miniaturized line array is obtained.d)Design of a 4×10 dual-polarized planar Array antenna.An eight channels dual-polarization broadband planar array antenna is designed based on the 10 element linear array.Compared with the traditional array antenna,the size of the planar array antenna is reduced by about 53.4%using the mutual coupling effect between the array elements. |
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