Abstract :
Performance Improvement of Planar Metasurface Antenna Using Composite
Materials
Typical printed microstrip based antennas used in communication systems are less efficient compared to waveguide antennas having limited bandwidth and are fabricated on Commercial of the Shelf (COTS) substrates. Conventional performance of printed microstrip antenna can be improved by using Metasurface on top of microstrip antennas thus providing improvement in gain, bandwidth, frequency re-configuration, aperture efficiency and switchable polarization. The use of COTS based substrates as a metasurface is limited to 2D surfaces and also can be an expensive solution as compared to using low cost Glass Fiber Reinforced Polymers (GFRP) composites.
In this thesis, GFRP based composites are explored which can be used as a metasurface. Multilayer GFRP based composites samples is indigenously manufactured using Vacuum Assisted Resin Transfer Molding (VARTM) technique. E-Glass Fiber mat and peel ply are used as a resin in combination with Bisphenol-A and Araldite epoxy to manufacture GFRP based composite samples. Three GFRP based composite samples (X, Y, Z) of different thicknesses (2.32mm, 2.62mm, 3.2mm) having 5,15 and 25 layers respectively are shortlisted and screened through 200x zoom optical microscopy to qualify these samples for their utility in metasurface application.
Relative Permittivity (εr) and Tangent Loss Factor (tanδ)of these three samples is found by electrical characterization of these GFRP based composite samples. Transmission Reflection Line Method (TRLM) is used for extracting the S-parameters of these samples. In the TRL method, two C-band endlauch coax to waveguide adapters are. required which is also indigenously designed with a fractional bandwidth of 39.6% using three step impedance transformer matching technique and optimized through Quasi Newton Algorithm. Extracted S-parameters of these GFRP composite samples were uniform and smooth throughout the measured frequency range from 5.4 to 5.9 which validates smooth and precise manufacturing of these GFRP samples.
Using these extracted S-parameters, two conversion methods, Nicholson-Ross-Weir (NRW) and New Non Iterative (NNI) are used for calculating the relative permittivity and dielectric loss tangent. Sample X having a thickness of 2.32mm with 05 number of E-glass fiber mat layers gives a calculated lowest relative permittivity value of 4.6 at 5.5 GHz and is short listed for metasurface antenna design application.
C-band microstrip patch antenna is initially designed, optimized, manufactured and tested with a net gain value of 7.5 dBi. Then, GFRP based metasurface patch antenna is designed, optimized and tested showing a net gain value of 9.7 dBi with a gain enhancement of 2.2 dB (30%). An additional layer of plain GFRP sample is added up on top of the metasurface patch antenna showing a net gain value of 10.4 dBi with a gain enhancement of 2.9 dB (39%). This resulted in an overall gain enhancement of 39% as compared to a simple microstrip patch antenna.
The same metasurface design approach is repeated for a 2 x 4 C-band planar patch array antenna. In GFRP based planar metasurface patch array antenna overall gain enhancement of 16% is observed. In the end, GFRP based composites have shown some very promising results for future utilization in metasurface antenna applications. GFRP based metasurface has the potential of utilized in various antenna applications including but not limited to commercial airplane weather and surveillance radar, unmanned air vehicle, satellite telemetry and telecommand antenna, etc.