Miniaturized Circuit Analog Absorber And Its Electrical Tunability Based On Hybrid Loading

Radar absorbers are integral to the ever-evolving fields of electromagnetic wave-related fields such as stealth technology and modern electrical and electronic equipment systems.In modern military operations and national defense systems,it is of strategic significance to reduce the visibility of one’s own side to the radar detection system to avoid enemy surveillance and information leakage of one’s own side.In some civil engineering systems and wireless communication application scenarios in daily life,absorbers can reduce electromagnetic interference between microwave components and electronic equipment,and play an important role in the management of electromagnetic pollution that is increasingly emerging.An ideal absorber needs to have good working performance such as miniaturization,wide frequency,tunability and strong absorption.In this paper,based on the frequency selective surface,the compact structure is used to enhance the resistance loss and the capacitance value of the varactor diode can be adjusted by applying an external bias voltage.The absorber and the tunable notch broadband absorber are deeply studied and an innovative unit structure design is proposed.The equivalent circuit model analysis method is used to understand and analyze its working principle.The main contents are as follows:In terms of expanding the frequency band of the radar wave absorber and reducing its unit size: According to the absorption principle of the absorber,the design of the target unit structure can bind the incident electromagnetic wave inside the absorber structure,and maximize the incident electromagnetic wave energy through the loss layer,converted into other energy for dissipation.Based on the widespread use of electronic devices in the microwave frequency band,for example,the main frequency bands of Wi-Fi signals are2.4GHz and 5GHz,a small broadband absorber with a resistive loading spiral structure based on LC distribution is designed to absorb the remaining interference at the surface of the signal source.The purpose of the signal is to ensure a good and stable electromagnetic wave working environment.The original operating frequency range of the designed unit structure is set to 2-6GHz,and the structure optimization considers the absorption of 10 d B.The designed wave absorber has the loss layer on the top,metal patches are laid on the upper and lower ends of the loss layer,folded and bent in the form of double rings,and the metal patches at the upper and lower ends are connected through metal vias to form a helical compact distribution structure.Resistance is loaded on the metal patch.The compact distribution is conducive to electromagnetic coupling to collect incident electromagnetic wave energy inside the wave absorber and convert it into electrical energy for dissipation to achieve wave absorption effect.The HFSS simulation results show that the amplitude of the reflection coefficient of the unit structure is less than-10 d B in the range of 1.78-8.44 GHz,the relative bandwidth is 130.33%,and there are 4 resonance points in the operating frequency range.By establishing an equivalent circuit model,the equivalent electrical parameters and impedance matching of the absorber are analyzed,and the physical dimensions of the relevant elements of the unit structure are all analyzed by parameter scanning to complete the design of the physical structure.Finally,through the comparison of the electric field distribution at close range of the Wi-Fi signal on the ceiling simulated by full wave simulation software,it can be seen that the designed wave absorber can achieve effective anti-interference.In terms of designing a tunable notch wideband radar wave absorber: Through the effective design of the absorber structure,a specific electromagnetic response can be generated.On the premise of no need to change the original physical size,the control of the phase of the reflection coefficient of the incident electromagnetic wave and the working performance of the absorber is realized.The varactor changes with the bias voltage so that the capacitance value can be changed,and it is loaded into a high-impedance surface with inphase reflection characteristics.After loading,the high-impedance surface can change the phase of the reflection coefficient of the incident electromagnetic wave at a specific frequency.The metal grounding plate of the broadband miniaturized absorber is replaced with the above-mentioned composite high-impedance surface.Without affecting the broadband absorption performance of the original absorber,it is realized that changing the external bias voltage can change the working performance of the absorber in a specific frequency band.By choosing different capacitance values,the wave absorber can absorb and reflect incident electromagnetic waves at the same time,and can choose to absorb or reflect in a specific frequency band according to actual needs.Through the analysis of full wave simulation software simulation results,when the capacitance value of the varactor diode is set to 0.3p F,the absorber can reflect the incident electromagnetic wave at the operating frequency f = 4GHz.With the reduction,the work performance can be adjusted at 2.5 to 4GHz.