| Nowadays,the millimeter-wave antennas are widely used in the Fifth-Generation/Beyond Fifth-Generation(5G/B5G)communication systems.For example,the millimeter wave devices are mainly adopted for the wireless access network for outdoor highways and provide users with WiFi signal coverage.Meanwhile,the 5G networking mode is commonly used for the millimeter-wave transmission and receiving in mobile terminal devices.Due to this background,the construction of 5G and B5G systems is increasing important for the modern communication systems with the increasing applications,including Internet of things(IOT),Internet of vehicles,automatic driving,UAV navigation and so on.Therefore,the research on novel low-profile and low-loss microwave/millimeter wave antenna elements and arrays in 5G/B5G communication systems has both promising academic values and considerable economic benefits.Against this background,the dissertation has in-depth conducted the following research works:antenna unit,array and the corresponding feed network in the microwave/millimeter wave band.The main research contents and design methods are concluded as follows:Firstly,a new method of the planar array with integrated feeding scheme has been proposed to solve the critical issues of narrow bandwidth,low gain,and high-complexity machining and assembling of the commonly array antennas in the E-band.Herein,the traditional waveguided-feeding network with the 1-to-4 coupled cavity is utilized to excite the radiating elements,aiming to achieve the desired wide bandwidth and high gain simultaneously for the array antenna.Meanwhile,the array consists of four layers of gap wave(GW)structure loaded with assembly stub,thus reducing the leaked energy from the side-edge metal of the array,and decreasing the complexity in machining process.The detailed design step is shown as below:1)Referencing to the scheme that the radiation horn unit at the front end of the array,we have adopted the metal cross division structure to forming the frequency doubling radiation aperture,which saves 50%of the divider number and space for the feed network.A 1-to-4 coupling cavity structure at the back-end of the radiation unit is used to decrease the side lobe level(SLL)and back lobe level caused by the asymmetry of the antenna horn unit.2)The conventional waveguide horn elements are used as the radiation unit of the array.They were connected by the beam-forming network composing the conventional waveguided-feeding network and the 1-feed-4 coupling feed structure,which can save 50%feed network space and achieve very good radiation by using high-density beam-forming network.Finally,the array size in the overall design is 112mm×112mm×11.5mm(29.31λ0×29.31λ0×3.93λ0).The experimental results show that the relative bandwidth of the antenna is about 19.1%with the horizontal polarization and vertical polarization gains of 35.5-38dBi and 35.4～38dBi,respectively,in the 71～86GHz band.The total efficiency is higher than 70%.Additionally,the overall radiation pattern envelope(RPE)meets the requirements of European Telecommunications Standards Institute(ETSI)for microwave base station antennas.Next,the feeding scheme based on the over-mode waveguide beam-forming network and cavity parabolic coupler has been proposed to design a low-loss and low-profile millimeter wave antenna array,which overcomes the shortcomes of the traditional waveguided-feeding network in V-band,such as low total efficiency and gain,especially for the large-scale array antenna.The detailed design step is shown as below:1)The over-mode waveguide horn is adopted.2)The back-end planar waveguide beam-forming network is used to reduce the profile of the array antenna,thus realizing a compact structure.3)The equal amplitude and in-phase over-mode waveguide beam-forming network is used to shaping the E-plane of the radiation pattern.4)The parabolic coupler is used to excite the units of the array with weighted amplitude to obtain a lower SLL in the H-plane.In final,the whole array volume is 160mm X 150mm X 35mm(32.8λ0×30.7λ0×7.18λ0).The experimental results show that the proposed array antenna has the impedance bandwidth of 9GHz(57-66GHz),the horizontal polarization and vertical polarization gains of 34.4～37.5dBi and 34.6-37.6dBi,and the cross polarization discrimination(XPD)of 28dB.The total efficiency is higher than 65%.Finally,to address the issue of efficiency decreasing of the communication system caused by the polarization rotation and mismatching when electromagnetic waves passing through the atmosphere in satellite communication and navigation application,a new low-profile circularly-polarized(CP)antenna with harmonic suppression has been proposed.By using the orthogonal non-degenerate modes,a wide harmonic suppression band as well as a reduced size is realized.The detailed design step is shown as below:1)Based on the traditional circular microstrip patch antenna(MA),a pair of orthogonal modes could be generated between these multi resonant modes.2)By loading the shorting stubs in a quarter fan-shaped patch,all these undesirable high-order modes could be suppressed.3)The higher and lower modes are moved closely to each other by cutting a long slot at the angle bisector of the fan-shaped patch,providing the CP radiation mode.Finally,a prototype of this proposed antenna has been designed,produced and measured to verify the design concept.The experimental results show that the proposed antenna has the impedance bandwidth of 286 MHz(13.774～14.06GHz),axial ratio(AR)bandwidth of 80 MHz(13.9～13.98GHz),and a left-hand CP peak gain of 4.8 dBic.Most importantly,the CP antenna has realized the harmonic suppression of about 15GHz,which has the obvious advantage compared to the traditional CP MA.The total efficiency could reach 80%.The characteristic of harmonic suppression can avoid a large number of fake resonance points in practical engineering application,reducing the workload of processing and debugging,and improving the efficiency of production and testing. |
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