Miniaturization Of Metamaterial Electromagnetic Structures For Microwave Applications

Metamaterials(MM)are artificial materials engineered to modify the characteristics of electromagnetic(EM)wave incident on structures.This class of MMs have demonstrated huge potential in many exctingapplications from low to high frequencies(Microwave to Optical).Metasurfaces(MS)are a unique category of planar MMs having two dimensional arrays of geometric elements which are optically thin and dense.Due to their subwavelength size,they can be utilized in designing compact devices and circuits such as filters,antennas,couplers,etc.Since portable applications such as laptops,tablets,mobile phones,require reduced weight and volume,therefore,miniaturized and compactness are essential parameters in high-end handy devices.Besides,wide BW,higher gain,reduced transmission line loss,and signal integrity is the key challenges in advanced devices,and systems.In the light of above mentioned background,this research investigates MM inspired structures at microwave frequency for filtering applications.Due to the availability of superior materials,recent innovation in fabrication techniques and advanced computer-aided design tools,designing and realizing such efficient filters has not been a nightmare nowadays.Keeping in view the big picture of applications,the first study relates to spatial filtering devices known as Frequency Selective Surfaces(FSS)which is a robustly studied topic of EM science.These are two dimensional periodic structures having planar metallic array elements(patch or apertures)on a dielectric substrate,exhibiting transmission and reflection at certain resonant frequency.Bulky FSSs(higher profile,large periodicity),difficult manufacturability,low out-of-band rejections,and sensitivity to polarization/angular stability are some of the challenging design features.Importantly,embedding all the aforementioned characteristics for a single optimized design would be a real achievement for the FSSs designers.The second study focuses is one of the recent hot topic of planar MM based plasmonics filtering structures,also called Spoof Surface Plasmon Polaritons(Spoof SPP).Earlier designs of microstrip transmission lines may not support the needs of high-speed communication in modern devices.Although differential microstrip transmission lines improve the signal integrity issues and reduce the interference however,this has resulted in bulky structures and power handling problems.Spoof SPPs have exotic properties of stronger field confinement and high resolution with dispersion properties;hence they can handle all above mentioned challenges.Following are contributions of this research:1.Miniaturization of FSS based on Fractal Arrays for Enhanced BW for higher angle of incidenceA novel approach is used to miniaturize the array size and broaden the bandwidth(BW)of a multilayer antenna-filter-antenna(AFA)based FSS.A wideband,maximally flat(Butterworth),third-order miniaturized FSS structure with Minkowski pre-fractal islands at oblique incident angle of 60°is designed and analyzed.The constitutive design parameters are manipulated in a manner such that the structure itself shows the selectivity.The periodicity of the structure is 0.25λo and overall thickness of 0.23 λo.Fractional bandwidth(FBW)of 60%is achieved at higher oblique incident angle of 60°.Stable frequency response is achieved with reduced patch length by 60%and 7%and reduced thickness by 12%than previous reported schemes.The proposal is extended to further miniaturize the fractal array size(0.2Aλc)with centre square slots on the patch layers to increase the capacitive effect whereas the fractal slots are etched on the ground for enhanced coupling.It is demonstrated through experiment in anechoic chamber;the proposed design can effectively minimize the element size and improve the BW for transmission and reflection coefficient higher than 87.4%and 92%respectively at normal incidence angle and sharper roll-off at 10.4dB/GHz on the upward frequency.2.Miniaturized FSS at Ka-bandIn another scheme,a novel,wideband miniaturized FSS is designed at Ka-band consisting of two metallic layers,separated by a thin dielectric substrate that works as a passband microwave spatial filter.Patch layer is slotted to increase the capacitance whereas the ground layer has a cross loop aperture for better coupling effect.Proposed design exhibits a passband resonating at 28.7 GHz with 3dB BW of 8.19GHz from 26.11 to 34.3GHz at normal incidence angle.Since the geometry is symmetric with minuscule array size,proposed FSS structure shows stability for both polarizations and at higher incidence angles(up to 30°).3.Semi-circular groove based Spoof SPPs transmission lineIn this research work on Spoof SPPs transmission line,we compare the normalized dispersion curves of different groove shapes engineered on the planar metallic strip with the variation of geometric parameters of the structure.It is found the dispersion characteristics are determined by the shape of the grooves and the asymptotic frequency can finely be tuned through the geometric parameters.Circular grooves behave comparably better than Vee-grooves and microstrip transmission line.A low pass plasmonic filter has been designed with semi-circular gradient grooves on a planar metallic strip with transition sections to match both the impedance and momentum of microstrip line and the plasmonic waveguide.Results of scattering parameters and magnitude of electric field distributions showexcellent transmission efficiency from fast guided wave to a slow Spoof SPPs.4.Novel low pass plasmonic filter with periodic semi-elliptical groovesTo solve the issue of high transmission losses at microwave frequency,a novel periodic plasmonic structure is proposed with semi-elliptical grooves on a lateral edge of microstrip line.A comparison with other structures confirms that more strong resonant modes are created by the coupling between upper textured metal strip and the lower ground layer which are confined near the surface of the structure.The cutoff frequency and the level of field confinement depend on the geometric parameters and semi-elliptical grooves based Spoof SPPs efficiently minimize the asymptotic frequency by 65%and 12%as compared to microstrip and Vee-groove structures,respectively.A planar and highly efficient,low-pass plasmonic filter with 3dB cutoff frequency of 11.4 GHz and significantly reduced insertion loss(>-1.9dB)in the passband.A fabricated prototype is tested and good agreement between experimental and simulation results confirms the excellent performance of this compact filter in the entire passband with smaller transmission losses.