Research On Isolation And Shielding Of Antenna With Low Frequency In 5G Communication System

In 5G communication system,the spurious signals generated by the antenna will interfere with other parts of the system,and the frequency of the spurious signals is generally the double working frequency of the antenna.In order to suppress EMI,many schemes have been put forward,among which the traditional filter and radome are the most widely used,but there are some disadvantages:(1)It is difficult to guarantee both the low insertion loss of the fundamental band and the high suppression of the spurious signals;(2)It will affect the working performance of the antenna when the traditional filter or radome is combined with the antenna;(3)The structure based on reflection will cause secondary radiation problem.In order to suppress the spurious signals at the double working frequency of the antenna in 5G communication system and make up for the shortcomings of the traditional scheme for interference suppression,this paper has designed two kinds of reflective FSS radomes which one has single metal layer and the other one has bimetal layer based on the Jerusalem-type cross with periodic hyper-surface technology and frequency-selective surface technology.The measured results show that the insertion loss in the passband from 3.4 GHz to 3.6 GHz is less than 0.63 d B and the suppression is greater than 15 d B in the stopband from 6.5 GHz to 7.5 GHz.In addition,It has good angle stability.However,the reflective FSS has the problem that the spurious signals near 7 GHz is easy to cause secondary radiation in the communication system after being reflected.In this paper,the absorptive FSS is further designed according to Salisbury screen theory,and three absorptive FSS with similar structure are proposed.The bottom metal layer and the middle dielectric layer of the structures are the same,and the top loss layer are respectively resistive film square ring and lumped resistance Y-type Metal ring,metal square ring of asymmetrical distribution lumped resistance.The three structures have their own advantages and disadvantages,among which the third structure is most suitable for 5G communication system.The measured results of system of the third structure and antenna show that the operating frequency band of the system below-10 d B is 3.36-3.61 GHz basically without insertion loss;The suppression in the stopband of 6.5-7.5 GHz is greater than 10.18 d B.The absorptive FSS radome with asymmetric distributed lumped resistance and metal square ring can be used to suppress the spurious signals in the 3.5 GHz antenna with high isolation directional without affecting the performance of the antenna.The research work in this paper has the following innovations:(1)The design of reflective and absorptive FSS radomes has the advantages of low insertion loss in passband and high suppression in stopband;(2)The absorptive FSS solves the problem of secondary radiation of reflective FSS,and the thickness of the plate is only 3.175 mm(0.037 ?),which is far less than the design requirement of 1 / 4 ? of the traditional absorber;(3)It is innovatively proposed that the design of FSS radome is based on the metal square ring.This structure can not only ensure the dual polarization of the radome,but also improve the absorption efficiency.