Study On Broadband Multi-mode Antennas

With the rapid development of wireless communication technology,more and more new frequency bands have been adopted in order to meet people's urgent needs for communication quality and speed.Consequently,the compatibility with multiple frequency bands has become an important trend of the development of wireless devices.Meanwhile,as the main component of receiving and transmitting electromagnetic waves,the antenna's wideband characteristic is an important guarantee for multi-band compatibility of wireless devices.So,wideband antenna has been a research hotspot in the field of electromagnetic and microwave.As a popular research field in antenna design in recent years,multi-mode technology has a strong guiding significance for the design of wideband antennas.To meet the development trend of modern communication,this thesis studies the wideband antenna based on multi resonant mode.The main work and achievements of the thesis are as follows: 1.Design of a wideband folded dipole antenna with three resonant modes based on multimode technology.By studying the impedance characteristics of a linear folded dipole antenna,we found that it has multiple movable resonance modes.In order to achieve the combination of multiple resonance modes,the folded dipole antenna was extended from a linear structure to a planar structure,as well as optimizing its feeding structure.Thus,a broadband folded dipole antenna with three resonance modes was successfully designed.2.Study of an omnidirectional antenna based on multimode folded dipole.The triple-mode folded dipole antenna has the advantages of wide frequency band,good pattern symmetry and convenient manufacture processing.Based on these advantages and the principle of far-field superposition,two identical triple-mode folded dipole antennas are arranged back-to-back to form a omnidirectional antenna,which achieves good omnidirectional radiation characteristics.The measurement results show that the antenna achieves a gain variation better than 1.27 dBi within an impedance bandwidth of 82%.3.Design of a circularly polarized antenna based on multimode folded dipole.In order to design a wideband circularly polarized antenna,wideband characteristics of the triple-mode folded dipole antenna and the sequential rotation feeding technology are used in this part.By arranging four triple-mode folded dipoles in the shape of windmill,and designing a wideband feeding network using weakly coupled transmission line for sequential rotary feeding,a circularly polarized antenna with an impedance bandwidth of 104% and a 3 dB axial ratio bandwidth of 80% is proposed.4.Applying the multimode technology to the design of a wideband microstrip patch antenna and a wideband microstrip patch antenna with three resonant modes is proposed.Based on the study of the cavity mode theory of rectangular microstrip patch,several odd resonance modes are analyzed and discussed.By combining the two dual-mode microstrip patch antennas with "bridge" resonant mode,a wideband microstrip patch antenna with three resonant modes is designed.5.Study of circularly polarized antenna based on multi-mode microstrip patch antenna.The triple-mode microstrip patch antenna has the advantages of wide frequency band,low profile and convenient manufacture processing.Based on these advantages,a dual-mode microstrip patch antenna element is designed by loading shorting pins and coupling patch.Four dualmode microstrip patch antenna elements are arranged in the shape of windmill,and a broadband feed network is designed by using weakly coupled transmission line to feed them sequentially.Thus,a circularly polarized antenna with an impedance bandwidth of 47% and a 3 dB axial ratio bandwidth of 53% is designed.