Design And Application Of Ultra-wideband Circuit Analog Absorber

Radar detection technology plays an important role in the modern war system,and stealth technology arises as a counter technology.As the main way to reduce the radar cross section,electromagnetic wave absorption materials have attracted more and more attention all over the world.Meanwhile,with the development of consumer technology,more and more spectrum are used in the military and civilian,which lead to the deterioration of the electromagnetic environment,then cause more and more electromagnetic compatibility problems.And the electromagnetic absorption materials can solve these electromagnetic interference problems by the conversion of electromagnetic energy into heat energy.Because of the broadband absorption and flexible design,the simulation of absorption materials is the focus of the research.Besides,the general band pass frequency selective surface have strong reflection outside the passband,which will resulting in the increase of radar cross section.Rasorber is proposed to reduce the reflection from the rejection bands of bandpass frequency selective.Therefore,the study of circuit analog absorbing materials and rasorber is of great significance for military and civilian.In this paper,using the equivalent circuit method,the design of the ultra-wideband analog absorption materials is realized by the load of the lumped resistors.At the same time,two absorption structures are designed respectively,one with two transmission windows,and the other one with an adjustable transmission frequency.The main research work is as follows:First,double-layer circuit analog absorber is proposed.The ultra-wideband absorption of absorber can be achieved by the multi-resonant and multi-resistive layers,and the conditions for the impedance of the double layer structure to achieve resonance are analyzed.Then the equivalent electrical parameters of multi resonant and ultra-wideband absorption structure are obtained through equivalent circuit model.Based on the obtained electrical parameters,the full wave mode is completed by the relationship between equivalent electrical parameters and physical structure.All resistive layers of this absorber are square loops loaded by ideal lumped resistors.The simulated result shows that the operating bandwidth with the reflectivity smaller than-10 dB indicates a fractional bandwidth of 157.40%under the normal incidence,the total thickness of the proposed absorber is only 0.098?_L at the lowest operating frequency.Four resonances are observed within the absorption band of the designed absorber.Actually,this absorber owns five resonances in the absorption band,but one of the resonances do not reflect in the reflection coefficient because of the mismatch of the input conductance.Moreover,five resonances are excavated by using the load matching layer.The relative bandwidth of the operating bandwidth is 165.5%,and the thickness is also controlled by 0.117?_L.Secondly,the parasitic effect of lumped resistor at high frequency is analyzed,and an ultra-wideband absorber loaded the actual resistors is designed.The reflection coefficient between the load actual and the ideal resistor is compared,which shows the parasitic parameters of the collector at high frequency will affect the absorption performance of absorber.A modified design is proposed in view of these parasitic parameters,and the experimental test shows that the relative bandwidth of the absorber have reached 157.6%,which means the thickness is only 0.1?_L in the operating band and total thickness is very close to the theoretical thickness.Finally,two rasorbers with dual passband and tunable passband are separately designed.The design idea and concept of rasorber are expounded at first.Then the equivalent circuit model and full wave model of rasorbers with dual passband or tunable passband are proposed.The resistive layer square loops loaded with lumped capacitance and inductance.The transmission function is realized at 4.24GHz and 7.87GHz by means of the parallel lumped capacitances and inductors,and insertion loss is 0.032dB and 0.105dB respectively.Furthermore,the reflection coefficients are less than-10dB from 2.62GHz to 12.03GHz.Lastly,the adjustable rasorber structure is designed.Tunable transmission frequency selective surface is realized by tunable varactor and act as the lossless transport layer.The final result shows that the tunable range of the transmission passband is 4.4GHz-6.5GHz with the reflection coefficient between 3.2GHz-9.9GHz is less than-10dB.