Modeling And Simulation Of Frequency Reconfigurable Milli-meter Wave Antenna Based On Electromagnetic Surface

The frequency reconfigurable antenna can flexibly select and switch the frequency band and adapt to the complex and changeable electromagnetic environment,so it has become a research hotspot in the field of millimeter wave antenna.The electromagnetic surface is a planar structure composed of metal elements of sub-wavelength size arranged periodically,which can change the frequency,amplitude and phase,polarization,and other characteristics of the incident electromagnetic wave.It has the advantages of simple structure,low loss,and is convenient to integrate with the antenna array.It is a new reconfigurable antenna implementation technology.However,reconfigurable antennas based on the electromagnetic surface still face many problems in practical applications,such as high profile size and a large volume of the antenna array,complex control network and low transmission rate of the electromagnetic surface.Point at above challenges,this paper explores the design method of frequency reconfigurable millimeter wave antenna based on an electromagnetic surface,focusing on the technical problems of three key devices:microstrip antenna array,RF MEMS regulatory switch,and adjustable electromagnetic surface.The main research content and innovation points of this paper are as follows:1.Aiming at the problem that the frequency bandwidth of multimode microstrip antenna is limited by profile size,a "single-cavity and dualmode" wideband antenna element design method is proposed.The modes of microship antenna TM01 and TM11 are coupled excited by a coplanar waveguide feed network.By adjusting the transition size between the coplanar waveguide and the patch gap,the center frequency of the two modes is narrowed to realize the wide-band radiation of the low-profile microstrip antenna unit.A Ka-band microstrip antenna unit is designed based on this method.The experimental results show that the frequency bandwidth of the antenna unit is 24.84GHz to 28.6GHz,the profile size height is 0.508mm,and the maximum gain is 7.9dBi.To improve the gain of the antenna array,a laminated antenna array with coplanar waveguide coupling feed network-excitation element-parasitic element is designed by using the above microstrip antenna element.The array size is 4×4×2(row×column × layer).The measured results show that the frequency bandwidth of the antenna array is 25GHz to 32GHz,and the relative bandwidth is 24.5%.The peak gain was 20.1 dBi.2.Aiming at the problems of high driving voltage and easy mechanical failure of RF MEMS switch,a folding and bending MEMS beam structure with uniform stress distribution was proposed,which can reduce the elastic coefficient of MEMS beam and then reduce the driving voltage of RF MEMS switch.A non-center electrode driving structure is designed to separate the DC voltage transmission line from the RF signal line to protect the RF system.A mechanical model of an RF MEMS switch based on the non-center electrode is constructed.A Ka-band RF MEMS switch is designed.Compared with the RF MEMS switch based on the fixed beam model in the same frequency band,the driving voltage is reduced by 22%to 61%.After 108 tests,the switch does not collapse,fracture and dielectric charging,which effectively improves the service life of the switch.3.Aiming at the problem of low transmission rate in the passband of the adjustable electromagnetic surface,a double-opening resonant ring structure integrated with RF MEMS switch is proposed.The fusion design of MEMS beam and resonant ring can reduce the parasitic resistance loss of the regulatory element,increase the equivalent inductance value of the electromagnetic structure unit,and thus improve the transmission rate.The circuit parameters of the RF MEMS switch and double-opening resonant ring are extracted from their structural characteristics,and they are equivalent to the parallel impedance load on the transmission line.The electromagnetic surface equivalent circuit model of an integrated RF MEMS switch was established,and the regulation relationship between the on-off state of the switch and the passband frequency was analyzed in detail.Based on the above structure,an electromagnetic surface with adjustable passband frequency is designed.The simulation results show that the central frequency of the passband can be adjusted in the range of 25GHz to 30GHz by changing the on/off state of the switch,and the transmission rate is higher than 90%.4.The integrated design and simulation verification of frequency reconfigurable antenna based on electromagnetic surface are presented.The adjustable electromagnetic surface designed above is loaded on top of the laminated microstrip antenna array as a cladding layer,and the RF MEMS switch on the electromagnetic surface is regulated to relize the reconfiguration of the antenna frequency.The simulation results show that by changing the on/off state of RF MMES switch,the antenna array can realize the reconfiguration of the two central frequency points of 26GHz and 29GHz,the frequency bandwidth of the low-frequency point is 24.8GHz to 27GHz,the maximum gain is 18.25dBi,and the frequency bandwidth of the highfrequency point is 28.3GHz to 29.6GHz.The maximum gain is 18.8dBi.