Design and development of microwave patch antennas using conductive polymers.

Abstract

Recent advances in the electrical conductivity levels of Conducting Polymers (CP) and impressive improvements in their stability are making these materials very attractive potential alternatives to copper in planar antennas. This is particularly so in applications where light weight, inexpensive and/or wearable/conformal antennas are a consideration. There have been isolated efforts in the past towards using CP as material for antenna and transmission line design. This thesis endeavours to provide a systematic study of key factors that are important for the understanding of these materials, their design and simulation as basis material for building microwave antennas. The thesis could be considered as made up of two parts. The first part (Chapter 2 and Appendix A) presents a mathematical model of electrical conduction and permittivity in CPs as a function of dopant concentration and frequency. The electrical conduction and permittivity are very dispersive for these materials primarily due to different relaxation times exhibited by the conduction electrons. This part also develops closed-form expressions formulas for rapid estimation of the effective permittivity of microstrip lines on multi-layer substrates. A 2D finite element eigen-mode analysis leading to the effective permittivity for two and three layer microstrip line structures is used as a reference solution and successfully validates the closed-form expressions. The second part (Chapter 3 and 4) presents the design, simulation and fabrication of microwave antennas using thin CP films. Results on CP based microstrip patch antennas operating at 2 GHz, 4.5 GHz and 6 GHz are presented. This part also presents a systematic study on the impact of CP film thickness, conductivity and fabrication method on antenna performance. An indirect method for determination of the permittivity of non-standard RF substrates and detection of dispersion in the electrical conductivity of CP film has been demonstrated. This part validates the possibility of using CPs as microwave antennas and gives credence to many possibilities in the field of conformal antennas, wearable antennas, sports and medical applications. The thesis is concluded in chapter 5 by summarising the results and presenting some exciting possibilities that these exotic materials open for future applications in the field of antenna applications.