Gain enhancement of microstrip patch antenna using dielectric DNG superstrate.

摘要

As the trend continues towards miniaturizing integrated electronic circuits, the need to reduce the size of the antenna continues to be a challenge particularly for the microstrip antenna. Several techniques that have been successfully implemented for size reduction up to 75%, by a variety of methods such as cutting slots in the patch or reconfiguring its size using MEMS, etc. in conjunction with optimization techniques such as genetic algorithms or particle swarm. However, antenna size reduction comes at the expense of a reduced gain by a few dBs. Recently, materials engineered to have negative permittivity and permeability (DNG) or left handed materials (LHM) have been used as a superstrate to focus the radiated field. While most of the work to date has used metallic DNG material, implementing dielectric DNG materials has been limited to optical applications. Dielectric DNG materials have advantages over metallic DNG materials primarily for low losses and wider bandwidths since they are non-resonance structures.;The present research uses a flat lens available in literature and developed in 2005 that has a negative refractive index in a certain frequency range as a superstrate for the microstrip patch antenna. It is a high dielectric material with a triangular lattice of holes drilled along its length. At first the superstrate has been analyzed using a finite difference time domain software tool (EM Photonics) for its left handed properties by exciting it with a point source and comparing the magnitude and phase of the electrical field in the transmission plane with that in the incident plane. It is shown that an image is formed at a distance about half the thickness of the slab. By comparing its behavior to that of a similar size slab without holes; it is conclusively shown that the slab with holes behaves as a DNG material.;In order to use this DNG slab as a superstrate, the rectangular microstrip patch antenna has been designed to resonate at 31.5 GHz which lies in the same frequency range where the superstrate has a negative refractive index. At first the DNG has been analyzed for its lens behavior properties with respect to focusing the electric field. In order to optimize the field focusing, the edges of the DNG slab had to be scalloped. Another optimization that is very critical is the height at which the superstrate is placed over the antenna. This is done by calculating and maximizing the gain using a 3D finite element full wave solver (Ansoft's HFSS). A gain enhancement of 3 dB to 4 dB for a single element has been achieved. The aperture field distribution for the optimized configuration has been plotted at selected heights. In addition, the E field distributions for the optimized configuration have been compared with E field distributions for the patch antenna without the DNG superstrate configuration. This comparison reveals that the field strength above the DNG superstrate is twice the value of the field for the antenna without a superstrate configuration. This further proves that the superstrate behaves as a DNG material.;Finally, the proposed superstrate has been scaled to exhibit a negative refractive index at 10 GHz and integrated with an X band (10 GHz) patch antenna, and the same type of characterization steps described have been repeated. Simulation results of the scaled configuration are consistent with the original configuration; where a gain enhancement of 3dB has been achieved. This ensures the scalability and robustness of the design.