Analysis, simulation and construction of optimized microstrip antenna with metamaterial roll and use of particle accumulation optimization algorithm (PSO)

Master's thesis in the field of electrical engineering (field)

Abstract

Analysis, simulation and construction of optimized microstrip antenna or metamaterial roll and use of particle aggregation optimization algorithm (PSO)

Microstrip antennas are widely used especially in wireless systems due to their unique features such as reasonable manufacturing cost and low weight. One of the disadvantages of this antenna is its inappropriate gain. Many efforts have been made to increase the gain of this antenna, one of these cases is the use of metamaterial structure as a roll [1] of the antenna. Metamaterials [2] have a structure consisting of geometric shapes whose dimensions of each unit cell are much smaller than the wavelength of free space. These materials have refractive index and electrical permeability and negative magnetic permeability in a certain frequency range. This causes the incident waves to propagate back to the metamaterial structure. In order to extract these parameters, different methods are investigated and the NRW method [3] is used because it provides a suitable answer. In this project, four new metamaterial cells are introduced. In order to improve the performance of the metamaterial structure, the particle aggregation optimization algorithm [4] is used. This algorithm is inspired by the natural behavior of organisms. In this optimization method, the particles are searching for the best location that is most compatible with the merit function. In this thesis, the minimum power value of return loss is defined as a merit function. This algorithm uses two softwares, Matal and HFSS, at the same time. These two software are connected to each other through API link and VBS interface language and the optimization algorithm is executed. Different boundary conditions are defined for this algorithm, in this thesis, undetectable walls are used to increase the efficiency of the optimization algorithm. The movement range of the particles and their speed are determined according to the structure of the antenna. The output of the content program is chosen as the optimal point. Then, according to the oscillation frequency of the metamaterial unit cell, the dimensions of the microstrip antenna are calculated. Due to the fact that determining the exact location of the feed plays a very important role in the performance of the antenna, the particle accumulation optimization algorithm is used to determine the location of the coaxial cable. Finally, the microstrip antenna is simulated in the HFSS software, along with the roulai, which is composed of the introduced metamaterial structures. According to the structure of the unit cell and the dimensions of the roll, an array of unit cells is placed on the antenna.  The gain of the antenna increases significantly compared to the antenna without coating. On average, an increase of 3 dB to 4 dB is observed. Also, the directionality of the antenna is improved and the amount of the rear lobe is also reduced. This shows that the use of optimized metamaterial improves the performance of the microstrip antenna.

Introduction

1-1- Microstrip antenna

Early human communication was through creating sound. is With the desire for a bit of extensive communication, equipment such as drums or smoke was used. The effort to communicate with distant places continued and in this field, mankind achieved great achievements. One of the first important creations of mankind was the use of the electromagnetic spectrum of radio, in which the antenna plays an essential role in this field for signal transmission. With the expansion of communications, there is an increasing need to build antennas with high frequency bandwidth and gain, and today human efforts are aimed at improving the radiation characteristics and reducing the size of the antenna.

One ??of the most widely used antennas is the microstrip antenna. The general structure of this antenna is such that a conductor patch and the ground plane are separated from each other by a dielectric substrate. This structure was not noticed until the revolution in size reduction and large-scale integration of electronic circuits in the 1970s. Munson then used this antenna as a low-volume antenna on rockets and presented a practical concept to solve antenna system problems. Various mathematical models were considered for this antenna and its applications were expanded in different fields.The number of articles published in the last ten years shows the importance of this antenna.

Generally, low dielectric constant is considered for better radiation. The patch that is placed on the dielectric can have various shapes, but rectangle and circle are more popular. The problem with other shapes is that their analysis is difficult and the numerical calculations are very heavy. The characteristics of the microstrip antenna are its length, width, input impedance, gain and radiation characteristics. Different parameters and their design methods are fully presented in the second chapter. The microstrip is such that a point current source is considered in the upper part under the dielectric layer that is connected to the ground as shown in Figure 1-1, it shows a unique behavior according to the direction in which the wave propagates. Pozar, 1995; Lee et al., 1997; Garg et al., 2000).

Figure 1-1: Dipole considered on a microstrip antenna (Garg et al., 2000)

2-1-1 Surface waves

Surface waves traveling down an angle between and They hit the ground plane with this angle, which causes the wave to reflect and move upwards, then they encounter the dielectric boundary with the air, which causes reflection again, this process continues repeatedly. This process is called total reflection. The amplitude of the field is amplified in some incident angles, which causes the excitation of a discrete set of surface wave modes (Pozar, 1995)).

As it is clear in Figure 1-2, the remaining fields are trapped inside the dielectric and decrease exponentially on the upper side of the surface. The ? vector shows the direction of the greatest damping. The wave propagates horizontally in the ? direction. With two directions ? and ? that are perpendicular to each other, the wave will be a non-uniform plane wave.

Surface waves absorb part of the signal energy, which reduces the signal range and antenna efficiency. Also, these waves create incorrect coupling between antenna components and different circuits, this effect significantly reduces the performance of the microstrip antenna.

Phased periodic arrays are very harmful due to the coupling effect of surface waves, and the array cannot transmit or receive at certain angles, because these waves hit the external boundary of the microstrip structure and are reflected and refracted by the edges. Refracted waves create additional radiation that causes lateral radiation[1] and increases the level of lateral polarization[2].

ABSTRACT

Analysis, simulation and fabrication of an optimized microstrip antenna in the presence of metamaterials superstrates using particle swarm optimization algorithm (PSO)

BY

Nooshin Feiz

Microstrip antennas due to unique features such as low cost and weight are useful; especially in wireless systems. Low gain is one of the disadvantages of this antenna. Many efforts have been made to increase the antenna gain, one of these cases is the use of metamaterials as a superstrate of the microstrip antenna. Metamaterial structures are composed of geometrical shapes which the dimension of unit cell is much smaller than the free space wavelength. This material has a negative refractive index and electrical permittivity and magnetic permeability in the specific frequency range. Thus, causes the backward propagation. To extract constitutive parameters many methods are discussed. So, NRW[1] method is used because it offers good response.

Four novel unit cells of metamaterial are introduced in this thesis.