Study On Dual-band High Gain Superstrate Shared Aperture Antennas

With the rapid development of spaceborne remote sensing satellite communication,synthetic aperture radar is widely used.By satisfying the requirement of detecting,dual-band shared aperture antenna becomes an attractive topic in recent years.How to achieve high gain is the main problem for this topic.With the limitation of space and load,large aperture antenna array is not a good choice.Therefore,shared aperture antenna with superstrate has been observed in this thesis.In order to achieve the high gain of shared aperture antenna,the Fresnel lens is inserted in single layer dielectric slab by combining the theories of EBG antenna and lens antenna.Successfully,high gain antenna can be obtained with the 1:5 frequency ratio.It is made into a method to design this such of superstrate.The work of this thesis is shown as the follows:First,it starts by studying the structure of EBG antenna.From the perspective of the theory,some simulations have done to determine the important parameters.It is effective to choose the size of dielectric slab greater than or equal to two times the wavelength and high dielectric constant material.And then we explain the principle of Fresnel lens so that to know more about the characteristic of it.It is shown that the thickness of the base is chosen as 2~4 mm,and the number of subzone P should be 6~8.The two parts of research is very significant.Then,based on the theory of EBG antenna and lens antenna,a design by inserting Fresnel lens into EBG dielectric slab is proposed.The new superstrate can work to obtain high gain,in which the EBG is for low frequency antenna and the Fresnel lens is for high frequency antenna.According to the simulation,it is just little influence on low frequency antenna by adding Fresnel lens into EBG structure.This discovery makes the basis of the design.Finally,a detail research on the parameters of the superstrate is made.It is found that the height between superstrate and ground should be H=m?_L/2=F,where?_L is the wavelength of low frequency.Low frequency is setting as 4.8 GHz and the wavelength is about 65 mm.After that,Fresnel lens with two kinds of focal length,F=136 mm and F=68mm have been designed.By changing the dimension of superstrate,the gain of both high frequency antenna and low frequency antenna will be changed.In order to make clear this relationship,the excited area has been proposed.The effective area of lens is limited,just when the design size and the excited area agree with each other,the aperture efficiency can be larger.In the proposed design,the gain of the shared aperture antenna is achieved to18.7 dB and 30.4 dB at 4.9 GHz and 24 GHz,respectively.The aperture efficiency is achieved to 64%and 39%,respectively.At the end of this thesis,a set of general design method is summarized,which can be used for other shared-aperture antennas in different frequencies.