Analysis and design of antenna and passive microwave circuit elements on flexible substrate

This dissertation is about the design and analysis of passive microwave circuits on flexible substrates. The work is divided into three parts material characterization, design, and fabrication. Two types of textile samples cotton, jeans, and two types of synthesized mold silicone PDMS, and AK-Sil1310T are selected for analysis. The dielectric properties of cotton, jeans, PDMS, and AK-Sil1310T are determined using a waveguide and modified ring resonator for a 1-12 GHz frequency band. The waveguide setup consists of X-band (8.2-12.5 GHz) rectangular waveguides, a vector network analyzer, the coaxial cables, and the N-type coaxial to waveguide converters. The scattering parameters of test materials are measured through a waveguide setup whereas the Nicolson-Ross-Wier algorithm is used to extract the dielectric properties from measured scattering parameters. To determine material properties using the resonant method two microwave structures microstrip transmission line a and microstrip ring resonator are realized. The dielectric properties obtained through both methods are significantly matched. The different conductive materials such as conductive ink, conductive textile, and conductive yarn are investigated to compare their performance when used in the fabrication of circuit elements on textiles. The fabrication techniques including screen printing, Physical Vapor deposition, sticking, and stitching are also examined. In the design phase, an X-band reflectarray with a rectangular patch element is simulated using Ansys HFSS electromagnetic simulation software. The phase range corresponding to patch dimension for single-layer and 2-layer unit cells is obtained. The single-layer unit cell has a phase range of around 330o but has steeper phase variation whereas the 2-layer unit cell has more the 300o has gradual phase variation Based on fabrication error tolerance and bandwidth criteria 2-layer unit cell is used to design complete reflectarray. The simulations of reflectarray for center feed configuration having 15x15 elements and offset feed configuration having 17x17 elements are carried out by using the ANSYS HFSS simulation tool. The radiation patterns, gains, and efficiencies are calculated for both antennas. The gain for center feed configuration is around 21 dB and the estimated efficiency is around 43%, similarly the gain for offset feed configuration is around 23 dB while the estimated efficiency is around 45%. Both designs are fabricated through computerized embroidery technique using silver-coated conductive thread while the ground plane is made using conductive textile. The fabricated design was tested with the help of a wooden structure built in the lab and compared with simulations.