Design Of New Electromagnetic Materials And Their Stealth Applications

In the field of military defense,the researches on the stealth performance of military weapons have always been a hot and difficult point in many countries.Stealth technology can control and suppress target characteristic signals to improve the survival rate of the weapon platform.The antenna is the main component of the communication signal transmission and receiving,and it is regarded as a strong scattering source.The stealth characteristics of the antennas determine the stealth capability of the overall structure.The antennas stealth can be divided into two parts,stealth within the operating frequency band and stealth outside the operating frequency band.In-bond and out-bond stealth performance of the antenna can be adjusted simultaneously or individually through loading different electromagnetic stealth metamaterials.The band-pass frequency selective surface can penetrate the in-band electromagnetic waves and reflect the out-band electromagnetic waves.The radome,which is based on band-pass frequency selective surface,can realize the out-band stealth of the antenna.The frequency selective rasorber is developed on the basis of band-pass frequency selective surface.The frequency selective rasorber penetrates the in-band electromagnetic waves and absorbs the out-band electromagnetic waves to achieve the dual/multi station stealth of the out-band electromagnetic waves.The checkerboard-shaped polarization conversion materials can passively cancel the incident electromagnetic waves.By covering this kind of materials,antenna can achieve in-band and out-band stealth simultaneously.This thesis aims at the researches of electromagnetic stealth metamaterials in recent years.The contents include the following aspects:1.The wideband band-pass frequency selective surface is studied and designed.The band-pass frequency selective surface realizes the transmission of electromagnetic waves in the band-pass frequency range and reflects out-band electromagnetic waves.The band-pass frequency selective surface is used in stealth fields such as radomes.The research adopts the multi-layer dielectric layer,which achieves high angular stability and low loss characteristics in the X-band.The principle of the wideband band-pass frequency selective surface is analyzed through equivalent circuit simulation.The-3d B pass-band of the wideband band-pass frequency selective surface can cover the X-band,during the incident angles of 0?-60?.2.The design method of high performance antenna based on polarization conversion materials is researched.The polarization conversion materials and its mirror periodic can reflect the incident wave into cross-polarized wave with phase difference of +90? and-90?,the phase difference between them is 180?.The checkerboard pattern of the polarization conversion materials and its mirror unit can scatter the electromagnetic wave into other directions through passive cancellation,achieving the stealth characteristics within wide frequency range.The artificial magnetic conductor unit can change the reflection phase of incident electromagnetic waves.Using the artificial magnetic conductor-loaded microstrip antenna and electromagnetic coating to form a Fabry-Perot resonant cavity,which can improve the gain of the microstrip antenna and achieve a low profile cavity design.The high performance antenna based on polarization conversion materials can increase gain at 9.84 GHz to 10.23 GHz and it is 7.4 d Bi at 9.9GHz.The RCS has been greatly reduced over 9.61GHz-21.5GHz.The profile height of the Fabry-Perot cavity is 0.35?.(where ? represents the wavelength at center frequency)3.The "absorbing-transmitting-absorbing" frequency selective rasorber is designed.The "absorbing-transmitting-absorbing" frequency selective rasorber has higher and lower bandwidth of absorbing at both sides of transmitting band.By insalling a lossy dielectric layer above the frequency selective rasorber,the lower bandwidth of absorbing is widened,while maintaining the character of passband and higher bandwidth of absorbing.Consequently,the overall bandwidth of absorbing is widended.As a result,the reflection coefficient of the "absorbing-transmitting-absorbing" frequency selective rasorber is less than-10 d B from 3.69 GHz to 17.12 GHz.The transmission coefficient is more than-3d B from 10.45 GHz to 11.83 GHz,The absorptivity is greater than 0.8 over 3GHz-9.42 GHz and 12.62GHz-17.32 GHz.