| With the increasing frequency of the electromagnetic wave research,antennas applied in satellite communication are subjected to very challenges specifications.In order to achieve long-distance transmission,antenna is usually required to achieve high gain,low side-lobe characteristics,performances of wideband,low cost and light weight are among the targets as well.It is generally known that the losses become much more with the increasing frequencies with the existence of dielectric.Therefore,metal structure is used to avoid dielectric loss.So far,there are various gain-enhancement low side-lobe approaches for antennas,such as planar antenna array,lens antenna and reflector,each with its strengths and weakness.In this paper,low-profiled planar array antennas and lens antennas are studied.Firstly,an X-band monopulse antenna is designed.According to the performance requirements,the antenna array is composed of eight narrow-edge slotted waveguides.The feed amplitude of slot satisfies Taylor distribution and is controlled by the physical dimensions of slot to achieve low side-lobe for azimuth pattern.At the end of the array,we connect the feed network,which consists of unequal power divider and a magic T,in order to realize the performance of low side-lobe and monopulse.Through simulation,the sidelobe of the antenna in the azimuth plane is lower than-27.5d B,and in the elevation plane is lower than-26 d B,and the VSWR of the antenna is less than 1.2 in the operating band.Secondly,this paper presents a broadband slot planar array antenna.This antenna can be divided into four layers,they are feeding network,coupling slot,high-order mode cavity and radiation slot.The feed network adopts Taylor distribution to realize low side-lobe.Due to the coupling slot and the resonant cavity,the bandwidth of the antenna is much wider than the conventional waveguide slot antenna.After simulation,the bandwidth of the antenna reaches 9.3% when the return loss of the antenna is less than-14 d B,and the side-lobe is lower than-20 d B.Next,The broadband planar array antenna based on ridge-gap waveguide is proposed,which is similar to the antenna aforementioned,consists of feed network,coupling slot,high-order mode cavity,and radiation slot.The feed network adopts Taylor distribution to realize low side-lobe.Through simulation,the bandwidth is 19.14% with the antenna return loss less than-14 d B and the side-lobe is lower than-20 d B.It can be seen that using the ridge gap waveguide structure,the working bandwidth of the antenna has been significantly improved.On the other hand,it does not require conductive connection between the upper and the lower plates,which makes this technology gain more advantages than the conventional rectangular waveguides.Finally,we have designed a lens antenna by using displaced half-height pins of gap waveguide.The whole lens consists of two mirrored metal plates with pins that are displaced exactly a half period of unit cell.The improved scheme has not only a stable refractive index over an extremely wide operating band but also no dielectric loss compared to other metamaterial based lens.Through simulation,the antenna bandwidth is 83.87%.In addition,it is easy to manufacture and also can largely reduce the production cost.By adjusting the height of the pin,the equivalent refractive index ranges from 1 to 1.41,which suffice the design of Luneburg lens.The complete Luneburg lens is simulated in CST Microwave Studio.To verify the antenna performance,a prototype of the lens antenna is fabricated.The measured results show that the lens also agree well with the simulated ones,which verified the feasibility of the design of the lens antenna. |
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