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

Master's Thesis in Electrical Engineering (Field)

Abstract

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

Microstrip antennas are widely used due to their unique features such as reasonable manufacturing cost and light weight, especially in wireless systems. takes 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 is significantly increased compared to the antenna without roll. 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. [1] Superstrate

[2] Metamaterial

[3] Nicolson Ross Weir

[4] Particle Swarm Optimization

1-1- Microstrip antenna

The primary human communication through It has been making noise. 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. 1-1-1 Wave on microstrip antenna The mechanism of transmission and radiation in a microstrip is that a point current source is considered in the upper part under the dielectric layer which is connected to the ground according to Figure 1-1. According to the direction in which the wave propagates, it shows a unique behavior. Pozar, 1995; Lee et al., 1997; Garg et al., 2000).

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

-2-1-1 Surface waves

Surface waves that move downward have an angle between and, with this angle they hit the ground plane, which causes wave reflection and then move up to The dielectric boundary encounters the air which again creates reflection, this process continues repeatedly. This process is called total reflection. The size of the field amplitude is amplified in some collision 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 ?, which 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 the antenna components and different circuits, this significantly reduces the performance of the microstrip antenna. It is harmful and the array cannot transmit or receive at some specific 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]. Surface waves are very harmful to antennas and circuits and should be reduced as much as possible.

Figure 1-2: Surface waves (Garg et al, 2000)).

-3-1-1 Incompressible waves[3]

When the waves are propagated in the angular range and ?, they are reflected by the earth plane, but only a part is re-reflected at the dielectric boundary to the air. Most of these waves are propagated from the sublayer to the air and in Antenna radiation has an effect. As it is clear in Figure 1-3, these waves are non-uniform plane waves, and the ? angle shows the direction of attenuation downwards, and their amplitude increases as they move away from the dielectric surface (Garg et al, 2000).

In more complex structures that consist of several layers, non-dense waves are caused by increasing the size and gain of the antenna. This happens in a specific frequency and arrangement. Also, infrequent waves may not be excited in other multi-layer structures. Figure 1-3: Infrequent waves (Garg et al, 2000). The function of the antenna becomes and creates a new reflection boundary. These waves are only available at some specific angles of the incident wave and provide discrete waveguide modes for antennas and circuits, and the electromagnetic field is more concentrated in the lower region of the upper conductor (Lee et al, 1997). It is a different specification that according to the type of application, the desired feature should be determined and efforts should be made to improve the desired parameter.