DESIGN OF PLANAR AND CONFORMAL FREQUENCY SELECTIVE SURFACE AS FILTER: FOR RADOME WIRELESS COMMUNICATION

Abstract

One of the major sources of radar cross section (RCS) in the frontal sector of the Aircraft is the Radome section. Radome is made of dielectric material which contributes to the RCS by the antenna used for surveillance and communication purposes. To counter this effect, a band-pass filter of frequency selective surface (FSS) is proposed with the dielectric substrate affecting the performance of a filter in the context of the resonant frequency. First influence of the dielectric layer on FSS element is analyzed then the insertion effect of planar, conformal FSS on antenna performance followed by proposed design of dual band-pass and band-stop FSS for wireless communication through CEM software is done. Initially effect of dielectric layer insertion on frequency selective surface element as band-pass filter is analyzed keeping resonant frequency stable. As seen that the real-time structures are not always found to be planar, structures may be conformal with a different angle. To meet the real-time scenario both planar and conformal structures are presented. The past researches have some advantages but face some challenges too like maintenance and application in the conformal airborne platform. To meet this requirement simple unit cell FSS element is taken and the simulation is performed with a horn antenna in CST software. The material used is FR-4 with a dielectric constant of 4.3. The size of designed unit cell FSS both Square slot and Cross dipole slot are 0.32λ0×0.32λ0 and thickness of 0.0256λ0, where λ0 is the resonant frequency. The results obtained is a single transmission pole with a band-width of 2.38 GHz and 0.86 GHz for Square slot and Cross dipole slot respectively at various incidence angles. The frequency selective surface element is replicated on the planar and conformal structure as a 3×3 FSS element array to observe the gain of the antenna with FSS. For observing the effectiveness of the filter throughout the frequency band of interest, the Insertion loss and gain of the antenna with FSS are analyzed. Maintaining the stable gain the performance of the antenna is analyzed V when frequency selective surfaces are inserted as a band-pass filter, for both planar and conformal structures. Finally using two FSS elements .i.e. two square slots with a center square patch and two cross dipole patches diagonally arranged is designed in a two-dimensional unit cell for wireless application. The designed unit cell is used to obtain two transmission poles and one transmission zero for good isolation. This design is a single layer tri-band frequency selective surface. Two band-pass filters is at resonant frequency 6.04 GHz and 9.60 GHz with a band-width of 0.89 GHz and 0.87 GHz respectively. One stop band filter at resonant frequency 7.6 GHz in between the C-band and X-band plays an important role in good isolation for wireless communication. The size of unit cell FSS is 0.40λ0×0.40λ0 and the thickness of 0.016λ0, where λ0 is the first lower resonant frequency. Both pass band resonant frequencies are spaced with a good shielding providing the frequency ratio of 1.57. Frequency selective surface element and dielectric material are examined through unit cell using floquet boundaries analysis method with the help of 3D EM Computational software. In view of this, in this project optimization of the insertion effect of dielectric substrate and designed FSS element is realized at an oblique incidence angle for both TE and TM polarization.