| Modern wireless systems have enjoyed a rapid development in recent years.The design of various high-performance antennas is becoming more and more difficult.Antenna features,such as broadband,miniaturization,high gain,low profile and reconfiguration,are receiving much attention from antenna designers.Circularly polarized antennas are widely used for its immunity to multipatch effect and polarization mismatch,while the design of broadband/multiband circularly polarized antennas is becoming a hot research point to expand the capacity of wireless systems.Metamaterial is a collection of artificial structures or materials.Usually,it has some unique properties which cannot be found in traditional materials.Metamaterial has been extensively investigated in both military and civil field,and many researches have been done on metamaterial-based antennas.Firstly,several broadband/multiband circularly polarized printed antennas are proposed in this dissertation.Then,some metamaterial-based printed antennas are designed and analyzed.Finally,several composite right/left-handed substrate integrated waveguide-based leaky wave antennas are investigated in detail.The major works and contributions of this dissertation are outlined as follows:1.Broadband/multiband circularly polarized printed antennas are studied.First,a novel dual-band circularly polarized antenna is proposed.Deformed monopole and asymmetrical ground are utilized to achieve the dual-band characteristic.The proposed antenna is simple in structure and easy to be integrated.Then,a novel broadband circularly polarized square-ring-loaded slot antenna is proposed.By loading the square-ring structure atop the primary radiator,the circular polarization bandwidth can be further enhanced from 2.2GHz to 3.85 GHz according to the results of both simulation and measurement.The 1-dBic gain bandwidth of the proposed antenna is from 4.75 GHz to 8.2 GHz,which means a flat gain feature.Finally,a novel broadband circularly polarized antenna based on the perturbation technique is designed.L-shaped stubs are introduced as perturbation structures for broadband feature.The comparison among the proposed antenna and some related existing antennas is presented.The proposed antenna occupies a wider circular polarization bandwidth of 72.4%.2.Novel high-performance antennas based on two dimensional metamaterials are investigated.First,a compact circularly polarized conical-beam antenna based on the reactive impedance substrate is proposed.This single-fed antenna utilizes a small circular patch and six curved branches as primary radiators,and thus the circularly polarized radiation with conical-beam is obtained.The overall volume of the proposed antenna is only 0.66?×0.66?×0.066?,and the maximum omnidirectional circular polarization is observed at ?=48°.Then,a novel dual-band frequency reconfigurable slot antenna is proposed.By altering the relative arrangement of the two metasurface layers,the effective permittivity changes accordingly,making the dual operating bands of the primary slot radiator reconfigurable.Measured results show that the proposed antenna has two tuning ranges of 13.14% for the lower band and 9.4% for the upper band.3.Leaky wave antennas(LWAs)based on the composite right/left-handed(CRLH)substrate integrated waveguide(SIW)are investigated.First,A CRLH SIW-based LWA with single column radiators is desgined.The unit cell is designed based on the mushroom-like structure,and the corrsponding cascaded antenna array is proposed,its field distribution is given to make the CRLH transmission feature clear.The designed LWA has a beam scanning range of 87° in 13.5-17.8GHz,and the cross-polarization levels in the beam scanning plane are less than-27 dB.Then,A CRLH SIW-based LWA with two column radiators is desgined to further improve the cross-polarization performance in the non-scanning plane.Based on the far field distribution of the unit cell,the cross-polarization reduction is investigated in detail according to the differetial excitation principle.Wide beam-scanning range from-71° to +30° is obtained in 9.7-16.4GHz,and less than-30 dB cross-polarization levels are achieved in the beam scanning plane.Besides,the cross-polarization levels are less than-20 dB in the non-beam-scanning plane.4.Leaky wave antennas based on the half mode substrate integrated waveguide(HMSIW)are also studied.The corresponding unit cell is analyzed firstly.Its equivalent circuit is extracted and validated.A back-to-back HMSIW-based LWA is designed based on the unit cell structure,and a beam-scanning range from-60° to +30° is obtained in 9.8-16 GHz.Less than-30 dB cross-polarization levels are achieved in the beam scanning plane.What?s more,to obtain larger ratio of beam scanning range to operating frequency bandwidth,a novel face-to-face leaky wave antenna with meandered-line-loading is also designed.Both simulation and measurement show a 1GHz reduction in operating frequency bandwidth under the condition that the beam scanning range keeps unchanged. |
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