| Because of its wide bandwidth,high spatial resolution,small size,easy miniaturization,and strong penetrating ability,millimeter-wave can apply to a large number of fields in communications,remote sensing,radar,and radio astronomy.In recent years,with the rapid development of modern millimeter-wave communication systems such as the fifth-generation mobile communication system,as a key component of the communication system,antennas with performances of high gain,broad bandwidth,low profile,multi-beam,and high efficiency have become the research hotspots of new generation mobile communication.Although millimeter-wave technology has great advantages in modern communication systems,its high path loss cannot be ignored due to the influence of atmospheric attenuation and absorption.Therefore,in the application of modern communication systems,antenna arrays with high gain characteristics are first recommended.Furthermore,millimeter-waves are susceptible to external interference,and the coverage of a single beam is small,which has certain limitations for applications such as high data rate satellite communication technology,local point-to-multipoint communication,and milli-meter wave imaging.The high-gain microstrip array antenna with beam scanning capability is a good solution because it can enhance the anti-interference ability of the antenna and expand the coverage of the beam.However,the design of the feeding network of traditional planar multi-beam microstrip array is complicated,resulting in large insertion loss,and it is also difficult to achieve a wide operating bandwidth.The planar air-fed array antenna is a new type of antenna that combines the advantages of planar structure,low cost of the microstrip array antenna and high gain of traditional lens antenna.It has the advantages of simple feeding network,low production cost,and easy integration with other systems,which has brought new ideas to the design of antennas in wireless communication systems.However,planar air-fed array antennas generally face two serious problems.One is the narrow gain bandwidth and the other is the higher profile,which largely limits the applications of planar air-fed array antennas in modern communication systems.In addition,because of the shorter wavelength and the more reflection component,"multipath effect" is easy to be caused in the millimeter-wave frequency band.Therefore,the circularly polarized air-fed array antenna that can effectively solve the problems of multipath effects and polarization mismatch in signal propagation also has high research value.This paper starts from the performance requirements of modern millimeter-wave wireless communication systems for antennas such as high gain,wide gain bandwidth,beam scanning,low profile,and high efficiency.In-depth resrarch work has been carried out about planar microstrip array and air-fed array,including reflectarray and transmitarray.The innovation of this thesis is mainly indicated in the publication of the paper and patent application.The main content can be summarized as follows:1.Research on compact multi-beam millimeter-wave microstrip array antennaA square 4 × 8 Butler matrix is proposed as a compact SIW feed network,which greatly reduces the longitudinal size of the traditional 4 × 4 Butler matrix,and uses cross-layer SIW coupling without further increasing the longitudinal size.The power splitter expands the output port of the Butler matrix to eight-port output,which is beneficial to the design of a larger antenna array.On this basis,the 4 × 8 Butler matrix is used as the feed network of the 8 × 10 microstrip array antenna by using the slot coupling feeding method,which realizes a multibeam antenna with high gain,small size and symmetrical radiation characteristics.2.Research on wideband and low-profile planar air-fed array antennaa)Broadband millimeter-wave folded reflectarray based on polarization rotation metasurface element with tunable phase: using the broadband resonance characteristics of the metasurface unit,combined with the differential feeding method,a broadband dual-polarization metasurface resonator element and a broadband polarization-selective metasurface resonator element are proposed.The characteristics of high isolation and polarization selection are applied to folded reflectarray antennas,and a novel broadband folded reflectarray antenna element is designed.On this basis,combined with the true delay line for phase compensation,the array obtains a wide impedance bandwidth and-1 d B gain bandwidth.Compared with the traditional patch-type folded reflectarray antenna,the distance between the antenna feed and the reflectarray surface is reduced by half,and the-1 d B gain bandwidth is increased from about5% to 20.2%.b)Broadband milimeter-wave folded circular-polarized reflectarray based on transmissive linear-to-circular polarization converter: based on a linear polarization feed,the working mechanism and antenna architecture of a circular polarization reflectarray antenna with the same profile as a traditional linear polarization folded reflectarray antenna are proposed for the first time.Based on the antenna architecture,the reflectarray element with polarization rotation function and the polarization converter element with linear-to-circular polarization convertion function are designed to form the antenna,and they are applied to the design of low-profile circularly polarized reflectarray.Combined with the true delay line for phase compensation,a new type of broadband folded circularly polarized reflectarray antenna is designed.In a wide frequency range,its profile is reduced to half of other circularly polarized reflector array antennas,and achieves a good circular polarization radiation performance.c)Broadband milimeter-wave multi-folded transmitarray based on ray tracing principle: a broadband transmissive array antenna element based on a metasurface antenna is proposed,which is combined with a slot-coupled differentially fed stripline to achieve better transmissive performance and a phase compensation range exceeding 360° and a linear phase response in a wide frequency range.When applied to the design of transmitarra,a broadband transmit array is realized.In addition,an improved transmitarray element is proposed,which has polarization selection characteristics and different reflection and transmission characteristics for incident waves with different polarizations.On this basis,combining the transmitarray element and the broadband polarization rotation reflected surface,a broadband low-profile millimeter-wave transmitarray is designed,which has a wide gain bandwidth and a low profile which is reduced to one third of the traditional transmit array antenna. |
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